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CORNEAL ULCERSDiagnosis and Management

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CORNEAL ULCERSDiagnosis and Management

JAYPEE BROTHERS MEDICAL PUBLISHERS (P) LTDNew Delhi • Ahmedabad • Bengaluru • Chennai • Hyderabad • Kochi • Kolkata • Lucknow • Mumbai • Nagpur

®

Namrata SharmaMD DNB MNAMS

Associate Professor of OphthalmologyCornea, Cataract and Refractive Surgery Services

Dr. Rajendra Prasad Centre for Ophthalmic SciencesAll India Institute of Medical Sciences, New Delhi

India

Rasik B VajpayeeMS FRCSEd FRANZCO

Head, Corneal and Cataract SurgeryCentre for Eye Research Australia

Royal Victorian Eye and Ear HospitalUniversity of Melbourne

Australia

Forewords

Hugh R TaylorPeter R Laibson

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Corneal Ulcers: Diagnosis and Management

© 2008, Namrata Sharma, Rasik B Vajpayee

All rights reserved. No part of this publication and DVD ROM should be reproduced, stored in a retrieval system, or transmitted in anyform or by any means: electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the editorand the publisher.

This book has been published in good faith that the materials provided by authors is original. Every effort is made to ensureaccuracy of material, but the publisher, printer and authors will not be held responsible for any inadvertent error(s). In case of anydispute, all legal matters are to be settled under Delhi jurisdiction only.

First Edition: 2008

ISBN 978-81-8448-217-1

Typeset at JPBMP typesetting unitPrinted at Ajanta

Dedicated to

My parents Dr Ramesh C Sharma and Maitreyi Pushpa,husband Subhash Chandra and daughter Vasavdatta

— Namrata Sharma

My wife Madhu and children Mihika and Shubhankar — Rasik B Vajpayee

Foreword

Corneal opacity and scarring is one of the leading causes of vision loss and blindness worldwide. Although cataractmay be the leading cause of bilateral blindness, corneal scarring accounts for a significant portion of unilateral andbilateral vision loss. Corneal scarring may result from specific conditions such as trachoma, xerophthalmia oronchocerciasis, or from less specific causes such as microbial keratitis following often relatively trivial trauma. Insome areas one quarter of blindness may be due to corneal scarring.

One hundred years ago, or even 50 years ago, our ability to treat microbial keratitis was extremely limited. Thedevelopment of a broad range of antimicrobial agents, anti-inflammatory drugs, and vastly improved and fasterdiagnostic methods has revolutionized our ability to treat corneal ulcers. The successful outcome for the managementof corneal ulceration depends on the prompt use of the appropriate antimicrobials and the careful management ofthe healing phase. This is easy to say, but is much more involved to achieve. It requires good clinical and diagnosticskills and excellent laboratory services to make the correct diagnosis so as to be able to select the appropriateantimicrobial. The careful management requires the early recognition and correct management of a host of possiblecomplications.

Professor Rasik Vajpayee is a corneal surgeon of international renown. He was the Head of the very busyCornea and Refractive Surgery Services at the RP Centre for Ophthalmic Sciences at the All India Institute ofMedical Sciences and recently has taken over as Head of Cornea and Cataract Surgery at Centre for Eye researchAustralia, University of Melbourne. Both he and Dr Namrata Sharma have a profound knowledge and broadexperience in the management of the whole range of corneal diseases and especially corneal ulceration. They havecrystallized their experience into a beautiful set of clear and succinct guidelines.

This book builds on a systemic approach with a clear statement of the fundamental issues relating to cornealulceration and the details that are important in the initial assessment. It covers in detail the microbiologic laboratoryassessment and treatment options. The section on the surgical management is superb and sets out in a series ofsimple steps the way to successfully manage the various complications.

Professor Vajpayee and Dr Sharma have done us all a real service in compiling so much insight and experienceinto this easy to follow text. I highly recommend this book to all who have to manage patients with cornealulceration.

Professor Hugh R TaylorAC MD BS FRANZCO FRACS FAAO FACS

Ringland Anderson, Professor of Ophthalmology and HeadUniversity of Melbourne, Department of Ophthalmology

Managing Director, Centre for Eye Research, Australia

Corneal Ulcers: Diagnosis and Management is a must-read reference and resource for every ophthalmologist interestedin anterior segment ocular pathology. It contains the most up-to-date information about the recognition and treatmentof this very severe and potentially blinding condition.

Dr. Rasik Vajpayee and Dr. Namrata Sharma have both published hundreds of papers and chapters in this areaand have a vast experience in diagnosing and treating corneal ulcers. They have put their combined knowledge toexcellent use by writing an outstanding textbook and guide to the management of these ulcers.

From the beginning chapters on the pathogenesis, microbiology and pharmacology of corneal ulcers, the writingis clear, concise and readily absorbed. It is not encyclopedic, but very practical, with superb color photographs andeasily read box inserts highlighting the most significant material in the chapters.

Their chapter in Section 2 on the work up of a corneal ulcer is particularly illuminating, especially the manycolor illustrations of microbiological organisms and the havoc they can bring to the cornea. There is an excellentstep by step approach to diagnosing and managing corneal ulcers, from the simple ones to the most complex.

Drs. Vajpayee and Sharma are particularly gifted in the field of microbiology, and their chapter on investigationsof corneal ulcers in Section 2 is extremely well designed, with inclusive but not overwhelming tables on how toproceed with an ulcer work up. In Section 4, the chapters highlight specific types of microbial and immunologickeratitis, including pediatric and peripheral ulcerative keratitis. The writing throughout is again very clear and thephotographs complement the text beautifully.

The surgical management section includes very high-quality illustrations on the use of glue and bandage contactlenses, conjunctival flaps, therapeutic keratoplasty and phototherapeutic keratectomy, with which both authorshave extensive expertise, due to the severe and late-stage ulcerations treated in India.

I can strongly suggest, if not emphatically state, that this treatise will be a best-seller around the world and aninvaluable aid in addressing the problems of corneal ulceration.

Peter R. Laibson MD

Professor of OphthalmologyThomas Jefferson University School of Medicine

Director EmeritusCornea Department

Wills Eye InstitutePhiladelphia, Pennsylvania

Foreword

Preface

Corneal ulcer is a major cause of blindness in the developing world. The condition requires early recognition andprompt management to minimize the impact of disease process. There are many books available on the cornealand external diseases and include details on various aspects of corneal ulcer. However, most of these books carryenormous amount of information, some of which may not be required for the routine management of a case ofinfectious keratitis. We felt that there is a need for a book on the specific aspect of corneal ulceration that carriesrelevant, specific and practical information and can help general ophthalmologists in treating cases of cornealulceration effectively. Our book includes a chapter highlighting a practical approach on how to examine a case ofinfectious keratitis and chapters on various types of keratitis. It also includes chapters on basic sciences relevant tocorneal ulcer and provides comprehensive information on various management issues including surgical options,if required. We have tried to provide a precise format for our book and have written it in a user-friendly style. Wehope that this book will serve as a useful guide for the residents as well as the general ophthalmologists.

Namrata SharmaRasik B Vajpayee

Acknowledgements

We would like to acknowledge Dr Tushar Agarwal, Dr M Vanathi, Dr Tishu Saxena and Dr Gunjan Prakash fortheir useful inputs. We would also like to thank Departments of Microbiology of All India Institute of MedicalSciences and St. Vincent Hospital for the photographs. Our heart felt to heartfelt gratitude to Ms Meena Verma,Ms Sudha, and Ms Lata for helping us with clinical photography.

Contents

SECTION 1: APPLIED BASIC SCIENCES

1. Anatomy and Physiology 3

2. Pathogenesis of Corneal Ulcer 8

3. Microbiology 13

4. Pharmacology 25

SECTION 2: WORK UP OF CORNEAL ULCER

5. Clinical Examination 35

6. Investigations 51

SECTION 3: TYPES OF MICROBIAL KERATITIS

7. Bacterial Keratitis 65

8. Fungal Keratitis 77

9. Viral Keratitis 91

10. Protozoal Keratitis 107

SECTION 4: SPECIFIC TYPES OF KERATITIS

11. Pediatric Keratitis 119

12. Contact Lens Related Keratitis 128

13. Infectious Crystalline Keratopathy 134

14. Post-surgical Microbial Keratitis 140

15. Keratitis and Endophthalmitis 150

16. Neurotrophic Keratitis 154

17. Peripheral Ulcerative Keratitis 162

SECTION 5: SURGICAL MANAGEMENT

18. Intracameral Antibiotics 177

19. Glue Application 180

20. Conjunctival Flaps 184

21. Therapeutic Keratoplasty 187

22. Phototherapeutic Keratectomy 197

Index 199

Anatomy and Physiology

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Cornea is the principal refractive surface of the humaneye and along with sclera forms the outermost coat ofthe eyeball. It constitutes up to one-sixth of the entireeyeball. The corneal epithelium is derived from thesurface ectoderm and the mesoderm gives rise toBowman’s layer, stroma, Descemet’s membrane andendothelium. The average diameters of the cornea varyfrom 11 to 12 mm horizontally and 9 to 11 mm vertically.Cornea accounts for approximately 48 diopters of thepower. The posterior surface of the cornea is morespherical than the anterior surface and the central corneais thinner (520 μm) than the peripheral cornea (650 μmor more). The tear film covers the anterior cornealsurface and the posterior corneal surface is in contactwith the aqueous.

PRE-CORNEAL TEAR FILMThe tear film forms an important defense mechanismagainst the microbial infection. It is 7 μm thick and hasa volume of 6.5 ± 0.3 μl.1 The tear film is made up of anouter lipid layer (0.1 μm), middle aqueous layer (7 μm)and innermost mucin layer (0.02 to 0.05 μm).2 It is now


Figure 1.1: Histology of the layers of corneaFigure 1.2: Histologic section of cornea consisting of epithelium,basement membrane and stromal layers

1

believed that the tear film is actually a two-layeredstructure where under the lipid layer lies an aqueous–mucin gel, in which the mucins have a decreasinggradient of concentration from the epithelium to thesurface.3 Tear film keeps the corneal surface moist andprevents the adherence of microbes. A deficient pre-corneal tear film may predispose to the occurrence ofcorneal infection.

More than 98 percent of the volume of the tears iswater. The tear film has many essential substances suchas electrolytes, glucose, immunoglobulins, lactoferrin,lysozyme, albumin and oxygen. It also has manybiologically active substances such as histamines,interleukins, prostaglandins and growth factors.4 Someof these factors modulate corneal epithelial migration,proliferation and differentiation.

STRUCTURE OF CORNEA

Cornea essentially consists of 5 layers namely—epithe-lium, Bowman’s layer, stroma, Descemet’s membraneand the endothelium (Figs 1.1 to 1.3).

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EPITHELIUM

Corneal epithelium has a thickness of 50-90 μm and iscomprised of five to seven layers of stratified, squamousand non-keratinized cells (Fig. 1.2). It represents 10percent of the total corneal thickness.

The cells of corneal epithelium can be classified into three categories—the superficial squamous cells,middle wing cells and deeper basal cells.5

Superficial Squamous Cells

Superficial or squamous cells form the outermost 1-2layers of corneal epithelial cells. They are the oldestepithelial cells and they disintegrate and shed into thetear film by the process of desquamation. These cellshave microscopic projections (microvilli, reticulations,microplicae) and fibrillar glycocalyx on their whichinteracts with the mucinous tear film. The epitheliumturns over approximately every 7 to 14 days.6

The superficial cells are connected to each other bydesmosomes and junctional complexes. This complexconsists of tight junctions, which surround the entirecell, and resist the flow of fluid through the epithelialsurface.

Middle Wing CellsThe middle layer of the corneal epithelium consists ofthe wing cells, which have lateral, thin wing likeextensions emanating from a more rounded cell body.The adjacent cells are joined by desmosomal junctionsand gap junctions.

Deep Basal CellsThe basal cells are cuboidal to columnar in shape andare 8 to 10 μm in diameter. Posteriorly, the cells are flatand are supported by a basal lamina to which they areattached by hemi-desmosomes. The basal cells aremetabolically active and divide giving rise to the wingand the superficial cells.

While corneal epithelium acts as a tough protectiveshield against microorganisms and foreign bodies, it hassome permeability to small molecules including glucose,sodium oxygen and carbon dioxide.

BASEMENT MEMBRANE

The basal cells of corneal epithelium are attached byhemi-desmosomes to a basement membrane, whichis located between the corneal epithelium and theBowman’s membrane and contains type IV and typeVII collagen and glycoproteins. The basement layer ofcorneal epithelium has two parts: Lamina lucida(superficial) and Lamina densa (deep).

BOWMAN’S LAYER

The Bowman’s layer is an acellular membrane like zone,8 to 14 μm thick and has numerous pores for the pas-sage of corneal nerves into the epithelium. Ultrastruc-turally it is made up of a fine meshwork of uniformcollagen fibrils of type I and III.

CORNEAL STROMA

The corneal stroma is approximately 500 μm thick andcomprises 90 percent thickness of the cornea and islocated between the Bowman’s layer and Descemet’smembrane (Fig. 1.2). It is composed of lamellae formedfrom flattened bundles of collagen, stromal keratocytesand ground substances like keratan sulphate. Collagen(type I is the major constituent, others are III and VI) isthe major structural component of corneal stroma. Thereare 200 to 250 bundles of collagen fibrils. Each bundleextends the width of the cornea and is 2 nm thick and 9to 260 nm wide. The collagen fibers are arranged in aregular manner, parallel to the corneal surface. Sucharrangement and equal spacing of collagen fibers createsa lattice or three-dimensional diffraction grating, whichis responsible for the ability of the cornea to scatter98 percent of the incoming light rays. The lamellae inthe posterior part of the stroma have an orthogonallayering, i.e. the bundles are at right angles to each other.

Figure 1.3: Histologic section of cornea consisting of stromal layers,Descemet’s membrane and endothelium


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1In the anterior one-third of the stroma, the lamellae havea more oblique layering.

The primary glycosaminoglycans of the stroma arekeratin sulfate and chondroitin sulfate, which occur inthe ratio 3:1. The lamellar stroma is secreted andmaintained by stromal fibroblasts called the keratocytes,which occupy 3-5 percent of the stromal volume. Theyare responsible for the maintenance of stromalcomponents and they synthesize collagen degradativeenzymes such as matrix metalloproteases (MMPs).5

The MMPs are particularly important in thepathogenesis of peripheral ulcerative keratitis as theyaccumulate in the tears and trigger an autoimmuneresponse involving the ocular tissue. Keratocytesundergo cellular differentiation in response to injuryconverting into fibroblasts. Keratocytes usually liebetween the lamellae being flat with long attenuatedprocesses extending from a central cell body in alldirections. Depletion of keratocytes is a characteristicfeature of Acanthamoeba keratitis.

DESCEMET’S MEMBRANE

Descemet’s membrane is the basement membrane of thecorneal endothelium and is synthesized by the endothe-lium.7 At birth, the human Descemet’s membrane is3 μm wide but in adulthood, the width increases to12 μm (Fig. 1.3). There are two distinct regions—anterior,one-half to one-third, which is banded, and posteriortwo-third, which is non-banded.

In certain types of bacterial keratitis and Mooren’sulceration, this membrane remains intact and protrudesas a descemetocele due to the intraocular pressurefollowing dissolution of overlying stroma.5

ENDOTHELIUM

The corneal endothelium is a single layered, lowcuboidal endothelium. There are approximately 400,000cells, 4 to 6 μm thick. These cells are hexagonal in shapeand 20 μm wide. The endothelial cells have tight lateralinterdigitations, preventing seepage of aqueous humorinto the stroma. Further, specific functional complexesare also present near the apical membranes.

The number of endothelial cells, present decreaseswith age at the rate of 0.3 to 0.6 percent per year. Atbirth, the cell densities range from 3,500 to 4,000 cells/mm2 whereas an adult has densities of 1400 to

2500 cells/mm2. As cells decrease in number, theybecome thinner and attenuated. Cornea loses it claritywhen the endothelial cell densities reach 400-700 cells/mm2 below which corneal edema occurs.

Unlike corneal epithelium, endothelial cells cannotundergo mitosis after birth. The endothelial cells arelinked to each other by junctional complex structuresand presence of gap junctions but no desmosomes arepresent.

The endothelial cells do not replicate in humanbeings. The endothelial cells decrease in density withincreasing age, raised intraocular pressure, followingintraocular surgery and inflammation.

The corneal endothelium plays a major role inmaintaining stromal hydration (which is normally 78%)through the Na-K-activated adenosine triphosphatase(ATPase) present in the basolateral borders of the cells.

INNERVATION OF THE CORNEA

The cornea is primarily supplied by the sensory nervesderived from the ciliary nerves of the ophthalmic branchof the trigeminal nerve. The long ciliary nerves supplythe perilimbal nerve ring. Nerve fibers penetrate thecornea in the deep peripheral stroma radially and thencourse anteriorly forming a terminal subepithelialplexus. The nerve fibers lose their myelination soon afterpenetrating the clear cornea and enter the Bowman’slayer and terminate at the level of the wing cells. Anautonomic sympathetic supply is also present in thecornea.

The physiologic role of corneal innervation is unclear.Presence of corneal sensation is vital to the maintenanceof the integrity of the cornea. In cases of herpes simplex,herpes zoster and diabetes, corneal sensations arediminished and this may lead to persistent epithelialdefects or delayed epithelial wound healing.

BLOOD SUPPLY

The cornea is one of the few avascular tissues in thebody. The normal healthy cornea does not have anyblood vessels. The anterior ciliary artery derived fromthe ophthalmic artery forms an arcade at the limbus.

OXYGEN AND NUTRITIONAL SUPPLY

Oxygen is supplied primarily from the diffusion fromthe tear film. Oxygen from the air is also dissolved inthe tear fluid. To a lesser extent oxygen is also obtained

1 Applied Basic Sciences

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from the aqueous and the limbal vessels. Thus duringcontact lens wear the oxygen diffusion from theatmosphere is less. Also, in patients who sleep with theircontact lenses on, the metabolism converts from aerobicto anaerobic causing lactic acid to accumulate in thecornea.

Applied Physiology of Cornea

The basis of corneal physiology consists of the under-standing of corneal epithelial barrier, endothelial barrierand metabolic pump functions. The factors which affectthe hydration of the cornea include the following: Thecorneal epithelial barrier, the endothelial barrier, themetabolic pump function, evaporation and the intra-ocular pressure. If either of these barriers is compro-mised, it manifests as corneal swelling. A greaterincrease in the corneal thickness occurs when endothelialcells are compromised (which may be as much as morethan two times) as compared to the damage of theepithelial cells. Metabolic pump function also plays avital role as the corneal stroma swells up due toincreased tonicity of the stromal components, whichcontains collagen, salts and proteoglycans.

The corneal stromal swelling pressure is 60 mm Hgand corneal stromal swelling occurs if endothelial barrieris disrupted as the intraocular pressure of 15 mmHg isunopposed and the aqueous seeps into the stroma.

Both the anterior and the posterior surfaces of thecornea contribute to its optical function. The totalrefractive index of the cornea is the sum of the refractionat the two interfaces as well as the transmissionproperties of the tissue. The refractive index of the air,tear, cornea and aqueous humor are 1.0,1.336, 1.376 and1.336 respectively. The refractive power at the curvedsurface is determined by the refractive index and theradius of curvature. Refractive power at the centralcornea is about +43 diopters and is the sum of therefractive power at the air-tear (+44 diopters), tear-cornea (+5 diopters) and cornea-aqueous humor(-6 diopters) interfaces.

The anterior and posterior corneal stroma is differentmorphologically. Dermatan sulphate, which has greaterwater retentive property, is located more in anteriorstromal layers whereas keratin sulphate is located morein the posterior stromal layers. Hence, clinically, ifedema is restricted to the posterior layers, it resolvesmore easily.

CORNEAL TRANSPARENCY

The corneal transparency is unique and is attributed toits avascular status, peculiar arrangement of collagenfibers, absence of myelin sheath in its nerves and cornealendothelial pump.

According to the lattice theory proposed by Maurice,the cornea maintains its transparency because thecollagen fibrils are of equal diameter (275-350A°) andare equidistant from each other.8 Thus the incident rayscattered by each collagen fiber is cancelled by theinterference of other scattered ray which allows it to passthrough the cornea. Corneal decompensation due tocorneal hydration occurs as the proteoglycans withinthe corneal lamellae imbibe water and this equilibriumis disturbed leading to a loss of transparency.

The biochemical and physical properties of thestroma are normally maintained by the presence of afunctional epithelial and endothelial barrier and ametabolic pump function so that the water content ismaintained at 78 percent.

Normal Defense MechanismCornea along with conjunctiva and tear film act as amajor component of ocular defense system against themicrobial infections. While corneal epithelium acts as amechanical barrier, the cellular and chemical compo-nents of conjunctiva and pre-corneal tear film act asbiologic protective systems.

There are multiple barriers to ocular infection.Anatomically, the eye is protected from the introductionof microbes due to trauma by the surrounding bonystructure of the protruding orbital rim. The cilia protectthe eyelid by a rapid blink reflex.

The eyelid skin, cilia and adnexal surfaces arenormally inhabited by nonpathogenic/saprophyticaerobic and anaerobic bacteria which decreases thechances of colonization by the pathogenic microbes.Additionally, the intact epithelial surfaces of theconjunctiva and cornea provide a formidable barrier tothe invasion by the microorganisms.

The presence of an intact tear film and its drainageby the lacrimal apparatus acts as an intrinsic barrier toinfection. The microorganisms, foreign bodies anddesquamated epithelial cells are continuously washedout of the eye due to blinking and lacrimal drainagesystem. The mucus layer of the tear film also providesantimicrobial properties which inhibits the bacterialadhesion to the epithelial cell layer. Other molecules


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which provide antimicrobial protection are microbe-specific antibodies (especially IgA) and non-specificantimicrobial molecules such as complement, lactoferrin,lysozyme and β-lysin (Table 1.1).

The conjunctiva has conjunctiva associated lymphoidtissue (CALT) wherein, immunity is initiated by expo-

TABLE 1.1Barriers to microbial infection

1. Anatomical • Bony orbital rim• Eyelids• Eyelid cilia• Intact epithelial surface of conjunctiva and cornea

2. Mechanical• Tear film• Blinking• Punctal drainage system

3. Antimicrobial• Tear film constituents

• Mucus layer• IgA• Complement• Lactoferrin• Lysozyme• β-lysin

• Conjunctiva• Conjunctiva associated lymphoid tissue (CALT)

sure to exogenous antigen by the production of antibodywhich is IgA isotype.

References

1. Scherz W, Doane MG, Dohlman CH. Tear volume innormal eyes and keratoconjunctivitis sicca.Albrecht VonGraefes Arch Klin Exp Ophthalmol 1974;192:141-50.

2. Holly FJ, Lemp MA. Tear physiology and dry eyes. SurvOphthalmol 1977;22:69-87.

3. Dilly PN. Structure and function of tear film. Adv ExpMed Biol 1994;350:239-47.

4. Ohashi Y, Motokura M, Kinoshita Y, Mano T, WatanabeH, Kinoshita S, et al. Presence of epidermal growth factorin human tears. Invest Ophthalmol Vis Sci 1989;30:1879-82.

5. Nishida T. Cornea. In: Krachmer JH, Mannis MJ,Holland EJ (Eds): Cornea: Fundamentals , Diagnosis andmanagement. 2nd edition, Elsevier Mosby, Philadelphia,2005;1:3-20.

6. Hanna C, Bicknell DS, O’Brien JE. Cell turnover in theadult human eye. Arch Ophthalmol 1961;65:695-8.

7. Johnson DH, Bourne WM, Campbell RJ. The ultrastruc-ture of Descemet’s membrane. I. Changes with age innormal corneas. Arch Ophthalmol 1982;100:1942-7.

8. Maurice DM. The cornea and sclera. In: Davison H (Ed):The eye, 3rd edn, Vegetative physiology andbiochemistry, Orlando, Academic Press 1984;1B.

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Applied Basic Sciences

IntroductionCorneal ulceration occurs due to the host cellular andimmunologic responses to the offending agent whichmay be bacterial, viral, fungal or protozoal organism.Sometimes it is sterile corneal ulceration, which mayoccur due to systemic dermatologic or connective tissuedisease and chemical or thermal injuries.

The host cellular responses are mainly responsiblefor corneal destruction in infections and sterile cornealmelting. In all cases, stromal melting is preceded by acorneal epithelial defect. The ulceration occurs secon-dary to the action of tissue collagenases. The polymor-phonuclear cells (PMNs) are secreted in response to thecorneal insult, which secrete various lytic enzymes suchas collagenase, elastase and cathepsin causing destruc-tion of the cornea.1 Simultaneously, reactive fibroblasts,synthesize collagen and cause repair of the cornea.

Apart from the infective processes, the immunologicmechanisms consequent to infection may also play arole. For example, in herpes simplex interstitial keratitisstromal cellular destruction occurs due to immunologicmechanisms as a consequence of acquisition of herpesantigens, thereby resulting in an influx of PMNs andphagocytes, which cause tissue destruction.

For the reparative phase of corneal ulcer, the inter-action between the keratocytes and blood vessels isessential. Stromal vascularization inhibits the ulcerativeprocess as nutrients (such as ascorbate) and antiprotea-ses are delivered by the vessels to the ulcerated area.2

STAGES OF CORNEAL ULCER

The course of events, which occur in the process ofcorneal ulceration, can be divided into three stages.

Stage 1: Progressive Stage

In the progressive stage, the ulcer is usually saucershaped and is associated with gray zone of infiltration

(Fig. 2.1). In this stage, the microbes adhere to theepithelium, release toxins and enzymes and cause tissuedestruction (Fig. 2.2).

Pathogenesis ofCorneal Ulceration

2

Figure 2.1: Corneal ulcer

Figure 2.2: Histologic section shows breach in the corneal epithelium(Courtesy: Dr Seema Sen)

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1Pathogenesis of Corneal Ulceration

Adhesion of the organisms is facilitated by bacterialpili and a glycocalyx envelope in bacteria such asPseudomonas and Gonococcus. In response to this, PMNsare generated at the ulceration site. The PMNs originatefrom the tears initially and limbal vessels consequentlyin response to the corneal injury. Progressive invasionof the cornea by the PMNs and the phagocytes increasesthe size of the ulceration, due to release of various lyticenzymes by the microbes.

This leads to necrosis and sloughing of the epithe-lium, Bowman’s membrane and the involved stroma(Fig. 2.3) .The walls of the active ulcer project due to theswelling of the lamellae by imbibition of fluid. Ulcerationmay progress further by lateral extension leading todiffuse superficial ulceration or by deeper penetrationof infection leading to descemetocele formation andpossibly corneal perforation .

Stage 2: Regressive Stage

The termination of the progressive stage and the onsetof the regressive stage is brought by the natural hostdefense mechanisms (humoral antibody response andcell mediate immune defenses) and the anti-microbialtreatment. There is an improvement in the sympto-matology and clinical signs. A line of demarcation formsaround the ulcer so that the margin and floor of theulcer become more smooth and transparent. The line ofdemarcation consists of leukocytes that neutralize andeventually phagocytose the offending organism and thenecrotic cellular debris. The digestion of the necroticmaterial may cause an initial enlargement of the ulcer.

This process may be accompanied by superficialvascularization.

Stage 3: Healing Stage

The process of epithelialization starts to occur at thisstage. The histiocytes and keratocytes convert tofibroblasts so that the scar tissue is formed. Vasculari-zation occurs towards the ulcer site, which furtherpromotes healing as a result of influx of fibroblasts andantibodies. When the healing is complete, the vesselsregress and become “ghost vessels” which may bevisualized by indirect illumination.2

The degree of scarring from healing varies accordingto the depth of involvement. Bowman’s membrane doesnot regenerate and is replaced by fibrous tissue, whichover a period of time becomes less dense, especially inyoung patients. The process of cicatrization occurs dueto regeneration of collagen and the formation of fibroustissue. Since the newly formed fibers are not laid downin a regular manner as in normal corneal lamellae, ascar is formed which causes the light to be refractedirregularly.3

SEQUEL AND COMPLICATIONS

Corneal ulcers involving the superficial lamellaegenerally heal by varying degrees of scarring dependingon the severity of inflammation. However, if theinfection is severe, there may be thinning, formation ofa descemetocele ectatic cicatrix or perforation.

Corneal Opacification

Depending on the depth of the corneal ulceration, diffe-rent types of corneal opacities may occur that is, nebular,macular (> 50% involvement) or leukomatous (> 75%involvement) (Figs 2.4A to D).

Descemetocele

Some corneal ulcers, especially due to Pneumococciextend rapidly in depth so that the entire thickness ofthe cornea except Descemet’s membrane or few isolatedcorneal lamellae are spared. The Descemet’s membranelike any other elastic membrane offers resistance to theinflammatory process, but is unable to withstand theintraocular pressure and therefore herniates through thecorneal ulcer as a transparent membrane called asdescemetocele or a keratocele (Fig. 2.5). This is often

Figure 2.3: Histologic section of corneal ulcer shows stromalinflammation (Courtesy: Dr Seema Sen)

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Figure 2.5: Descemetocele formation with perforation Figure 2.6: Perforated corneal ulcer with pseudocornea formation

Figures 2.4A to D: Healing corneal ulcer with end stage leukomatous corneal opacity

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1Pathogenesis of Corneal Ulceration

surrounded by a white cicatricial ring and under theinfluence of a raised intraocular pressure may eventuallyrupture.

Perforation

Perforation of corneal ulcer occurs due to suddenexertion by the patient such as coughing, sneezing,straining or spasm of the orbicularis muscle. An increasein intraocular pressure occurs due to these maneuversso that the weak floor of the ulcer gives way. When anulcer perforates, the aqueous suddenly escapes and theintraocular pressure falls to the atmospheric levels.Subsequently, the lens iris diaphragm moves forwardand adheres to the back of the cornea. Due to thedecreased intraocular pressure, the pain is alleviated;extension of the ulcer decreases and the process of scarformation is initiated.

If the perforation is small, the iris is plugged to theback of the cornea, adhesions from the iris get organizedand the scar tissue is formed which is called as“pseudocornea” (Fig. 2.6). The iris, which is plasteredat the back of the cornea, allows anterior chamber toform and hence aqueous is secreted.

If the perforation is large, the iris prolapses out ofthe site of perforation; in cases of longstanding of irisprolapse, fibrin and exudates deposition occurs on thesurface, thinning of the iris stroma occurs and the blackpigmentary epithelium becomes visible. Thus anyadherence of iris tissue to the back of cornea, which issubsequent to a perforated corneal ulcer, is called as acorneo-iridic scar (Fig. 2.7).

In very large perforations, only a small rim of thecornea remains and the total prolapse of the iris andthe lens may occur (Fig. 2.8). If the perforation occurs

Figure 2.7: Corneo-iridic scar Figure 2.8: Large corneal perforation and corneal melting

suddenly, the suspensory ligament of the lens gives way,causing subluxation of the lens, anterior dislocation andspontaneous expulsion of the lens and the vitreous throughthe perforation (Figs 2.9A and B).

Ectatic Cicatrix

Due to the presence of anterior synechiae and pluggingof the iris, adherent leukoma is formed and this leadsto secondary glaucoma. The cicatricial tissue is too weakto support this raised intraocular pressure and hencethe cicatrix becomes ectatic. An ectatic cicatrix into whichthe iris is incarcerated is called as the anterior staphyloma,which may be partial or total. It is so called due to thelobulated appearance (Fig. 2.10).

Corneal Fistula

If the perforation occurs near the pupillary margin, theiris becomes adherent to the back of the cornea and theaperture is filled with the fibrin and the exudates. Asthe anterior chamber reforms, the aperture is subjectedto repeated strain, so that a permanent opening formswhich is called as the corneal fistula (Fig. 2.11).

Hemorrhage

The sudden decrease in the intraocular pressure whenperforation occurs dilates the intraocular blood vessels,which may rupture causing an intraocular hemorrhage.Rupture of retinal vessels may give rise to vitreoushemorrhage, choroidal, a subretinal or subchoroidalhemorrhage. It may be so profuse that it may lead toexpulsion of the intraocular components leading on toexpulsive hemorrhage.

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Endophthalmitis

The organisms, which are causing the ulceration of thecornea, may gain access to the interior of the eye as aresult of perforation and cause purulent iridocyclitis,endophthalmitis (Fig. 2.12) and even panophthalmitis.

References1. Kenyon KR, Ghinelli E, Chaves HV. Morphology and

pathologic response in corneal and conjunctival disease.In: Foster CS, Azar DT, Dohlman CH (Eds): Smolin andThoft’s Cornea. Lippincott Williams and Wilkins NY;4th edition, 2005;4:103-40.

2. Kenyon KR. Inflammatory mechanisms in cornealulceration. Trans Am Ophthalmol Soc 1985;83:610-63.

3. Nordlund M, Pepose JS. Corneal Response to Infection.In: Krachmer JH, Mannis MJ, Holland EJ (Eds): Cornea,2nd Edition Elseivier Co. NY. 2005;7:95-114.

Figure 2.10: Anterior staphyloma subsequent to perforatedcorneal ulcer

Figure 2.11: Corneal fistula

Figures 2.9A and B: Perforation causing spontaneous expulsion of lens and vitreous

Figure 2.12: Corneal ulcer with endophthalmitis

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1Microbiology

Microbiology3

IntroductionThe various microorganisms which can cause infectiouskeratitis can be classified into eukaryotic and prokaryoticorganisms (Table 3.1). The eukaryotic organisms includethe relatively complex cells such as protozoa and thefungi and the prokaryotic organisms are more primitivecells, which include the filamentous bacteria, truebacteria, spirochaetes, mycoplasma and rickettsiae andchlamydiae.

ProtozoaProtozoa are unicellular organisms which exist in twomorphologic phases. Examples which cause ocularinfections include the Acanthamoeba and theMicrosporidia.

AcanthamoebaPrimarily, Acanthamoeba is the protozoa, which can causekeratitis. The pathogenic species of Acanthamoebainclude Acanthamoeba castellanii, Acanthamoeba polyphaga,Acanthamoeba culbertsoni, Acanthamoeba palestinensis,Acanthamoeba astronyxis, Acanthamoeba hatchetti, Acan-thamoeba rhysodes, Acanthamoeba divionesis, Acanthamoebaequina, Acanthamoeba lugdunensis, and Acanthamoebagriffini.1

Acanthamoeba are ubiquitous organisms and havebeen isolated from soil, water (including natural andtreated water), air, and dust. They are free living, patho-genic amoeba. Most persons are exposed to thisorganism during their lifetime, as 50-100 percent ofhealthy people have serum antibodies directed againstAcanthamoeba.

The life cycle consists of 2 stages: a trophozoite(which is 14-45 microns in diameter) and a cyst (whichhas a double-layered wall with a diameter of 10-25microns). The trophozoites are motile and usually haveone nucleolus and huge cytoplasmic vacuoles and feedson bacteria (Fig. 3.1). In unfavorable conditions thetrophozoites encyst.2 The cyst has a double wall, whichis made of cellulose (Fig. 3.2). The cyst is resistant toalterations in temperature, pH, osmolarity and anti-microbial agents.

MicrosporidiaMicrosporidia are eukaryotic, spore forming obligateintracellular parasites. Microsporidial keratitis occurs intwo forms keratoconjunctivitis is usually seen inimmunocompromized individuals or in contact lenswearers, mostly by genus Encephalitozoon while Nosemaand Microsporidium cause the stromal keratitis which isgenerally seen in the immunocompetent host.3 Mostinfections are transmitted by feco-oral route but cornealinfections occur due to direct inoculation. These

TABLE 3.1Classification of microorganisms causing infectiouskeratitis

EUKARYOTESProtozoa

Sporozoa : ToxoplasmaAmoebae: Entamoeba, Naegleria, AcanthamoebaMicrosporidia

FungiMould like: AspergillusYeast like: CandidaDimorphic : Histoplasma. Blastomyces, CoccidioidesTrue yeasts: Cryptococcus

PROKARYOTESFilamentous bacteria

Actinomyces, Nocardia, Mycobacterium, StreptomycesTrue Bacteria

Gram-positive Bacilli and CocciGram-negative Bacilli and Cocci

SpirochaetesBorrelia, Treponema, Leptospira

MycoplasmaRickettsiae and Chlamydia

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organisms stain poorly with the routine stains such asthe Gram’s, Giemsa, Gomori methanamine silver,Periodic acid Schiff and immunofluorescent techniques.However, they stain well with calcoflor white stain.4

MycologyKeratomycosis is common in tropical climatic regionsand is a common cause of corneal ulcer. Fungi areopportunistic organisms and rarely affect intact cornea,but in a compromised or immunosuppressed state suchas ocular surface disease, topical steroid use or traumawith vegetable matter particularly, they becomepathogenic.

The cell wall of the fungi is primarily made up ofpolysaccharide (80 to 90%) and the remainder is proteinor lipid.

Keratomycotic fungi can be broadly classified intofilamentous fungi, yeasts, or dimorphic fungi (Table 3.2).

More than 105 species of fungi classified in 56 generahave been reported to cause oculomycosis. Fungi aresaprophytic, and/or pathogenic organisms. Saprophyticfungi obtain their nutrients from decaying organicmatter, whereas pathogenic fungi feed on living cells.Pathogenic fungi are actually saprophytic microbes,which cause disease in humans. Many fungi associatedwith ocular infections are saprophytic.

Fungal isolates can be classified into four groups:Moniliaceae, which are nonpigmented filamentary fungiincluding Fusarium spp and Aspergillus spp; Dematiaceae,which are pigmented filamentary fungi includingCurvularia spp and Lasiodiplodia spp; yeasts, which includeCandida spp; and other fungi.

FILAMENTOUS FUNGI

Molds are filamentous fungi, which are multicellularorganisms and possess hyphae and grow by apicalextension or branching. They have a rigid cell wallcomposed of outer chitin and inner sterol containingcytoplasmic membrane. According to the presence orabsence of cross walls in the hyphae the filamentousfungi are classified as septate or non-septate. Most fungalkeratitis is caused by filamentous fungi which haveseptate hyphae.

Fungi with septate hyphae may be divided into non-pigmented fungi or pigmented fungi based upon

Figure 3.1: Acanthamoeba trophozoite (phase contrast microscopy)(Courtesy: Dr H Sheorey, Dept. of Microbiology, St Vincent Hospital,Melbourne)

Figure 3.2: Acanthamoeba cyst (phase contrast microscopy)(Courtesy: Dr H Sheorey, Dept. of Microbiology, St Vincent Hospital,Melbourne)

TABLE 3.2Fungal organisms causing keratitis

I. FILAMENTOUSA. SEPTATED

1. NonpigmentedFusarium: Solani, oxysporum, moniliforme,episphaeriaAspergillus: fumigatus, flavusAcremonium (Cephalosporium)PaecilomycesPenicillium

2. Pigmented (Dematiaceous)Curvularia: Senegelensis, verruculosa, pallescensLasiodiplodiatheobromaeAlternariaCladosporiumCelletotrichumDrechslera (Helminthosporuim)

B. NONSEPTATEDRhizopus (mucormycosis)

II. YEASTCandida: Albicans, parapsilosis, krusei, tropicalis

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1Microbiology

whether the hyphae are pigmented or non-pigmentedon the culture media. Filamentous septate fungi can thusbe broadly classified into:

i. Moniliaceae (light colored fungi like Fusarium andAspergillus species)

ii. Dematiaceae (dark colored fungi such as Alternariaand Curvularia).

YEASTS

Yeasts are unicellular fungi, represented by Candida, andare characterized by an oval or round blastoconidium.Yeasts reproduce by budding and are characterized bythe presence of pseudohyphae (Fig. 3.3). The phase,which has pseudohyphae, is the most virulent phase.The cell walls of pseudohyphae have constrictions andare not parallel to each other unlike the hyphae.

Candida species especially Candida albicans commonlycauses majority of the cases of keratitis. In culture theyform smooth creamy white colonies resemblingstaphylococci in the early phases of growth. Thepresence of budding yeasts in corneal scrapings isdiagnostic for Candida.5 This organism produces bothtrue hyphae and pseudohyphae. Both yeast and hyphalforms can be seen in corneal scrapings. Candida coloniesare white to tan and opaque with smooth, round, flatcontour and pasty consistency. They have a distinctivefruity odor, which aids in easy identification.

DIMORPHIC FUNGI

Some fungi appear as yeasts in vivo at 37 oC and moldsin the environment at 25oC. They are called as dimor-

phic fungi. These include Blastomyces, Coccidioides,Histoplasma and Sporothrix.

Moniliaceae

ASPERGILLUS

This is a common contaminant in hospital air. Aspergillusfumigatus is the most commonly isolated species, whileAspergillus flavus and Aspergillus niger may also causekeratitis. The Aspergillus fungi are readily recognizedby their morphology (Fig. 3.4). The conidospore withits swollen terminal end is surrounded by a flask shapedsterigmata, each of which produces long chains ofconidia that radiate from the terminal end (Fig. 3.5).Their hyphae are septate and branch dichotomously.6

In infections progressing rapidly they are more uniformbut in more indolent infections the hyphae may beirregular in shape.

Colonies of A. fumigatus are at first white but asspores are produced they become velvet green due topigmentation of conidia. A. niger on the other hand,turns completely black as they undergo sporulation.

FUSARIUMFusarium causes localized infection after trauma inotherwise healthy patients. Fusarium solani is the mostcommon species. It has sickle shaped macroconidia andclusters of fusiform microconidia (Fig. 3.6). Fusariumcolonies are white initially and later acquire a buffcoloration. A range of color pigments from yellow tored to purple is produced on the undersurface of thecolony (reverse pigmentation).7

Figure 3.3: Gram stains shows yeast cells (Courtesy: Dr N Nayak)Figure 3.4: Gram stain shows Aspergillus (Courtesy: Dr H Sheorey,Dept. of Microbiology, St Vincent Hospital, Melbourne)

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DEMATIACEAE

Dematiaceous fungi have melanin in their hyphal wallsand hence are dark pigmented (olive, brown or black)when viewed under a microscope. Only 27 percent ofcorneal ulcers caused by dematiaceous fungi appear tobe darkly pigmented macroscopically. Curvularia(Fig. 3.7), Alternaria (Fig. 3.8) and Cladosporium belongto this category.

BacteriologyBacteria are unicellular prokaryotic organisms. Thecornea does not generally have any colonizing bacteria.Bacteria from eyelids may contaminate the ocularsurface and cause corneal ulcer.

Pathogenic bacteria consist of virulence factors,which is responsible for infectious keratitis. Theseinclude specific antigens, proteolytic enzymes, hemo-lysins and toxins. In general non-pathogenic bacteria donot cause keratitis except in compromised conditionswhen they gain access to the cornea.

The classical differential system of staining thebacteria divides the bacteria into gram-positive andgram-negative bacteria depending on the presence ofpeptidoglycan and lipid layer of the cell wall. Gram-positive bacteria are more frequently isolated ascompared to the gram-negative bacteria in the ratio ofapproximately 60 to 40 percent. Apart from this thereare other stains such as acid-fast, which may be, usedto characterize the mycobacteria species.

Figure 3.5: Aspergillus fumigatus (Courtesy: Dr N Nayak) Figure 3.6: Fusarium species (Courtesy: Dr N Nayak)

Figure 3.7: Curvularia species (Courtesy: Dr N Nayak) Figure 3.8: Alternaria species (Courtesy: Dr H Sheorey, Dept. ofMicrobiology, St Vincent Hospital, Melbourne)

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1Microbiology

Specific Bacteria

GRAM-POSITIVE BACTERIA

Gram-positive bacteria have a high content of peptido-glycan and a low content of lipid compared to gram-negative bacteria. When the lipid layer is dissolved,crystal violet and iodine form a complex on the cell wallthat appears blue under the microscope, depicting gram-positive bacteria.

The most common organisms which infect the eyeare the Staphylococcus aureus, Coagulase negative Staphy-lococci, Streptococcus pneumoniae and Streptococcusviridans.

Staphylococcus aureus

Staphylococcus aureus are gram-positive cocci (0.5 to1.5 μm), which are seen under the microscope in pairsor grape like clusters and grow as routine culture mediawithin 18 to 24 hours. On blood agar, they appear asgolden hemolysis (clear area). They are non-motile, non-spore forming, facultative anaerobes and are usuallyencapsulated. They are coagulase and catalase positive.Staphylococcus species resistant to oxacillin agentsconstitutes the methicillin resistant Staphylococcus aureus(MRSA).

Antibiotic susceptibility: The widespread use ofaminoglycosides, penicillins, cephalosporins andfluoroquinolones (third generation) is responsible for theincreasing resistance of these organisms against these

drugs. They are susceptible to, bacitracin, chlorampheni-col, cefazolin and fluoroquinolones.

Coagulase Negative Staphylococci

The genus Staphylococcus consists of 32 species out ofwhich 3 are coagulase positive and the rest are coagulasenegative. Coagulase negative Staphylococci are normalinhabitants of human body especially the skin, mucousmembrane and the eyelid margins.

Coagulase negative Staphylococci are microscopi-cally similar to Staphylococcus aureus and appear in pairsor grape like clusters, but on blood agar isolation, theyappear as white to grayish colonies within 24 to 48 hoursof incubation. These bacteria are non-motile, non-sporeforming, facultative anaerobes, usually non-encapsula-ted, catalase positive. The most common bacteriaimplicated in bacterial keratitis is negative coagulaseStaphylococcus.

Antibiotic susceptibility: Just like Staphylococcus aureus theresistance rate of 55 percent has been noted to fluoro-quinolones in coagulase negative Staphylococcus. Theyare susceptible to vancomycin, bacitracin and chloram-phenicol.

MICROCOCCUS SPECIES

They are gram-positive cocci, which may be present assaprophytes and inhabit the eyelid margins. They appearon blood agar as yellow distinct colonies.

Streptococcus and Related Bacteria

Streptococci appear microscopically as gram-positivecocci (Fig. 3.9), usually coccoid or coccobacilli and appearin chains of cocci on broth medium. They may be presentas normal inhabitants especially in children. Streptococciare distinguished from Staphylococcus and Micrococcusspecies by negative catalase reaction S.pneumoniae is lessvirulent as compared to S.viridans. They are responsiblefor corneal ulcers, recalcitrant graft infections andinfectious crystalline keratopathy.

Streptococcus species are differentiated by theirhemolysis patterns on blood supplemented agar mediainto the following:1. Alpha-hemolytic streptococci which partially lyse the

red blood cells and a greenish halo appears arounda colony. Examples of alpha-hemolytic streptococciinclude Streptococcus pneumoniae and Streptococcusviridans.

Figure 3.9: Gram-positive pneumococci (Courtesy: Dr H Sheorey,Dept. of Microbiology, St Vincent Hospital, Melbourne)

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2. Beta-hemolytic streptococci lyse red blood cellscompletely and a clear halo appears around a colony.An example of beta-hemolytic streptococci is Strepto-coccus pyogenes which when identified from corneais pathogenic.

3. Gamma-hemolytic or non-hemolytic streptococciwhich have no hemolysis pattern around a colony.

Antibiotic SusceptibilityThey exhibit high resistance to polymyxin. They aresusceptible to cefazolin, bacitracin, chloramphenicol andsulphacetamide. The in vitro susceptibility of Streptococ-cus species to fluoroquinolones is low.

EnterococcusEnterococcus species are gram-positive ovoid cocci orcoccobacilli and are isolated or broth media with orwithout red blood supplementation. Enterococcus fecalisis the most common species isolated from the corneawhich can cause corneal ulcer.

DiphtheroidsDiphtheroids appear microscopically as gram-positivepleomorphic rods. They are aerobic non-spore formers.The most common diphtheroid isolated from thecompromised corneas include Corynebacterium andPropionibacterium. They grow well on blood-supplemen-ted media, in a CO2 atmosphere but it may require 24to 48 hours extra for the colonies to appear. Enrichedthioglycollate, liquid broth is a good medium for thecolonies to appear. Diphtheroids are known to occur assaprophytes, although in compromised conditions theymay also cause infectious keratitis.

Corynebacterium diphtheriae and Listeria monocytogenesare corneal pathogens, which can breach the intactepithelium without prior trauma.

Antibiotic susceptibility: They are susceptible to vanco-mycin, chloramphenicol, ofloxacin and partially tocefazolin. Diphtheroids demonstrate a good in vitrosusceptibility to most antibiotics except to trimethoprim.

Mycobacterium

Mycobacteria are obligate parasites and opportunisticpathogens. They are gram-positive bacteria which areslightly curved or straight bacilli. They appear as“ghosts” or beaded gram-positive rods on Gram stain.

Mycobacterium chelonae and Mycobacterium fortuitum areresponsible for keratitis after refractive surgery. Onblood agar and chocolate agar plates, the colonies maytake a week to appear. Routine mycobacterial isolationmedium such as Löwenstein-Jensen medium is moredefinitive for isolation or organisms.

When mycobacteria are suspected to cause keratitis,special acid-fast stains should be used to stain them asthey have a cell wall with high content of lipid whichresists Gram staining.

Antibiotic susceptibility: They are susceptible to clarithro-mycin and amikacin.

Bacillus

Bacillus species are large, gram-positive rods but maysometimes be gram-variable. They are spore bearing,catalase positive, motile and grow aerobically or asfacultative anaerobes. The most important cornealpathogens are Bacillus cereus and Bacillus anthracis, whichappear as large, grainy, dry beta-hemolytic colony onagar media. Most organisms are opportunisticpathogens.

Antibiotic susceptibility: They are susceptible to aminogly-cosides, fluoroquinolones and sulphacetamides.

Nocardia

Nocardia species belong to the group of actinomycetesand appear as gram-positive, branching, filamentousbacteria. They are aerobic, non-motile, partially acid-fastand appear as white, tiny, dry colonies.

They are associated with infections after trauma,contact lens wear and following laser in situ kerato-mileusis (LASIK) surgery. The pathogenic species areNocardia asteroids and Nocardia brasiliensis.

Antibiotic susceptibility: They are susceptible to sulpha-cetamide, trimethoprim – sulfamethoxazole andamikacin.

GRAM-NEGATIVE BACTERIA

Gram-negative bacteria appear red because the lipidlayer is not removed by the decolorizing step. A bluecrystal violet complex cannot form in the cell wall andsafranin counter stains the bacteria (Fig. 3.10).

The common gram-negative bacteria, which infectcornea include Pseudomonas aeruginosa, Serratia marce-

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1Microbiology

scens, Moraxella species and Haemophilus species.Generally gram-negative infection occurs due to bacilli.Rarely, gram-negative cocci may cause infection suchas in cases of Neisseria gonorrhoeae, Neisseria meningitidesand Branhamella catarrhalis.

Pseudomonas aeruginosa

P. aeruginosa are aerobic bacteria, which appear as gram-negative bacilli. It grows between 30-37°C and ontrypticase broth supplemented with 5 percent sheepblood appear grayish or greenish, metallic-appearing asgelatinous colonies. These colonies have a grape-likeodor. The colonies of P. aeruginosa are oxidase positive.

The infections due to this organism are generallyfulminant because of the presence of virulence factors(exotoxin A, proteolytic enzymes), presence of pili,which attach to the cells and production of alginate,which is a polysaccharide polymer, which inhibitsphagocytosis.

Contact lens wearers, debilitated patients, patientswith systemic diseases and in intensive care units are atrisk for Pseudomonas keratitis.

SERRATIA MARCESCENS

Serratia marcescens is an opportunistic pathogen, whichalong with corneal epithelial breakdown due to traumaor contact lenses can lead to corneal ulceration. On Gramstain they appear as coccobacilli and its colonies arereddish in color. They are a frequent contaminant ofcontact lenses and contact lens solutions.

Antibiotic susceptibility: They are susceptible to fluoroqui-nolones and aminoglycosides and have intermediatesusceptibility to chloramphenicol, trimethoprim andsulfasoxazole.

MORAXELLAMicroscopically, they appear as gram-negative brickshaped diplobacilli (Fig. 3.11). They cause chronicconjunctivitis and acute corneal ulceration. Moraxellalacunata is the commonest species involved. The coloniesappear grayish in color and appear pitted.

HAEMOPHILUSHaemophilus appear as tiny gram-negative coccobacilli.These bacteria require factor V and factor X for theirgrowth and hence grow better on chocolate agar thanon blood agar. The colonies appear as grayish in colorand have a musty smell.

GLUCOSE FERMENTERS AND NON-FERMENTERSGlucose fermenters include Stenotrophomonas andAlcaligenes species and glucose non-fermenters includeEscherichia coli, Enterobacter, Klebsiella and Proteus species.

Stains and Culture Media

Various methods have been used to identify theorganisms from a case of infectious keratitis. Theseinclude various stains to identify the morphology of theinciting organisms and culture media, which are usedto grow these organisms.

Figure 3.10: Gram-negative bacilli Figure 3.11: Gram-negative diplobacilli (Moraxella) (Courtesy:Dr H Sheorey, Dept. of Microbiology, St Vincent Hospital, Melbourne)

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STAINING METHODS

The stains used to routinely identify various organismsinclude potassium hydroxide wet mount preparation,Gram’s stain, Giemsa stain and special stains such asZiehl-Neelsen acid-fast stain, fluorochromatic stains andmodified Grocott-Gomori methenamine-silver nitratestain.

Potassium Hydroxide Wet Mount Preparation

We recommend simple microscopic examination ofcorneal scrapping using 10 percent KOH preparation inall cases of suspected infectious keratitis. This is a simpletest and can be performed in outpatient area and doesnot involve too much of cost.

The scraped material is spread out as thinly aspossible with the help of spatula on the slide. One dropof 10 percent KOH solution is put on the scrapings anda slide cover is placed. The slide is examined under amicroscope. The KOH helps in loosening the cornealstromal lamellae and exposing more fungal filaments.It also stains the filaments in a very light yellow color(Fig. 3.12). Ten percent KOH mount examined byconventional microscope is a useful test in helpingidentification of fungi and Acanthamoeba. The test hashigh sensitivity (92%) and a high specificity (96%).8,9

Gram’s Stain

Gram’s stain classifies the bacteria into two major groupsbased on the cell wall of the bacteria. Gram-positivebacteria retain the gentian violet-iodine complex andappear blue-purple, whereas the gram-negative bacterialose their gentian violet–iodine complex with decolo-rization step and appear pink when counterstained withsafranin. A 5 minute Gram’s staining procedure as wellas a 5 seconds Gram’s staining procedure is alsoavailable. We prefer to use the 5 minutes Gram’s stainingprocedure (Table 3.3).

Overall, Gram’s stain is accurate in 61 percent ofcases of bacterial keratitis. If performed correctly, Gram’sstain identifies the organism correctly in upto 75 percentof the cases caused by a single organism and in 37percent cases of polymicrobial keratitis.10

Giemsa StainGiemsa stain is one of the Romanowsky type stain,which uses eosin, methylene blue and azure dyes. Itstains the DNA in the nuclei of the human cells andcytoplasmic RNA in the lymphocytes.

Figure 3.12: Pseudohyphae on KOH wet mount (Courtesy: Dr NNayak)

The Giemsa stain is usually used to determine thetype of inflammatory cells present. We do not recom-mend its use routinely. This stain differentiates bacteriafrom fungi, and also identifies chlamydia inclusionbodies and cysts and trophozoites of Acanthamoebaspecies. It identifies the normal and inflammatory cells.With Giemsa technique the bacteria appear dark bluein color. The yeast cells and fungal hyphae absorb thestain and appear purple or blue while the cell walls andthe septations do not stain. The staining solution shouldbe freshly prepared daily.

The conventional Giemsa stain takes 60 minutes toperform (Table 3.4), although a rapid 15 minutes modi-

TABLE 3.3Gram stain procedure

· • Fix smear by either of the following methods:• Place in methanol for 5-10 min and allow to air dry:

preferred method• Pass the slide, through flame two or three times. Allow

cooling• Flood the slide with crystal violet stain• Allow stain to remain on for 1 minute• Rinse gently with tap water• Flood slide with Gram’s iodine solution. Allow solution

to remain on for 1 minute• Rinse gently with tap water• Decolorize with decolorizer solution until the color stops

running from the smear• Rinse gently with tap water• Flood the slide with Safranin stain. Allow stain to remain

on for 30 seconds• Rinse gently with tap water• Allow to air dry

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fication of the stain is also available. The pH of thedistilled water should be 6.8 to 7.0.

Ziehl-Neelsen Acid-fast Stain

Special stains include the use of carbol-fuchsin or Ziehl-Neelsen acid-fast stain for identification of suspectedMycobacteria, Actinomyces or Nocardia. Mycobacteria areacid-fast, Nocardia stain variably, whereas Actinomycesare non-acid fast.

The principal of this stain is based on the resistanceof the mycobacterial species and certain strains ofNocardia to decolorization by strong mineral acids afterstaining with basic carbol fuchsin. This resistance is dueto the presence of intact cells that contain specific lipidunsaponifiable wax fraction.

Fluorochromatic Stains

Fluorochromatic stains such as acridine-orange andcalcofluor-white require the use of an epifluorescencemicroscope to visualize the organisms and the cells.

Calcofluor WhiteCalcofluor white binds to chitin and cellulose. Becausethe cell walls of the yeast and filamentous fungi arecomposed of chitin and cellulose, these organisms stainbright green with calcofluor white under epifluorescentmicroscope.11 The cysts of Acanthamoeba likewise alsohave chitin and cellulose and also stain bright green.The trophozoites of Acanthamoeba stain reddish-orangein color.

Acridine Orange

The acridine orange is a chemofluorescent dye, whichstains fungi and bacteria yellow-orange against a green

background when the pH is acidic and a fluorescencemicroscope is used. It is a valuable stain as it identifiesgram-positive and gram-negative bacteria, yeast andhyphal forms of fungi and both the trophozoite and cystform of Acanthamoeba. The Gram’s stain can be directlydone on a slide where prior staining with acridineorange has been done without destaining. The acridineorange stains accurately predicts culture results in71 to 84 percent of cases in comparison to 62 to79 percent for Gram’s stain.12,13

Modified Grocott-Gomori Methenamine-Silver Nitrate Stain

The Grocott-Gomori methenamine-silver nitrate stain isa histopathologic stain used to show fungi and has beenmodified for the examination of corneal scrapings. Forfungal infections, this stain is more reliable than theGram’s, Giemsa, or KOH stain. The staining procedureis described in the Table 3.5. The specimens should bespread onto gelatin-coated slides, which can be preparedby spreading a drop of warm gelatin (1%) over the slideto form a thin coat. The slides can be stored in the freezerat –20 to 0oC until used. The working solution ofmethenamine-silver nitrate must be made fresh beforeeach use. With the methenamine-silver nitrate stain,fungus cell walls and septa black and can be easily seenagainst the background, which is a faint transparentgreen (Fig. 3.13).

Procedure• Spread the specimen on a gelatin-coated slide to form

a thin smear.

TABLE 3.5Modified methenamine-silver nitrate staining

Solution1. Methenamine-silver nitrate solution

a. Solution ABorax (5%) 8.0 mlDistilled water 100.0 ml

b. Solution BSilver nitrate (10%) 7.0 mlMethenamine (3%) 100.0 ml

To make working solution of methenamine-silver nitrate, mixequal parts of solutions A and B. The working solution shouldbe prepared fresh before each use.2. Stock light green solution

Light green SF (yellow) 0.2 gmDistilled water 100.0 mlGlacial acetic acid 0.2 ml

TABLE 3.4Giemsa staining procedure

• Fix slide in a Coplin jar containing methyl alcohol for5 min

• Prepare fresh stain solution in a Coplin staining jar• Place 2 ml of stock Giemsa stain in the bottom of

the Coplin jar• Add distilled water to within 1/2 inch of the top

(approximately 70 ml)• Incubate slide in stain at 35°C for 60 min• Differentiate using two changes of 95 percent ethyl

alcohol• Rinse in tap water• Allow to air dry

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• Fix the slide in methyl alcohol for 5 minutes.• Oxidize the slide in 5 percent chromic acid for 30

minutes.• Preheat the working methenamine-silver nitrate

solution to 58-60°C and place the oxidized slide inthe heated solution for 20 minutes. The smear willbe amber in color.

• Promptly rinse the slide in six changes of distilledwater.

• Tone the slide in 0.1 percent gold chloride for 2-4minutes (the gold chloride can be reused).

• Rinse in two changes of distilled water.• To reduce the silver, place the slide in a 2 percent

sodium thiosulfate solution for 2 minutes.• Rinse in tap water.• Counterstain briefly (40-60 seconds) using a fresh

solution of 1:5 stock light green in distilled water.• Allow to air dry.

The summary of various stains used to diagnosedifferent types of organisms is given in Table 3.6.

CULTURE MEDIA

Most bacteria appear on culture media with distinctcharacteristics, which allows easy identification. Thefeatures to be noted while studying the colonies on solidmedia include the following: shape, size, elevation,margins, surface, edges, color, structure and consistency.

There various culture media are used to identify thebacteria include the following:

Nutrient agar

Nutrient agar is the simplest medium used in mostlaboratories. It is made by adding 2 percent agar tonutrient broth (Fig. 3.14).

Nutrient agar contains beef extract (which suppliescarbohydrates, organic nitrogen, salts, vitamins),peptone (enzymatic digest of certain proteins; providesreadily available nitrogen), agar (extract of marine algaewhich is used as a solidifying agent) and water. It has apH of 6.8.

Blood agar

The agar is derived from seaweed with the addition of5 to 10 percent red blood cells, which provide nutrients,

Figure 3.14: Nutrient agar

TABLE 3.6Diagnostic stains used for preparation of smear

Type of stain Organism Color

Gram stain Bacteria Gram-positive-purpleGram-negative-pink

Acridine orange Bacteria Yellow-orangeFungi Yellow-orangeAcanthamoeba

Calcofluor white Fungi Bright greenAcanthamoeba Bright greencystsAcanthamoeba Reddish orangetrophozoitesMycobacteria

Acid-fast MycobacteriaFigure 3.13: Grocott-Gomori Methenamine silver nitrate stain showingAspergillus (Courtesy: Dr Seema Sen)

23

1Microbiology

as well as an index of hemolysis (Fig. 3.15). This is astandard medium for isolation of aerobic bacteria at35°C. It also supports the growth of saprophytic fungiand Nocardia at room temperature.

Chocolate agar

Chocolate agar is incubated with 10 percent carbondioxide to isolate facultative organisms. It is preparedby heat denaturation of blood to 56oC to provide humanand diphosphopyridine nucleotide for the growth oforganisms such as Haemophilus, Neisseria and Moraxella.

Thioglycolate broth

This is a liquid media, which is incubated at 35°C forand is used for the isolation of aerobic and anaerobicbacteria. It contains a sulfhydryl compound which actsas an oxygen-reducing agent to facilitate recovery ofanaerobic bacteria. Thiol is a variation of thioglycollatebroth and contains special complexes and 0.1 percentsemisolid agar to prevent convection currents andpromote the growth of aerobic bacteria as well asobligate and facultatively anaerobic organisms.

Sabouraud agar

This consists of Sabouraud glucose and peptone agarand is a non selective media for opportunistic fungi.Yeast extract is used to improve the nutrition and anantibiotic such as gentamicin is added to inhibit thebacterial contamination (Fig. 3.16). The medium shouldnot contain cycloheximide as this inhibits the growth ofthe saprophytic fungi.

Sabouraud agar is incubated at room temperatureand is used for isolation of fungi and Nocardia.

Löwenstein-Jensen Medium

Mycobacteria are specifically isolated on Löwenstein-Jensen media. Glycerol and egg mixture which areadded to this media provide fatty acids and proteinrequired for the metabolism of mycobacteria. Thecoagulated egg albumin provides a solid medium forinoculation purposes. It also contains malachite greenas an inhibitor to microorganisms other than acid-fastbacilli. Cultures should be read within 5-7 days afterinoculation and once a week thereafter for up to 8 weeks.

Thayer-Martin Medium

This is a special, selective, chemically enriched chocolateagar, which is used to isolate Neisseria gonorrhoeae bysuppressing the growth of other inhibitory fungi andbacteria.

Brain-heart Infusion (BHI) broth

Brain-heart infusion broth with neopeptone is incubatedat room temperature and is used to enhance the isolationof filamentous fungi and yeasts and less frequentlyBacillus species.

Robertson Cooked Meat Medium

Robertson cooked meat medium provides a favorableenvironment for the growth of anaerobes. The muscle

Figure 3.15: Blood agar

Figure 3.16: Aspergillus growth on Sabouraud’s dextrose agar

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tissue is a source of amino acids and reducingsubstances, particularly glutathione, which permits thegrowth of strict anaerobes. Glucose, Hemin and VitaminK1 is supplemented with yeast extract, to enhance thegrowth of anaerobic microorganisms ( Fig. 3.17). Growthis indicated by turbidity and, with some organisms, bythe presence of gas bubbles in the medium. Disinte-gration and blackening of the meat particles indicatesproteolysis.

References1. Bacon AS, Frazer DG, Dart JK, Matheson M, Ficker LA,

Wright P. A review of 72 consecutive cases of Acantham-oeba keratitis, 1984-1992. Eye 1993;7:719-25.

2. McCulley JP, Alizadeh H, Niederkorn JY. The diagnosisand management of Acanthamoeba keratitis. CLAO J.2000;26:47-51.

3. Rauz S, Tuft S, Dart JK, Bonshek R, Luthert P, Curry A.Ultrastructural examination of two cases of stromalmicrosporidial keratitis. J Med Microbiol 2004;53:775-81.

4. Joseph J, Murthy S, Garg P, Sharma S. Use of differentstains for microscopic evaluation of corneal scrapingsfor diagnosis of microsporidial keratitis. J Clin Microbiol2006;44:583-5.

5. Forster RK, Wirta MG, Solis M, Rebell G. Methenamine-silver-stained corneal scrapings in keratomycosis. Am JOphthalmol 1976;82:261-5.

6. Kozlowski M, Stepien PP. Restriction enzyme analysisof mitochondrial DNA of members of the genusaspergillus as an aid in taxonomy. J Gen Microbiol1982;128:471-6.

7. Nelson PD, Toussoun TA, Marasas WF. Fusariumspecies: An illustrated manual for identification,University Park: The Pennsylvannia State UniversityPress, 1983;3-48.

8. Sharma S, Silverberg M, Mehta P, Gopinathan U,Agrawal V, Naduvilath TJ. Early diagnosis of mycotickeratitis: Predictive value of potassium hydroxidepreparation. Indian J Ophthalmol 1998;46:31-5.

9. Vajpayee RB, Angra SK, Sandramouli S, Honavar SG,Chhabra VK. Laboratory diagnosis of keratomycosis:Comparative evaluation of direct microscopy andculture results. Ann Ophthalmol 1993;25:68-71.

10. Jones DB. Initial therapy of suspected microbial cornealulcers. II. Specific antibiotic therapy based on cornealsmears.Surv Ophthalmol 1979;24:97, 105-16.

11. Marines HM, Osato MS, Font RL. The value of calcofluorwhite in the diagnosis of mycotic and Acanthamoebainfections of the eye and ocular adnexa. Ophthalmology1987;94:23-6.

12. Gomez JT, Robinson NM, Osato MS, Wilhelmus KR.Comparison of acridine orange and Gram’s stains inbacterial keratitis. Am J Ophthalmol 1988;106:735-7.

13. Groden LR, Rodnite J, Brinser JH, Genvert GI. Acridineorange and Gram’s stains in infectious keratitis. Cornea1990;9:122-4.

Figure 3.17: Robertson cooked meat medium

25

1Pharmacology

Pharmacology4

Medical therapy forms the first line of treatment ofinfectious keratitis. The drugs used to treat microbialkeratitis include antimicrobial agents, cycloplegics, anti-glaucoma medications and adjuvants.

Antibacterial AgentsThe various anti-bacterial agents can be given bytopically, subconjunctivally or by systemic route in acase of bacterial keratitis (Table 4.1).1 Topical route usingconcentrated or fortified antibiotics is generally preferredas higher concentration of the antibiotics are achievedby this route.

Fortified antibiotics are prepared by adding therequired amount of parenteral agent to an artificial tearsolution or to a commercially prepared topical solution.

Subconjunctival injections of antibiotic can achievetherapeutic levels due to leakage from the injection siteinto the tear film and direct penetration into the adjacenttissue. However, since there is no added benefit overtopical administration we do not use subconjunctivalantibiotics routinely.

Systemic therapy is usually less effective in achievingtherapeutic drug levels and carries the risk of systemictoxicity. These are usually used to treat corneal infections

in cases of scleral involvement, perforated corneas orimpending perforations disease.

ANTIBACTERIAL AGENTS

Beta Lactam Antibiotics

Penicillin is the prototype drug of this group. They actby interfering in the synthesis of the bacterial cell wallproteoglycans.Topical beta lactam antibiotics are neveravailable commercially they are somewhat unstable insolution and tend to breakdown in days or weeks.

Cephalosporins

Like penicillins, cephalosporins contain a beta lactamring which is required for its bactericidal action. Thenucleus of the cephalosporins is 7 aminocephalosporanicacid, which is resistant to the action of penicillinasesproduced by staphylococci.

Cefazolin is primarily effective against gram-positiveorganisms.

Ceftazidime is a third generation cephalosporin,which acts against Pseudomonas species. It also hassome activity against gram-positive organisms. It isparticularly useful in cases of Pseudomonas keratitis

TABLE 4.1Emperical therapy for bacterial keratitis

Gram’s stain Topical Subconjunctival Systemic

Gram-positive cocci Cefazolin, 50 mg/mL Cefazolin, 100 mg Cefazolin, 200 mg/kg/dayGram-negative cocci Penicillin, 100,000 U/mL Penicillin, 1 million U Penicillin, 2- 6 million U q 4 hrGram-positive rods Gentamicin, 14 mg/mL Gentamicin, 20- 40 mg Gentamicin, 3 mg/kg/dayGram-positive filaments Penicillin, 100,000 U/mL Penicillin, 1 million U Penicillin, 2- 6 million U q 4 hrGram-negative rods Cefazolin, 50 mg/mL, and Cefazolin, 100 mg, and Cefazolin, 200 mg/kg/day, and

gentamicin, 14 mg/mL gentamicin, 20- 40 mg gentamicin, 3 mg/kg/dayAcid-fast bacilli Amikacin, 10 mg/mL Amikacin, 25 mg Amikacin, 5 mg/kg/day

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which are resistant to aminoglycosides or fluoroquino-lones.2

Tetracyclines

Tetracyclines are broad-spectrum bacteriostaticantibiotics. Various forms of tetracycline are available,including chlortetracycline (topical), oxytetracycline,doxycycline, minocycline, and tetracycline. They act byinhibiting bacterial protein synthesis by binding to the30-S ribosomes.

They are active against gram-positive organisms,gram-negative bacteria, mycoplasma, chlamydia andamoeba. They are not effective against P. aeruginosa,Bacteroides species, or group B streptococci. The variousmicroorganisms acquire a plasmid-mediated resistanceto tetracycline.

Glycopeptides

Vancomycin is a glycopeptide, which is effectivepenicillin-resistant Staphylococci. It inhibits the synthesisof peptidoglycan polymers during bacterial cell wallformation. It is active against gram-positive bacteria andremains one of the most potent agent against methicillinresistant Staphylococcus aureus and coagulase negativeStaphylococci. Vancomycin should be reserved forcephalosporin-resistant Staphylococci. Vancomycin iseffective against Streptococci and also against gram-positive bacilli such as Clostridia, Corynebacteria,Bacillus, L. monocytogenes, Actinomyces, and lactobacilli.

Aminoglycosides

Aminoglycosides act particularly against, gram-negativebacilli. They have a selective affinity to bacterial 30-Sand 50-S ribosomal subunits to produce a nonfunctional70-S initiation complex that results in inhibition ofbacterial cell protein synthesis. Unlike other antibioticsthat impair protein synthesis, they are bactericidal.Aminoglycosides have a bactericidal activity againstaerobic, gram-negative bacilli such as Pseudomonasaeruginosa. However, there is resistance developingagainst Pseudomonas to gentamicin, tobramycin and tosome extent amikacin. For Pseudomonas keratitis anaminoglycoside may be combined with a thirdgeneration cephalosporin. For Nocardia keratitisamikacin is the drug of choice.3

Macrolides

Macrolides are bacteriostatic agents (e.g. erythromycin,tetracycline) that can suppress the growth of susceptiblegram-positive cocci. These drugs cause inhibition ofbacterial protein synthesis by reversibly binding to the50-S ribosomal unit thereby preventing elongation ofpeptide chain in bacteria. Erythromycin acts both as abactericidal and a bacteriostatic agent depending on theconcentration of the drug and is effective against gram-positive and some gram-negative organisms. S.pneumoniae and S. pyogenes are highly susceptible . It isone of the least toxic and best tolerated antibiotic agents.However, its penetration into cornea is sub-optimal dueto lack of solubility and bioavailability.

Newer macrolides such as azithromycin and clari-thromycin have higher tissue concentrations and aremore effective against C. trachomatis, and non-tuber-culous mycobacteria where they are used topically.4

Fluoroquinolones

The fluoroquinolone agents are the latest class ofantibacterials. Four generations of fluoroquinolones haveevolved :1. First generation: Nalidixic acid-rarely used2. Second generation: Ciprofloxacin and ofloxacin3. Third generation: Levofloxacin4. Fourth generation: Moxfloxacin and gatifloxacin.

Mechanism of Action

Fluoroquinolone agents act by inhibiting the supercoiling of DNA by the enzyme DNA gyrase. This actionis bactericidal and occurs during cell replication.Fluoroquinolones have the advantage of low toxicity dueto the lack of DNA gyrase in mammalian cells. Theavailable topical agents include norfloxacin (0.3%), cipro-floxacin (0.3%), lomefloxacin, fleroxacin, perfloxacin,and ofloxacin (0.3%), moxifloxacin (0.5%) andgatifloxacin (0.3%).

Moxfloxacin and gatifloxacin are C8-methoxyfluoroquinolones, and demonstate increased activityagainst gram-positive bacteria and atypical mycobac-teria when compared to ciprofloxacin, ofloxacin andlevofloxacin in vitro and in vivo.

The available formulations of gatifloxacin (Zymar,Allergan, Inc.) and moxifloxacin (Vigamox, Alcon Inc.)are 0.3 percent and 0.5 percent respectively. The

27

1Pharmacology

chemical structures of the C8-methoxy fluoroquinolonesadd protection from bacterial resistance in addition toenhancement of bactericidal properties. The substitutionof the methoxy group at the eighth carbon on the basicring in both gatifloxacin and moxifloxacin reduces thelikelihood of ocular pathogens developing resistance tothese fluoroquinolones. The methoxy group allowsbinding of the antibiotics to two bacterial enzymes -DNA gyrase and topoisomerase IV. As a result, C8methoxy fluoroquinolones require two simultaneousmutations for development of resistance, the chance ofwhich are one in ten trillion . Previous generations offluoroquinolones required only a single mutation.Moreover, a bulky side chain at the C7 position of theseantibiotics makes it the difficult for the antibiotics toreach out of the bacterial cells.

Spectrum of Activity

The fluoroquinolones have broad-spectrum of activityand are more active against gram-negative bacteria thangram-positive bacteria. They are active against entericgram-negative rods, such as Haemophilus influenzae andNeisseria gonorrhoeae. The third generation fluoroquino-lones are active against Staphylococcus aureus, Non-coagulase Staphylococci, and Pseudomonas aeruginosa.Ofloxacin and ciprofloxacin have a comparable spectrumof activity against gram-positive and gram-negativeorganisms.5

The pathogens with respond less to fluroquinolonesinclude Streprotoccus Pneumoniae, S. Viridans MRSA,anaerobes and non-aerugines Pseudomonas.6,7

Side Effects

The side effects of the fluoroquinolones may occurlocally or they may be systemic. The topical adminis-tration of ciprofloxacin has been associated with crystaldeposits in the cornea. This occurs in approximately20 percent of patients treated with ciprofloxacin in casesof bacterial keratitis8 (Fig. 4.1). This crystallization hasnot been seen with norfloxacin or ofloxacin, presumablydue to their high solubility. The advantage of crystallinedeposits is that it acts as a depot from which the drug isreleased. However the disadvantage is that its presenceretards epithelialisation.

The systemic side effects of fluoroquinolone includetoxicity, fever, rash, and nausea which occurs in4 percent of patients. Occasionally patients haveelevation of levels of liver enzymes. The drugs can

crystallize in the urine, especially in patients who aredehydrated. Interstitial nephritis has been reported afterhigh doses of ciprofloxacin. Insomnia and restlessnesshave occurred in elderly patients taking fluoroquino-lones. Children should not be given quinolones becauseanimal studies have shown crystal deposits in cartilageand hence the topical fluoroquinolones are notrecommended for children younger than 2 years.

PREPARATION OF FORTIFIEDTOPICAL ANTIBIOTICS

(Adapted from Basic Clinical and Science Course 2000-2001. American Academy of Opthalmology)1. Cefazolin 50 mg/ml or ceftazidime 50 mg/mL

a. Add 9.2 mL of artificial tears to a vial of cefazolin,1 g (powder for injection).

b. Dissolve. Take 5 mL of this solution and add it to5 ml of artificial tears.

c. Refrigerate and shake well before instillation.2. Tobramycin 14 mg/mL or gentamicin 14 mg/mL

a. Withdraw 2 mL of tobramycin or gentamicininjectable vial (40 mg/mL).

b. Add 2 mL to a tobramycin or gentamicin ophthal-mic solution (5 mL) to give a 14 mg/mL solution.

3. Vancomycin 15 mg/mL, vancomycin 25 mg/mL orvancomycin 50 mg/mLa. Add 33 mL of 0.9 percent sodium chloride for

injection (no preservatives) or artificial tears to a500 mg vial of vancomycin to produce a solutionof 15 mg/mL. Add 20 mL of 0.9 percent sodiumchloride for injection (no preservatives) or

Figure 4.1: Ciprofloxacin deposit in a case of corneal transplantation

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artificial tears to produce a solution of 25 mg/mL. Add 10 mL of 0.9 percent sodium chloridefor injection (no preservatives) or artificial tearsto produce a solution of 50 mg/mL.

b. Refrigerate and shake well before instillation.4. Amikacin

Intravenous formulation can be used (80 mg/2 ccampules).

5. Trimethoprim/sulfamethoxazole16 mg/mL and 80 mg/mL commercial preparationcan be used.

Antifungal AgentsCLASSIFICATION OF ANTIFUNGAL AGENTS

1. Polyenesi. Large polyenes

Nystatin, amphotericin Bii. Small polyenes

Natamycin2. Azoles

i. ImidazolesMiconazole, ketoconazole, clotrimazole

ii. TriazolesFluconazoles, itraconazoles

3. PyrimidinesFlucytosines

POLYENES

Mechanism of ActionPolyene antibiotics are produced from a Streptomycesspecies. They interact with cell membrane sterols presentin fungi, mainly ergosterol, which causes increasedpermeability that leads to cell lysis. It is this binding tomammalian cell membrane cholesterol that isresponsible for their toxicity.

Two mechanisms of action of the polyene antibioticsare known depending on the size of the antifungalmolecule. Small molecules such as natamycin work byan all-or-none mechanism of action. They bind to theesterols in the fungal cell wall, forming “blisters” andcausing lysis of the cell. This action is not concentrationdependent. The larger molecules, such as amphotericin,work by creating “pores” in the cell wall, allowing smallions such as potassium to leak out and causingimbalances in the osmotic gradient and eventual celllysis. This mechanism of action is concentration

dependent and may be altered by changes in the osmoticenvironment.

Nystatin

Nystatin was the first polyene antibiotic identified. It isnot used routinely because of its corneal toxicity andpoor ocular penetration .

Natamycin

Natamycin is a small semisynthetic tetraene and isconsidered the least toxic, the least irritating, and themost stable of all polyenes. It has broad spectrum ofactivity, especially against Fusarium species.9 It haslow penetration in the presence of an intact epithelium.Surface debridement of the cornea increases itspenetration. Since natamycin is used as a suspension, itcan dry on the ocular surface forming white depositson the cornea and adenexa. Natamycin can be toxic tothe corneal and conjunctival epithelium, causinghyperemia and epithelial defects.

Dosage

It is available for topical use as a 5 percent suspension(Table 4.2). Topical therapy is given every hour for thefirst 48 to 72 hours, and treatment is usually continuedon a tapering basis for 3 to 6 weeks depending on theactivity of the keratitis.

Amphotericin B

Amphotericin B is a haptene polyene that is insolublein water and degrades rapidly on exposure to light. It isactive against Candida, Aspergillus and Cryptococcus.10 Itsactivity against the filamentous fungi is variable. It hasgood penetration in the cornea and aqueous in inflamedeyes.11 As with natamycin, its penetration increases withdebridement of the cornea. Topical use causes punctateepithelial erosions and a greenish discoloration of theconjunctiva (Table 4.2). Even a small dose of 0.1 mggiven subconjunctivally is extremely toxic. This cancause conjunctival nodules which are transient in natureand yellow discoloration which can be permanent.

Dosage

Amphotericin B is used as topical drops in concentrationof 0.15 percent (Table 4.2). It has to be prepared fresh indextrose. The mixture should be stored in dark bottles

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1Pharmacology

and stored under refrigeration at 2-8°C to preventchemical degradation.

AZOLES

Imidazoles

The imidazoles have a broad spectrum of antifungalactivity. In contrast to the polyenes, they are relativelyresistant to light, hydrolysis and are soluble in organicsubstances.

The imidazoles have various mechanisms for theirantifungal activity action. At low concentrations,miconazole, econazole, and ketoconazole affect theformation of ergosterol needed by the cell membranes.At higher concentrations, clotrimazole and miconazolecan disrupt lysosomes, causing direct damage to cellmembrane. Moreover, most imidazoles inhibit catalaseand cytochrome C peroxidase intracellulary, causingaccumulation of hydrogen peroxide and leading to celldeath.

Clotrimazole

Clotrimazole has a wide spectrum of activity againstnumerous fungi excluding fusarium.12 It is used bothtopically and systemically. The topical preparation ofclotrimazole is made by dilution in arachis oil to form a1 percent solution (Table 4.2). It has been applied hourlyfor 48 to 72 hours and then tapered over 8 to 12 weeks.Orally, it is administered in a dosage range of 60 to 150mg/kg/day. Clotrimazole is considered to be effectiveagainst Aspergillus keratitis. However, it is not givenroutinely due to its toxicity. Side effects of the systemicadministration of clotrimazole may include anorexia,nausea, hallucinations, confusion, and gastritis. It shouldnot be given in the first 3 months of pregnancy or topatients with a history of adrenal, or liver problems.Liver enzyme level elevations are seen normally withthe use of clotrimazole, and these tend to return tonormal once the drug is withdrawn.

Miconazole

Miconazole is a phenethylimidazole that is extremelystable in solution form. It has a broad spectrum ofactivity against Cryptococcus, Aspergillus, Curvularia,Candida, and Trichophyton.13

For topical use, a 1 percent solution in arachis oil ora 10 mg/mL is used (Table 4.2). It is also available as a2 percent dermatologic ointment.

Topical use of miconazole may cause surface toxicityafter prolonged use.

KetoconazoleKetoconazole can be used topically as well assystemically.13

A topical preparation may be formulated in a 1 to5 percent concentration by dissolving in arachis oil(Table 4.2). Ketoconazole is primarily used for oraladministration. It is well absorbed from the gastrointesti-nal tract and high therapeutic blood levels aremaintained after oral administration. It is available in200 mg tablets with a recommended daily dose of 200to 400 mg. Systemic side effects associated with the useof ketoconazole include pruritus, nausea, vomiting,diarrhea, cramps. A reversible gynecomastia andelevations in liver enzyme levels have also been seen.Liver function tests should be done every 2 weeks whenpatients are on oral ketoconazole.

TriazolesThe triazoles were developed in order to increase thespectrum of activity and reduce the side effects of theirpredecessors, the imidazoles.

Fluconazole

Fluconazole is now used mainly for the treatment ofCandida keratitis. A topical 1 percent solution is

TABLE 4.2Routes and dosage of antifungal agents

Antifungal agent Route Dosage

Amphotericin B Topical 0.15%(freshly prepared)

Natamycin Topical suspension 5%Clotrimazole Topical 1%Ketoconazole Topical 5%

Oral 300 mg dailyMiconazole Topical suspension 1%

Subconjunctival 5-10 mgItraconazole Topical 1%

Oral 200 mg BDFluconazole Topical 0.2%

Oral 200 mg dailyFlucytosine Topical 2%

Oral 50-150 mg/kg/day BDVoriconazole Topical 1%

Oral 200 mg/day BD

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available.14 The 2 mg/L aqueous solution forintravenous use can also be applied topically to providea higher concentration of the antifungal agent.

Oral fluconazole can be given in a dose of 50 to 40mg/day, with the usual adult dose being 200 mg/day.Systemic side effects of fluconazole include gastritis,headaches, rash, hepatotoxicity, Stevens-Johnsonsyndrome, and thrombocytopenia.

Itraconazole

Itraconazole also has, like fluconazole, a wider spectrumof activity than the imidazoles in vitro. However, clini-cally it is found to be active against Candida species.15

The oral administration of itraconazole appears tohave less penetration than other triazoles into the corneaand aqueous. Itraconazole is used in its oral preparationas an adult dose of 200 mg/day. Systemic side effects ofitraconazole include gastrointestinal upset, hypertrigly-ceridemia, and hypokalemia.

Voriconazole

A new azole antifungal agent, Voriconazole, is derivedfrom Fluconazole and exhibits a wider spectrum ofactivity against Candida, Aspergillus and Fusarium. Itexerts its effect from inhibition of cytochrome P450-dependant 14 alpha sterol demethylase, an enzymeinvolved in the ergosterol biosynthetic pathway. Theminimal inhibitory concentration of voriconazole(0.5 μg/ml) is less as compared to other imidazoles.

Topical variconazole 1% has to be prepared inpharmacy as it is not commercially available and is givenin recalcitrant fungal keratitis if there is not response totopical natamycin and amphotericine B therapy.16

Antiviral Agents

IDOXURIDINE

Idoxuridine is a nucleoside analog of thymidine. It wasthe first topically effective antiviral drug produced(Table 4.3). However, due its need for frequentapplication, toxicity and availability of newer and betterantiviral drugs, it is no longer used.

VIDARABINE

Vidarabine is a water insoluble antiviral agent. It actsby the inhibiting viral DNA synthesis. It can be

administered topically in ointment form and systemi-cally through the intravenous route (Table 4.3).

TRIFLURIDINE

Trifluridine is a fluorinated nucleoside analog ofthymidine.

It is used topically in the form 1 percent solution. Itis not used systemically as it rapidly degrades in thebloodstream and is not very selective in sparing the hostDNA .

ACYCLOVIR

Acyclovir is a synthetic purine nucleoside analogderived from guanine. It is a highly potent antiviralagent. Acyclovir interferes with DNA synthesis, thusinhibiting virus replication. It can be administered bothtopically and systemically. In the topical form it is usedas a 3 percent ointment (Table 4.3).

Acyclovir has antiviral activity against HSV types 1and 2 (HSV-1 and HSV-2), Varicella zoster virus,Epstein-barr virus and Cytomegalovirus.

Topical use of acyclovir ointment is well tolerated.No significant toxic effects have been seen in patientsfollowing topical treatment of herpetic ocular infectionswith 3 percent acyclovir ophthalmic ointment for 14days.17,18 Systemic side effects of oral acyclovir includenausea, vomiting, and headache. Other adversereactions include diarrhea, dizziness, anorexia, fatigue,edema, skin rash, leg pain, medication taste, and sorethroat.

VALACYCLOVIR

Valacyclovir is a prodrug of acyclovir and has been usedin the treatment of herpes simplex keratitis. It is givenorally in the dose of 1000 mg 3 times a day for 7 days.

TABLE 4.3Dosage and route of administration of antiviral agents

Idoxuridine Topical 0.1% solution and0.5% ointment

Vidarabine Topical ointment 3% Trifluridine Topical solution 10 mg/ml Acyclovir Topical ointment 3%

Systemic 200-800 mg(oral capsules)

Valacyclovir Systemic 1000 mg

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1Pharmacology

The advantage of using this drug is that it has to begiven less frequently.

Adjuvants

CORTICOSTEROIDS

Topical corticosteroids have a role to play in healingcorneal ulcers as well as herpetic stromal viral keratitis.They decrease the inflammation and also the consequentcorneal scarring.

Topical Corticosteroids

Topical preparations are available in the form ofsolutions, suspensions, or ointments. Phosphate andhydrochloride preparations are relatively hydrophilicand thus are water soluble. Acetate and alcoholderivatives are hydrophobic and fat soluble. Owing tothe respective polarities, phosphates are generallyformulated as solutions, whereas acetates are generallyformulated as suspensions and ointments. Acetates,owing to their hydrophobic nature, appear to penetratethe cornea more than the phosphates.

Dexamethasone phosphate penetrates into the corneaand aqueous within 10 minutes. It reaches a peak within30 to 60 minutes and remains there from several hoursto 24 hours.

Likewise, one percent prednisolone phosphate ishighly soluble with optimal corneal levels.

CycloplegicsInfectious keratitis can induce a ciliary spasm which ispartially responsible for the severe pain associated withmost types of infectious keratitis. Topical cycloplegicshelp to alleviate this pain by relieving the ciliary spasmby paralyzing the ciliary muscle.

TYPES OF CYCLOPLEGICS

Atropine

It is the strongest cycloplegic available and is used aseither 1 percent solution or 1 percent ointment appliedthree times a day.

Homatropine

It is available in the form of a 2 percent solution and isadministered 3 to 4 times per day.

Anti-glaucoma Medications

Intraocular pressure may rise in the acute phase ofinfectious keratitis.

TOPICAL ROUTE

For a mild to moderate rise in intraocular pressuretopical therapy is instilled in the form of beta blockerslike timolol maleate 0.5 percent.

SYSTEMIC ROUTE

Acetazolamide is used frequently to control intraocularpressure in cases of microbial keratitis. In case of veryhigh intraocular pressure mannitol may be given.

Acetazolamide

It is a carbonic anhydrase inhibitor and is available inthe form of oral tablets. It is given in the dose of 500 mgqid. The main side effects are nausea, gastritis andhypokalemia.

MannitolMannitol is an osmotic agent which is available as a 20percent solution and is given intravenously. It is notmetabolized in the body. Its dosage is 1.5 to 2 g/kg bodyweight and it is given rapidly over 30 to 45 minutes. Itcan cause volume overload in the body. For this reasonblood pressure should be monitored during itsadministration.

References1. Huang AJW, Wichiensin P, Yang MC. Bacterial keratitis.

Chapter 81. In: Krachmer JH, Mannis MH, Holland EJ(Eds): Cornea: Fundamentals, Diagnosis and Manage-ment, NY, 2005;1005-33.

2. Goldstein MH, Kowalski RP, Gordon YJ. Emergingfluoroquinolone resistance in bacterial keratitis: a 5-yearreview. Ophthalmology 1999;106:1313-8.

3. Sridhar MS, Sharma S, Garg P, Rao GN. Treatment andoutcome of nocardia keratitis. Cornea 2001;20:458-62.

4. Daines BS, Vroman DT, Sandoval HP, Steed LL,Solomon KD. Rapid diagnosis and treatment ofmycobacterial keratitis after laser in situ keratomileusis.J Cataract Refract Surg 2003;29:1014-8.

5. Ofloxacin monotherapy for the primary treatment ofmicrobial keratitis: a double-masked, randomized,controlled trial with conventional dual therapy. TheOfloxacin Study Group. Ophthalmology 1997;104:1902-9.

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6. Alexandrakis G, Alfonso EC, Miller D. Shifting trendsin bacterial keratitis in south Florida and emergingresistance to fluoroquinolones. Ophthalmology 2000;107:1497-502.

7. Wilhelmus KR, Abshire RL, Schlech BA. Influence offluoroquinolone susceptibility on the therapeuticresponse of fluoroquinolone-treated bacterial keratitis.Arch Ophthalmol 2003;121:1229-33.

8. Wilhelmus KR, Abshire RL. Corneal ciprofloxacinprecipitation during bacterial keratitis. Am J Ophthalmol2003;136:1032-7.

9. Jones DB, Sexton R, Rebell G. Mycotic keratitis in SouthFlorida: a review of thirty-nine cases. Trans OphthalmolSoc. UK. 1970;89:781-97.

10. Jones DB. Decision-making in the management ofmicrobial keratitis. Ophthalmology 1981;88:814-20.

11. Wood TO, Tuberville AW, Monnett R. Keratomycosisand amphotericin B. Trans Am Ophthalmol Soc 1985;83:397-409.

12. Mselle J. Use of topical clotrimazole in human kerato-mycosis. Ophthalmologica 2001;215:357-60.

13. Thomas PA. Fungal infections of the cornea. Eye2003;17:852-62. Review.

14. Sonego-Krone S, Sanchez-Di Martino D, Ayala-Lugo R,Torres-Alvariza G, Ta CN, Barbosa L, et al. Clinicalresults of topical fluconazole for the treatment offilamentous fungal keratitis. Graefes Arch Clin ExpOphthalmol 2006;244:782-7.

15. Galarreta DJ, Tuft SJ, Ramsay A, Dart JK. Fungal keratitisin London: microbiological and clinical evaluation.Cornea 2007;26:1082-6.

16. Jhanji V, Sharma N, Mannan R, Titiyal JS, Vajpayee RB.Management of tunnel fungal infection with vorico-nazole. J Cataract Refract Surg 2007;33:915-7.

17. Uchoa UB, Rezende RA, Carrasco MA, Rapuano CJ,Laibson PR, Cohen EJ. Long-term acyclovir use toprevent recurrent ocular herpes simplex virus infection.Arch Ophthalmol 2003;121:1702-4.

18. Sudesh S, Laibson PR. The impact of the herpetic eyedisease studies on the management of herpes simplexvirus ocular infections. Curr Opin Ophthalmol 1999;10:230-3. Review.

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2Clinical Examination

Clinical Examination5

IntroductionHistory taking and clinical examination are crucial forthe diagnosis and management of microbial keratitis. Ameticulous history helps to identify predisposingincidents, risk factors and can provide clues to etiologicaldiagnosis of microbial keratitis. The ophthalmologistmust be able to distinguish microbial keratitis from otherinflammatory diseases of the cornea. Similarly, a carefulclinical examination with slit-lamp biomicroscopy mayhelp in establishing the diagnosis.

Multiple factors may alter the clinical symptoms ofkeratitis. Antecedent partial antibiotic therapy, orcombination antibiotic-corticosteroids therapy maymask or blunt the distinctive symptoms.

History and SymptomsThe classical symptoms of corneal ulceration include thepresence of pain, watering, discharge, photophobia,decrease in visual acuity and swelling of lids.

PAIN

The occurrence of pain is a significant symptom ofcorneal ulcer. The severity of pain may range fromminimal discomfort to an excruciating pain. The typeof causative organism and the depth of the ulcerationinfluence the severity of pain.

In general, superficial ulcers are more painful thandeep corneal ulcers. This is due to the rich sensory nervesupply present in the superficial part of the cornea.

A small dendrite of Herpes simplex or a Candidaspecies cause minimal pain and may only be associatedwith foreign body sensation. In contrast, a patient withAcanthamoeba keratitis presents with an excruciatingpain, during corneal epithelial involvement due to radialkeratoneuritis. The pain is usually out of proportion to

the objective clinical findings, the alleviation of whichmay require strong analgesics and narcotics.

A sudden relief in pain, in a case of progressingcorneal ulcer may be indicative of the perforation of theulcer.

REDNESS AND PHOTOPHOBIA

Like pain, redness and photophobia are prominentsymptoms in cases of corneal ulcer. The severity andduration of these symptoms may vary from case to case.An associated conjunctivitis may cause severe rednessas in gonococcal, pneumococcal and Haemophilusinfections.

DISCHARGE

Almost all cases of corneal ulcer present with a comp-laint of discharge from the affected eye. The type of thedischarge may be watery, mucoid, mucopurulent orfrankly purulent.

A watery discharge usually occurs due to a viral ulceror a small bacterial ulcer or else it may also be due toreflex tearing. However, microbial keratitis caused byPseudomonas and Gonococcus species is associated witha mucopurulent discharge (Fig. 5.1). Corneal ulcerscaused due to Pseudomonas are particularly associatedwith a greenish-yellowish discharge (Fig. 5.2). A memb-ranous discharge is seen with keratitis caused byCorynebacterium diphtheria.

DECREASED VISUAL ACUITY

Most cases of corneal ulcer report with history of suddendecrease in vision. The extent of decrease in visiondepends on duration, severity and location of the lesion,involvement of other ocular structures and the successof concurrent therapy, if any.

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Work Up of Corneal Ulcer

Central corneal ulcers, particularly those caused byorganisms like Pseudomonas species, Staphylococcusaureus, and Fusarium species are invariably associatedwith significant loss of visual acuity. Other factors thatcan reduce visual acuity include the presence of anassociated pupillary membrane, hypopyon, cataract,glaucoma and endophthalmitis.

The vision may not be severely reduced in caseswhich have small, peripheral ulcers, such as thosecaused by Herpes simplex and non-coagulase Staphylo-coccus.

In Acanthamoeba keratitis, vision may not besignificantly reduced during the initial stages, when thecorneal epithelium alone is involved. Later, as theinfection spreads deeper into the corneal stroma, visualacuity is severely reduced.

Onset of DiseaseThe pattern of onset of microbial keratitis depends onthe nature of predisposing factor/s, virulence of theoffending organism and status of the ocular andsystemic immunity of the patient.

Cases of bacterial keratitis usually report with asudden onset and rapid progression of the corneal infec-tion. This in fulminant cases may also cause a threat tovision loss and potential corneal perforation. If a patientpresents with history of pain, photophobia, suddendiminution of vision and discharge of 1-2 days durationbacteria like Staphylococcus aureus (Fig. 5.3), Pseudomonasaeruginosa and Pneumococcus species are likelyorganisms responsible for the occurrence of corneal ulcer

However, certain bacteria like Moraxella, coagulasenegative Staphylococcus, Nocardia species and atypicalMycobacteria cause corneal ulcers that present withgradual onset and have an indolent course.

Microbial keratitis caused by fungi and parasites likeAcanthamoeba, also have a chronic course. The course ofdevelopment of Acanthamoeba keratitis is variable. It mayemerge slowly over weeks or months or may rapidlyworsen within several days after presumed incitingevent. The course of infection is usually chronic andgradually progressive and may have some periods oftemporary remission.

PREDISPOSING FACTORS

Identification of a predisposing factor is an integralcomponent of history taking in a case of corneal ulcerand is essential for successful management of microbialkeratitis.

Figure 5.1: Corneal ulcer with yellow discharge Figure 5.2: Corneal ulcer with greenish discharge

Figure 5.3: Corneal ulcer due to Staphylococcus aureus (diffuse)

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Normally, corneal epithelium along with the tear filmis a formidable barrier against the invasion of themicrobes. However, in certain situations this barrier iscompromised and organisms invade the corneal tissueand cause infection.

Various risk factors may make the cornea susceptiblefor developing microbial keratitis (Table 5.1). These riskfactors may be ocular, systemic and occupational. Insome cases more than one factor may be present or aco-existence of an ocular or systemic factor may bepresent.

Ocular Factors

The various ocular factors which may predispose to theoccurrence of corneal ulcer include corneal trauma,prolonged use of topical corticosteroids, use of contactlenses, precorneal tear film disorders, eyelid disease, andocular surface disease.1

TRAUMACorneal injuries cause a breach in the intact cornealepithelial barrier which is the first line of defense againstthe occurrence of infectious keratitis.2 Seemingly trivialtrauma with contaminated matter, foreign bodies,makeup or contact lenses may also cause inoculation ofthe organism.3

Corneal trauma caused by vegetative matter isknown to predispose to occurrence of mycotic (Fig. 5.4)and Acanthamoeba keratitis.4

If there is history of human or animal bites alongwith extensive necrosis of the tissue, anaerobic infectionsshould be suspected.5

CONTACT LENS

The contact lens wear is one of the commonest predis-posing factor for the occurrence of keratitis especiallyin series from western literature.6 The type of contactlens use, the duration of use of contact lenses and themethod of lens care hygiene and disinfection andfrequency of lens replacement should be enquired.Proper contact lens hygiene decreases the chances ofmicrobial keratitis but infections have been reported tooccur even when the patients were compliant with anadequate lens care hygiene.6

It has been demonstrated that the risk of contact lensinduced keratitis is more with the extended wear softcontact lenses and overnight wear as compared to dailywear hard and soft contact lenses (Fig. 5.5).7,8 Infectionswith organisms such as Pseudomonas species have alsobeen reported with orthokeratology.9

History of smoking coupled with contact lens wearis known to increase the risk of microbial keratitis as itincreases the amount of corneal hypoxia.8 The dailydisposable soft contact lenses in our experience have alower risk of infectious keratitis compared with otherlens wear regimens. However, reports have shown thatat least some risk remains.10,11

Figure 5.4: Mycotic keratitis due to vegetative trauma

TABLE 5.1Predisposing factors in case of corneal ulcer

• OcularTraumaContact lensesLid and adnexal infectionsOcular surface diseaseAllergic eye disordersBullous keratopathyTopical medicationsPrior ocular surgery

• SystemicDiabetes mellitusSjögren’s syndromeSteven-Johnson syndromeAIDSAdvanced malignanciesConnective tissue disordersAlcoholicsExtremes of ageMeasles malnutrition

• OccupationalFarmersAnimal handlersGardeners

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Use of contaminated and non-sterile solutions suchas homemade saline solution or tap water may be usedto rinse, store or lubricate contact lenses which is typicalof contact lens induced keratitis due to Acanthamoeba.Acanthamoeba keratitis may also occur due to conta-mination from swimming pool and muddy water(Fig. 5.6).

LID AND ADNEXAL INFECTIONS

Ulcerative keratitis caused by Pneumococcus has aknown association with dacryocystitis.12 Likewise,infection with Actinomyces occurs more commonly incases of canaliculitis. Any abnormality in the lid suchas trichiasis, coloboma, ectropion, entropion, lagophthal-

mos, exophthalmos, proptosis, blepharitis and meibomi-tis may predispose the occurrence of infectious keratitis.

OCULAR SURFACE DISEASES

Conditions that affect the ocular surface causing areduction of the integrity of and adherence of cornealepithelium such as dry eye syndrome, chemical injuries,allergic eye disease,13 can predispose to infection byopportunistic organisms (Fig. 5.7). All ocular surfacedisorders particularly the dry eye disturb precorneal tearfilm and increase the chances of adhesion of micro-organisms to corneal epithelium.14

BULLOUS KERATOPATHY

Bullous keratopathy caused by corneal endothelialdecompensation disturbs the barrier function of theprecorneal tear film and the corneal epithelium. Thecorneal surface becomes irregular and corneal erosionsand epithelial defects develop. All these factors facilitatethe entry of microbes in the corneal tissues. The riskfactors for development of corneal infection in thesecases include prolonged bullous keratopathy time,steroid use and use of bandage soft contact lens.Ulcerative keratitis developed in 4.7 percent of patientswith bullous keratopathy in a study by Luchs et al.15

TOPICAL MEDICATIONS

Amongst the topical medications, the prolonged use oftopical corticosteroids is known to predispose theoccurrence of infectious keratitis (Fig. 5.8). Topical

Figure 5.5: Contact lens induced ulcer

Figure 5.6: Acanthamoeba keratitis Figure 5.7: Keratitis with ocular surface disorder

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corticosteroids adversely affects the precorneal tear filmand local ocular immunity, and can cause bacterial andfungal keratitis.9 Also, corticosteroids prevent neutrophilmigration in response to chemotactic factors releasedduring microbial keratitis.9 Moreover, there is impairedopsonization when encapsulated bacteria causemicrobial keratitis. Corneal super-infection has beenreported after indiscriminate use of corticosteroids incases of Apollo conjunctivitis.16

Continued use of non-steroidal anti-inflammatoryagents,17 anesthetics, inappropriate use of antibiotics,antiviral and anti-glaucoma medications such as timo-lol may also predispose the occurrence of infectiouscorneal ulcer if used for a very long time. All these drugscause toxic changes in the corneal epithelium.

The use of traditional eye medicines in developingcountries has also been known to predispose theoccurrence of keratitis (Fig. 5.9).18

PRIOR OCULAR SURGERYOcular surgeries like cataract surgery,19 pterygiumsurgery, keratoplasty19-22 (Fig. 5.10) photorefractivekeratectomy23 and laser in situ keratomileusis (LASIK)may be complicated by the occurrence of microbialkeratitis24 (Fig. 5.11). Infectious keratitis particularly withMycobacterium chelonei has been reported after LASIKsurgery both in sporadic as well as in epidemic forms.25

Systemic FactorsCertain systemic diseases like diabetes mellitus (Fig.5.12), acquired immunodeficiency syndromes, Sjögren’s

Figure 5.8: Microbial keratitis (Prolonged topical corticosteroid use) Figure 5.9: Microbial keratitis after traditional eye medicine (honey)

Figure 5.11: Microbial keratitis after LASIK surgeryFigure 5.10: Microbial keratitis after keratoplasty

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syndrome and Steven-Johnson syndrome may act as riskfactors for the occurrence of microbial keratitis. Moraxellalacunata ulcers are usually associated with alcoholics,diabetics and debilitated patients.27

Diabetes MellitusThe basement membrane and the hemidesmosomeattachments to the corneal epithelium are impaired inthe diabetes. Diabetics also have duplicated andthickened basement membrane and its anchoring fibrilsto the stroma are weak. These changes in basementmembrane may cause persistent corneal epithelialerosions predisposing it to the occurrence of infectiouskeratitis (Fig. 5.12).

Acquired Immunodeficiency Syndromes andAdvanced Malignancies

An impaired immune status, as seen in acquiredimmune deficiency syndromes and advanced malig-nancy render the patient susceptible to developingmicrobial keratitis, especially by the unusual bacteria.26

These cases are prone to develop Candida keratitis.Further, the course of keratitis is more fulminant in thesecases.

Connective Tissue Diseases

Systemic diseases like rheumatoid arthritis may adver-sely affect the healing of the corneal ulcer (Fig. 5.13).They may also predispose to corneal melting andpredispose to secondary infectious keratitis.

Figure 5.12: Microbial keratitis in a case of diabetes mellitus Figure 5.13: Microbial keratitis in a case of rheumatoid arthritis

Other Systemic Factors

Pseudomonas keratitis occurs more frequently in cases ofburn patients, semicomatose or comatose patients,patients with corneal exposure and patients on pro-longed ventilator support.9 In children, microbialkeratitis may occur in association with conditions suchas measles, diarrhea and malnutrition.28

Occupational Factors

Some occupations may render a person susceptible todeveloping microbial keratitis. Mycotic keratitis occursmore commonly in persons involved in farming andagriculture and outdoor laborers.9 They are prone to beinflicted by minor vegetative or plant trauma whilehandling farms. It also occurs more commonly inconjunction with the use of gardening tools (e.g. nylon–line lawn trimmers) without protective eyewear. Certaintype of keratitis such as due to Listeria monocytogenes isknown to occurs in cases of animal handlers.8

Clinical Examination and SignsExamination of any patient of an ocular disease beginswith the general examination of patient. A close look ismade at the facial structures to look for the presence ofany lesion like blisters of herpes zoster or simplex,presence of any facial palsy, abnormal blink rate andexcessive corneal and conjunctival exposure.

The level of visual acuity and the size of the lesionare two important indicators of severity of a case of

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infectious keratitis. A particular type of organism maypresent with a characteristic type of clinical picture thatmay provide an important clue to etiological diagnosis.A patient of ulcerative keratitis should be examined asfollows:

Record of Visual AcuityIt is usually possible to record only uncorrected visualacuity (UCVA) in an eye with ulcerative keratitis. ASnellens’ chart may be used to record the visual acuity.UCVA should be recorded at the time of presentationand also at subsequent follow-up visits. Monitoring ofthe visual acuity is an important parameter to check theseverity and the progress of the ulcer. In young childrenan attempt should be made to record the visual acuityusing Teller’s acuity cards.

External Ocular ExaminationEyelids and lacrimal sac area should be examined forany abnormality besides recording usual concomitantpresence of lid swelling and circumciliary congestion.

EYELIDSEyelids should be examined for the presence of anyabnormality such as trichiasis, coloboma, entropion, lidlag, ectropion, lagophthalmos, proptosis, exophthalmosand blepharitis. These conditions act as predisposingfactors and may require simultaneous managementalong with that for infectious keratitis.

If there is a history of foreign body going in to theeye, the eyelids should be everted and the fornicesshould be examined. If required and possible a doubleeversion of upper eyelid should be done to find andremove the foreign bodies.

LACRIMAL SACA gross external examination of lacrimal sac area shouldundertaken to rule out dacryocystitis. Pneumococcal cor-neal ulcers may be associated with lacrimal sac infec-tions. A sac pressure test or regurgitation test is performedby pressing over the lacrimal sac area just medial to themedial canthus and observing regurgitation of dischargefrom the puncta. A positive regurgitation test indicatesthe presence of dacryocystitis.

Slit-lamp BiomicroscopyA detailed slit-lamp biomicroscopic examination ismandatory to examine a case of infectious keratitis. Slit-

lamp biomicroscopy should include an examination ofthe precorneal tear film, conjunctiva, cornea, anteriorchamber, iris, lens and anterior vitreous.29

CONJUNCTIVA

The bulbar conjunctiva and the upper and lower tarsalconjunctiva should be examined for the presence of anylesion or diseases like vernal catarrh and atopicconjunctivitis. Conjunctival reaction is usually not speci-fic but may occasionally help in diagnosis. An associatedsevere conjunctivitis is present in gonococcal, pneumo-coccal and Haemophilus infections usually withchemosis and sometimes with conjunctival pseudo-membranes. Presence of chemosis or membranes shouldthus be recorded.

Bacterial infections may be characterized by the pre-sence of papillae which are tufts of capillaries infiltratedby inflammatory cells and separated by septa bounddown by tarsus and are suggestive of inflammation ofthe conjunctiva. Prominent limbal vessels or circum-ciliary flush is usually seen in bacterial keratitis.

Presence of discharge may also be seen and a noteof its color and consistency should be made. A waterydischarge is generally seen with viral keratitis, whereasa mucoid or mucopurulent discharge is associated moreoften with bacterial keratitis. The color of the dischargemay also help in clinching the final diagnosis, as agreenish purulent discharge is seen in cases ofPseudomonas keratitis (Figs 5.2 and 5.14).

PRECORNEAL TEAR FILM

In a case of active keratitis the precorneal tear film andthe meniscus typically consist of numerous cells anddebris unlike an inactive corneal ulcer. A breach in thecorneal epithelium is more characteristically seen incases of active keratitis unlike a non-infective infiltratewhere the overlying epithelium is intact. However, insome cases of deep ulceration, the overlying epitheliummay be completely intact.

One should also look for the presence of filamentsin the precorneal tear film to rule out the presence offilamentary keratitis. Fluorescein dye may be used tostain the filaments.

CORNEA

The examination of the cornea includes the examinationof the corneal ulcer as well as the examination of thesurrounding cornea.

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Corneal Ulcer

The location, size and depth of the corneal ulcer, thedimensions of the epithelial defect and the infiltrate andthe status of the surrounding cornea and underlyingendothelium should be recorded in great detail usingthe slit-lamp biomicroscopy (Fig. 5.15). Documentationof the size and features of ulcer are done by clinicalphotography and using color-coded diagrams. Apartfrom this if there is any scleral involvement, it shouldbe recorded.

On examination under the slit-lamp the followingfeatures of the corneal ulcer should be recorded:

LOCATION OF CORNEAL ULCER

The location of the ulcer should be carefully marked on aschematic diagram of the cornea. Some organisms havea predilection for certain specific locations on the cornea.The ulcer may be central (Fig. 5.9), paracentral, peripheral(within 3 mm of limbus) or total. In some of the caseshalf or whole of the cornea may be involved. Shield ulcersassociated with vernal keratoconjunctivitis usually havelower border in the upper half of the visual axis (Figs5.16A and B).

Central ulcers cause a severe reduction in visualacuity and carry a poor visual prognosis even after

Figure 5.14: Pseudomonas keratitis Figure 5.15: Slit-lamp biomicroscopy of corneal ulcer

Figure 5.16A: Giant papillary conjunctivitis in a case of vernal conjunctivitis Figure 5.16B: Shield corneal ulcer in same case in Figure 5.16A

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resolution as compared to the peripheral ulcers. Centralulcers are usually caused by Staphylococcus species (Fig.5.17). Myobacterium tuberculosis and herpes simplex virusmay cause peripheral corneal ulcers.

SHAPE OF THE ULCER

Bacterial corneal ulcer usually appear as punched outlesions (Fig. 5.17), where as fungal ulcers are usuallydry looking and may have hyphate or feathery margins(Fig. 5.18). Infectious keratitis caused by herpes simplexmay have classically dendritic pattern or appear to haveamoeboid or geographic patterns (Figs 5.19A and B).Corneal ulcers due to Acanthamoeba may have a ringshaped lesion (Fig. 5.6).

MARGINS OF ULCER

The margins or the edges of the ulcer may vary accord-ing to the stage of the ulcer. For instance, a healinginfectious ulcer and sterile corneal ulcers have well-defined margins (Fig. 5.20A) whereas an active cornealulcer has indistinct margins (Fig. 5.20B). Mooren’s ulcerhave a classical overhanging margins (Fig. 5.21).

SIZE OF CORNEAL ULCER

Micrometer present in a standard slit-lamp should beused to record the size of corneal ulcer at the initialpresentation and all follow-up visits till the resolutionof ulcer. In a case of ulcerative keratitis measurement of

Figure 5.18: Fungal corneal ulcer due to Candida (Feathery margins)Figure 5.17: Bacterial corneal ulcer due to Staphylococcus species

Figure 5.19A: Dendritic ulcer due to herpes simplex (Rose Bengaldye)

Figure 5.19B: Dendritic ulcer due to herpes simplex (Fluoresceinstaining)

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size of the lesion is an important parameter for monitor-ing the success of the treatment modality.

A grading system of corneal ulcers may be used toobjectively study and monitor the progress of a case ofinfectious keratitis30 (Table 5.2).

EPITHELIAL DEFECT

The size of the epithelial defect and the size of the infil-tration should be measured separately in the two largestmeridians. They should be measured separately as theirsizes may not be similar. In some of the cases the cornealepithelium may be intact over an infiltrated area in thestroma such as in cases of non-infections corneal ulcersor corneal abscesses. Also, the size of the epithelial defectmay be smaller or larger than the size of the infiltration(Figs 5.22A and B). Change in the size of epithelial defect

TABLE 5.2Grading of corneal ulcer

Feature Mild Moderate Severe

Size of ulcer (mm) < 2 2-5 > 5Depth of ulcer (%) < 20 20-50 > 50Infiltrate— Density Dense Dense Dense— Extent Superficial Extension Deeper than

upto mid- mid stromastroma

Scleral involvement Not Not May beinvolved involved involved

Ann Ophthalmol 1975;7(4):537-9

Figure 5.21: Mooren’s corneal ulcer with over hanging margins

is an indicator of evaluation the progress of any case ofulcerative keratitis.

The epithelial defects should be stained with fluore-scein dye and the size should be measured with the helpof slit-lamp micrometer at all follow-up visits (Fig.5.22B). The staining of the lesion may be achieved eitherby putting a drop of the dye from the dropper orapplying dye stained strips in the conjunctival sac. Mostcorneal specialists prefer to use fluorescein or rose bengalstrips to stain the lesion. These strips are more useful asthey are sterile as compared to the drop of the dyesolutions. Because of the fluorescence property of thefluorescein dye, the stained epithelial defect is examinedusing the cobalt blue light of the slit-lamp. The minute

Figure 5.20B: Healing corneal ulcer with distinct marginsFigure 5.20A: Active corneal ulcer with hazy margins

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Figure 5.22A: Corneal ulcer with epithelial defect and infiltration

details of the fluorescien in staining pattern may be lostwithin 2-3 minutes; therefore, it is imperative that thelesion is examined soon after putting the dye in theconjunctival sac. Characteristic corneal staining patternsmay be seen in different types of infectious keratitis (Figs5.19B and 5.22A).

Rose bengal dye may be used to stain the marginsof the epithelial defects particularly in cases of herpetickeratitis the margins of which stain with the dye as theseare loaded with virus particles.

Apart from the size of the epithelial defect, anyassociated epithelial edema, if present, should also benoted and graded.

INFILTRATION

Infiltration is an intrinsic component of suppurativeinfectious keratitis. The infiltrates may be single ormultiple and may be of varying sizes depending on theorganism involved and the duration of the infection (Figs5.22A and 5.23). The infiltrate should be measured inthe two largest dimensions and recorded on a schematiccornea diagram. If there are multiple infiltrates as seenin some fungal corneal ulcers, or cases of polymicrobialkeratitis31 each one of them is measured separately atall visits (Fig. 5.23). An estimated depth of the stromalulceration may be determined by comparing theadjacent uninvolved corneal thickness. It should berecorded at every follow-up visit.

The ulcers may be graded as mild, moderate orsevere depending on the size of the ulcer, depth of ulcer,

Figure 5.22B: Florescein staining shows size of epithelial defect issmaller than size of infiltrate

infiltrate depth and density and involvement of sclera.30

(Table 5.2).

Corneal Sensations

Corneal sensations should be assessed with the help ofa cotton wisp or esthesiometer, if available. In cases ofherpetic keratitis the corneal sensations are markedlydecreased.

Special CharacteristicsSome organisms produce lesions of particular shapes,color or have some distinctive features. A mere clinical

Figure 5.23: Multiple infiltrates

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examination of such lesions may aid in establishing theetiological diagnosis, although clinical observationshould not replace the laboratory investigation of directmicroscopy and culture of corneal scrapings.2

The classical examples of such features are dendritickeratitis, radial neurokeratitis, satellite lesions, hyphateextensions, black/brown color of the lesion, etc. Thelesions clinical characteristics and the possible etiologicaldiagnosis are highlighted in Table 5.3.

Surrounding Cornea

The cornea surrounding the lesion may be, clear or hazydue to edema depending on the virulence of the orga-nisms. Gram-positive cocci and Candida tend to cause

TABLE 5.3Characteristics of various corneal ulcers

Dendritic keratitis—Herpes simplex, Herpes zosterRadial neurokeratitis—AcanthamoebaAmoeboid ulcer—Herpes simplexBlack/brown discoloration—Demetacious fungal keratitis,corneal ulcer in a tattooed corneal opacityYellow-greenish discharge—PseudomonasSatellite lesions—Fungus, AcanthamoebaRing shaped stromal infiltrates—Acanthamoeba, fungusDisk shaped corneal edema—Herpes simplexLimbal peripheral lesions—Staphylococcus aureus, Herpessimplex, immunological and connective tissue disorders,Mooren’s ulcerEndothelial plaques—FungusFeathery hyphate edges—FungusDry surface—FungusCrystalline infiltrates—Streptococcus viridansOverhanging margins—Mooren’s ulcer

Figures 5.24A to C: Healing corneal ulcer

localized lesions with distinct borders and minimalsurrounding edema. Some organisms like Pseudomonasproduce ulcers in which the surrounding corneabecomes hazy and grossly edematous appearing like aground glass. Clearing of surrounding corneal edemaafter the initiation of medical therapy is an early sign ofresolution of the ulcer.

Corneal VascularizationSuperficial or deep corneal vascularization of varyingextent may be seen in cases of infectious keratitis. Aquadrant wise record of corneal vascularization shouldbe made. Presence of corneal vascularization suggeststhe commencement of the healing of the corneal ulcer(Figs 5.24A to C).

CORNEAL THINNING/PERFORATION

The ulcer should be closely monitored for the develop-ment of corneal thinning, descemetocele and perforation.In the presence of shallow anterior chamber and lowintraocular pressure a Seidel’s test should be performedin all cases.32

When the escape of aqueous is suspected, fluoresciendye is applied directly to the site of the leakage. Whenpresent, escaping aqueous dilutes the fluorescien to flowdown the surface of the eye. The application of concen-trated fluorescien results in a dark non-fluorescingbackground against which the diluted and now brightlyfluorescing dye is highly visible, even in the presenceof modest flow.

Occurrence of corneal perforation is an indication offailure of medical therapy (Figs 5.25A and B). Severecorneal thinning and corneal perforation warrantimmediate surgical therapy in the form of applicationof glue or a tectonic patch graft.

47


DOCUMENTATIONThe documentation of the corneal ulcer may be doneusing color clinical photographs or using detailedschematic drawings.

Color Photographs

In all cases of corneal ulcer a colored photograph of thediffuse as well as the slit section of the corner should betaken. Measurements should be made which includesthe diameter of the ulcer in maximum diameter and themeridian perpendicular to it. Apart from it themaximum diameter of the infiltrate is measured alongwith its diameter in the meridian perpendicular it.Linear measurements are made by focusing the slit-beam and adjusting the slit length to match the distancemeasured and recording the micrometer reading in thefrontal sketch33,34 Alternatively calibrated reticules mayalso be placed in the slit-lamp microscope ocular toobtain the measurements.

Schematic Drawings

In places where clinical photography is not available,drawings of the corneal ulcer along with the surround-ing cornea should be made using a standard scheme ofcolor-coding and shading.33,34

Drawings are less expensive than photographs,provide immediate record, present total picture at aglance and highlight details which may be difficult tophotograph.29 This allows the ophthalmologist to followthe course of the disease. It also provides a standard

form of notation, which assures better communicationwhere more than one ophthalmologist follows-up thepatient.

Black color is used to outline the corneal limbus andto indicate scars resulting from keratitis degenerationand foreign bodies. Thus a scar resulting from bacterialkeratitis, calcific band keratopathy and lipid keratopathyare denoted in black.22,29

Blue designates edema, using shading for diffusestromal edema, small circles for epithelial edema or lakesof fluid within the stroma, and wavy lines to depict theDescemet’s membrane.

The contours of the cornea are drawn in black bothin frontal and cross-sectional views. In the frontal picturethe level of the cross-sectional view is indicated by anarrow. The cross-sectional view is drawn at 3 levels—first at epithelium, other at stroma and the last at thelevel of endothelium.34

Brown indicates melanin or iron pigmentationincluding pupil and iris.

Red is used to depict blood vessels and rose bengalstaining. Red wavy lines indicate subepithelial vessels,straight lines indicate stromal vessels and dotted linesindicate ghost vessels. The wavy lines of superficialvessels begin outside the limbus circle, whereas straightlines of stromal vessels begin at the margin of the circle.Solid shading depicts hemorrhage and red dots indicatearea stained by rose bengal.

Orange denotes inflammation and indicates presenceof white blood cells, which may be in the followingforms—stromal infiltrate, hypopyon or keratic

Figures 5.25A and B: Thining (A) progressing to perforation (B) in a case with corneal ulcer

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48


precipitates (The use of orange/yellow color for opacitiessuch as lipid degeneration and spheroidal degenerationshould be avoided).

Green indicates fluorescien staining of the cornea andcolored dots represent punctuate epithelial keratopathy,small lines depict filaments and shaded outline demons-trate epithelial defects. Green color is also used to depictthe location of lens and the vitreous.

ANTERIOR CHAMBERThe anterior chamber reaction may range from mild flareand cells to severe hypopyon formation. A record ofhypopyon and its characteristics should be made usinga slit-lamp biomicroscopy (Fig. 5.26). The size of thehypopyon should be measured using the slit-lampmicrometer.

Fixed immobile hypopyon is a feature of fungalkeratitis. In order to test for the mobility of thehypopyon, following a slit lamp examination, the patientis asked to lie supine for 10 minutes and a slit-lampevaluation is then done. In cases of the fixed hypopyon,there is no change in position of the hypopyon asdemonstrated by the height of the hypopyon which issimilar. However, in cases of mobile hypopyon, theposition, i.e. the upper level or the height of the hypo-pyon decreases and there is actual movement (Figs 5.27Aand B).

IRIS

Uveal inflammation is a common occurrence withinfectious keratitis. Iris involvement may occur in the

form of synechiae. Presence of rubeosis iridis should alsobe noted.

If the ulcer perforates uveal prolapse may occur andthis may later form a corneoiridic scar.

PUPIL AND LENSAny abnormality in the pupil size, its shape and locationshould be recorded using the slit-lamp biomicroscopy.If visible, lens should be examined for the presence ofcataract or any other abnormality.

Scleral Involvement

Any involvement of the sclera should be recorded asthis helps in prognosticating the case as well as change

Figure 5.26: Hypopyon corneal ulcer

Figures 5.27A and B: Hypopyon moves as the patient moves from erect (A) to supine position (B)

49


in the management protocol, since this warrants the useof systemic antimicrobial agents. Sclerokeratitis usuallyoccurs in cases of immunologic disorders andAcanthamoeba keratitis.

POSTERIOR SEGMENT

Usually, it is not possible to view the vitreous and retinain a case of corneal ulcer due to the presence of hazycornea. However, if the ulcer is small and peripheral,slit-lamp biomicroscopy may be done to visualize theanterior one-third of the vitreous. Additionally, anindirect ophthalmoscopy may be performed to checkfor the involvement of the posterior segment (Fig. 5.28).

INTRAOCULAR PRESSUREDigital tonometry in the experienced hands is the mostpractical method of assessing intraocular pressure incases of corneal ulcer in our experience. Secondaryglaucoma may be present in some cases and should beappropriately treated.

UltrasonographyIn cases where it is not possible to view the posteriorsegment, an ultrasonography A scan and B scan maybe undertaken to assess the posterior segment. A clearposterior segment evaluation rules out the presence ofvitritis/endophthalmitis. In cases of perforated cornealulcers, endophthalmitis, choroidal and retinaldetachment should be excluded. This helps to progno-ticate the cases, especially if a therapeutic keratoplastyis contemplated in these cases.

Varying Clinical Picture

Based on the presenting clinical history, antecedent riskfactors, predisposing ocular and systemic factors anddistinctive clinical signs, infectious keratitis may be easyto diagnose. However, there may be following factors,which may alter the typical clinical features of infectiouskeratitis:1. Previously partially treated corneal ulcers with

antibiotic therapy alone or combination antibiotic-corticosteroid therapy may mask or blunt thedistinctive/classical features of corneal ulcer.Withdrawal of the previous topical corticosteroidsmay cause an initial resurgence of the stromalinflammation and necrosis if they are withdrawnabruptly, and hence during the initial managementthis can confuse the initial response to treatment.

2. In cases of partially treated ulcers especially withtopical antibiotics, the normal conjunctival flora issuppressed and this leads to invasion withsaprophytic bacteria so that the typical features ofinfection are masked.

3. Additionally, the toxicity of certain topical drugssuch as aminoglycosides, anesthetics, idoxuridineand amphotericin B may simulate corneal infectionby causing epithelial and stromal ulceration andmultiple focal suppurative inflammation.

4. Non-infectious keratitis may mimic suppurativekeratitis especially, if the inflammation is marked.

5. The clinical features may be different in a patientwith previously compromised corneas. Individualswith neurotrophic or exposure keratopathy maydevelop ulceration, which may be indistinguishablefrom infectious keratitis.

References

1. Ormerod LD, Hertzmark E, Gomez DS, et al. Epidemio-logy of microbial keratitis in southern California. Amultivariate analysis. Ophthalmology 1987;94:1322-33.

2. Ogawa GSH, Hyndiuk RA. In: Smolin G, Thoft RA (Eds):The Cornea Scientific Foundations and Clinical Practice.3rd ed, Lippincott Williams and Wilkins Philadelphia.Bacterial Keratitis and Conjunctivitis. Chapter 5, p125

3. Wilson SE, Bannan RA, McDonald MB, Kaufman HE.Corneal trauma and infection caused by manipulationof the eyelashes after application of mascara. Cornea1990;9:181-2.

4. Bharathi MJ, Ramakrishnan R, Vasu S, Meenakshi R,Palaniappan R. Epidemiological characteristics and

Figure 5.28: Corneal ulcer with posterior segment involvement

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laboratory diagnosis of fungal keratitis. A three-yearstudy. Indian J Ophthalmol 2003;51:315-21.

5. Zaidman GW, Coudron P, Piros J. Listeria monocyto-genes keratitis. Am J Ophthalmol 1990;109:334-9.

6. Najjar DM, Aktan SG, Rapuano CJ, Laibson PR, CohenEJ. Contact lens-related corneal ulcers in compliantpatients. Am J Ophthalmol 2004;137:170-2.

7. Poggio EC, Glynn RJ, Schein OD, Seddon JM, ShannonMJ, Scardino VA, et al. The incidence of ulcerativekeratitis among users of daily-wear and extended-wearsoft contact lenses. N Engl J Med 1989;321:779-83.

8. Schein OD, Buehler PO, Stamler JF, Verdier DD, Katz J.The impact of overnight wear on the risk of contact lens-associated ulcerative keratitis. Arch Ophthalmol1994;112:186-90.

9. Young AL, Leung AT, Cheng LL, Law RW, Wong AK,Lam DS. Orthokeratology lens-related corneal ulcers inchildren: A case series. Ophthalmology 2004;111:590-5.

10. Sankaridurg PR, Sweeney DF, Holden BA, NaduvilathT, Velala I, Gora R, et al. Comparison of adverse eventswith daily disposable hydrogels and spectacle wear:Results from a 12-month prospective clinical trial.Ophthalmology 2003;110:2327-34.

11. Su DH, Chan TK, Lim L. Infectious keratitis associatedwith daily disposable contact lenses. Eye Contact Lens.2003;29:185-6.

12. Aasuri MK, Reddy MK, Sharma S, Rao GN. Co-occurrence of pneumococcal keratitis and dacryocystitis.Cornea 1999;18:273-6.

13. Vajpayee RB, Gupta SK, Bareja U, Kishore K. Ocularatopy and mycotic keratitis. Ann Ophthalmol 1990;22:369-72.

14. Sridhar MS, Garg P, Das S, Vemuganti G, GopinathanU, Rao GN. Infectious keratitis in climatic droplet kerato-pathy 2000;19:455-8.

15. Luchs JI, Cohen EJ, Rapuano CJ, Laibson PR. Ulcerativekeratitis in bullous keratopathy. Ophthalmology1997;104:816-22.

16. Vajpayee RB, Sharma N, Chand M, Tabin GC, VajpayeeM, Anand JR. Corneal superinfection in acute hemor-rhagic conjunctivitis. Cornea 1998;17:614-7.

17. Guidera AC, Luchs JI, Udell IJ. Keratitis, ulceration, andperforation associated with topical nonsteroidal anti-inflammatory drugs. Ophthalmology 2001;108:936-44

18. Yorston D, Foster A. Traditional eye medicines andcorneal ulceration in Tanzania. J Trop Med Hyg 1994;97:211-4.

19. Cosar CB, Cohen EJ, Rapuano CJ, Laibson PR. clearcorneal wound infection after phacoemulsification. ArchOphthalmol 2001;119:1755-9.

20. Vajpayee RB, Boral SK, Dada T, Murthy GV, PandeyRM, Satpathy G. Risk factors for graft infection in India:a case-control study. Br J Ophthalmol 2002;86:261-5.

21. Vajpayee RB, Sharma N, Sinha R, Agarwal T, SinghviA. Infectious keratitis after keratoplasty. Surv Ophthal-mol 2007;52:1-12.

22. Sharma N, Gupta V, Vanathi M, Agarwal T, VajpayeeRB, Satpathy G. Microbial keratitis following lamellarkeratoplasty. Cornea 2005;24:989-91.

23. Donnenfeld ED, O’Brien TP, Solomon R, Perry HD,Speaker MG, Wittpenn J. Infectious keratitis afterphotorefractive keratectomy Ophthalmology 2003;110:743-7.

24. Solomon R, Donnenfeld ED, Azar DT, Holland EJ,Palmon FR, Pflugfelder SC, et al. Infectious keratitis afterlaser in situ keratomileusis: Results of an ASCRS survey.J Cataract Refract Surg 2003;29:2001-6.

25. Karp CL, Tuli SS, Yoo SH, Vroman DT, Alfonso EC,Huang AH, et al. Infectious keratitis after LASIK.Ophthalmology 2003;110:503-10.

26. Aristimuno B, Nirankari VS, Hemady RK, RodriguesMM. Spontaneous ulcerative keratitis in immunocom-promised patients. Am J Ophthalmol 1993;115:202-8.

27. Garg P, Mathur U, Athmanathan S, Rao GN. Treatmentoutcome of Moraxella keratitis: Our experience with 18cases—A retrospective review. Cornea 1999;18:176-81.

28. Vajpayee RB, Ray M, Panda A, Sharma N, Taylor HR,Murthy GV, et al. Risk factors for pediatric presumedmicrobial keratitis: A case-control study. Cornea 1999;18:565-9.

29. Waring GO. Slit-lamp microscopy of the cornea. In:Leibowitz HM, Waring GO (Eds): Corneal disorders:Clinical diagnosis and management. 2nd edition, WBSaunders Co. Philadelphia 1998;2:34-81.

30. Harrison SM. Grading corneal ulcers. Ann Ophthalmol1975;7:537-9, 541-2.

31. Miedziak AI, Miller MR, Rapuano CJ, Laibson PR,Cohen EJ. Risk factors—microbial keratitis leading topenetrating kertoplasty. Ophthalmology 1999;106:1166-70.

32. Romanchuck KG. Seidl’s test using 10% fluorescein. CanJ Ophthalmol 1979;14:253-6.

33. Waring GO, Laibson PR. A systematic method of draw-ing corneal pathologic conditions. Arch Ophthalmol1977;95:1540-2.

34. Warmg GO. Slit beam ruler. Am J Ophthalmol 1976;82:802-3.

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2Investigations

Investigations6

Ocular and systemic investigations including micro-biological investigations are an integral part of work-up of a case of infectious keratitis. These investigationshelp in making accurate etiological diagnosis andinitiation of appropriate therapy.

Systemic InvestigationsSystemic investigation should be done in cases of sterilecorneal ulcers.

Systemic investigations in cases of peripheralulcerative keratitis include laboratory tests, whichshould focus on the systemic diseases (Table 6.1). Thisinclude a hemogram in cases of immuno compromisedindividuals and blood sugar examination in suspectedcases of diabetics.

A complete blood count including ESR, urineanalysis, blood urea, nitrogen and creatinine. IgM-rheumatoid factor, which is positive in cases ofRheumatoid arthritis, scleroderma, polyarteritis nodosa,Wegner’s granulomatosis, systemic lupus erythematosis,sarcoidosis should also be sent for. Circulatingantibodies such as ANA (>90%), anti-DNA (70%) arepositive in systemic lupus erythematosis. Angiotensinconverting enzyme (ACE) is elevated in sarcoidosis andantineutrophil cytoplasmic antibodies (ANCA) arepresent in 96 percent cases of Wegner’s granulomatosis.Hepatitis B surface antigen is sent for in suspected casesof polyarteritis nodosa and fluorescent treponemal

antibody –absorption (FTA-ABS) in suspected cases ofsyphilis.

Ocular InvestigationsThe ocular investigations include the clinical investiga-tions and the microbiological investigations.

Clinical InvestigationsThe clinical investigations include the estimation of theintraocular pressure and posterior segment evaluationby ultrasonography to rule out any evidence ofconcomitant endophthalmitis.

INTRAOCULAR PRESSURE

Tonopen can be used to measure intraocular pressurein cases of non-perforated corneal ulcers. Digitalestimation of the intraocular pressure may also be doneto rule out secondary glaucoma. The intraocular pressurewill be low in cases of perforated corneal ulcers.

ULTRASONOGRAPHY

Ultrasonography B scan should be done to evaluate thestatus of the posterior segment in cases of corneal ulcerswhere endophthalmitis is suspected.

Microbiological InvestigationsLaboratory procedures for the diagnosis of keratitis aredirected towards the detection of bacteria, fungi orparasites. A well-equipped dedicated ocular microbio-logy laboratory staffed with trained technicians who arespecially oriented towards handling ocular specimens,have a greater leverage over a general microbiologylaboratory. The samples should be collected and a smearexamination should be done. Further, the scrapingsshould also be directly inoculated into the culture media

TABLE 6.1Investigation in a case of peripheral ulcerative keratitis

1. Complete blood count2. Urine analysis3. Blood urea4. Serum creatinine5. Ig M Rheumatoid factor

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and sensitivity of the organisms to the antibiotics shouldbe obtained.

COLLECTION OF SAMPLESThe samples should be collected at the initial presenta-tion prior to the start of anti-microbial therapy. Thetreatment can be initiated based on the results of smearexamination and, if required modified in accordancewith the culture and sensitivity results.

Various types of samples may be collected to aid thediagnosis of corneal ulcer (Table 6.2). The most impor-tant sample for microbiological examination is thecorneal scraping1,2 (Fig. 6.2). The samples should alsobe obtained from the contact lenses, contact lens caseand contact lens solutions if the patient is a contact lenswearer. If there is any lacrimal sac discharge, it shouldalso be sent for microbiological investigations. Althoughit has also been recommended to obtain samples suchas a conjunctival swab and an eyelid swab, it has notproved to be of much help in our experience.

Corneal ScrapingCorneal scraping is the most valuable specimen in cases

of corneal ulcer and its examination is the main stay inthe diagnosis and subsequent management (Fig. 6.1).

Anesthesia

Corneal scraping is performed under topical anesthesiapreferably after instillation of two drops of 0.5 percentproparacaine in the lower fornix of the affected eye.Topical 0.5 percent proparacaine is least bactericidal ascompared to other anesthetic agents such as tetracaineand xylocaine.1,3 Proparacaine provides adequateanesthesia within one minute and does not cause intensestinging on first installation.

General anesthesia and sedation may be required inchildren, uncooperative adults or mentally impairedpatients.3, 4

InstrumentsCorneal scraping is obtained using a Kimura’ s spatula(Fig. 6.3). The other instruments for corneal scraping,are 26-gauge needle, Bard Parker blade #57 (Becton

TABLE 6.2Samples for diagnosis of corneal ulcer

Eyelid swab- Not of much useConjunctival swab - Not of much useCorneal scraping- Most importantContact lens, contact lens case and solution- Must in contactlens wearAC paracentesis (Hypopyon)- Deep ulceration or wheninsufficient material is present

Figure 6.2: Fixation of smear by heating

Figure 6.3: Kimura’s spatula

Figure 6.1: Corneal scraping

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Dickinson, Franklin Lakes, New Jersy), hypodermicneedle, surgical blade no 15 and calcium alginate swab.The platinum spatula has been traditionally used forcorneal scraping. It is rapidly sterilized with a Bunsenburner and cools rapidly between scrapings. A modifiedplatinum spatula is also available with a roundedflexible tip, which is modified with a honing stone tocreate a narrow tapered roughened edge to enhanceremoval of corneal material.3

We routinely use a 23-gauge needle to scrap the ulcer.It is easier to get good quantity of corneal scrapings dueto the sharpness of this instrument. However extremecaution is need in cases of dry and deep ulcers especiallythin corneas.

Technique

A lid speculum is applied gently to separate the lids.Care should be taken not to rub the cornea against thesuperior flange especially while applying the speculum.

The scraping may be done under a slit lamp or underan operating microscope. Under direct illumination, theulcer is inspected. Any mucous or debris on and aroundthe ulcer is carefully cleaned with a sterile swab stick.Then, using a Kimura Spatula or a Bard Parker Knife ora 23-gauge needle, the leading edges and base of theulcer are scraped. Streptococci pneumoniae is more readilyfound at the edge of the ulcer whereas Moraxella is morelikely to be present at the ulcer base.1 Since the materialobtained from corneal scraping may not be adequate, itshould be directly inoculated into the culture mediarather than placing it first into the transport media.4 Careshould be taken to ensure that the instrument is movedin one direction only. Multiple scrapings must beobtained to enhance the yield of the organisms. Oneshould be careful not to touch the eyelids or the lasheswhile collecting the sample to avoid contamination.

More recently, calcium alginate swabs moistenedwith trypticase soy broth provides another method ofcollecting corneal specimens.6 Studies have demonstra-ted higher yield of bacteria7 as well as fungi8 when thismethod was used as compared to the platinum spatulas.

Difficulties in Collection of Corneal Scrapings

There may be various situations where it is difficult toobtain the samples for corneal scraping.9

In cases of small corneal ulcers, which are less severe,and in cases of non-suppurative cases of keratitis theremay be insufficient material to inoculate.

In advanced keratitis with severe keratolysis anddescemetocele, it may not be possible to obtain multiplescrapings.

In some cases the overlying epithelium may be intactand it may be required to disrupt the corneal epitheliumusing a surgical blade. In cases of deep stromal keratitis,microsurgical scissors, a no. 11 Bard Parker blade or asmall trephine may be used to obtain an adequatesample.

EXAMINATION

Smears are prepared by scraping the ulcer and gentlytransferring the material on the spatula on to the glassslide over an area of approximately 1 cm in diameter.An etched or wax pencil mark on the slide obviates theneed to search for the area smeared under the micro-scope. At least two slides are prepared, one for Gramstaining, and the second for KOH wet preparation. Anadditional smear may be prepared for special stains suchas Giemsa, periodicacid-Schiff, calcofluor or Gomorimodified methenamine silver stain for which gelatincoated slide is preferred. 9 KOH wet mount preparationis undertaken to identify the fungal organisms. Gramstaining of the corneal smears is done in all casesroutinely to identify the organisms (Table 6.3). Specialstains may be needed only in certain circumstances(Table 6.3).

In order to use the smear to guide the anti-microbialtherapy, an adequate material should be there andcareful staining techniques should be followed. Prior useof anti-microbial agents, an insufficient sample, excessiveheat fixation, mechanical damage to the cell wall, poorstaining techniques and failure to examine the wholeslide may give erroneous results.4

Routine Smears and Stains

Potassium Hydro-oxide Wet Mount Preparation

The scraped material is spread out as thinly as possiblewith the help of spatula on the slide. One drop of10 percent KOH solution is put on the scrapings and aslide cover is placed. The slide is examined under amicroscope. The KOH helps in loosening the cornealstromal lamellae and exposing more fungal filaments(Fig. 6.4A). It also stains the filaments in a very lightyellow color. 10 percent KOH mount examined byconventional microscope is a useful test in helpingidentification of fungi and Acanthamoeba. The test hashigh sensitivity (92%) and a high specificity (96%), can

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Overall, Gram’s stain is accurate in 61 percent ofcases of bacterial keratitis.4 If performed correctly,Gram’s stain identifies the organism correctly in upto75 percent of the cases caused by a single organism andin 37 percent cases of polymicrobial keratitis.12

Difficulties in Gram StainingSometimes only small number of organisms is presentin the smear, which may be difficult to identify as theseare usually present in areas which contain necroticepithelial cells and numerous large polymorphonuclearcells.

Gram-negative organisms are more difficult toidentify than the Gram-positive organism due to their

Figure 6.4A: KOH wet mount preparation Figure 6.4B: Gram positive cocci

Figure 6.4C: Gram negative bacilli Figure 6.4D: Acid fast Mycobacteria

be performed in outpatient area and does not involvetoo much of cost.10,11

Gram’s Staining

Gram’s stain classifies the bacteria into two major groupsbased on the cell wall of the bacteria (Table 6.4). Gram-positive bacteria retain the gentian violet-iodine complexand appear blue-purple (Fig. 6.4B), whereas the Gram-negative bacteria lose their gentian violet-iodine complexwith decolorization step and appear pink whencounterstained with safranin (Fig. 6.4C). A 5-minuteGram staining procedure as well as a 5-second Gramstaining procedure is also available.12,13 We prefer to usethe 5-minute Gram staining procedure (Table 6.3).

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2Investigations

lighter color. Gram-negative organism may appeargram-positive if decolorization is inadequate.

Caution is also mandatory against various artifacts,which may accompany Gram’s stain such as staineddeposits, carbon particles, talcum powder, sodiumchloride, crystals, melanin and granules. Precipitatedgentian violet may mimic gram-positive cocci.13 If theGram stain reagents are not used frequently, yeast maygrow in the solutions and periodic filtering helps toremove these particles.4

Special Stains

Giemsa Staining

The Giemsa stain is usually used to determine the typeof inflammatory cells present. We do not recommendits use routinely. This stain differentiates bacteria fromfungi, and also identifies chlamydia inclusion bodies andcysts and trophozoites of Acanthamoeba species. Itidentifies the normal and inflammatory cells. WithGiemsa technique the bacteria appear dark blue in color.The yeast cells and fungal hyphae absorb the stain andappear purple or blue while the cell walls and theseptations do not stain. The conventional Giemsa staintakes 60 minutes to perform, although a rapid 15-minutemodification of the stain is also available.

Ziehl-Neelsen Acid-fast Stain

Special stains include the use of carbol-fuchsin or Ziehl-Neelsen acid-fast stain for identification of suspectedMycobacteria, Actinomyces or Nocardia. Mycobacteria areacid fast (Fig. 6.4D), Nocardia stain variably, whereasActinomyces are non-acid fast.

The use of this stain is based on the resistance of themycobacterial species and certain strains of Nocardia todecolorization by strong mineral acids after stainingwith basic carbol fuchsin. This resistance is due to thepresence of intact cell walls that contain specific lipidunsaponifiable wax fraction.

Calcofluor White

Calcofluor white binds to chitin and cellulose. Becausethe cell walls of the yeast and filamentous fungi arecomposed of chitin and cellulose, these organisms stainbright green with calcofluor white under epiflorescentmicroscope (Fig. 6.5).14 Blankophone stain, which issimilar to calcofluor can also be used to identify fungalhyphae (Fig. 6.6). The cysts of Acanthamoeba likewise alsohave chitin and cellulose and also stain bright green.The trophozoites of Acanthamoeba stain reddish –orangein color.15

Acridine Orange

The acridine orange is a chemoflorescent dye, whichstains fungi and bacteria yellow-orange against a greenbackground when the pH is acidic and an epi-flourescent microscope is used to visualize theseorganisms. It identifies gram-positive and gram-negativebacteria, yeast and hyphal forms of fungi and both the

TABLE 6.3Gram Stain Procedure

• Fix smear by either of the following methods: Place in methanol for 5-10 min and allow to air dry:preferred methodPass the slide, through flame two or three times. Allowcooling.

• Flood the slide with crystal violet stain. - Allow stain toremain on for 1 minute

• Rinse gently with tap water. • Flood slide with Gram’s iodine solution. Allow solution-

to remain on for 1 minute.• Rinse gently with tap water.• Decolorize with decolorizer solution until the color stops

running from the smear• Rinse gently with tap water.• Flood the slide with Safranin stain. Allow stain to remain

on for 30 seconds.• Rinse gently with tap water.• Allow to air dry.

TABLE 6.4Gram stain morphology of organisms

Type of stain Organism Color of thevisualized organism

Gram stain Bacteria Gram positive-purpleGram negative-pink

Acridine orange Bacteria Yellow–orangeFungi Yellow-orangeAcanthamoeba

Calcofluor white Fungi Bright greenAcanthamoeba cysts Bright greenAcanthamoeba Reddish orangetrophozoitesMycobacteria

Acid fast Mycobacteria

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Figure 6.5: Fungal hyphae stained with calcofluor white (Courtesy:Dr H Sheorey, Dept. of Microbiology, St Vincent hospital, Melbourne)

Figure 6.6: Fungal hyphae stained with blankophore (Courtesy:Dr H Sheorey, Dept. of Microbiology, St Vincent hospital, Melbourne)

trophozoite and cyst form of Acanthamoeba. The Gram’sstain can be directly done on a slide where prior stainingwith acridine-orange has been done without destaining.The acridine orange stains accurately predicts cultureresults in 71 to 84 percent of cases in comparison to 62to 79 percent for Gram’s stain.16,17

Modified Grocott-Gomori MethenamineSilver Nitrate Stain

For fungal infections, this stain is more reliable than theGram, Giemsa, or KOH stain. The specimens should bespread onto gelatin-coated slides. With the methena-mine-silver nitrate stain, fungus cell walls and septablack and can be easily seen against the background,which is a faint transparent green.

CULTURE EXAMINATION

Culture on the standard media is the gold standard forthe diagnosis of microbial keratitis.4 The culture mediaused to culture the organisms should be stored in adedicated refrigerator and should be re-stockedfrequently to avoid any contamination. In order toenhance the recovery of the organisms, the media shouldbe warmed to the room temperature to prevent lethalcold shock to the organism.1

The corneal scrapings are routinely inoculated ontoblood agar plate (Fig. 6.7), chocolate agar plate,Sabouraud’s dextrose agar (if fungus is suspected) (Fig.6.8) and anaerobic media (if anaerobes are suspected)(Table 6.5). The selective media agar plates areinoculated by streaking the platinum spatula lightly over

Figure 6.7: Culture on blood agar Figure 6.8: Sabouraud’s agar

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2Investigations

the surface to produce a row of separate inoculationmarks in a C shaped configuration.4 Fresh materialshould be obtained for each row of C streaks (Fig. 6.7).C streak method of inoculation differentiates validgrowth from contamination as growth on the C streakis considered significant whereas outside this is apossible contamination.

Liquid thioglycolate broth is inoculated by trans-ferring the material to cotton tipped applicator whichhas been moistened with trypticase soy broth or calciumalginate swab (Fig. 6.9). The swab is inserted to thebottom of the tube to enhance the growth of anaerobicorganisms.

Blood Agar

Enriched media such as blood and chocolate agar helpto isolate the fastidious organisms. Blood agar is thestandard medium for the isolation of aerobic bacteria at35oC and helps to support the growth of most sapro-

phytic fungi at room temperature (Fig. 6.7). The agar isderived from the seaweed and produces optimal surfacemoisture, and addition of 5 to 10 percent red blood cellsprovides nutrients and an index of hemolysis. Rabbitand horse serum are preferred for supporting the growthof Haemophilus.

Chocolate AgarChocolate agar is prepared by the heat denaturation ofblood and provides hemin (X factor) and diphosphopyri-dine nucleotide (V factor) essential for the growth ofHeamophilus. It should be incubated at 35°C with10 percent carbon dioxide. It also supports the growthof Neisseria and Moraxella.

Sabouraud’s Agar

Sabouraud’s agar consists of glucose and peptone agar.Yeast extract is added to improve nutritional characteri-stics and an antibiotic such as gentamicin or chloram-

TABLE 6.5Culture media for various organisms

Culture medium Growth Incubation temperature

RoutineSoybean casein digest broth Saturation of swabs 35oC(trypticase soy broth)Blood Agar plate Aerobic bacteria 35oC

Facultative anaerobic bacteriaFungi

Chocolate Agar plate Aerobic bacteria 35oCFacultative anaerobic bacteriaNeisseriaHaemophilusMoraxella

Thioglycolate broth Aerobic bacteria 35oCAnaerobic bacteria

Sabouraud’s dextrose agar plate Fungi Room temperaturewith antibiotic NocardiaBrain Heart infusion broth plate Fungi Room temperaturewith antibiotic Nocardia

SpecialCooked meat broth Anaerobic bacteria 35oCSchaedler agar Anaerobic bacteria 35oC Thayer Martin Blood agar plate Neisseria 35oCBrucella blood agar plate 35oCLowenstein-Jensen media Myocobacteria species 35oC with 3 to 10% CO2

Middlebrook-Cohn agar MyocobacteriaNocardia 35oC with 3 to 10% CO2

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58


phenicol is added to inhibit bacterial contamination (Fig.6.8). The Sabouraud’s agar should not contain anyadditives such as cycloheximide as this inhibitssaprophytic fungi commonly responsible for ocularinfections.

Following primary cultures the fungi are transferredto the sporulating media for subculture of the species.Sabouraud’s agar plates are preferred to the slantsbecause of the ease of inoculation, observation of colonygrowth, transfer to secondary media and dilution ofinhibitory substances to the fungi.1

Thioglycolate Broth

It promotes the growth of aerobic bacteria, as well asobligate and facultatively anaerobic organisms.18

Thioglycolate broth grows aerobic and anaerobicbacteria at 35oC (Fig. 6.9). It consists of the basic nutrientsrequired to support the growth of aerobic bacteria andalso has sulf-hydryl compound that act as an oxygen-reducing agent to facilitate the recovery of the anaerobicbacteria. It also supports a number of saprophytic fungi.

The limitation of this media for the growth ofanaerobic organisms is its inability to restrict the growthof the aerobic organisms.

Pre-reduced Anaerobically Sterilized Media (PRAS)

This is an ideal medium for the isolation of the anaerobicbacteria. A PRAS brucella blood agar plate enriched withvitamin K and hemin allows the growth of the anaerobeswithin 4 to 7 days. This is also recommended for isola-

tion of nutritional variant streptococci, which may be acausative organism for infectious crystalline kerato-pathy.19 The anaerobic media should not be exposed toair and should be incubated in an anaerobic system suchas anaerobic jar, anaerobic bag system or anaerobicchamber. In the GasPack Pouch system (BactonDickinson, Cockeysville) a packet that has sodiumborohydride, sodium bicarbonate and citric acidgenerate hydrogen and carbon dioxide after water isadded in order to create an anaerobic environment.

Brain Heart Infusion (BHI)

Brain Heart Infusion (BHI) broth at room temperatureenhances the growth of filamentous fungi and yeasts. Itis especially relevant in ocular infections as the inoculummaterial is small and it provides a more even exposureto the essential nutrients.

Thayer-Martin Media

This is an enriched chocolate media that suppresses thegrowth of the inhibitory components and selectivelyallows the growth of the N. gonorrhoeae.

Lowenstein Jensen Media

In cases of suspected atypical microorganisms, thecultures should also be sent on Lowenstein Jensenmedia. This medium allows the growth of Mycobacteria.It contains glycerol and egg mixture which providesfatty acids and proteins (Fig. 6.10).

Figure 6.9: Thioglycolate broth Figure 6.10: Lowenstein Jensen medium

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2Investigations

Micro-Antimicrobial Removal Device (Micro-ARD)

In cases, which have been treated with anti-biotics pre-viously, antimicrobial removal device can be used toincrease the yield of the positive cultures. The commer-cially available blood ARD is modified for smallerophthalmological samples by transferring 2.5 ml aliquotsof all components to test tubes. The ARD is composedof sterile resins(amberlite XAD4 and C-249) which bindsantibiotics suspended in sodium chloride. In a study byOsato et al the use of micro-ARD increased the isolationof organisms from 88 to 100 percent.20

Duration of Isolation of Organism

Most aerobic bacteria responsible for keratitis are seenon standard culture media within 48 hours. In somecases the pathogen may be recognized in 12 to 15 hours.All plates should be examined daily with the help ofdissecting microscope and liquid media should beevaluated for the presence of turbidity. In cases of severekeratitis the media should be evaluated after 12 to 18hours of inoculation.

Growth outside the C streak should be disregardedas it implies contamination and circled with wax pencil.Indigneous organisms in the tear film may appear onthe inoculation marks but may be distinguished on thebasis of their sparse growth and isolation of the sameorganism from the ipsilateral lids or the conjunctiva, ifthese specimens have been taken.

Aerobic cultures of the corneal specimens should beheld for 7 days, anaerobic cultures for 7 to 14 days andMycobacterial and fungal cultures for 4 to 6 weeks beforebeing reported as no growth.

Interpretation of Culture Results

The interpretation of the culture results should be madewith regard to the clinical situation, the adequacy ofthe sample and the possibility of contamination byorganisms present on the skin, eyelids and conjunctiva.

Positive Culture

Reported culture positive rates in presumed infectiouskeratitis varies from 40 to 73 percent.21,22

Criteria for a significant positive culture by someinvestigators include the clinical signs of keratitis plusone of the following: (i) growth of the organism in twoor more media (ii) confluent growth of a known ocularpathogen in one solid medium or (iii) growth in one

medium of an organism with positive smear results orgrowth of same organism in liquid media.22 Jones criteriafor positive culture include: clinical signs of infectionplus isolation of bacteria (10 or more colonies) on onesolid medium and one additional medium, or isolationof fungi (any detectable growth) on any two media orone medium in the presence of a positive smear. 23

Although liquid media provide a highly sensitivemethod for demonstrating a pathogen, a positive culturefrom broth is less specific than a positive culture fromsolid media as it is difficult to quantify the broth cultures.Anaerobic bacteria are suspected in following situations:Pleomorphic, slender or fusiform morphology seen onGram stain of corneal smear or culture, growth in theanaerobic zone of liquid medium or within the depthof solid agar, production of gas on liquid media andfailure to grow organism in aerobic media despiteorganism detection in Gram stain.21

Negative Cultures

Negative cultures may be present truly in cases ofsterile/non-infectious ulcers or due to prior partialantibiotic treatment, inadequate sampling methods,improper selection of the media and incubationconditions and false interpretation of the data.1 Negativecultures have been reported in 44 percent of cases in aseries of 663 cases of microbial keratitis.22

When the culture results are negative, antibiotictreatment can be suspended temporarily for 24 hoursand rescraping is done following which repeat culturesare sent and examined.

Mixed Organisms/Polymicrobial keratitis

Polymicrobial keratitis is a distinct clinical entity23. Morethan one organism in corneal cultures may be identifiedin 6 to 32 percent of cases depending on the laboratorytechniques and the criteria for for positive or negativeculture.22,23 The most frequent combination in mixedmicrobial infections is an aerobic gram-positive coccusand a gram-negative rod. Rarely it may be a combinationof bacteria and fungi.1

As soon as the growth is detected, an estimate of thenumber of the colonies should be made, with adescription of the colony morphology. Determinationof the antibiotic sensitivities is done. Minimal inhibitoryand bactericidal concentrations are usually availablewithin a few days.

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ANTIMICROBIAL SUSCEPTIBILITY TESTING

The preferred methods for testing the susceptibility ofthe antimicrobial agents are the standard disk diffusionmethod and the micro-dilution techniques (Fig. 6.11).The limitation of the ocular antimicrobial susceptibilitytesting is that the results of agar disk diffusion tests relateto the levels of drug in the serum rather than the concen-tration of the antibiotics achieved in the ocular tissuesand fluids.

The quantitative minimal inhibitory concentration(MIC) estimation by the broth microdilution methodsprovide greater information about the ocular infections.Once a MIC value of a particular antibiotic is found outthe bactericidal effect of the antibiotic may be titratedby sub culturing the clear broth on the antibiotic freezone.

Minimal Bactericidal concentration (MBC) is theconcentration of the antibiotic, which reduces the growthof the bacterial strain by 99.9 percent. The minimumantibacterial concentration (MAC) is the inhibitory effectof the antibacterial agent, which is observed in 5.5 hoursin which 90 percent of the bacterial population isinhibited.4 The post antibiotic effect (PAE) is the resultobserved after the bacterial population is exposed toantibiotics for approximately one hour followed byremoval of the antibiotic either after enzymatic treatmentor dilution and then subculturing to see the amount ofbacterial population that remains.4

SEROLOGICAL INVESTIGATIONS

A variety of DNA probe assays are available for theconfirmation of the results of the culture and for directdetection of the organisms. The expensive molecularmicrobiologic tests however, should not replace the time-tested culture and staining techniques, the efficacy ofwhich have a proven track record. Such serological testmay be divided into three categories4:

i. Target amplification systems such as polymerasechain reaction (PCR), cell sustaining sequence repli-cation (3 SR) or strand displacement amplification(SDA)

ii. Probe amplification systems which includes ligasechain reaction (LCR)

iii. Signal amplification in which the signal generatedfrom each probe is increased by using compoundprobes or branched chain technology

These techniques detect whether DNA and RNAfrom a particular organism is present but do not detectthe viability of the organism.

The advantages of PCR include greater speed thanculture methods (up to 4 hours) and the ability to ana-lyze specimens far from where they are collected. Thecost of PCR to diagnose infections generally exceeds thatof conventional culture methods, a factor that currentlylimits its widespread use.24 16S rDNA typing has beenused as a rapid alternative to culture for identifyingpathogens in patients with bacterial keratitis, 25 whereas18S ribosome gene is used to detect fungal keratitis.24

CONFOCAL MICROSCOPY

It is particularly useful when relatively large infectingorganisms (15 microns) are present, as are seen in Acan-thamoeba , filamentous fungal, microsporidial, and, possi-bly, Lyme Borrelia keratitis.25,26 Confocal microscopy canclearly demonstrate both the cyst and often the tropho-zoite forms of acanthamoeba in suspected keratitis. Italso shows the enlarged corneal nerves accompanyingradial neurokeratitis and the characteristic honeycomb-pattern intrastromal microcavities seen during the latestages of the disease.25

Retina Tomograph II—Rostock Cornea Module(HRTII-RCM) has also demonstrated the presence offungi. Filamentous fungi-infected patients’ corneasreveal numerous high-contrast lines 200–300 μm inlength and 3–5 μm in width, with branches at 90° angles(in cases of Fusarium) or 45o at angle (Aspergillusspecies).26

Candida albicans—infected patient’s cornea revealnumerous high-contrast elongated particles measuring

Figure 6.11: Antimicrobial Susceptibility Testing

61

2Investigations

10–40 μm in length and 5–10 μm in width in the anteriorstroma resembling Candida pseudo-filaments.

CORNEAL BIOPSY

Sometimes repeated smear examinations and culturesof corneal scrapings done by standard method do notdemonstrate presence of any microorganisms. This maybe true for certain cases of deep mycotic keratitis andintrastromal abscesses.27 A vertical or oblique incisioncan allow sampling using a sterile needle or a mini-spatula. Alternatively, a deep lamellar excision may beundertaken to reach a focal abscess.

In such cases, a diagnostic superficial keratectomyor corneal biopsy may be necessary to obtain microbe-infested tissue to make an accurate microbiologicaldiagnosis. Corneal biopsy is superior to scraping forisolating fungus from a case of mycotic keratitis. Theprocedure is performed under topical anesthesia underan operating microscope. A dermatologic 2-3 mmtrephine or a small Elliot microtrephine is advanced into the anterior corneal stroma, to incorporate both theinfected and the clinically normal 1 mm rim. Care istaken to avoid the visual axis as far as possible. Acrescent blade or Bard Parker knife is then used toundermine the tissue, which may then be cut with asurgical blade or a microscissors and the tissue is excised(Fig. 6.12).28 The biopsy tissue is excised with a fine toothforceps taking care not to crush the tissue. The specimenthus obtained should be divided in to pieces andsubjected to smear examination, cultures and histo-pathological examination.

References1. Herbert E Kaufman, Bruce A Barron, Marguerite B

McDonald, Stephen C Kaufman. The Cornea, SecondEdition. Boston, Massachusetts, Butterworth-Heinemann, 1999.

2. Jones BR. Principles in the management of oculomycosis.XXXI Edward Jackson memorial lecture. Am JOphthalmol 1975;79:719-51.

3. Huang AJW, Wichiensui P, Yang MC. Bacterial keratitis:In: Krachmer JH, Mannis MJ, Holland EJ (Eds): CorneaFundamentals, Diagnosis and Management, 2nd edition2005;1:1005-34.


5. Sridhar MS, Sharma S, Gopinathan U, Rao GN. Anteriorchamber tap: diagnostic and therapeutic indications inthe management of ocular infections. Cornea 2002;21:718-22.

6. Allen HF. Current status of prevention, diagnosis, andmanagement of bacterial corneal ulcers. Ann Ophthal-mol 1971;3:235-46.

7. Benson WH, Lanier JD. Comparison of techniques forculturing corneal ulcers. Ophthalmology 1992;99:800-4.

8. Jacob P, Gopinathan U, Sharma S, Rao GN. Calciumalginate swab versus Bard Parker blade in the diagnosisof microbial keratitis. Cornea 1995;14:360-4.

9. Forster RK, Wirta MG, Solis M, Rebell G. Methenamine-silver-stained corneal scrapings in keratomycosis. Am JOphthalmol 1976;82:261-5.

10. Vajpayee RB, Angra SK, Sandramouli S, Honavar SG,Chhabra VK. Laboratory diagnosis of keratomycosis:comparative evaluation of direct microscopy and cultureresults. Ann Ophthalmol 1993;25:68-71.

11. Gopinathan U, Garg P, Fernandes M, Sharma S,Athmanathan S, Rao GN. The epidemiological featuresand laboratory results of fungal keratitis: a 10-yearreview at a referral eye care center in South India. Cornea2002;21:555-9.

12. Jones DB. Initial therapy of suspected microbial cornealulcers. II. Specific antibiotic therapy based on cornealsmears. Surv Ophthalmol 1979;24:97, 105-16.

13. Popescu A, Doyle RJ. The Gram stain after more than acentury. Biotech Histochem 1996;71:145-51.

14. Sutphin JE, Robinson NM, Wilhelmus KR, Osato MS.Improved detection of oculomycoses using inducedfluorescence with cellufluor. Ophthalmology 1986;93:416-7.

15. Marines HM, Osato MS, Font RL. The value of calcofluorwhite in the diagnosis of mycotic and Acanthamoebainfections of the eye and ocular adnexa. Ophthalmology1987;94:23-6.

16. Gomez JT, Robinson NM, Osato MS, Wilhelmus KR.Comparison of acridine orange and Gram stains inbacterial keratitis. Am J Ophthalmol 1988;106:735-7.

Figure 6.12: Corneal biopsy with dermatologic trephine

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17. Groden LR, Rodnite J, Brinser JH, Genvert GI. Acridineorange and Gram stains in infectious keratitis. Cornea1990;9:122-4.

18. Jones DB, Robinson NM. Anaerobic ocular infections.Trans Am Acad Ophthalmol Otolaryngol 1977;83:309-31.

19. Ormerod LD, Ruoff KL, Meisler DM, Wasson PJ, KintnerJC, Dunn SP, et al. Infectious crystalline keratopathy.Role of nutritionally variant streptococci and otherbacterial factors. Ophthalmology 1991;98:159-69.

20. Osato MS, et al. Clinical applications of Antimicrobialremoval device in ocular infectious diseases. Ophthal-mology (Suppl) 1983;90:103.

21. Asbell P, Stenson S. Ulcerative keratitis. Survey of30 years’ laboratory experience. Arch Ophthalmol.1982;100:77-80.

22. Liesegang TJ, Forster RK. Spectrum of microbial keratitisin South Florida. Am J Ophthalmol 1980;90:38-47.

23. Jones DB. Polymicrobial keratitis. Trans Am OphthalmolSoc 1981;79:153-67.

24. Gaudio PA, Gopinathan U, Sangwan V, Hughes TE.Polymerase chain reaction based detection of fungi ininfected corneas. Br J Ophthalmol 2002;86:755-60.

25. Parmar DN, Awwad ST, Petroll WM, et al. Tandemscanning confocal corneal microscopy in the diagnosisof suspected acanthamoeba keratitis. Ophthalmology2006;113:538-47.

26. Brasnu E, Bourcier T, Dupas B, Degorge S, Rodallec T,Laroche L, et al. In vivo confocal microscopy in fungalkeratitis. Br J Ophthalmol 2006.

27. Knox CM, Cevellos V, Dean D. 16S ribosomal DNAtyping for identification of pathogens in patients withbacterial keratitis. J Clin Microbiol 1998;36:3492-6.

28. Alexandrakis G, Haimovici R, Miller D, Alfonso EC.Corneal biopsy in the management of progressive micro-bial keratitis. Am J Ophthalmol 2000;129:571-6.

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3Bacterial Keratitis

Bacterial Keratitis7

Bacteria are the most important cause of infectiouskeratitis. Prompt recognition, expedient evaluation andrapid initiation of antibiotic therapy are of vitalimportance. Most cases respond to medical therapy andyield gratifying results. With an advanced infection,devastating complications such as corneal thinning,corneal perforation scleral extension and consequently,endophthalmitis may occur.

There are no pathognomic clinical signs that confirma definite bacterial etiology. However, based ondistinctive corneal signs such as the status of theepithelium, type of stromal inflammation and the siteof the inflammation, a possible suspicion of the bacterialetiology may be reached which is confirmed on thelaboratory examination.

Risk Factors

The eye is continuously exposed to a large number ofbacteria, which form a part of ocular flora. However,

Figure 7.1: Keratitis in a case of repaired corneal perforation

only a small number of these bacteria cause keratitis.There are various pre-disposing factors, which mayprecipitate bacterial keratitis which include thefollowing:

CORNEAL TRAUMA

Corneal trauma causing a breach in the intact epitheliumalong with concurrent inoculation of organisms canoccur from vegetable matter, industrial foreign bodies,contact lenses, cosmetic application and administrationof ocular medications causing bacterial keratitis1-3

(Fig. 7.1).

EYELID DISEASE

Ocular adnexal disorders such as blepharitis, dacryo-cystitis, ectropion with exposure, entropion (Fig. 7.2)with trichiasis or lagophthalmos (Fig. 7.3) lead todisturbed precorneal tear film that can predispose tobacterial keratitis.

Figure 7.2: Keratitis in a case of entropion

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Types of Microbial Keratitis

OCULAR SURFACE DISORDER

Ocular surface disorders such as dry eye, StevensJohnson syndrome and ocular burns can cause chroniccorneal decompensation may predispose the eye tobacterial keratitis. Ocular surface disorders causes thedisturbance of the tear film dynamics and leads topersistent epithelial defects (Fig. 7.4) which aresecondarily infected and cause stromal ulceration.1

TEAR FILM DYSFUNCTION

Tear film dysfunction which predispose to bacterialkeratitis include dry eye due to aqueous layer insuffi-ciency, mucin layer abnormality due to goblet cell loss/dysfunction, lipid layer instability or lacrimal drainageobstruction.

PREVIOUSLY COMPROMISED LOCAL/SYSTEMIC DEFENSE MECHANISMS

Topical corticosteroids, antifungal medications,contaminated ocular medications and anesthetics impairthe immune mechanisms. The use of topical corticoste-roids causes localized immune suppression by prevent-ing neutrophil migration in response to chemotacticfactors released as a consequence of microbial keratitis(Fig. 7.5).

Patients with diabetes are also more prone to bacte-rial keratitis.4 Patients with acquired immunodeficiencysyndrome (AIDS) from infection of human immuno-deficiency virus (HIV) do not appear to be at increased

risk for bacterial corneal ulcers, but when they developbacterial keratitis it takes a more fulminant course andulcers are most often caused by Pseudomonas.5

CONTACT LENS USE

The contact lens keratitis may occur due to the contactlens per se, which compromises the corneal health as itcauses corneal hypoxia (Fig. 7.5). Contact lenses causehypoxia and increased corneal temperature.5-8 Extendedsoft contact lens wearers are at 10 to 15 times increasedrisk for bacterial keratitis as compared to daily lenswearers.7 Aphakic contact lens wearers have 6 to 9 times

Figure 7.4: Corneal ulcer following persistent epithelial defectFigure 7.3: Corneal ulcer due to lagophthalmos in a case with thyroiddisease

Figure 7.5: Contact lens induced ulcer

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greater rate of infectious corneal ulceration as comparedto cosmetic wearers due to longer wear intervals,reduced defense mechanisms of a postoperative corneaor increased corneal hypoxia.8 Pseudomonas is the mostcommon organisms causing contact lens - related ulcers,followed by Staphylococcus sp. and Serratia marcescens.

Further, the contact lens used may also be infectedand infection may also occur as a consequence ofimproper care of the contact lenses or the contact lenscase and the contact lens solution.

Etiologic OrganismsAlthough virtually any bacteria may cause keratitis, fourprincipal groups of bacteria are primarily responsible.These include – the Micrococcaceae, Streptococcaceae,Pseudomonas and the Enterobacteriaceae(Table 7.1).Eighty seven percent of the bacterial keratitis has beenattributed to these organisms.1

Bacteria may be divided into two groups based onthe structure of the cell wall. Gram-positive organisms,possess a thick pepti-doglycan layer, which resistsphysical forces. Gram-negative organisms, on the otherhand, have a comparatively thicker peptidoglycan layeradjacent to the cytoplasmic membrane and a cell wall,which has large amounts of lipoprotein and lipo-polysaccharide.

Mycobacteria have cell walls made of long chain fattyacids (mycolic acids), which resist decolorization bystrong organic solvents and hence are acid fast.

Some bacteria may produce endospores, which arerefractile bodies within the vegetative bacterial cell, sothat the bacteria survive in adverse environmentconditions of heat and dryness.

REGIONAL DIFFERENCESThe bacterial organisms most commonly identified showregional differences based on the prevalence, the typeof pre-existing corneal pathology, the climate and thenature of referrals.

The predominant causative organism of bacterialkeratitis in most studies are gram-positive organisms.9

Staphylococcus species is the most common cause ofbacterial keratitis in most parts of the world in pre-viously normal corneas as well as the already compro-mised corneas.9 Staphylococcus aureus is common in northand north-eastern United States, New York, SouthernCalifornia, Florida, Canada and London.9

Pseudomonas aeruginosa has been identified morefrequently in southern United States, Hong Kong andGhana.10,11

In India the organisms, which have been identifiedmost commonly, include Staphylococcus epidermidis12 andStreptococcus species.13

SPECIFIC ORGANISMS

Staphylococcal OrganismsStaphylococcal species are the most frequently isolatedbacterial organisms from corneal ulcers. The mostsusceptible corneas to these infectious include those with

TABLE 7.1Classification of bacterial organisms causing microbialkeratitis

Aerobic bacteria Anaerobic bacteria

Gram-positive cocci Gram-positive cocciMicrococcaceae Peptococcaceae– Staphylococcus aureus – Peptococcus– Staphylococcus epidermidis – PeptostreptococcusStreptococcaceae– Streptococcus pneumoniae– A and B hemolytic streptococci– Aerococcus– Enterococcus

Gram-positive bacilli Gram-positive bacilliBacillaceae Propionibacterium acne– Bacillus cereus – Actinomyces– Bacillus subtilis – Clostridium– Corynebacteria diphtheriae– Conynebacteria xeroses– Listeria monocytogenes

Gram-negative bacilli Gram-negative bacilliPseudomonaceae Fusobacterium– Pseudomonas aeruginosa BacteriodesAcinetobacter CapnocytopagaAzotebacterEnterobacteriaceae– Klebsiella– Serratia– Proteus– Citro bacter– Enterobacter– EscherichiaGram-negative diplococci Gram-negative cocci– Neisseria – VeillomellaGram-negative diplobacilli Spirochaetales– Moraxella – TreponemaGram-negative coccobacilli – Boncha– Hemophilus - LeptospinaGram-positive filaments– Mycobacterium

(Non-tuberculosis)– Nocardia

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Corynebacterium diphtheriaeConynebacterium diphtheriae may penetrate intactcorneal epithelium due to its toxin. Corynebacteriumxerosis is frequently associated with Moraxella infections.

Actinomycetes

Actinomycetes and related organisms such as Nocardiaresemble bacteria more than fungi. Actinomycetes aregram positive, branching filamentous fungi, which mayrarely cause keratitis. Nocardia organisms are ubiquitousin soil and cause keratitis especially after trauma.20

Spore Forming Anaerobic Bacteria

Spore forming anaerobic bacteria such as Clostridia mayrarely cause keratitis especially after contamination withsoil and may be associated with gas bubbles in thecorneal tissue or anterior chamber.

Nonspore-forming Anaerobic Organisms

Nonspore-forming anaerobic organisms should besuspected as a cause of keratitis following human oranimal bites.21 They are associated with extensivenecrosis of the tissue, gas formation in tissue or fouldischarge.21 The most frequent anaerobes are Peptostrep-tococcus, Peptococcus, Propionibacterium, Bacteroides andFusobacterium species. Propionibacterium species are non-spore forming anaerobic bacteria and can cause keratitisin healthy and compromised cornea.

Non-tuberculous Mycobacteria

Recently, non-tuberculous mycobacteria, includingMycobacterium fortuitum, M. chelonae, M. gordonae andM.avium intracellular are emerging as causes of indolentkeratitis especially after surgical procedures such aslaser-in-situ keratomileusis.22 Out of all the species ofMycobacteria, Mycobacterium chelonae is most frequencyisolated.22,23 They may also cause keratitis after injurywith a foreign body. Mycobacterium leprae may also causekeratitis with involvement of the peripheral cornealnerves.

Less Common Organisms

Organisms which are associated less commonly withkeratitis include Enterobacteriaceae (Serratia, Proteus),Azotobacter and Neisseria species, Serratia marcescens hasbeen associated with keratitis in contact lens wearer and

prior herpetic infection, dry eye syndrome, bullouskeratopathy,14 previous surgery and atopic disease.15

In the more recent studies, the indigenous bacteriaincluding the coagulase negative Staphylococcus species,which are being more frequently isolated as causativeorganisms of keratitis. These pathogens invade asprimary pathogens or more frequently as co-pathogensin cases of polymicrobial/mixed-microbial keratitis.Amongst the various species of coagulase negativeStaphylococci, Staphylococcus epidermidis has been mostfrequently isolated.

Streptococcus pneumoniae

Previously, Streptococcus pneumoniae was the predomi-nant cause of bacterial keratitis especially in cases ofchronic dacryocystitis. With the advent of modernantibiotics and refinement in the surgical technique ofdacryocystorhinostomy, pneumococcus has decreasedin frequency as a causative organism, especially in thedeveloped countries. However, it may still be animportant cause of bacterial keratitis in the developingworld.13

Pseudomonas species

Pseudomonas species has also been increasingly isolated,more so in daily or extended wear soft contact lenswearers.16 This organism is present in the hospitalenvironment, fluorescein solution and cosmetics.Pseudomonas keratitis is seen in patients with burns, withaltered levels of consciousness (semi-comatose orcomatose) or those maintained on mechanical ventila-tory assistance and immunocompromized patients suchas those infected with human immunodeficiency virus(HIV).17

Gram-positive aerobic bacilli

Gram-positive aerobic bacilli such as Bacillus Cereus havebeen associated with keratitis following foreign bodyinjury.18

Moraxella species

Moraxella species have been isolated in 0.3 percent ofnormal patients. Moraxella species, a gram-negativediplobacilli causes keratitis in cases of malnourishedindividuals, alcoholics, diabetics and in immunocompro-mized patients or patients with other debilitatingconditions.19

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contaminated eye drops. Listeria monocytogenes causessevere suppurative keratitis in animal handlers andfarmers.1 Syphillitic as well as non-syphillitic spiro-chaetal infection can cause non-suppurative stromalkeratitis.1

Clinical Features

GENERAL SYMPTOMS

The general symptoms of bacterial keratitis includedecreased visual acuity, photophobia, pain, redness anddischarge. The severity of symptoms depends on theorganisms, the condition of the host and the durationof the symptoms before the patient is examined.

GENERAL SIGNS

An infectious corneal ulcer should be distinguished froma noninfectious corneal ulcer by the following features:The precorneal tear film and meniscus in an activelyinfected ulcer are typically seen via slit lamp examina-tion to contain numerous cells and debris, which areabsent in a non-infected corneal ulcer. The cornealepithelium is absent over areas of active infection (unlikea non-infected ulcer) and the stromal inflammation issuppurative.

Associated conjunctivitis is present with Gonococcal,Pneumococcal and Haemophilus infections.1 They mayfrequently present with chemosis and sometimesconjunctival pseudomembrane also. Papillae, which aretufts of capillaries infiltrated by inflammatory cells andseparated by septa bound down by tarsus, usuallyaccompany bacterial infections and are indicative ofconjunctival inflammation.

Discharge varies from copious amount of clear fluidto a greenish- yellow purulent material.

SPECIFIC FEATURES

Bacteria, which can invade an intact cornea, includeNeisseria, Corynebacterium, Haemophilus, Shigella andListeria.

Gram-positive Organisms

Staphylococcal Ulcers

Staphylococcus aureus is present in 15 percent of culturesobtained from lids of normal individuals and non-

coagulase Staphylococcus is present in 85 percent ofcultures obtained from lids of normal individuals.1

Staphylococcal ulcers occur in compromised corneas suchas in patients with bullous keratopathy, chronic herpetickeratitis, dry eyes, rosacea keratitis or atopic disease.

The ulcer tend to remain localized with distinctborders and non-edematous surrounding stroma(Fig. 7.6). Long standing Staphylococcal ulcers tend toinfiltrate deeper areas and may cause intrastromalabscess (Fig. 7.6) and may lead to corneal perforation.Occasionally, multiple stromal micro infiltrate satellitesmay be seen resembling fungal infections. They aregenerally associated with mild to moderate anteriorchamber reaction.

Pneumococcal Ulcers

They generally occur following trauma to the corneaand cannot invade a healthy cornea directly. They areparticularly associated with the cases of dacryocystitis.1

Infiltration starts at the site of injury and rapidlyspreads towards the center of cornea. Severe anteriorchamber reaction associated with hypopyon is usuallypresent. Fibrin deposition may be seen on endothelialside of the ulcer and a deep stromal abscess may form,with intervening stroma relatively clear. If untreatedcorneal perforation and melting may occur rapidly(Fig. 7.7).

Alpha Hemolytic StreptococciThey are responsible for infectious crystalline kerato-pathy which has been discussed in details in chapter.

Gram-negative Organisms

Pseudomonas ulcers

Pseudomonas keratitis presents as a rapidly evolvinginfection that may lead to perforation and loss of eye, ifleft untreated. Occasionally they may also be slowlyprogressive or have an indolent course.

Infection results when a traumatized cornea isexposed to the organism. Following adhesion of theorganisms to the damaged epithelium and stroma,invasion into stroma occurs within an hour. Theinfection begins with an epithelial defect, superficialedema and micro-infiltration of stroma, which occursas early as 6 to 8 hours after injury. The infiltrationextends peripherally and deeply and within 18 to 24hours it is extensive. The ulcer spreads symmetrically

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and concentrically to involve whole width and depth ofcornea.

A characteristic feature of Pseudomonas ulcer isdiffuse epithelial graying which characteristically occursaway from the main site of epithelial and stromalinfiltration. A ring ulcer is often seen at 48 to 96 hourswith an untreated infection. The progressive untreatedulcer is associated with melting of the cornea (Figs 7.8Aand B), and with greenish-yellow mucopurulentdischarge which is adherent to the ulcer. This leads todescmetocele formation and eventual perforation within2 to 5 days of onset of infection.

Other Gram-negative Rods

Other gram-negative bacilli include Klebsiella,Escherichia coli and Proteus, which most commonly causeindolent ulcerations in previously compromised corneaswith milder anterior chamber reaction.

Moraxella Ulcers

The ulcer caused due to Moraxella is typically indolentwith only mild to moderate anterior chamber reaction.It is usually oval and located in the inferior part of thecornea.19 It tends to remain localized as it spreads into

Figure 7.6: Ulcer due to Staphylococcus with intrastromal abscess Figure 7.7: Corneal ulcer due to Pneumococcus

Figures 7.8A and B: (A) Pseudomonas keratitis (B) Pseudomonas keratitis with corneal melting

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the deep stroma. Some ulcers may have prolonged,moderately severe stromal and anterior chamberreactions with endothelial decompensation despiteproper treatment.

Anaerobes

Anaerobic infections usually follow corneal injuries withcontaminated soil.21

Clostridium species are suggested by the presence of gasbubbles, which are visualized in the anterior chamberin the corneal stroma or under the epithelium.

Listeria monocytogenes causes ulcerative keratitis inanimal handlers.1 Propionibacterium acnes and Pepto-streptococcus are rare anaerobes. Actinomyces infectionsare associated with canaliculitis.1

Nocardia species inhabit the soil and cause indolentulceration and are introduced into the eye followingtrauma.24 These ulcers simulate fungal corneal ulcersand occasionally have elevated, hyphate edges and oftenproduce satellite lesions and cracked-windshieldappearance of the cornea.

Mycobacterium fortuitum inhabits the soil and causeindolent ulcers, which progress slowly over weeks.22,23

The bed of the ulcer has cracked windshield appearancewith minimal changes in the surrounding cornea or theanterior chamber.

Microbiologic Work UpA provisional diagnosis can be reached after the clinicalwork up of a case which is confirmed on microbiology.

Traditionally, the treatment regimen should bestarted only after smears and cultures have been taken.Corneal scraping from the ulcer area is obtained and issent for microbiologic work up which includes directmicroscopy and culture.

The smears include the Gram’s smear, Giemsastaining, KOH wet mount preparation and Grocott-Gomori methenamine-silver staining, especially if fungalinfection is suspected. Acid-fast stains are necessarywhen M. fortuitum, Actinomyces sp. or Nocardia sp. aresuspected as in cases of indolent corneal ulceration.

The material obtained should also be inoculateddirectly on the culture media, rather than placed oncarrier or transport media, since specimen obtainedusually contain very few organisms. The specimens areC streaked on Blood agar plate, Chocolate agar,

Sabrouraoud agar plate or blood agar plate at roomtemperature (Fig. 7.9) for fungi and chopped meatglucose broth or Thioglycolate medium with hemin andvitamin K for anaerobes.

In case of contact lens keratitis, contact lens, case andsolution should also be sent for microbiologicexamination.24

However, sometimes the Gram stain may fail toreveal the offending organisms, in that case, it isinadvisable to delay treatment while awaiting the resultsof culture. The empirical treatment with the broad-spectrum antibiotic drops should thus be started whilewaiting for the culture reports.

TreatmentIdeally a patient of bacterial keratitis should behospitalized especially if the compliance of the patientis in doubt or it is a more severe form of disease. Reliablepatients with mild or moderate ulcers may be treatedas outpatients with careful follow-up. In general themost rapidly destructive microbial keratitis is bacterialand should be treated as bacterial corneal ulcer until adefinitive diagnosis is made.

Until the results of the definitive cultures areavailable, Gram’s stain is a quick and helpful tool forinitiating a rational antibiotic therapy. If done properly,

Figure 7.9: Blood agar at room temperature (A) and at 37 degreecentigrade (B), Chocolate agar (C), Sabouraud’s agar (D)

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hourly dosage. Some people prefer to use 10% cefazolinsodium instead of 5% cefazolin sodium in thecombination therapy. The cephalosporin providescoverage against gram-positive cocci and some of thegram-negative rods while the aminoglycoside are coversmost of gram-negative bacilli.24,25

Following clinical response the frequency of theantibiotics is reduced 4 hourly after 72 hours and issubsequently tapered over the next few days.

Monotherapy

Ciprofloxacin 0.3 percent, ofloxacin 0.3 percent,Gatifloxacin 0.3 percent or moxifloxacin 0.5 percent canbe given as monotherapy and is effective against mostcorneal pathogens.27 Additionally they are also effectiveagainst most strains of aminoglycoside resistantPseudomonas, methicillin resistant Staphylococcus and

Gram’s stain may identify pathogen in upto 75 percentof the cases caused by single organism and 37 percentof the cases caused by mixed organisms.1 We do routineGram’s staining and KOH wet mount preparation in allcases of suspected microbial non-herpetic keratitis.

The initial management of cases of bacterial keratitisincludes the use of medical therapy. However, in casesof corneal perforation surgical modalities may beresorted to.

MEDICAL THERAPY

The frequent administration of the broad-spectrumantibiotic topical drops is the mainstay of the treatment.Additional supportive therapy includes the use of topicalcycloplegic agents, antiglaucoma medications and useof lubricants.

Choice of Antibiotics

The treatment with topical antibiotics is initiated witheither a combination fortified therapy or monotherapy.

Types of Antibiotic Therapy

In cases where no treatment has been given earlier it ismandatory to take corneal scrapings and send them forculture examination.

In case where topical antibiotics were given beforeone can suspend the topical medications for 12 to24 hours before obtaining the specimen for cornealscraping.

Combination Therapy

We prefer to use the combination therapy in cases ofbacterial keratitis. A combination therapy consists of acephalosporin, which acts against the gram-positivecocci and some of the gram-negative rods and anaminoglycoside which acts against the gram negativeorganisms.25 Alternatively one of newer generationfluoroquinolones may also be combined with fortifiedcefazolin. The newer generation fluoroquinolones coversome gram-positive organisms and most of thesignificant gram-negative rods including manyPseudomonas species.25

Combined fortified 5 percent cefazolin sodium and1.3 percent tobramycin sulphate are given in hourlydosage for the initial 48 hours (Table 7.2).26 Followingan initial response to this therapy, the frequency of thedrugs is tapered and the topical drugs are given two

TABLE 7.2Preparation of fortified topical antibiotics*

1. Cefazolin 50 mg/ml or ceftazidime 50 mg/mLa. Add 9.2 mL of artificial tears to a vial of cefazolin,

1 g (powder for injection).b. Dissolve. Take 5 mL of this solution and add it to

5 ml of artificial tears.c. Refrigerate and shake well before instillation.

2. Tobramycin 14 mg/mL or gentamicin 14 mg/mLa. Withdraw 2 mL of tobramycin or gentamicin injectable

vial (40 mg/mL).b. Add 2 mL to a tobramycin or gentamicin ophthalmic

solution (5 mL) to give a 14 mg/mL solution.3. Vancomycin 15 mg/mL, vancomycin 25 mg/mL or

vancomycin 50 mg/mLa. Add 33 mL of 0.9 percent sodium chloride for injection

(no preservatives) or artificial tears to a 500 mg vialof vancomycin to produce a solution of 15 mg/mL.Add 20 mL of 0.9 percent sodium chloride for injection(no preservatives) or artificial tears to produce asolution of 25 mg/mL. Add 10 mL of 0.9 percentsodium chloride for injection (no preservatives) orartificial tears to produce a solution of 50 mg/mL.

b. Refrigerate and shake well before instillation.4. Amikacin

Intravenous formulation can be used (80 mg/2 ccampules).

5. Trimethoprim/Sulfamethoxazole 16 mg/ml and 80 mg/ml commercial preparation used.

*(Adapted from Basic Clinical and Science Course 2000-2001,Section 8, External Disease and Cornea. American Academyof Ophthalmology

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but are best avoided as they may cause increasedchances of corneal melting.

Topical CorticosteroidsTopical corticosteroids are started 48 hours after theorganism have been identified on the culture along withthe topical antibiotics.23 This is done after the fungalorganisms as causative agents have been ruled out.Alone with the combination therapy it may decreasethe amount of inflammation and reduces chances ofcorneal scaring. Topical corticosteroids should not beused in cases of corneal thinning for impendingperforation.

MODIFICATION OF THERAPYThe results of microbial culture an the antimicrobialsusceptibility testing data may suggest a modificationfrom the intial therapeutic plan. If the patient isresponding clinically to the original therapeutic plan,no modification in antibiotic drugs is instituted.However, if the patients is not responding to the therapyor there is worsening of the clinical features , theantibiotic drugs may be changed according to the culturesensitivity reports.

If microbial culture fails to grow an organism,topical medications are stopped for 24 hours before are-scrape is done and cultures are sent again.

SPECIFIC DRUGSSpecific drugs may be used when the keratitis occursdue to specific agents. For Nocardia keratitis combination

Figure 7.10: Healing corneal ulcer

exquisitely potent against Neisseria keratitis.27 They arewell-tolerated and more convenient to use.

Monotherapy is advocated in cases of small cornealulcers not involving the visual axis.

The patients are followed up daily and detaileddrawings and measurements are taken to monitor theprogress of the therapy.

This includes the resolution of the parameters whichinclude the lid edema, conjunctival congestion, the ulcersize in mm and the depth, the size of the infiltration,corneal epithelial edema and the size of the hypopyon(if any) (Fig. 7.10).

Due to emergence of methicillin resistant Staphylo-coccus aureus (MRSA), vancomycin should not be usedroutinely but should be reserved for very severe orrecalcitrant infections.

ADJUNCTIVE THERAPY

Topical cycloplegics should be administered along withthe antimicrobial therapy. This relieves the ciliary spasm,alleviates pain and prevents the formation of synechiae.Homatropine eye drops 1 percent is used in three tofour times daily.

Significant inflammation may cause a rise inintraocular pressure and hence in such cases anti-glaucoma medications may be added. These include theuse of topical beta blockers such as 0.5 percent timololmaleate or systemic carbonic anhydrase inhibitors suchas Acetazolamide in more severe cases.

The precise role of non-steroidal anti-inflammatoryagents has not been studied in cases of bacterial keratitis

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trimethoprim (16 mg/ml) and sulfametoxazole ( 80 mg/ml) is the treatment of choice.28 Alternatively, sulfona-mides, tetracyclines, erythromycin or amikacin may beused.

In cases of acid fast-stained positive corneal scrapingstopical amikacin 10 to 20 mg/ml one drop every houris indicated.22,23 Systemic amikacin may be used in casesof corneal perforation or scleral involvement. Morerecently, the fluroquinolones have found to be effectiveagainst mycobacteria and can be used as a first line oftreatment.

Subconjunctival Route

Subconjunctival antibiotics can produce high cornealdrug levels. The injections are painful and anxietyprovoking. We do not advocate the use of subconjuncti-val antibiotics as these injections may result insubconjunctival hemorrhage, and if repeated, may leadto subconjunctival fibrosis.

SYSTEMIC THERAPY

Systemic antibiotics are started along with the topicalantibiotics in cases of severe keratitis with scleralmelting, impending perforation, frank perforationswhich have a propensity for intraocular spread and alsowhen the infection occurs in children due to H. influenzaand P. aeruginosa.25

SIGNS OF HEALING

The signs of healing of bacterial keratitis or response totherapy include the following: The signs and symptomsdecrease and visual acuity continues to improve. Thestromal infiltrates consolidate and the anterior chamberreaction decreases. Epithelialization is complete andnecrotic stroma is replaced by scar tissue laid down byfibroblasts. Vascularisation occurs and followingcomplete healing the vessels regress completely butsometimes leave “ghost vessels” which are visiblethrough indirect illumination.

SIGNS OF PROGRESSION/NON-RESPONSE

Signs of progression include increase in the size of theinfiltrate, epithelial defect, height of hypopyon, cornealthinning and eventually perforation.

When culture results are negative but infection is stillsuspected, and the progression of the disease is suchthat antibiotic treatment can be suspended temporarily,it is wise to discontinue antibiotics and obtain specimensfor re-culture. Antibiotics may then be re-instituted onan empirical basis if there is clinical deterioration untilan organism is identified to allow for more specifictreatment.

SURGICAL THERAPY

The surgical modalities to treat bacterial corneal ulcerinclude the use of cyanoacrylate glue, patch grafts andtherapeutic keratoplasty.

TISSUE ADHESIVES

Cyanoacrylate glue to treat small perforations (less than3 mm), progressive stromal keratolysis and thinneddescemetoceles (Figs 7.11A and B). The tissue adhesiveis known to have anti-bacterial activity. However, sinceit is toxic to the corneal endothelium , it should be usedwith caution. It restores the integrity of the cornea, tillthe antimicrobial therapy can reduce the ulceration size.The edges and the bed of the site of the perforation isdried completely before application of the glue followingwhich a therapeutic bandage contact lens is placed.

PATCH GRAFTS

Patch grafts of upto 5 mm diameter may be used todebulk the cornea and to remove the clinically visiblemargin of the infected area (Fig. 7.12). It is preferable toencompass 1 mm of the normal cornea in the trephinatedarea.

THERAPEUTIC KERATOPLASTY

If there are large areas of perforation or necrotic tissue,a therapeutic keratoplasty is indicated. Pre-operatively,maximal antibiotic therapy to eradicate infection and toreduce inflammation is recommended. It is preferableto encompass one mm of the normal cornea in thetrephinated area (Figs 7.13A and B). Further, the cornealbutton obtained should be sent for microbiologicalculture and histopahological examination. Postoperatively, systemic antibiotic therapy should also begiven along with the topical antimicrobial agents andtopical corticosteroids.

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Figure 7.11A: Impending perforation (Courtesy: Medical PhotographicImaging Centre, Royal Victorian Eye and Ear Hospital, Melbourne)

Figure 7.12: Patch graft in a case of perforated corneal ulcer

Figures 7.13A and B: Perforated corneal ulcer (A) therapeutic keratoplasty done (B)

Figure 7.11B: Glue applied (Courtesy: Medical Photographic ImagingCentre, Royal Victorian Eye and Ear Hospital, Melbourne)

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References1. Terrence PO Brien. Bacterial keratitis. In: Smolin G, Thoft

RA, Foster C, Azar D, Dohlman C (Eds): The CorneaScientific Foundations and Clinical Practice, 4th edition,Lippincott Williams and Wilkins Philadelphia 235-88.

2. Wilson SE, Bannan RA, McDonald MB, Kaufman HE.Corneal trauma and infection caused by manipulationof the eyelashes after application of mascara. Cornea1990;9:181-2.

3. Upadhyay MP, Rai NC, Brandt F, Shrestha RB. Cornealulcers in Nepal. Graefes Arch Clin Exp Ophthalmol1982;219:55-9.

4. Ormerod LD, Hertzmark E, Gomez DS, Stabiner RG,Schanzlin DJ, Smith RE. Epidemiology of microbialkeratitis in southern California. A multivariate analysis.Ophthalmology 1987;94:1322-33.

5. Hemady RK. Microbial keratitis in patients infected withthe human immunodeficiency virus. Ophthalmology1995;102:1026-30.

6. Najjar DM, Aktan SG, Rapuano CJ, Laibson PR, CohenEJ. Contact lens-related corneal ulcers in compliantpatients. Am J Ophthalmol 2004;137:170-2.

7. Poggio EC, Abelson M. Complications and symptomsin disposable extended wear lenses compared withconventional soft daily wear and soft extended wearlenses. CLAO J 1993;19:31-9.

8. Glynn RJ, Schein OD, Seddon JM, Poggio EC,Goodfellow JR, Scardino VA, et al. The incidence ofulcerative keratitis among aphakic contact lens wearersin New England. Arch Ophthalmol 1991;109:104-7.

9. Liesegang TJ, Forster RK. Spectrum of microbial keratitisin South Florida. Am J Ophthalmol 1980;90:38-47.

10. Lam DS, Houang E, Fan DS, Lyon D, Seal D, Wong E.Hong Kong Microbial Keratitis Study Group. Incidenceand risk factors for microbial keratitis in Hong Kong:comparison with Europe and North America. Eye2002;16:608-18.

11. Leck AK, Thomas PA, Hagan M, Kaliamurthy J,Ackuaku E, John M, et al. Aetiology of suppurativecorneal ulcers in Ghana and south India, and epidemio-logy of fungal keratitis. Br J Ophthalmol 2002;86:1211-5.

12. Bharathi MJ, Ramakrishnan R, Meenakshi R,Padmavathy S, Shivakumar C, Srinivasan M. Microbialkeratitis in South India: influence of risk factors, climate,and geographical variation. Ophthalmic Epidemiol 2007;14:61-9.

13. Srinivasan M, Gonzales CA, George C, Cevallos V,Mascarenhas JM, Asokan B, et al. Epidemiology andaetiological diagnosis of corneal ulceration in Madurai,south India. Br J Ophthalmol 1997;81:965-71.

14. Luchs JI, Cohen EJ, Rapuano CJ, Laibson PR. Ulcerativekeratitis in bullous keratopathy. Ophthalmology 1997;104:816-22.


16. Mah-Sadorra JH, Yavuz SG, Najjar DM, Laibson PR,Rapuano CJ, Cohen EJ. Trends in contact lens-relatedcorneal ulcers. Cornea 2005;24:51-8.

17. Asbell P, Stenson S. Ulcerative keratitis. Survey of 30years’ laboratory experience. Arch Ophthalmol 1982;100:77-80.

18. Choudhuri KK, Sharma S, Garg P, Rao GN. Clinical andmicrobiological profile of Bacillus keratitis. Cornea 2000;19:301-6.

19. Das S, Constantinou M, Daniell M, Taylor HR. Moraxellakeratitis: predisposing factors and clinical review of 95cases. Br J Ophthalmol 2006;90:1236-8.

20. Bharathi MJ, Ramakrishnan R, Vasu S, MeenakshiChirayath A, Palaniappan R. Nocardia asteroideskeratitis in South India. Indian J Med Microbiol 2003;21:31-6.

21. Brook I. Ocular infections due to anaerobic bacteria. IntOphthalmol 2001;24:269-77.

22. Donnenfeld ED, Kim T, Holland EJ, Azar DT, PalmonFR, Rubenstein JB, et al. American Society of Cataractand Refractive Surgery Cornea Clinical Committee.ASCRS White Paper: Management of infectious keratitisfollowing laser in situ keratomileusis. J Cataract RefractSurg 2005;31:2008-11.

23. Karp CL, Tuli SS, Yoo SH, Vroman DT, Alfonso EC,Huang AH, et al. Infectious keratitis after LASIK.Ophthalmology 2003;110:503-10.

24. Das S, Sheorey H, Taylor HR, Vajapyee RB. Associationbetween cultures and contact lens and corneal scrapingin contact lens related microbial keratitis. ArchOphthalmol 2007;125:1182-5.

25. Huang AJW, Wichiensin P, Yang MC. Bacterial keratitis.Chapter 81. In: Krachmer JH, Mannis MH, Holland EJ(Eds): Cornea: Fundamentals, Diagnosis and Manage-ment, NY, 2005;1005-33.

26. Ofloxacin monotherapy for the primary treatment ofmicrobial keratitis: a double-masked, randomized,controlled trial with conventional dual therapy. TheOfloxacin Study Group. Ophthalmology 1997;104:1902-9.

27. Contstantinou M, Daniell M, Snibson GR, Vu HT, TaylorHR. Clinical efficacy of moxifloxacin in the treatment ofbacterial keratitis randomized clinical trial.Ophthalmology 2007;114:1622-9.

28. Sridhar MS, Sharma S, Garg P, Rao GN. Treatment andoutcome of nocardia keratitis. Cornea 2001;20:458-62.

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3Fungal Keratitis

Fungal Keratitis8

Fungal keratitis is one of the most difficult forms ofmicrobial keratitis for the ophthalmologist to diagnoseand treat successfully.1,2 It is more common in thedeveloping countries as compared to the developedcountries. Problems encountered in cases of fungalkeratitis include establishing the correct clinical diag-nosis and obtaining confirmation of the fungal orga-nisms on laboratory diagnosis. Problems related totherapy include suboptimal penetration of the anti-fungal drugs, difficulty in preparation and availabilityof the anti-fungal medications.

The treatment of fungal keratitis is quite challenging.Generally, prolonged and intensive topical, intracameraland systemic anti-fungal therapy is required to eradicatethe fungal infections, and surgical intervention in theform of penetrating keratoplasty, vasculoplasty orcryotherapy may be undertaken when the medicaltherapy fails.

Epidemiology

INCIDENCE

The incidence of fungal keratitis is low (6 to 20%) ascompared to bacterial keratitis in various studies ofmicrobial keratitis especially in the developed countries.2

However, the incidence of fungal keratitis may begreater in developing countries where it has been repor-ted in almost half of the cases of microbial keratitis.3

GEOGRAPHICAL DISTRIBUTION

Worldwide Aspergillus species is the most commonfungus responsible for fungal keratitis.4 In northernUnited States, Candida species and Aspergillus species isthe most common cause of fungal keratitis whereas insouthern United States Fusarium species is the mostcommon organism.4-6 Fusarium solani was the mostfrequently isolated organism earlier, whereas in the

more recent series, Fusarium oxysporum is more commonorganism (37%) as compared to Fusarium solani (24%).1,7

Fungal keratitis is a major blinding eye disease inAsia. One of the studies from south India has reportedthat 44 percent of all corneal ulcers were due to fungi,8

whereas its prevalence has been reported to be 17 per-cent in Nepal,9 36 percent in Bangladesh,10 37.6 percentin Ghana as opposed to 35 percent in Florida.11 In India,the most common isolated organism was Aspergillus sp.(27 to 64%) followed by Fusarium sp. (6 to 32%) andPenicillium sp. (2 to 29%).3,8 Fungal keratitis is usuallyseen in the rural areas and warm climates.

AGE DISTRIBUTION

Approximately, 65 percent of the patients are in the agegroup 21 to 50 years, although it has been reported inextremes of age also.2

SEX DISTRIBUTION

In general, fungal keratitis does not have any genderpredilection, although it has been reported to occur morecommonly in males than females in the ratio varyingfrom 1.5:1 to 4.5:1.2

SEASONAL VARIATIONA higher preponderance of these cases occurs duringmonsoons and early winter because of the high humidityfound during these months.12 A higher incidence hasalso been reported during harvest seasons, springs, andearly winter, probably because of a larger number ofvegetative injuries during these seasons.

Risk FactorsVarious risk factors, which have been incriminated inthe causation of fungal keratitis, may be ocular or relatedto the systemic status of the patient.

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OCULAR FACTORS

Various ocular factors that may predispose to theoccurrence of fungal keratitis include trauma, contactlens wear, medications and prior ocular surgery (Table8.1).13-15 Fungal keratitis also occurs more commonly incases of previously compromised corneas or cornealscars.

TraumaThe initiating trauma in cases of fungal keratitis isusually trivial and is associated with vegetable or organicmatter13 (Fig. 8.1). It most often occurs outdoors andinvolves plant matter such as leaves and paddy grains .It may also occur after injury with mud or sand andeven injury from animal origin such as due to cow dungand cow tail and may occur even with metal pieces.

Fungal keratitis should be especially suspected inchildren especially in cases when trauma with organicmatter occurs. In one series fungal keratitis composed18 percent of all cases of keratitis cultured in children.16

All children with a suspected keratitis should be culturedfor fungi.

Chronic Corneal Inflammation

Less common risk factors for fungal keratitis includechronic keratitis due to vernal or allergic keratoconjunc-

tivitis and neurotrophic ulcers secondary to varicellazoster or herpes simplex viruses ocular surface disorders,dry eye, Steven Johnson syndrome and bullous kerato-pathy. It may also occur in cases of ocular atopy.17

Contact Lens Wear

Fungal keratitis following contact lens wear is rare andis responsible for only 3-29 percent of cases associatedwith contact lens wear.13,18,19 Filamentous fungi are morecommonly associated with cosmetic or aphakic lenswear, and yeasts are more frequently associated withtherapeutic lens use.18-20

Drugs

A history of use of prior medications should be obtainedin all cases. Most patients of fungal keratitis are alreadyon treatment with topical antibiotics or corticosteroids.The indiscriminate use of topical antibiotics and topicalcorticosteroids has been associated with fungal keratitisespecially in developing countries where the drugs areavailable over the counter without any prescription. Theuse of latter has been particularly associated with theworsening of fungal keratitis.21 They appear to activateand increase the virulence of fungi.21 The infiltrates aremore extensive in such cases and response to anti-fungaltherapy is more sluggish. Systemic use of corticosteroidsmay predispose the patient to fungal keratitis as theimmune response of the host is suppressed. The use oftraditional eye medicines may also predispose to theoccurrence of fungal keratitis (Fig. 8.2).

Figure 8.1: Fungal keratitis after vegetative trauma

TABLE 8.1Risk factors for the development of fungal keratitis

OCULAR FACTORSTraumaChronic corneal inflammation

Herpes simplexHerpes zosterVernal allergic conjunctivitisOcular surface problemsDry eyeBullous keratopathyExposure Keratopathy

Contact lens wearDrugs

CorticosteroidsAnesthetics

Corneal surgeryPenetrating KeratoplastyRefractive surgery

SYSTEMIC FACTORSDiabetes mellitusHIV positive patientsLeprosy

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3Fungal Keratitis

Corneal Surgery

Fungal keratitis may occur virtually after any ocularsurgery, which includes keratoplasty (Fig. 8.3), cataractsurgery, and refractive surgery. Predisposing factors forthe development of fungal keratitis in patients afterpenetrating keratoplasty include suture related prob-lems, topical steroid and antibiotic use, failed grafts andpersistent epithelial defects.22-24 The contamination ofdonor corneas with fungal organisms may occur as noanti-fungal therapy is routinely used to decontaminatethe donor eyes.

Cases of delayed fungal keratitis have also beenreported months or years after the refractive surgerywas performed.25,26 This was also true for radial kerato-tomy and now more recently photorefractive keratec-tomy and laser in situ keratomileusis (Fig. 8.4).26-28 Itmay appear in the early post-operative period or later.The early appearance is usually associated with thesurgical contamination whereas the late appearance isoften related to trauma.

SYSTEMIC FACTORS

Some systemic diseases associated with immunosup-pression may increase the risk for the development offungal keratitis. These include diseases such as diabetesmellitus, patients with chronically debilitated diseaseswho are hospitalized in the intensive care units, HIVpositive patients and cases of leprosy (Table 8.1).29, 30

Figure 8.3: Fungal keratitis after Keratoplasty

EtiopathogenesisFungal organisms of ophthalmic interest may be classi-fied into four classes–Filamentous septated, Filamentousnon-septated, yeasts and others (Table 8.2).

More than 105 species of fungi classified in 56 generahave been reported to cause oculomycosis. Fungi aresaprophytic, and/or pathogenic organisms. Saprophyticfungi obtain their nutrients from decaying organicmatter, whereas pathogenic fungi feed on living cells.Pathogenic fungi are actually saprophytic microbes,which are known to cause disease in humans. Manyfungi associated with ocular infections are saprophytic.

Figure 8.4: Fungal keratitis (due to Alternaria) after LASIK surgery

Figure 8.2: Fungal keratitis after using traditional eye medicine

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Fungal isolates can be classified into four groups:Moniliaceae, which are nonpigmented filamentary fungiincluding Fusarium sp and Aspergillus sp; Dematiaceae,which are pigmented filamentary fungi includingCurvularia sp and Lasiodiplodia sp; yeasts, which includeCandida sp; and other fungi.

Fungi are a part of normal microbial environmentand in the absence of a precipitating event, rarely causeinfection in human cornea. They gain access into thecorneal stroma through a defect in the epithelium. Thisdefect may be due to external trauma, including contactlenses, a compromised ocular surface, or previoussurgery. In the stroma, they proliferate and can causetissue necrosis and a host inflammatory reaction. Theseorganisms can penetrate deep into the stroma eventhrough an intact Descemet’s membrane. When theorganisms gain access into the anterior chamber or iris,their eradication becomes difficult. Blood-borne growth

inhibiting factors may not reach the avascular tissuesuch as the cornea, anterior chamber and sclera, andhence the fungi continue to multiply and persist despitetreatment. This is also the basis for the vasculoplastyprocedure, which in the form of a conjunctival flap helpsin healing of the fungal keratitis by bringing the blood-borne growth-inhibiting factors from the vascular areastowards the avascular areas.

Clinical FeaturesIn general, the symptoms of fungal keratitis are lesssevere as compared to bacterial and viral keratitis.Fungal keratitis may be associated with certain generalsymptoms and signs and also specific features whichmay clinically point to an etiological agent (Table 8.3).

GENERAL SYMPTOMS

The onset of fungal keratitis is almost always insidious.Symptoms are usually non-specific, although possiblymore prolonged duration (5 to 10 days). Patients gene-rally complaint of a foreign body sensation for severaldays with a slow onset of increasing pain anddiminution of vision especially if the keratitis involvesthe visual axis.

GENERAL SIGNS

On slit lamp examination, the infiltrates appear grayishwhite or yellowish white and the base of the ulcer is

TABLE 8.2Fungi causing human keratitis

I. FILAMENTOUS

A. SEPTATED

1. NonpigmentedFusarium

solani, oxysporum, moniliforme, episphaesia, nivaleAspergillus

fumigatus, flavusAcremonium (Cephalosporium)PaecilomycesPenicillium

2. Pigmented (Dematiacious)Curvularia

senegelensis, verruculosa, pallescensLasiodiplodia

theobromaeAlternariaCladosporiumCelletotrichumDrechslera (Helminthosporuim)

B. NONSEPTATEDRhizopus (mucormycosis)

II. YEASTCandidaalbicans, parapsilosis, krusei, tropicalis

TABLE 8.3Clinical features of fungal keratitis

SymptomsForeign body sensationGradually increasing painDiminution of visionSignsNonspecificConjunctival injectionEpithelial defectSpecificFeathery marginsElevated edgesRough textureSatellite lesionsGray/Brown pigmentationCollar button configurationFixed hypopyon

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3Fungal Keratitis

often filled with soft, creamy and raised exudates (Fig.8.5). The fungal ulcers have characteristic findings,which include elevated areas, hyphate (branching)ulcers, irregular feathery margins, a dry rough texture(Fig. 8.6), and satellite lesions. Feathery borders orhyphate edges are seen in 70 percent of the patients andsatellite lesions are seen in 10 percent of the patients.29,30

Hypopyon is generally fixed and may be present in 45to 66 percent of the cases.12 An immune ring, endothelialplaque and a posterior corneal abscess may be presentrarely3 (Fig. 8.7).

SPECIFIC FEATURES

Each case of fungal keratitis may exhibit these basicfeatures but may differ in the clinical course depending

upon the etiological agent.31 The most commonmanifestations of culture-proven mycotic keratitis arereported to be a gray or dirty-white surface, anterior-chamber cellular reaction, irregular feathery margins,elevated borders, dry rough texture, satellite lesions,Descemet’s folds, hypopyon, ring infiltrate, endothelialplaque, and keratitic precipitates .

Dematiacious Fungi

The appearance of macroscopic brown pigmentation infungal keratitis may be due to the presence of a dematia-ceous fungus (Curvularia lunata)32,33 (Fig. 8.8). Thepigmentation has been related to the alteration in themelanin metabolism and when present indicates a moresuperficial infection, low virulence of the organism and

Figure 8.7: Endothelial plaque with perforation Figure 8.8: Keratitis due to Curvularia species

Figure 8.6: Irregular feathery margins and dry texture in fungal keratitisFigure 8.5: Raised margins and creamy exudates in fungal keratitis

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less inflammatory reaction. In some cases of dematia-ceous keratitis where absence of pigmentation is correla-ted with a masking by a more intense inflammatoryreaction.33 The presence of an intact epithelium with adeep stromal infiltrate may also be found in fungalkeratitis.

Fusarium

Fusarium solani keratitis has a more severe course so thatdeep extension and perforation may occur in few weeks(Fig. 8.9). Aspergillus species on the other hand, causes aless severe and not so rapidly progressive keratitis,which is amenable to therapy (Fig. 8.6).

YeastA “collar button” configuration is typical of the keratitiscaused by yeasts, which is often associated with a smallulceration and an expanding discreet stromal infiltrate(Fig. 8.10). The stromal keratitis caused by C. albicansand related fungi resembles bacterial keratitis, with anoverlying epithelial defect, a more discrete infiltrate, andslow progression. Such ulcers frequently occur in eyeswith preexisting corneal disease and in areas of exposuretypically at the junction of the superior two-thirds andinferior one-third of the cornea.

Laboratory DiagnosisCorneal ulcer scrapings from the ulcer edge and the baseform the mainstay of the diagnosis of a case of fungalkeratitis. Corneal scraping with a spatula or a surgicalblade is preferred to the use a calcium alginate, dacron/

rayon swab, or a sponge-type material. The organismsmay be deeper in the tissues and may not be accessibleto a more superficial scraping. Corneal scraping not onlyprovides diagnostic clues but also may be therapeuticas it also aids in the initial debridement and debulkingof the organisms. Further, it also breaches the epithe-lium, which may provide a barrier to the penetration ofthe anti-fungal agents.

Cultures should also be sent from topically appliedmedications, cosmetics, contact lenses and their storageand cleaning solutions, wherever indicated. In case ofdeeper lesions in fungal keratitis, a surface is passedthrough the lesion and may be sent for cultureexamination.

Apart from this anterior chamber tap and cornealbiopsy may be done especially in cases of deep keratitisand endothelial plaques.

Laboratory diagnosis of fungal keratitis primarilyincludes direct microscopy, fungal cultures and newerdiagnostic modalities such as polymerase chain reaction(PCR) and confocal microscopy.

DIRECT MICROSCOPY

Direct microscopy uses KOH wet mount preparationand smears, which are stained by Gram and Giemsastain.

KOH Wet Mount PreparationIn our experience, 10 percent KOH wet mount is simple,cheap, rapid and easy to interpret and is particularlyuseful in tropical countries. KOH smear has a sensitivityof 72.2 to 91 percent.34,35

Figure 8.9: Fungal keratitis due to Fusarium Figure 8.10: Fungal keratitis due to Candida

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Gram’s Stain

Gram stain is equally sensitive in detecting fungalorganisms. Gram stain identifies fungal species in 31.6to 98 percent.34,35

Giemsa Stain

Giemsa stain identifies fungal elements in 27 to 85percent of the cases.34,35

Lactophenol Cotton Blue

Lactophenol cotton blue has a sensitivity of 70 to 80percent in cases of fungal keratitis.36

Grocott’s Methenamine-silver Stain

Grocott’s methenamine-silver staining has a sensitivityof 89 percent. A shortened method of Grocott’s methena-mine-silver staining is also available which is reliableThe stain can also be reused for re-staining the Gramand the Giemsa stained slides and often reveals hyphaenot visualized by other stains.

Calcofluor White

Calcofluor white has a sensitivity of 80 to 90 percent.Excellent results can be achieved when the nonspecificfluorescent stain calcofluor white was used to staincorneal scrapes or biopsy specimens prior to directmicroscopic examination.36

Staining Technique Sensitivity

Gram’s stain 31.6% - 98%KOH wet mount 72.2% - 91%Gomori Methenamine stain37 56%Giemsa smear 27%- 85%Acridine orange 76%

FUNGAL CULTURE

Culture media for suspected fungal keratitis shouldinclude the same culture media used for a generalmicrobial keratitis work-up. Sheep blood agar,Sabouraud dextrose agar (without cycloheximide) andthioglycollate broth should be inoculated. Sabourauddextrose agar should contain 50 micrograms /mlgentamicin and should be without cycloheximide as thelatter inhibits saprophytic fungi. Thioglycollate broth isinoculated for the possible growth of anaerobic bacteriaat 35oC to 37oC.

A definitive diagnosis of fungal keratitis is made if1. Corneal scrapings reveal fungal elements in smears.2. Fungus grows in more than one medium in the

absence of fungus in smears.3. Fungus grows on a single medium in the presence

of fungus in smears.4. Confluent growth of fungus appears at the

inoculated site on a single solid medium.A fungus grown on the primary isolation medium

may be sub-cultured onto a potato dextrose agar (PDA)medium and incubated for a period of 10 days tofacilitate sporulation. Following adequate growth of thefungal isolate on PDA, the identification may be carriedout based on its macroscopic and microscopic features(Fig. 8.11).

Positive cultures should be expected in 52 to 68percent of cases. Initial growth occurs within 72 hoursin 83 percent of cultures and within 1 week in 97 percentof cultures.11, 29, 30 Most in fact are visible with dissectingmicroscope or naked eye within 36 hours. But we shouldwait for at least a week before declaring a culture nega-tive for fungi. Because both yeast and hyphae readilygrow in sheep blood agar and Sabouraud dextrose agarat room temperature, other media such as brain heartinfusion may not be used routinely. Increasing thehumidity of the medium by placing the inoculated agarplates in plastic bags has also been recommended forenhancement of fungal growth.

NEWER DIAGNOSTIC MODALITIESMore recent methods for the identification of fungi,although still not widely available, include immuno-

Figure 8.11: Culture media showing growth of various fungi

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fluorescence staining, electron microscopy, polymerasechain reaction,38 and confocal microscopy.39,40 Thesenewer diagnostic modalities may not be available at allplaces.

Polymerase Chain Reaction

Gaudio et al have reported that PCR and culture resultsmatched in 74 percent of the cases.38 This techniquerequires only 4 hours to obtain the results which isquicker than the 2 days to 2 weeks required by culturemethods and in future may become a valuable adjunc-tive tool for the diagnosis of fungal keratitis, although itcan not replace culture methods as the possibility offalse-positive results needs to be considered.

Confocal Microscopy

Confocal microscopy has recently been used in cases offungal keratitis, which helps to identify the hyphalelements and the yeasts. Confocal microscopy is animaging technique that allows optical sectioning ofalmost any material, with increased axial and lateralspatial resolution and better image contrast, which maybe useful for the identification of corneal pathogens inthe early stages of infection. In clinical keratitis due toAspergillus sp., fungal hyphae can be imaged as high-contrast filaments, 60 to 400 Å long and 6 Å wide.39 Inpatients with mycotic keratitis, in vivo scanning slitconfocal microscopy helps in establishing the diagnosisand demonstrating non-responsiveness to medicaltherapy by showing an increased load of fungalfilaments, therefore aiding the treatment decision. Thus,confocal microscopy is a potentially useful, noninvasivetechnique to determine the presence of fungal hyphaein vivo within the human cornea. Limitations in the useof this technique for routine diagnosis relate toinstrument configuration, movement of either the tissueor the microscope, difficulty in reproducibly returningto the area of interest for serial examination, lack of adistinctive morphology of some pathogens, and limitedresolution of the microscope.

KERATECTOMY/BIOPSY

If corneal scrapings for smears and cultures are negative,a diagnostic superficial keratectomy or corneal biopsymay become necessary. The biopsy can be performedin the minor operating room or at the slit lamp undertopical anesthesia using 0.5 percent proparacaine and

2 percent xylocaine eye drops. Other anesthetic agents,which may be used, are tetracaine, or cocaine. In somecases, eyelid and retrobulbar anesthesia may be required.Under the microscope, a round 2 to 3 mm sterile dis-posable dermatologic trephine is used and partialthickness trephination is done in such a manner so thatit encompasses both the clinically infected area and theadjacent clear cornea. Care is taken to avoid the visualaxis, if possible. The base is then undermined with asurgical blade to complete the lamellar keratectomy. Thecorneal biopsy specimen should be sent for smears,cultures, and histopathological examination.

Corneal biopsy is considered to be superior to cornealscraping for the isolation of the fungal organisms.

Management

The management consists of medical therapy andsurgical intervention in cases, which are non-responsiveto medical therapy.

MEDICAL THERAPY

Prompt and appropriate anti-fungal therapy is themainstay of the treatment of fungal keratitis. Anti-fungaltherapy should only be instituted where corneal scrapingreveals the presence of fungal elements or cultures revealthe presence of fungal organisms at 36-48 hours. We donot recommend an empirical anti-fungal therapy basedon the clinical evidence of fungal keratitis alone.

Since the corneal epithelium serves as a barrier tothe penetration of most tropical anti-fungal agents,debridement of the corneal epithelium is an essentialcomponent of the medical management of fungalkeratitis especially early in the course of treatment.

The topical anti-fungal therapy is the mainstay offungal keratitis.

Topical Antifungal Agents

Commercially available natamycin 5 percent suspensionis the initial drug of choice for fungal keratitis.

It should be given hourly during the day and twohourly during night time. In addition to the anti-fungaldrugs a broad-spectrum antibiotic such as afluroquinolone may be given to prevent secondarybacterial infection. Additionally, cycloplegics such ashomatropine eye drops may be given three times a dayto relieve the component of iridocyclitis along with the

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anti-glaucoma medications in cases where theintraocular pressure is high on digital tonometry. Theeye should be examined twice daily preferably underthe slit lamp. Once the infiltrate started resolving, thefrequency of topical natamycin is reduced to 2-hourlyuntil the completion of resolution (Figs 8.12A and B).The natamycin should be continued for 2 weeks afterthe resolution of infection in all cases.

If worsening of the keratitis is observed on topicalnatamycin, topical amphotericin B 0.15 percent with orwithout fluconazole 2 percent may be added as a secondagent. In cases of proven Candida sp., amphotericin B0.15 percent or fluconazole 0.3 percent is the first drugsof choice.

Amphotericin B has to be prepared extempora-neously. It is available as a systemic preparation. In orderto prepare the topical form, the compound has to bediluted with dextrose or distilled water to obtain aconcentration of 0.15 percent. It is not effective againstFusarium species.

The efficacy of Econazole 1 percent against filamen-tous fungi has been found to be equivalent to natamycin5 percent.41 Clotrimazole is available in 1 percent topicaldrops and ointment form and has been used in thetreatment of fungal keratitis.42 The imidazoles (ketoco-nazole and miconazole) are used systemically for thetreatment of keratomycosis because of their relativelyreduced systemic toxicity. Fluconazole is a fungistaticbitriazole which is used topically and systemically inthe treatment of Candida and Aspergillus keratitis. It doesnot show encouraging results against Aspergillus speciesand Fusarium species.43

A new azole antifungal agent, Voriconazole, isderived from Fluconazole and exhibits a wider spectrumof activity against Candida, Aspergillus and Fusarium. Itexerts its effect from inhibition of cytochrome P450-dependant 14 alpha sterol demethylase, an enzymeinvolved in the ergosterol biosynthetic pathway.44 Theminimal inhibitory concentration of voriconazole(0.5 μg/ml) is less as compared to other imidazoles.45

Topical voriconazole 1% has to be prepared inpharmacy as it is not commercially available and is givenin recalcitrant fungal keratitis if there is not response totopical natamycin and amphotericine B therapy.

Echinocandins have also been used for systemicmycoses.47 These agents target the synthetic cell wallenzyme complex beta-1, 3-D glucon synthase. Theantifungal spectrum is however limited to Candida andAspergillus species.48

Response to Therapy

Since fungal keratitis responds slowly over a period ofweeks, clinical signs of improvement should be notedwhich include the following: diminution of pain,decrease in size in size of infiltrate, disappearance ofsatellite lesions, rounding out of the feathery marginsof the ulcer and hyperplastic masses, or fibrous sheets.

Duration of Treatment

In general the duration of treatment is longer than thatfor cases of bacterial keratitis. The clinician mustdetermine the length of treatment for each individual

Figures 8.12A and B: Resolution of fungal keratitis on topical therapy

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based on clinical response. The duration of the treatmentfor topical treatment has not been firmly establishedclinically or experimentally and varies from 30 to 39days.16. Problems that can rise from prolonged treatmentare due to toxicity. The inflammatory response from thistoxicity can be confused with persistent infection. Iftoxicity is suspected and if adequate treatment has beengiven for at least 4 to 6 weeks, treatment should bediscontinued and the patient carefully observed forevidence of recurrence.

Drug Interactions

Several topical anti-fungal medications act synergi-stically against a particular fungal organism.49,50 Inclinical series more than one concurrent topical anti-fungal has been needed 5 percent of the time.16 Synergi-stic drugs include a combination of amphotericin B andflucytosine, (for Candida keratitis) and a combination ofnatamycin and ketoconazole (for Aspergillus keratitis).Likewise, experimental models have demonstrated thepotential antagonism between anti-fungals such asamphotericin B and the imidazoles.

Drug Resistance

Resistance to anti-fungal agents is rare and generallyoccurs when they are used for systemic mycoses.Competition for volume in the pre corneal tear film andwashout may be of more concern when using twotopical anti-fungals.

Systemic Antifungal Agents

Treatment with a systemic anti-fungal agent is recom-mended in cases of very large ulcers, severe deepkeratitis, scleritis and endophthalmitis. Systemic anti-fungals also may be used as prophylactic treatment afterpenetrating keratoplasty for fungal keratitis.

The drugs, which have been used systemically,include ketoconazole (oral), miconazole (intravenous)51

itraconazole (orally 200 mg/day) and fluconazole (orally200 mg/day).52 More recently oval voriconazole 200 mgbd has shown good results in recalcitrant fungalkeratitis.46

The most frequently used oral anti-fungal isketoconazole, which is given in the dose of 600 mg perday. It is mandatory to assess liver function tests every2 weeks after starting ketoconazole. Systemic therapy isgiven for a period of 6 to 8 weeks.

Topical Corticosteroids

Topical corticosteroid in the treatment of fungal keratitisshould not be used.56 The topical corticosteroids worsenthe disease when given alone and adversely influencethe efficacy of natamycin, flucytosine and miconazolewhen given in combination.

Intracameral Therapy

Intracameral amphotericin B may be a useful modalityin the treatment of severe keratomycosis not respondingto topical natamycin.53 It ensures adequate drug deliveryinto the anterior chamber and may be especially usefulto avoid surgical intervention in the acute stage of thedisease (Figs 8.13A and B).

The procedure should be performed under strictaseptic conditions. If the infection involves the anteriorcapsule of the lens, care should be taken to avoid injuryto the lens. Patients with deep keratomycosis unrespon-sive to conventional medical treatment are candidatesfor intracameral injections of 5 μg to 7.5 μg amphotericinB in 0.1 mL 5 percent dextrose.53-55 Injections can berepeated in case of inadequate response.

Intrastromal Therapy

A recent modality advocated for non healing fungalcorneal ulcers is the use of intracorneal Amphotericin Binjection in 5-7.5 μg dosage, given in the vicinity of thestromal site of fungal growth.56 This would raise the localconcentration of the antifungal agent enough to beeffective in the eradication of the deep corneal infection.This approach proves effective, with total eliminationof the infection (Figs 8.14A and B). The intrastromalinjection can be repeated after a period of 48 to 72 hours.Although further experience is required, intrastromalcorneal injections of Amphotericin B may offer a goodchoice for recalcitrant cases of fungal keratitis.

SURGICAL THERAPY

Debridement

Daily debridement with a spatula or blade is the simplestform of surgical intervention and is usually performedat the slit lamp under topical anesthesia. Debridementis performed every 24 to 48 hours and works bydebulking organisms and necrotic material and byenhancing the penetration of the topical antifungal.

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Biopsy

A biopsy may be used not only for the diagnosis butalso as a therapeutic intervention.

Therapeutic Keratoplasty

Approximately one third of fungal infections result ineither medical treatment failures or corneal perfora-tions.57 The main goals are to control the infection andmaintain the integrity of the globe.

Most retrospective series indicate that keratoplastywas performed within 4 weeks of presentation, primarilybecause of medical treatment failures; in some cases itmay be required because of recurrence of infection.

When progression of the keratitis is noted, penetratingkeratoplasty should be performed. If the infectiousprocess is allowed to progress until it involves the limbusor sclera, unfavorable outcomes secondary to scleritis,endophthalmitis, and recurrence are more common.Therapeutic keratoplasty should be performed in casesof impending perforations, frank perforations > 2 mmor if there is no response to therapy.

The technique of the keratoplasty is similar to thatperformed for other forms of microbial keratitis. Thesize of the trephination should leave a 1 to 1.5 mm clearzone of clinically uninvolved cornea to reduce thepossibility of residual fungal organisms peripheral tothe trephination. Interrupted sutures with slightly longer

Figures 8.13A and B: Resolution of fungal keratitis on intracameral amphotericin B therapy

Figures 8.14A and B: Resolution of fungal keratitis on intrastromal amphotericin B therapy

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bites should be used to avoid cheese wiring of the sutureif the edge of the recipient becomes involved with apersistent organism. Irrigation of the anterior segmentshould be performed to eliminate any organisms. Asfar as possible the lens should be left untouched toprevent the spread of infection in the posterior segment.However, if affected the intraocular structures includingthe iris, lens, and vitreous may be excised. The specimensremoved should be submitted to both the mcirobiologyand pathology laboratories for culture and fixed sectionexamination. If involvement of intraocular structures orendophthalmitis is suspected, an antifungal agentshould be injected which includes amphotericin B (5 μg/0.1 ml) or miconazole (25 μg/0.1 ml).

It is mandatory to submit surgical specimens fromcases of microbial ketatitis for histopathologic exami-nation especially if the microbiologic diagnosis is notknown. Histopathologic examination of corneal buttonscan reveal the presence of fungal elements in 75 percentpatients.57 It has been shown that 59 percent of corneasinfected by fungi are still culture-positive at the time ofkeratoplasty, with 90 percent of eyes exhibiting hyphalelements on pathologic examination.58,59 Fungal hyphaeusually lie parallel to the corneal surface and lamellae.A vertical or perpendicular arrangement of fungalhyphae in the corneal stroma has been associated withincreased virulence and in patients on topical cortico-steroid therapy.58,59

After penetrating keratoplasty, topical antifungalagents should be continued to prevent recurrence of

infection. Postoperatively, systemic ketoconazole orfluconazole may be used in addition to topical anti-fungal agents. If the pathology laboratory reports thatno organisms were seen at the edge of the cornealspecimen, anti-fungals could be stopped after 2 weeksand the patient followed carefully for recurrences. Areport from the microbiology laboratory regardinggrowth of organisms from the corneal or intraoculartissues should indicate the need for more prolongedtopical and systemic anti-fungal therapy, possibly for 6to 8 weeks.

At the time of keratoplasty, if the infection has beencontrolled clinically, topical corticosteroids may be used.If it is not known whether the infection is controlled,corticosteroids should be avoided during the earlypostoperative period.13 Although the main goal ofpenetrating keratoplasty in fungal keratitis is toeliminate the infecting organism, a secondary goal isthe maintenance of a clear corneal transplant for opticalreasons (Figs 8.15A and B). Even if graft failure orrejection occurs, the patient can undergo a second opticalkeratoplasty once the rejection is controlled. The effectsof other immunosuppressive medications such ascyclosporin A and its effect on fungal growth has notbeen well documented clinically.

References1. Liesegang TJ, Forster RK. Spectrum of microbial keratitis

in South Florida. Am J Ophthalmol 1980;90:38-47.

Figures 8.15A and B: Non-resolving fungal keratitis (Alternaria) on maximal anti-fungal medications (A) in which therapeutic keratoplasty (B)was done

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2. Thomas PA. Fungal infections of the cornea. Eye 2003;17:852-62.

3. Srinivasan R, Kanungo R, Goyal JL. Spectrum ofoculomycosis in South India. Acta Ophthalmol 1991;69:744-9.

4. Foster CS. Fungal keratitis. Infect Dis Clin North Am1992;6:851-7.

5. Chin GN, Hydiuk RA, Kwasny GP, Schultz RO. Kerato-mycosis in Wisconsin. Am J Ophthalmol 1975;79:121-5.

6. Doughman DJ, Leavenworth NM, Campbell RC,Lindstrom RL. Fungal keratitis at the University ofMinnesota: 1971-1981. Trans Am Ophthalmol Soc1982;80:235-47.

7. Jones DB, Sexton R, Rebell G. Mycotic keratitis in SouthFlorida: A review of thirty-nine cases. Trans OphthalmolSoc UK 1970;89:78-1797.

8. Sharma S, Srinivasan M, George C. The current statusof Fusarium species in mycotic keratitis in south India.J Med Microbiol 1993;11:140-7.

9. Upadhyay MP, Karmacharya PC, Koirala S, TuladharNR, Bryan LE, Smolin G, et al. Epidemiologic charac-teristics, predisposing factors, and etiologic diagnosisof corneal ulceration in Nepal. Am J Ophthalmol 1991;111:92-9.

10. Dunlop AA, Wright ED, Howlader SA, Nazrul I, HusainR, McClellan K, et al. Suppurative corneal ulceration inBangladesh. A study of 142 cases examining themicrobiological diagnosis, clinical and epidemiologicalfeatures of bacterial and fungal keratitis. Aust NZJOphthalmol 1994;22:105-10.

11. Leck AK, Thomas PA, Hagan M, Kaliamurthy J,Ackuaku E, John M, et al. Aetiology of suppurativecorneal ulcers in Ghana and south India, and epidemio-logy of fungal keratitis. Br J Ophthalmol 2002;86:1211-5.

12. Hagan M, Wright E, Newman M, Dolin P, Johnson G.Causes of suppurative keratitis in Ghana. Br JOphthalmol 1995;79:1024-8.

13. Chowdhary A, Singh K. Spectrum of fungal keratitis inNorth India. Cornea 2005;24:8-15.

14. Kremer I, Goldenfeld M, Shmueli D. Fungal keratitisassociated with contact lens wear after penetratingkeratoplasty. Ann Ophthalmol 1991;23:342-5.

15. Cruz OA, Sabir SM, Capo H, Alfonso EC. Microbialkeratitis in childhood, Ophthalmology 1993;100:192-6.

16. Wilson LA, Ajello L. Agents of oculomycosis: fungalinfections of eye. In: Collier L, Balows A, Sussman (Eds):Topley and Wilson’s Microbiology and microbialinfections, 9th edition, Medical Mycology Arnold:London, 1998;4:525-67.


18. Wilhelmus KR, et al. Fungal keratitis in contact lenswearers. Am J Ophthalmol 1998;106:708-14.

19. Wilhelmus KR. Review of clinical experience withmicrobial keratitis associated with contact lens. CLAO J1987;13:211-4.

20. Jones BR. Principles in the management of oculomycosis.XXXI. Edward Jackson Memorial Lecture. Am JOphthalmol 1975;79:719-51.

21. Berson EL, Kobayashi GS, Becker B, Rosenbaum L.Topical corticosteroids and fungal keratitis. InvestOphthalmol 1967;6:512-7.

22. Fong LP, Ormerod LD, Kenyon KR, Foster CS. Microbialkeratitis complicating penetrating keratoplasty.Ophthalmology 1988;94:1269-75.

23. Driebe WT, Stern GA. Microbial keratitis followingcorneal transplantation. Cornea 1983;2:41-5.

24. Harris DJ, Stulting RD, Waring GO III, Wilson La. Latebacterial and fungal keratitis after corneal transplanta-tion. Spectrum of pathogens, graft survival and visualprognosis. Ophtahlmology 1988;95:1450-7.

25. Maskin SL, Alfonso E. Fungal keratitis after radialkeratotomy. Am J Ophthalmol 1992;14:369-70.

26. Periman LM, Harrison DA, Kim J. Fungal keratitis afterphotorefractive keratectomy: delayed diagnosis andtreatment in a co-managed setting. J Refract Surg 2003;19:364-6.

27. Verma S, Tuft SJ. Fusarium solani keratitis followingLASIK for myopia. Br J Ophthalmol 2002;86:1190-91.

28. Tuli SS, Yoo SH. Curvularia keratitis after laser in situkertomileusis from a feline source. J Cataract RefractSurg 2003;29:1019-21.

29. Bharathi MJ, Ramakrishnan R, Vasu S, et al. Epidemio-logical characteristics and laboratory diagnosis of fungalkeratitis. A three-year study. Indian J Ophthalmol 2003;51:315-21.

30. Srinivasan M, Gonzales CA, George C, et al. Epidemio-logy and aetiological diagnosis of corneal ulceration inMadurai, South India. Br J Ophthalmol 1997;81:965-71.

31. Gopinathan U, Garg P, Fernandes M, Sharma S,Athmanathan S, Rao GN. The epidemiological featuresand laboratory results of fungal keratitis. A 10-yearreview at a referral eye care centre in South India. Cornea2002;21:555-9.

32. Garg P, Vemuganti GK, Chatterjee S, Gopinathan U, RaoGN. Pigmented plaque presentation of demataticiousfungal keratitis. A clinico-pathologic correlation. Cornea2004;23:571-6.

33. Berger ST, Katsev DA, Mondino BJ, Pettit TH. Macro-scopic pigmentation in dematiaceous fungal keratitis.Cornea 1991;10:272-6.

34. Vajpayee RB, Angra SK, Sandramouli S, Honavar SG,Chhabra VK. Laboratory diagnosis of keratomycosis:comparative evaluation of direct microscopy and cultureresults. Ann Ophthalmol 1993;25:68-71.

35. Garg P, Gopinathan U, Choudhary K, et al. Keratomyco-sis: clinical and microbiologic experience withdematiaceous fungi. Ophthalmology 2000;107:574-80.

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36. Srinivasan M. Fungal keratitis. Curr Opin Ophthalmol2004;15:321-7.

37. Forster RK, Wirta MC, Solis M, Rebell G. Methenamine-silver-stained corneal scrapings in keratomycosis. Am JOphthalmol 1976;82:261-5.

38. Gaudio PA, Gopinathan U, Sangwan V, et al. Polyme-rase chain reaction based detection of fungi in infectedcorneas. Br J Ophthalmol 2002;86:755-60.

39. Florakis GJ, Moazami G, Schubert H, et al. Scanning slitconfocal microscopy of fungal keratitis. Arch Ophthal-mol 1997;115:1461-3.

40. Avunduk AM, Beuerman RW, Varnell ED, et al.Confocal microscopy of Aspergillus fumigatus keratitis.Br J Ophthalmol 2003;87:409-10.

41. Prajna NV, John RK, Nirmalan PK, et al. A randomizedclinical trial comparing 2% econazole and 5% natamycinfor the treatment of fungal keratitis. Br J Ophthalmol2003;87:1235-7.

42. Mselle J. Use of topical clotrimazole in the treatment ofhuman keratomycosis. Ophthalmologica 2001;215:357-60.

43. Rao SK, Madhavan HN, Rao G, et al. Fluconazole infilamentary fungal keratitis. Cornea 1997;16:700.

44. Jeu L, Piacenti FJ, Lyakhovetskiy, et al. Fung HB;Voriconazole. Clin Ther 2003;25:1321-81.

45. Shah KB, Wu TG, Wilhelmus KR, et al. Activity ofvoriconazole against corneal isolates of Scedosporiumapiospermum. Cornea 2003;22:33-6.

46. Jhanji V, Sharma N, Mannan R, Titiyal JS, Vajpayee RB.Management of tunnel fungal infection withvoriconazole. J Cataract Refract Surg 2007;33:915-7.

47. Denning DW. Echinocandin anti-fungal drugs. Lancet2003;4:362;1142-51.

48. Goldblum D, Frueh BE, Sarra GM, Katsoulis K, ZimmerliS. Topical Caspofungin for the treatment of fungal

keratitis caused by Candida albicans in a rabbit model.Antimicrob Agents Chemother 2005;49:1359-63.

49. Stern GA, Okumoto M, Smolin G. Combined ampho-tericin B and rifampin treatment of experimentalCandida albicans keratitis. Arch Ophthalmo 1979;l 97:721-2.

50. Beggs WH. Mechanisms of synergistic interactionsbetween amphotericin B and flucytosin. J AntimicrobChemother 1986;17:402-4.

51. Fitzsimons R, Peters AL. Miconazole and ketoconazoleas a satisfactory first-line treatment for keratomycosis.Am J Ophthalmol 1986;101:605-8.

52. Rao SK, Madhavan HN, Rao G, et al. Fluconazole infilamentary fungal keratitis. Cornea 1997;16:700.

53. Sridhar MS, Sharma S, Gopinathan U, Rao GN. Anteriorchamber tap: diagnostic and therapeutic indications inthe management of ocular infections. Cornea 2002;21:718-22.

54. Kuriakose T, Kothari M, Paul P, Jacob P, Thomas R.Intracameral amphotericin B injection in the manage-ment of deep keratomycosis. Cornea 2002;21:653-6.

55. Kaushik R, Ram J, Brar GS, Jain AK, Chakraborti A,Gupta A. Intracameral amphotericin B: initial experiencein severe keratomycosis. Cornea 2001;20:715-9.

56. Garcia-Valenzuela E, Song CD. Intracorneal injection ofamphotericin B for recurrent fungal keratitis andendophthalmitis. Arch Ophthalmol 2005;123:1721-3.

57. Portnoy SL, Insler MS, Kaufman HE. Surgicalmanagement of corneal ulceration and perforation. SurvOphthalmol 1989;34:47-58.

58. Cristol SM, Alfonso EC, Guildford JH, Roussel TJ,Culbertson WW. Results of large penetrating kerato-plasty in microbial keratitis. Cornea 1996;15:571-6.

59. Killingsworth DW, Stern GA, Driebe WT, Knapp A,Dragon DM. Results of therapeutic penetratingkeratoplasty. Ophthalmology 1993;100:534-41.

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3Viral Keratitis

Viral Keratitis9

Viral keratitis is the commonest cause of keratitis in thedeveloped world. The virus can infect individual layersof the cornea or in more severe form it may involve allthe layers of cornea. The various viral infections thatcan affect the cornea can be broadly grouped under thefollowing categories herpes simplex keratitis, varicellazoster induced keratitis and the adenoviral keratitis.

Herpes Simplex VirusThe herpes simplex virus is a DNA virus, which belongsto the Herpesviridae family of viruses. The virus specificantigens differentiate HSV into two types that is theherpes simplex virus type-1(HSV-1) and the herpessimplex virus type-2.

EpidemiologyHerpes simplex keratitis is the most common infectivecause of blindness in many developed countries. Theocular disease affecting the cornea may be classified intoprimary or recurrent.

The incidence of all episodes of of herpes simplexkeratitis was repaired as 20.7 cases/100,000 populationand the prevalence of ocular HSV disease in thecommunity was calculated at 149 per 100,000 populationin one study. The incidence of new episodes of HSVwas reported to be 8.4/100,000/year.1

The disease may occur bilaterally in 11.9 percentpatients and is more common in atopes and immuno-suppressed.2

The recurrences are generally caused by the samestrain of virus as the initial infection. Recurrences gene-rally occur in 20 percent patients by 2 years, 40 percentby 5 years and 67 percent by 7 years.1 Generally therecurrence of the same type of ocular disease occurs thatis the patients with epithelial keratitis have an epithelialrecurrence and that of stromal keratitis have stromalrecurrence.2

HSV keratitis patients are also more prone toinfection with HIV virus and such patients are associatedwith increased rates of recurrences.1

Over 90 percent of the patients maintain a visualacuity of 20/20 and about 20-25 percent develop stromalkeratitis. In half of the patients there may be history oforofacial lesions. Ocular HSV is at least 6 times moreprevalent after keratoplasty.

Pathophysiology

INFECTION

Herpes simplex virus is a large and complex envelopedvirus measuring 150-200 nm. It has a double strandedDNA core, which is surrounded by a protein capsid thatis made up of 162 subunits called capsomer. The capsidis surrounded by the tegument, membrane of theinfected cell that has been altered by virus-inducedproteins.

Humans are the only natural reservoirs of herpes.The sources of infection are by direct contact withinfected lesions, by salivary droplets or fomites fromchildren and adults with active disease and also ofasymptomatic virus shedding carriers. A patient can alsoacquire the infection iatrogenically by physician’sunwashed hands or by contaminated Schiotz orapplanation tonometer head.

It is estimated that > 90 percent of population havehad a type 1 HSV infection during their lifetime, usuallyduring childhood or early adolescence.

The most common type of herpes simplex virus isHSV-1which causes cold sore or fever blister in themouth, face and upper body and may affect the eye.HSV-2 causes genital herpes, a sexually transmitteddisease. Ocular herpes is caused primarily by HSV-1 andoccasionally by HSV type-2 virus.

Primary HSV-1 infection occurs usually in the muco-cutaneous distribution of the trigeminal nerve. After the

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primary infection, the virus spreads from the infectedepithelial cells to nearby sensory nerve endings and istransported along the nerve axon to the cell body locatedin the trigeminal ganglion. The virus genome enters thenucleus of a neuron, where it persists indefinitely in alatent state. The primary infection of any of the 3branches (i.e. ophthalmic, maxillary, mandibular) ofcranial nerve V can lead to latent infection of nerve cellsin the trigeminal ganglion. Inter-neuronal spread of HSVwithin the ganglion causes ocular disease even in caseswhich have not had primary ocular HSV infection.

Infection is spread by direct contact of infectioussecretions with epidermis or mucous membrane. HSV-2 may rarely infect the eye by means of direct contactwith infectious genital secretions and occasionally istransmitted to neonates as they pass through the birthcanal of a mother with genital HSV-2 infection.3

Recurrent HSV infection traditionally has beenthought of as reactivation of virus in the sensory gang-lion, which migrates down the nerve axon to produce alytic infection in ocular tissue.4 The virus may be presentin a latent phase within the corneal tissue, acting as apotential source of recurrent disease and also responsiblefor the donor-derived HSV in transplanted corneas.5

The triggering agents for reactivation of an acuteattack of herpes includes fever, hormonal changes,ultraviolet exposure, psychological stress, ocular trauma,immunocompromised and trigeminal nerve manipula-tion. The excimer laser ablation may also trigger areactivation of herpetic keratitis.

IMMUNE MECHANISMSThe cell mediated and the humoral immunity areactivated which limit the spread of infection and arealso responsible for the sequel to the pathologic process.Stromal inflammation and endothelitis occur as aconsequence of replicating virus or altered antigenicityof the stromal cells causing immune mediateddestruction. Secretion of glycoproteins is responsible forstromal inflammation which occurs in a greater quantityin stromal inflammation as compared to cases in whichepithelial involvement occurs alone.

Clinical FeaturesCONGENITAL OCULAR HERPES

HSV-1 and HSV-2 can be acquired in utero, by trans-placental or ascending infection, by exposure to genitallesions during delivery, or postnatally from relatives orattendants.3 The clinical manifestations of this rare, but

devastating disease depend on the stage or trimesterwhen HSV is contracted. Of all the neonatal HSV, 4percent is acquired during intrauterine life, 86 percentinfection occurs at the time of birth and remaining 10percent occurs in the postnatal period.3 Congenital HSVinfection is characterized by the triad of skin vesicles,eye disease and microencephaly.

NEONATAL HSV KERATITIS

Neonatal HSV infection usually presents as a bilateraldisease at 2 days to 2 weeks of age.3 HSV keratitis in aneonate is invariably associated with conjunctivitis.Keratitis may manifest as diffuse microdendritis,serpiginous epithelial defects or a punctate keratitis. Thediagnosis of ocular HSV must be considered in anyinfant with nonpurulent conjunctivitis or keratitis. Treat-ment of neonatal ocular herpetic disease comprises oftopical antivirals (1% Trifluridine ophthalmic solutionor 3% acyclovir ophthalmic ointment) in addition tosystemic Acyclovir (2 g/day IV every 8 hourly for 14days).6

PRIMARY OCULAR HERPES

Primary ocular HSV is an acute HSV infection of thenon-immune host. It occurs after 6 months of agefollowing decline in maternal antibodies. Most primaryinfections occur between 1-5 years of age and aresubclinical. Only 6 percent of those infected actuallydevelop clinical manifestations, which typically affectthe perioral area rather than the eye.6 Clinically overtdisease begins 3-9 days after exposure and usuallycauses more symptoms than the recurrent disease. Itmanifests as intense occasionally hemorrhagic, vesi-cular, periocular dermatitis or blepharitis, follicularconjunctivitis that may be pseudomembranous orgeographic ulceration or both, corneal ulceration, iritisand non-suppurative periocular lymphadenopathy.

The primary infection is self-limited with completerecovery and disappearance of virus from initial site ofinfection in immunocompetent individuals. The site ofprimary infection determines the pathway of the viralspread and the site of viral latency. The most commonsite of primary HSV infection in the facial area is thatserved by maxillary division of trigeminal nerve. Thisresults in latency in the trigeminal ganglion. Herpessimplex virus can also establish latent infection in otherneurons of the sensory and autonomic ganglia thatsupply the affected area. It occurs within 3 weeks of

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primary infection whether clinically overt or asympto-matic. This latency is life long and the virus can bereactivated by number of trigger mechanisms. Thetrigeminal ganglion is the most common site for HSV-1latency. The superior cervical, vagus, sacral andautonomic ganglia are other sites of latent virus. Apartfrom the sensory and autonomic ganglia, there areevidences which suggest that cornea can also serve as anon-neuronal site of latency and as a source of futureinfectious virus during reactivation.5

RECURRENT OCULAR HERPESThe recurrence rate of ocular herpes has been reviewedby Liesegang and is reported to be 36 percent at 5 yearsand 63 percent at 20 years after primary episode.1 Aftera second episode, 70-80 percent of patients haverecurrence with in 10 years.1 Recurrent herpes simplexcan present as blepharitis, conjunctivitis, epithelialkeratitis, stromal keratitis, uveitis, trabeculitis and evenchorioretinitis.6

Although the mechanism of viral reactivation is notcompletely understood a variety of trigger factors arerecognized which include fever, ultraviolet light, coldwind systemic illness, surgery, menstruation, minor localtrauma, immunosuppression from either endogenousdisease or iatrogenic drug management of disease andlaser photokeratectomy.7

MANIFESTATIONS OF KERATITISHSV keratitis is predominantly a unilateral disease andbilateral herpetic keratitis occurs only in 3 percent ofpatients with ocular HSV infection.7 Bilateral disease ismore common in cases of atopy and in younger patients.

HSV keratitis can manifest as one of the following(Table 9.1):• Infectious epithelial keratitis• Neurotrophic epithelial keratitis• Herpetic stromal keratitis• Endothelitis.

INFECTIOUS EPITHELIAL KERATITIS

Infectious epithelial keratitis is caused by the presenceof live virus. The patient presents with lacrimation,photophobia, irritation and occasionally blurred vision.The corneal lesions may manifest in various forms.

Punctate KeratitisThese lesions begin as punctate or stellate whitishopaque plaques of swollen epithelial cells.

Dendritic KeratitisThe plaques of swollen infected epithelial cells enlargeto form branching dendrites. The epithelium in thecenter sloughs to form dendritic ulcers. Dendritic ulcersmay be single or multiple (Fig. 9.1) and have linearbranches with terminal bulbs (Fig. 9.2). The edges ofthe ulcers are raised and contain replicating virus. Theseulcers are usually central or paracentral. The area ofdendritic ulceration is typically anesthetic whereas thesurrounding cornea may retain normal sensation. Theseulcers stain with fluorescein along the length of thelesion whereas the rose bengal stains the devitalized cellsand is typically taken up by the swollen epithelial cellsat the ulcers border.

TABLE 9.1Pathogenesis of herpetic keratitis

Clinical presentation Pathogenesis

Epithelial involvementInfectious epithelial keratitis Live virus in epithelium

Immune response in stromaNeurotrophic keratopathy Impaired corneal nerves

Damaged basement membraneof epitheliumDrug toxicity

Stromal involvementImmune stromal keratitis Antigen antibody complex

mediatedNecrotizing stromal keratitis Direct viral invasion Endothelium involvementEndothelitis Immune reaction involving

endothelium

Figure 9.1: Dendritic keratitis due to herpes simplex virus (Courtesy:Medical Photographic Imaging Centre. Royal Victorian Eye and EarHospital, Melbourne)

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Geographic Ulcers

Some of the dendrites enlarge and develop intogeographic ulcers. These ulcers have amoeboid shapeand like dendrites have virus laden devitalized epithelialcells at their margins that take up rose bengal stain(Fig. 9.3). However if viral cultures or polymerase chainreaction (PCR) are to be performed in these cases thecultures should be taken first as rose bengal is toxic toHSV and hence may affect the yield of the cultures aswell as the PCR testing.

Marginal Keratitis

HSV marginal ulcer is an uncommon manifestation ofviral reactivation and is often confused with staphy-

lococcal marginal disease (Fig. 9.4). It is classically adendritic ulcer present marginally, generally near ablood vessel and is associated with stromal infiltrateadjacent to an area of limbal injection (Fig. 9.5). It shouldbe differentiated from a staphylococcal marginalulceration.

HSV marginal ulcer begins as an ulcer and then isassociated with an infiltrate whereas a staphylococcalulcer begins as an infiltrate with intact epithelium andsubsequently ulcerates (Table 9.2). With HSV infectionthere is generally limbal injection which can result inneovascularization whereas in staphylococcal marginalkeratitis there is a lucid interval between the limbus andthe ulcer. HSV generally progresses centrally where itmay evolve into a dendrite whereas the staphylococcal

Figure 9.2: Linear dendrite stained with fluorescein stain Figure 9.3: Amoeboid ulcer stained with rose bengal dye

Figure 9.4: Herpetic marginal keratitis Figure 9.5: Diffuse herpetic limbitis

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ulcer progresses circumferentially. Blepharitis is moreoften associated with staphylococcal infection and thisoccurs classically at 2, 4, 8 and 10 O’ clock where thelids are in contact with cornea unlike HSV ulcerationwhich can occur anywhere.

Sequelae of Infectious Epithelial Keratitis

Patients with infectious epithelial keratitis may undergoone of the four sequelae: A complete resolution of adendritic or geographic ulcer may occur without any

tell tale signs of previous epithelial keratitis.The patientsmay have dendritic epitheliopathy that is heaping ofepithelium on the dendrite which is healing without anyarea of ulceration. The subepithelial branching patternof HSV may occur as “ghost patterns” or the dendriticulceration (Fig. 9.6) may progress to stromal keratitisand leave a dense scar with corneal thinning.

Neurotrophic Epithelial Keratitis

Neurotrophic keratopathy develops in patients withprevious HSV epithelial disease. It occurs due toimpaired corneal innervation and decreased tearformation, exacerbated by chronic use of topical medica-tions, especially antiviral agents. Numerous epithelialor stromal recurrences or a prolonged and refractoryepithelial infection may decrease corneal sensitivity anddamage the basement membrane of the corneal epithe-lium. This results in recurrent epithelial erosions, andpersistent non-healing sterile ulceration known asneurotrophic ulceration. These are also called trophic,indolent or metaherpetic ulceration. They are round oroval ulcers with grey, thickened and rolled up margins(Fig. 9.7). These ulcers may look similar to the infectiousamoeboid herpetic ulcers and should be differentiatedfrom them as the treatment of these two entities aredifferent (Table 9.3).

Complications of neurotrophic keratitis includescarring, neovascularization, necrosis, perforation andsecondary bacterial infection (Fig. 9.8).

TABLE 9.2Differentiation between HSV marginal keratitis andstaphylococcal marginal keratitis

Characteristics HSV marginal Staphylococcalkeratitis marginal keratitis

Etiology Infective ImmunologicEpithelial defect Present Generally absent, may

occur late in the courseProgression Centrally CircumferentiallyLimbal injection More MinimalLucid interval Absent Presentbetween limbusand ulcerNeovasculari- Present AbsentzationBlepharitis Absent PresentLocation Any meridian Generally 2, 4 8 10 O’

clock

Figure 9.7: Metaherpetic keratitis

Figure 9.6: Healing herpetic epithelial keratitis (Courtesy: MedicalPhotographic Imaging Centre. Royal Victorian Eye and Ear Hospital,Melbourne)

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HERPES SIMPLEX STROMAL KERATITIS

Stromal involvement in primary cases is reported in2 percent cases whereas it is responsible for 20 to48 percent cases of recurrent ocular herpes.7 Stromalinflammation may occur primarily or may occur as aconsequence of the epithelial infectious keratitis orendothelitis.7

The two manifestations of herpes simplex virusstromal disease include the immune stromal keratitisand necrotizing stromal keratitis.7 It may also presentas limbal vasculitis, immune ring of Wessely, necroticinterstitial keratitis, disciform keratitis and endothelitiswith or without trabeculitis.

In stromal keratitis the patient presents with blurredvision and eye pain.

Immune Mediated Stromal KeratitisImmune mediated stromal keratitis is also called inter-stitial keratitis and is the most common form of herpeticstromal disease. It is mediated by type III immunereaction to herpes simplex viral antigen and is associatedwith the deposition of antigen-antibody complex in thecorneal stroma.7

Clinically the disease is characterized by occurrenceof stromal infiltration, neovascularization, thinning ofthe cornea, and recurrent inflammation. The overlyingepithelium is always intact except in cases where epithe-lial ulceration leads to stromal involvement. However,corneal necrosis and ulceration are not seen. Secondarylipid keratopathy may occur as a result of persistent andrecurrent inflammation.

Immune mediated stromal keratitis may manifest asone of the following:

Punctate Stromal Opacities

Punctate stromal opacities may be present which areassociated with haze. They may be focal, diffuse ormultifocal and may also be associated with anteriorchamber inflammation.

Immune Ring of Wessely

It s a distinct clinical entity and is a type of immunemediated herpetic stromal keratitis. There is a circulardeposition of antigen-antibody complex withpolymorphonuclear leukocyte infiltration. It may becomplete or incomplete and is present in the mid-stromaof central or paracentral cornea. Sometimes there maybe two rings of stromal infiltrates called as doubleimmune ring of Wessely (Fig. 9.9).

TABLE 9.3Differentiation between neurotrophic and infective herpetic ulcer

Characteristic Neurotrophic ulcer Infectious ulcerHistory of recurrent Always positive May be positiveepithelial infectionsDuration of ulcer Long duration (indolent) Relatively shortLocation of ulcer Interpalpebral area AnywhereSize of ulcer Almost constant over a Increasing or decreasing depending

period of time on the success of antiviral treatmentMargins of ulcer Shallow, clean Raised, greyish and has devitalized virus

laden epithelial cellsRose bengal stain Margins are not stained Margins are heavily stainedAntiviral therapy May make it worse Promotes resolution

Figure 9.8: Neovascularization and perforation in neurotrophic cornealulcer

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Figure 9.9: Double immune ring of Wessely Figure 9.10: Sectoral stromal neovascularization

Figure 9.11: Circumferential stromal neovascularization

Figure 9.12: Necrotizing stromal keratitis (Courtesy: MedicalPhotographic Imaging Centre, Royal Victorian Eye and Ear Hospital,Malbourne)

Stromal Neovascularization

Stromal neovascularization may occur acutely or in achronic manner. It may be sectoral (Fig. 9.10) or mayoccur circumferentially (Fig. 9.11) when it occurs in achronic manner. Aggressive therapy may cause theformation of “ghost vessels” which are empty channelsof blood vessels devoid of any blood. Ghost vessels donot cause a diminution of vision or increase the chancesof graft rejection subsequent to a penetratingkeratoplasty.

Necrotizing Stromal KeratitisNecrotizing stromal keratitis is a less common presen-tation of herpetic stromal disease. It is thought to be

caused by direct invasion of HSV in corneal stroma,active viral replication and intense immune stromalinflammation.9 It generally occurs when topical cortico-steroids have been given without the antiviral coverage.

Corneal necrosis, ulceration and dense infiltrationof stroma with an overlying epithelial defect are theclassical clinical features of this disease (Fig. 9.12).9

Secondary complications include hypopyon, uveitis,posterior synechiae, glaucoma, retrocorneal membrane,cataract and perforation.

HERPETIC ENDOTHELITIS

Herpetic endothelitis is caused by a delayed hyper-sensitivity reaction (Cell mediated type IV immune

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Figure 9.13: Herpetic endothelitis (diffuse)

Figure 9.14: Disciform keratitis Figure 9.15: Herpetic endothelitis (slit)

reaction) to herpes simplex viral antigen mediated by Tlymphocytes. Endothelitis may present as disciformkeratitis, diffuse endothelitis and linear endothelitisdepending on the location of the KPs and the presenceof overlying edema (Fig. 9.13).

Disciform Keratitis

The patient usually presents with symptoms of watering,photophobia, discomfort and blurred vision. It is themost common form of endothelitis in which disk shapedarea of stromal edema overlying few KPs occurs with-out any corneal infiltration or vascularization. The areaof involvement may be diffuse and central or eccentric.Disciform keratitis can occur without previous occur-rence of herpetic corneal epithelial disease. Disciform

keratitis may resolve without significant scarring (Fig.9.14) or more severe attacks may develop into interstitialkeratitis with stromal thinning and stromal necrosis.Perforation may occur if it is treated with steroidswithout antiviral cover. It may also be associated withtrabeculitis and uveitis.

Diffuse Endothelitis

It is a rare presentation of ocular herpes simplex keratitis.Patients characteristically have scattered KPs over theentire cornea with overlying diffuse stromal edema andassociated iritis (Fig. 9.15). It is an immune reactiontargeted against the corneal endothelium. Aggressivetreatment with topical corticosteroids lead to completeresolution of inflammation and edema.

Linear Endothelitis

It clinically appears as a line of KPs on cornealendothelium that progresses centrally from the limbus.It is accompanied by peripheral stromal and epithelialedema between the KPs and limbus.

HERPES SIMPLEX TRABECULITIS

Herpetic peripheral corneal involvement may extend totrabecular meshwork and cause trabeculitis andsecondary glaucoma.

HERPES SIMPLEX IRIDOCYCLITIS

Herpes simplex keratitis may present as recurrent non-granulomatous anterior uveitis. The patient complainsof pain, photophobia and ciliary flush. Iritis in a patient

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of previously known herpetic keratitis and should beconsidered herpetic until proved otherwise. It is thoughtto be an immunological reaction but live virus has alsobeen demonstrated in some cases in the anteriorchamber8 and in the iris.9 Anterior chamber inflamma-tion is present and there may be iris atrophy, posteriorsynechiae and even iris hemorrhages.

Laboratory DiagnosisThe diagnosis of ocular herpetic disease, primary orrecurrent is generally based on clinical examination.However in cases of atypical presentations or in caseswhere confirmation of diagnosis is required, laboratorydiagnosis may be required.

GIEMSA STAINING

Corneal scraping in suspected herpes simplex keratitis istypically reserved for problematic cases, such asnecrotizing stromal keratitis. Cytologic examination ofGiemsa or Wright-stained specimens reveals multi-nucleated giant cells and the more pathognomonicCowdry type A inclusions that are multi-nucleated,epithelial cells with ballooning degeneration. However,this test is not very sensitive and if negative does not ruleout herpetic infection.It was found to have a sensitivityof 57.1 percent and specificity of 85.9 percent.10

POLYMERASE CHAIN REACTION (PCR)

PCR is another useful diagnostic tool with high sensiti-vity. The sensitivity is almost equal to viral culture andthe results are obtained much earlier. Its specificity hasbeen found to be 67.9 percent in one study.10

It can detect HSV in tear film and in cornealscrapings. Rose bengal and lissamine green may inhibitdetection of HSV virus by PCR and therefore samplesfor PCR should be taken before staining.11

VIRAL CULTURE

It is a definitive method of diagnosis but it may takeseveral days before the test becomes positive. The lesionis swabbed and placed in viral transport medium or intothe viral monolayer tubes and sent directly to the labora-tory where the carrier medium is inoculated into culturesand the inoculated cells monolayers incubated at 37oC.

A typical cytopathic effect is generally noticed in2-4 days but may require 5-10 days.12 The recovery rate

from acutely infected ulcer is 70 percent if the specimenis taken within 2-3 days of the appearance of the lesionand then decreases as the clinical findings become moreprominent. The use of antiviral drugs may decrease therecovery rate to 40 percent even in early disease.

IMMUNOLOGICAL TESTS

These tests include immunofiltration test, latex aggluti-nation test and the enzyme linked immunoadsorbentassay (ELISA) test.

ELISA test is the immunologically based tests whichproduces results within hours. This test has 85 percentsensitivity in detecting the virus.

Serological Test to Measure Circulating Antibodies

Serum antibody titers can be used to differentiateprimary herpetic infection from first ocular occurrenceof recurrent disease. It is done by drawing paired serafrom the patient. First sample is taken within 5-7 daysof onset of the symptoms and the second sample is taken3-4 weeks later. Presence of low neutralizing antibodiesin the first sample followed by four-fold rise in thesecond titer indicate primary infection, whereas presenceof moderate titers in the first sample followed four-foldrise in the second sample indicates re-infection orreactivation of the disease. Antibody titers can fluctuateindependently of the presence of disease, and lowpositive titers are nearly ubiquitous in the adultpopulation due to the widespread nature of herpeticdisease. Both false-positive and false-negative test resultsare common. A suspicious flare up of keratitis associatedwith high HSV titers, along with a lower titer obtainedduring a period of inactive disease, can be consideredstrongly suggestive of HSV as an etiologic agent.

Medical TreatmentThe drugs which are used for treatment of herpessimplex keratitis consist of antiviral agents andcorticosteroids. Antiviral therapy may have to be giventopically or systemically depending on the stage of thedisease. The antiviral agents used for the treatment ofviral keratitis include topical agents such as acyclovir,idoxuridine (IDU), vidarabine and trifluridine, and oraldrugs such as acyclovir, valacylcovir, and famcyclo-vir.13,14 These antivirals are virostatic and inhibit viralreplication by interfering with protein synthesis (Table9.4).

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Management of Specific ConditionsThe etiopathogenesis and management strategies invarious manifestations of viral keratitis is shown inTable 9.5.

INFECTIOUS EPITHELIAL KERATITIS

The treatment of the infectious epithelial keratitisconsists of physical debridement, topical antiviral agents,cycloplegics and tear substitutes.15

Physical debridement of the infected epithelial cellsshould be done with cotton tipped applicator. Topicalantiviral drugs in the form of 3 percent acyclovirointment 5 times/day or 1 percent trifluridine solution2 hourly when awake are given for the first week. Incases which are responsive to therapy, after a week oftreatment, these drugs are tapered that is, acyclovir isgiven three times a day and trifluridine is given 5 timesper day. These are then continued in these doses for therest of the treatment which lasts for 21 days. These drugsare discontinued after 3 weeks of therapy even whenthe ulcer does not heal completely. Generally, infectiousepithelial keratitis shows signs of healing by 2 weeks.

Cycloplegics (2% Homatropine hydrobromide or 1%Cyclopentolate hydrochloride) are added when iritis ispresent. Topical antivirals are very epitheliotoxic and itis imperative to give concomitant preservative freeartificial tears (Hydroxypropyl methylcellulose 0.3% eyedrops) to keep the epithelium lubricated.

In certain cases, if the dendritic patterns still persistafter 2 weeks of therapy, a careful assessment is requiredif it is a true ulceration or a dendriti form epitheliopathy.The latter is a healing response of epithelium and is thereis absence of any ulceration.

Corticosteroid drops are not recommended in themanagement of infectious epithelial keratitis unlesssignificant stromal involvement coexists. In the event

of coexisting stromal disease topical 3 percent acyclovireye ointment is applied 5 times a day for 4-5 days todecrease the viral load and then topical corticosteroids(1% prednisolone acetate ophthalmic suspension) isstarted at a frequency of 2 to 4 hourly depending on theseverity of stromal disease.19 After a week both theantiviral and corticosteroid are tapered very graduallyover a period of 6 to 8 weeks. Sometimes tapering shouldbe done over a longer period of time as the stromaldisease has a tendency to recur immediately after thetopical corticosteroids are stopped.

At times infectious epithelial keratitis maynot respond to the topical antiviral medications. It ismandatory to re-scrape and send them for culturesas Acanthamoeba may be isolated in 70% of these cases.20

Resistance generally does not occur in cases ofviral keratitis; however if it occurs, and the patient ison acyclovir, vidarabine may be tried instead ofacyclovir; trifluridine in these cases should not be usedinstead as trifluridine and acyclovir work by the samemechanism.

NEUROTROPHIC KERATOPATHY

Treatment is aimed at protecting the damaged basementmembrane. Therapeutic approaches include stoppingtopical antiviral agents which may be epitheliotoxic andusing preservative free artificial tears and ointment. Incase the epithelium becomes boggy gentle debridementshould be done. In cases of non-healing ulcers thera-peutic bandage contact lenses may be given along withtopical antibiotics to prevent contact lens inducedmicrobial keratitis. Alternatively, a surgical tarsorrhaphymay be done or botulinium toxin injection may be givento cause a temporary lid closure. In severe cases,conjunctival flaps may be undertaken or amnioticmembrane transplantation may be done (Figs 9.16Ato C).

Table 9.4Antiviral agents

Antiviral agent Route Strength frequency Mechanism of action

Vidarabine (Ara-A) Topical 3% ointment Five times a day Inhibits viral DNA polymeraseTrifluridine Topical 1% solution 2 hourly while awake Inhibits viral thymidylate synthaseAcyclovir Topical, Oral 3% ointment Five times a day Activated by viral thymidine kinase

200,400 mg tablets to inhibit DNA polymeraseValacyclovir Oral 1000 mg Three times a day Activated by viral thymidine kinase

to inhibit DNA polymerase

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IMMUNOLOGIC DISEASEA combination of antiviral drug and topical steroids isthe recommended line of treatment of immune mediatedHSV keratitis such as immune stromal keratitis andnecrotizing stromal keratitis.

Immune Stromal Keratitis

Topical steroids are the mainstay for cases of immunestromal keratitis. Topical steroids reduce the severity andof stromal inflammation, decrease the duration of

stromal keratitis and reduce corneal scarring, neovascu-larization and posterior synechiae formation.

Topical corticosteroids (1% Prednisolone acetateophthalmic suspension, 4 times a day) should be startedin mild cases. In more severe cases topical corticosteroidsshould be instilled every hour. In all the casesadministration of topical corticosteroids should beaccompanied with instillation of antiviral drugs (1%trifluridine solution or 3% acyclovir ointment).

A mydriatic–cycloplegic drug (2% homatropinehydrobromide or 1% cyclopentolate hydrochloride)added to reduce ciliary spasm.

Table 9.5Summary of clinical manifestations and management of viral keratitis

Lesion Etiopathogenesis Topical treatment Systemic treatment Remarks

Dendritic keratitis Infection by live herpes 3% topical acyclovir ointment None Heals without significantsimplex virus (5 times/day) or 1% trifluridine corneal scarring

solution (2 hourly)Epithelial debridement ±

Amoeboid/ Infection by live 3% topical acyclovir ointment None Heals without significantgeographical ulcer herpes simplex virus (5 times/day) or 1% trifluridine corneal scarring

solution (2 hourly)Epithelial debridement ±May add topical antibioticdrops prophylactically

Neurotrophic keratitis Noninfectious, Lubricants, BCL, patching, Collagenase Low dose topical↓ corneal sensitivity tarsorrhaphy, amniotic inhibitors like corticosteroids and

membrane tetracycline topical antiviral ifstromal edema andinflammation present

Immune mediated Immune reaction to Topical antivirals and None Very gradual tapering ofstromal keratitis herpes virus antigen topical corticosteroids topical therapyNecrotizing stromal Active viral replication Topical corticosteroids Gradual tapering offkeratitis in corneal stroma (1% prednisolone acetate topical therapy

suspension, 4 times a day)with 3% topical acyclovirointment (5 times/day) or1% Trifluridine solution(9 times/day) ± mydriatic –cycloplegic drug (2%Homatropine hydrobromideor 1% cyclopentolatehydrochloride)

Endothelitis/ Immune reaction to Topical corticosteroids (1% Gradual tapering offDisciform keratitis viral antigen Prednisolone acetate ophthalmic topical therapy

suspension, 4 times a day) with3% topical acyclovir ointment(5 times/day) or 1% trifluridine± mydriatic – cycloplegic drug(2% homatropine hydrobromideor 1% cyclopentolate hydrochloride)solution (2 hourly)

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Necrotizing Stromal Keratitis

Topical corticosteroids (1% Prednisolone acetateophthalmic suspension, 4 times a day) should be startedin mild cases. In more severe cases topical corticosteroidsshould be instilled every hour. In all the casesadministration of topical corticosteroids should beaccompanied with instillation of antiviral drugs (1%trifluridine solution or 3% acyclovir ointment).

A mydriatic–cycloplegic drug (2% homatropinehydrobromide or 1% cyclopentolate hydrochloride)added to reduce ciliary spasm.

Topical corticosteroids should be tapered verygradually over months (more than 10 weeks) to avoidreactivation and rebound inflammation. In somepatients topical corticosteroids cannot be tapered offwithout reactivation of the disease and in such caseslow dose topical corticosteroids (0.01% dexamethasoneophthalmic solution or 0.125% prednisolone acetateophthalmic suspension, 1 drop every day or everyalternate day) should be continued indefinitely.

IRIDOCYCLITIS AND TRABECULITIS

It is mainly an immune reaction to viral antigen and insome cases to intact virus. The Herpetic Eye DiseaseStudy (HEDS) found a trend toward improved responseof herpetic iridocyclitis and trabeculitis when oralacyclovir was added to topical trifluridine andcorticosteroids.19 A combination of oral antivirals andtopical corticosteroids may provide sufficient antiviralcoverage to allow for the desired suppression of immuneresponse.

Patients are treated with combination of topicalcorticosteroids (1% Prednisolone acetate suspension, 4times a day) and antiviral drugs (1% trifluridine solu-tion or 3% acyclovir ointment) along with cycloplegics

(2% homatropine hydrobromide or 1% cyclopentolatehydrochloride). Beta blocker (0.5% timolol maleate2 times/day) and carbonic anhydrase inhibitor shouldbe added to the above treatment if there is secondaryglaucoma. Oral acyclovir 200 mg 5 times a day may beadded in cases of severe uveitis or if live virus is isolatedfrom the anterior chamber.

Recently, the efficacy of topical cyclosporine 0.05percent (Restasis) in patients with herpes simplex virusnon-necrotizing stromal keratitis unresponsive to topicalprednisolone has been studied. It was found that herpessimplex virus stromal keratitis can be treated effectivelywith topical cyclosporine.21

Surgical TreatmentThe surgical therapies which need to be performed insevere cases of herpetic keratitis may includeconjunctival flap, amniotic membrane transplantation,tarsorrhaphy, application of cyanoacrylate glue and alamellar or penetrating keratoplasty (PKP).

Surgical treatment is required most often in cases ofnecrotizing stromal keratitis. In cases of recurrentherpetic keratitis with no potential vision, a gundersonflap may be done.

Penetrating keratoplasty following herpetic diseaseis accompanied by an increased risk of graft failure andrecurrence of herpetic disease.22

Complications after transplantation in herpetic eyesinclude corneal graft rejection, as well as herpesrecurrences within the graft, persistent epithelial defect,corneal melting, secondary infection and graft failure.When PKP is performed for herpetic scar the risk ofrecurrence of herpetic infection is 12 to 19 percent (Fig.9.17).16,22 There are chances of occurrence of herpetickeratitis in eyes after PKP, even in patients with noprevious history of HSV infection (Fig. 9.18).16,23

Figures 9.16A to C: (A) Neurotrophic keratitis (B) Amniotic membrane transplantation (C) Healing of neurotrophic keratitis

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Figure 9.19: Skin lesions in varicella zoster (Courtesy: MedicalPhotographic Imaging Centre, Royal Victorian Eye and Ear Hospital,Melbourne)

PREVENTION

The HEDS study has established that long-term (oneyear) oral antiviral therapy, with a dose of acyclovir 400mg twice a day, can reduce the recurrence of epithelialkeratitis and stromal keratitis.22 The benefit of suchtherapy was found to be greatest among patients withprevious stromal keratitis, but in all groups benefits werefound even if the previous episode of eye disease hadoccurred up to a year before therapy. For patients withepithelial keratitis only, the decision to begin prophy-lactic therapy must be made on an individual basis, buttypically such prophylaxis is reserved for patients withtwo or more episodes in a year. In the treatment ofepithelial keratitis, the HEDS study group did not finda benefit to adding 3 weeks of intensive oral acyclovirtherapy to topical trifluridine.23

Patients with any previous herpes simplex kerato-pathy who are undergoing PK may benefit from bothpreoperative and postoperative prophylaxis, and we dothis routinely.17 Long-term oral acyclovir use seems toremain effective in decreasing the number of ocularherpes simplex virus recurrences.18 Similar prophylaxisis much more important for patients with suspectedherpetic eye disease undergoing PRK or LASIK, sincethe short-wavelength laser can reactivate herpetickeratitis and lead to significant morbidity.24

Oral valacyclovir 1000 mg three times a day has alsofound to be useful in prevention of herpetic keratitis.

Varicella Zoster Virus

Varicella zoster virus (VZV) belongs to the herpes virusfamily and cause varicella that is the chickenpox andthe herpes zoster that is the shingles (Fig. 9.19). Varicellazoster virus causes a benign exanthematous illnessmanifested by prodromal symptoms and vesicular rash.

Figure 9.17: Herpetic dendrite in a graft stained with florescein dye(Courtesy: Medical Photographic Imaging Centre, Royal Victorian Eyeand Ear Hospital, Melbourne)

Figure 9.18: Geographic ulcer in a graft stained with Rose Bengaldye (Courtesy: Medical Photographic Imaging Centre, Royal VictorianEye and Ear Hospital, Melbourne)

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After acute infection the VZV travels down theperipheral axons to cells in the dorsal root ganglionwhere it remains in the latent phase.

The herpes zoster occurs due to reactivation of theVZV within the dorsal root ganglion and virions travelto skin or mucous membrane or skin along the axonaltransport.

EPIDEMIOLOGY

The annual incidence of herpes zoster is 1.5/1000 to 3.0/1000 cases. The incidence is more in patients more than75 years of age. There is no predilection for gender, race,or seasonal variation.

Herpes zoster has a greater preponderance in caseswith altered cell mediated immunity, those takingimmunosuppressive agents, organ transplant recipients,syphilis, tuberculosis, and those having HIV. It is alsoprecipitated by physical or emotional stress.

The varicella zoster keratitis occurs in two forms:• Primary (varicella)• Recurrent (herpes zoster).

The ocular manifestations are uncommon in varicellabut common in ophthalmic zoster. The various ocularmanifestations in ophthalmic VZV include:• Eye lesions which are manifested as pocks on lids

and lid margins.• Keratitis occurs rarely in cases of VZV.• Epithelial keratitis with or without pseudodendrites

occurs more rarely.• Disciform keratitis with uveitis of varying duration

can occur.

Ophthalmic varicella zoster infection is accompaniedby keratouveitis that varies in severity according toimmune status of the patient. The manifestations ofophthalmic varicella zoster infection are benign inchildren as compared to adults who have severe andsometimes blinding disease. Corneal complications inophthalmic zoster are associated with skin eruption inareas supplied by branches of the nasociliary nerve.

Differences between dendrites of HSV and HZVinfections (Table 9.6).

TREATMENT OF OPHTHALMIC VARICELLA ZOSTER

• Intravenous and oral acyclovir has been usedsuccessfully for treatment of herpes zoster ophthal-micus. This treatment regime is particularlyimportant in immunocompromised patients. Theappropriate timing of the therapy is vital. Therapyneeds to be started within 72 hours after appearanceof the rash. The use of oral acyclovir in a dosage of800 mg five times daily for 10-14 days has beenrecommended. Although varicella zoster viruskeratopathy is an uncommon indication forpenetrating keratoplasty, effective visual rehabili-tation can be achieved in these patients. Carefulpostoperative management, frequent lubrication, andlateral tarsorrhaphies to protect the corneal surfaceare major factors in the successful outcome of thesecases.25

ADENOVIRAL INFECTIONS

It is causative agent for epidemic keratoconjunctivitiswhich is predominantly caused by the serotypes 8, 19,and 37. The infection is highly contagious, withapproximately 10 percent transmission in householdcontacts via hands and fomites. Transmission has alsobeen associated with instrumentation, industrial trauma[shipyard workers (i.e. shipyard eye)], contaminatedophthalmic solutions, and the hands of health careworkers. Corneal trauma facilitates infection. After an8 days incubation period, an insidious onset of unilateralred eye occurs, which spreads to involve both eyes.Patients have photophobia, tearing, and pain (indicatingcorneal involvement). Children may have fever andlymphadenopathy. Malaise and headache are reported.Inflammation may persist for weeks, and residualscarring and visual impairment may occur. Theassociated findings in epidemic keratoconjunctivitis are:• Severe follicular keratoconjunctivitis.

TABLE 9.6Differentiation between dendrites of herpes simplexand zoster

Feature HSV VZV

Overall Fine, lacy Thick ropyEpithelium Linear defect with Elevated, painted-on

bared stroma, appearancesurrounded byedematousepithelial cells

Staining Base stains with Minimal fluororesceinfluorescein stainingDiseased borderepithelial cells stainwith rose bengal

Terminal bulbs Frequent None

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3Viral Keratitis

• Palpebral edema.• Preauricular lymphadenopathy is not common but

is a pathognomonic finding with adenovirusinfection.

• Hemorrhagic conjunctivitis may develop.In stage I corneal epithelial vesicle like elevations

are present which are 25 to 30 microns and barelyperceptible on slit lamp. Two to five days later ,thelesions coalesce with each other , become clearly visibleon slit lamp and involve deeper epithelium. These arethe classical deep epithelial punctuate keratitis lesionswhich may resolve or progress further (Fig. 9.20). Instage III faint subepithelial infiltrates are present besidethe deep punctate keratitis. Stage IV is characterized bynummular opacities which may be present months toweeks after the initial episode (Fig. 9.21).

Visual haziness or impairment resulting fromkeratitis develops due to the occurrence of nummularopacities (Fig. 9.21) and may persist for months to years.

A molecular assay for detection of human adenovirusbased on automated nucleic acid extraction and real timepolymerase chain reaction is being evaluated for thediagnosis of ocular adenoviral infections. The newmolecular assay is suitable for rapid diagnosis ofadenoviral keratoconjunctivitis in the routine diagnosticlaboratory. It allows for a rapid diagnosis of adenoviralkeratoconjunctivitis.26

ManagementMedical management can range from cold compressesand artificial tears to topical vasoconstrictors (e.g.

Figure 9.21: Healed adenoviral keratoconjunctivitis (nummularopacities)

Figure 9.20: Subepithelial infiltration in adenoviral keratoconjuncti-vitis

naphazoline) and steroids (vexol, flarex, pred forte) twoto four times daily. Recently, cidofovir an antiviral drugused intravenously to treat cytomegalovirus retinitisappears to be effective in adenoviral keratoconjunctivitis.The topical form creates a faulty viral DNA structure.Twice daily instillation is recommended.27

References1. Lisegang TJ. Herpes simplex virus epidemiology and

ocular importance. Cornea 2001;20:1-13.2. Liesegang TJ. Epidemiology of ocular herpes simplex.

Arch Ophthalmol 1989;107:1160-5.3. Jeffries DJ. Intrautrine and neonatal herpes simplex virus

infection. Scand J Infect Dis Suppl 1991;80:21-6.4. Whitley RJ, Nahmias AJ, Visintine AM, et al. The natural

history of herpes simplex virus infection of mother andnewborn. Pediatrics 1980;66:489-94.

5. Kaye S, Lynas C, Patterson A, et al. Evidence of herpessimplex viral latency in the human cornea. Br JOphthalmol 1991;75:195-200.

6. Kaufman HE, Rayfield MA. Viral conjunctivitis andkeratitis: Herpes simplex virus. In: Kaufman H, et al(Ed): The cornea, New York, 1988, Churchill Livingstone.

7. Wilhelmus KR. Diagnosis and management of herpessimplex stromal keratitis. Cornea 1987;6:286-91.

8. Kaufman H, Kanai A, Elison E. Herpetic iritis: Demons-tration of virus in the anterior chamber by fluorescentantibody techniques and electron microscopy. Am JOphthalmol 1971;71:465-9.

9. Witner R, Iwamoto T. Electron microscopic observationof herpetic particles in the iris. Arch Ophthalmol 1968;79:331-7.

10. Subhan S, Jose RJ, Duggirala A, Hari R, Krishna P,Reddy S, et al. Diagnosis of herpes simplex virus-1keratitis: Comparison of Giemsa stain, immuno-

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fluorescence assay and polymerase chain reaction. CurrEye Res 2004 Aug-Sep;29:209-13.

11. Seitzman GD, Cevallos V, Margolis TP. Rose bengal andlissamine green inhibit detection of herpes simplex virusby PCR. Am J Ophthalmol 2006;141:756-8.

12. Goodman JL. Infections caused by herpes simplexviruses. In: Herprich PD, Jordan C, Ronald AR (Eds).Infectious diseases, 5th edn, Philadelphia, JB Lippincott1994.

13. Schwartz GS, Holland EJ. Oral acyclovir for themanagement of herpes simplex virus keratitis inchildren. Ophthalmology 2000;107:278-82.

14. The Herpetic Eye Disease Study Group. A controlledtrial of oral acyclovir for the prevention of stromalkeratitis or iritis in patients with herpes simplex virusepithelial keratitis. Arch Ophthalmol 1997;115:703-12.

15. Wilhelmus KR. The treatment of herpes simplex virusepithelial keratitis. Trans Am Ophthalmol Soc 2000;98:505-32.

16. Tambasco FP, Cohen EJ, Nguyen LH, Rapuano CJ,Laibson PR. Oral acyclovir after penetrating keratoplastyfor herpes simplex keratitis. Arch Ophthalmol 1999;117:445-9.

17. Barney NP, Foster CS. A prospective randomized trialof oral acyclovir after penetrating keratoplasty for herpessimplex keratitis. Cornea 1994;13:232-6.

18. Uchoa UB, Rezende RA, Carrasco MA, Rapuano CJ,Laibson PR, Cohen EJ. Long-term acyclovir use toprevent recurrent ocular herpes simplex virus infection.Arch Ophthalmol 2003;121:1702-4.

19. Wilhelmus KR, et al. Herpetic eye disease study, acontrolled trial of topical corticosteroids for herpes

simplex stromal keratitis. Ophthalmology 1994;101:1883-96.

20. Thebpatiphat N, Hammersmith KM, Rocha FN,Rapuano CJ, Ayres BD, Laibson PR, et al. Acanthamoebakeratitis: a parasite on the rise. Cornea 2007;26(6):701-6.

21. Rao SN. Treatment of herpes simplex virus stromalkeratitis unresponsive to topical prednisolone 1% withtopical cyclosporine 0.05%. Am J Ophthalmol 2006;141:771-2.

22. The Herpetic Eye Disease Study Group. Oral acyclovirfor herpes simplex virus eye disease: Effect on preven-tion of epithelial keratitis and stromal keratitis. ArchOphthalmol 2000;188:1030-6.

23. Rezende RA, Uchoa UB, Rabwe IB, Rapuano CJ, LaibsonPR, Cohen EJ. New onset of herpes simplex viralepithelial keratitis after penetrating keratoplasty. Am JOphthalmol 2004;137:415-9.

24. Perry HD, Donnenfeld ED, Doshi SD, et al. Perforatedcorneal ulcer following LASIK. CLAO 2002;28:69-71.

25. Tanure MA, Cohen EJ, Grewal S, Rapuano CJ, LaibsonPR. Penetrating keratoplasty for varicella-zoster viruskeratopathy. Cornea 2000;19:135-9.

26. Koidl C, Bozic M, Mossbock G, Muhlbauer G, Berg J,Stocher M, et al. Rapid diagnosis of adenoviral kerato-conjunctivitis by a fully automated molecular assay.Ophthalmology 2005;112:1521-8.

27. Hillenkamp J, Reinhard T, Ross RS, Bohringer D,Cartsburg O, Roggendorf M, et al. Topical treatment ofacute adenoviral keratoconjunctivitis with 0.2% cidofovirand 1% cyclosporine: A controlled clinical pilot study.Arch Ophthalmol 2001;119:1487-91.

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3Protozoal Keratitis

Protozoal Keratitis10

Keratitis can occur due to various protozoa, of whichAcanthamoeba is the most notorious. Other protozoawhich has been increasingly isolated from cases ofcorneal ulcer includes Microsporidia.

Acanthamoeba KeratitisIt was first described in the early 1970s, and a dramaticincrease in cases of Acanthamoeba keratitis has beenobserved in the early to mid-1980s.

ETIOLOGY

The pathogenic species of Acanthamoeba includeAcanthamoeba castellanii, Acanthamoeba polyphaga,Acanthamoeba culbertsoni, Acanthamoeba palestinensis,Acanthamoeba astronyxis, Acanthamoeba hatchetti,Acanthamoeba rhysodes, Acanthamoeba divionesis,Acanthamoeba quna, Acanthamoeba lugdunensis, andAcanthamoeba griffini.

The life cycle of Acanthamoeba consists of 2 stages:an active stage that is the trophozoite (which is 14-40microns in diameter) stage and a cyst stage (which hasa double-layered wall with a diameter of 12-16 microns)which is the dormant phase (Fig. 10.1).

EPIDEMIOLOGY

The incidence of Acanthamoeba keratitis varies dependingon the geographic region and the type of contact lensuse. In the UK, Europe and Hong Kong, the rate ofincidence of Acanthamoeba keratitis was estimated to be0.33 per 10 000 in hydrogel contact lens wearers peryear.1 In the recent years an increased incidence of newcases of Acanthamoeba has been noted from USA.2 Theincidence of Acanthamoeba keratitis associated with useof rigid contact lenses is 9.5 times lower than for softlens wearers.1

The disease is generally unilateral; however bilateralcases have also been reported. There is no sexpredilection.

RISK FACTORS

There are various risk factors which predispose toAcanthamoeba keratitis (Table 10.1).3-5 The majority of thecases occur in contact lens wearers.5 However, in theIndian subcontinent it has also been reported in non-contact lens wearers.6 Apart from this there may be otherrisk factors which are associated apart from this in the

Figure 10.1: Acanthamoeba cysts (Blankophore stain) (Courtesy:Dr H Sheorey, Dept. of Microbiology, St Vincent Hospital, Melbourne)

Table 10.1Risk factors for Acanthamoeba keratitis

• Contact lens wearers• Contaminated water/solutions especially home made

solutions• Corneal trauma• Orthokeratology

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Indian subcontinent including patients who haveundergone orthokeratology.

Contact Lens Wear

Classically, it occurs in immunocompetent, healthy,young individuals and the most important factor in thesecases is contact lens wear which occurs in 80 to 86percent of these cases.3-5 No type of contact lens has beenexcluded from an association with Acanthamoebakeratitis. Out of the 75 percent of the patients who arecontact lens wearers, 40 percent were soft contact lenswearers, 22 percent were rigid gas permeable wearersand 38 percent were either extended wear contact lenswearers or other types of contact lenses.7

The safest form of contact lens wear remains dailydisposable lenses as very few cases of Acanthamoebakeratitis have been reported in patients using dailydisposable lenses.2

The first generation of silicone hydrogel contactlenses which used balafilcon A material showedincreased chances of adherence of trophozoites8 ascompared to the second generation silicone hydrogelcontact lenses which use galyfilcon A.9

It is to be noted that most commercially availablecontact lens-disinfection solutions are ineffective againstAcanthamoeba.10

Non-Contact Lens Wearer

In India Acanthamoeba keratitis has also been reportedin cases of non-contact lens wearers6 and the major riskfactor for Acanthamoeba keratitis in these cases wascorneal trauma.

Orthokeratology

Orthokeratology, that is the use of contact lens wear toshape the cornea has also been associated withAcanthamoeba keratitis the incidence of which wasfound to be as high as 30 percent out of all pathogens.11

Other Risk FactorsOther risk factors associated with Acanthamoeba keratitisinclude use of contaminated water or solutions includingthe home made solution to disinfect contact lenses,swimiming with contact lenses on and corneal trauma.

SYMPTOMSThe major clinical symptoms are severe or moderatepain, decreased vision, redness, irritation, foreign bodysensation, photophobia, mucous discharge and tearing

(Table 10.2). One of the most important symptoms ofAcanthamoeba keratitis is severe pain especially in theearly phase of the infection.

Classically Acanthamoeba keratitis follows aprotracted waxing and waning course. The phase ofremission reflects the presence of dormant cysts,whereas the progression of keratitis is due to theemergence of replicating trophozoites from the cysts.

SIGNS

Acanthamoeba infection classically involves the cornea.However, in some cases lids, anterior chamber and scleramay also show signs of inflammation (Table 10.2).

CORNEAL INVOLVEMENT

Early corneal signs included epithelial stippling withmicrocystic edema; coarse, opaque streaks; fine epithelialand subepithelial curvilinear opacities; and dendritiformepithelial lesions (Fig. 10.2).

Table 10.2Clinical features of acanthamoeba keratitis

Symptoms—waxing and waning course• Severe pain/foreign body sensation• Redness• Watering, mucus discharge• Decreased vision• Photophobia

Signs—corneal• Corneal epithelial abnormalities• Epithelial haze• Elevated lines• Microcysts• Pseudodendrites• Punctate epithelial erosions• Stromal infiltrates• Radial keratoneuritis (Along nerves of anterior stroma)• Ring shaped stromal infiltrate• Stromal thinning and furrowing• Satellite lesions• Stromal ulceration and perforation (rare)

Signs—others• Lid edema, pseudoptosis• Conjunctival injection, chemosis• Iritis, hypopyon• Dacryoadenitis• Reactive Ischemic Retinitis• Secondary Glaucoma• Cataract• Severe anterior and posterior scleritis

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Radial keratoneuritis as a presenting sign inAcanthamoeba keratitis has been described by Mooreet al.12 Radial keratoneuritis is characterized by linearradial, branching infiltration by the parasites alongcorneal nerves in the anterior stroma. This infiltrationbegins paracentrally and extends to the limbus in aradial pattern, and is responsible for the severe degreeof pain (Fig. 10.3).

The late stromal infection is characterized by densesingle or multiple stromal infiltrates which may becentral or paracentral and a characteristic ring infiltrate.The overlying epithelium may remain intact and anintrastromal abscess may occur. However, stromalneovascularization is never seen even in severe andlongstanding cases.

A ring-shaped stromal infiltrate is an indicator ofadvanced infection and is nearly pathognomonic forAcanthamoeba keratitis which may be present in 19 to 93percent of cases.5,13 The infiltrate may be segmental orcircumferential, progressive, and often involves stromalthinning (Fig. 10.4) or furrowing, and may be associatedwith a variable overlying epithelial defect. It is due topolymorphonuclear leukocyte infiltrates generated bychemotaxis after antigen-antibody precipitation due tocollagenolytic enzymes released by Acanthamoeba whichdegrades collagen and produces ring infiltrates.

As the disease progresses, there may be progressiveloss of corneal stroma with formation of descemetoceleand perforation and this is more common when there isbacterial super-infection (Fig. 10.5).

Figure 10.3: Radial keratoneuritis: florescein stain along the radialnerves (Courtesy: Medical Photographic Imaging Centre, RoyalVictorian Eye and Ear Hospital, Melbourne)

Figure 10.2: Subepithelial opacities in early Acanthamoeba keratitis(Courtesy: Medical Photographic Imaging Centre, Royal Victorian Eyeand Ear Hospital, Melbourne)

Figure 10.4: Stromal thining in Acanthamoeba keratitis Figure 10.5: Acanthamoeba keratitis: stromal lysis and perforation

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Lids and Conjunctiva Involvement

Other associated clinical signs include lid abnormalities,lid edema, reactive pseudoptosis and associated iritis.Conjunctival injection and chemosis are almost alwayspresent.

Iritis and Hypopyon

In severe cases there may be an associated iritis andhypopyon formation.14

Cataract and Glaucoma

Other complications of prolonged Acanthamoeba keratitisinclude cataract formation, with incidence ranging from20 percent to slightly less than 40 percent.13,15 This mayoccur as a result of organism-specific inflammation andinfection, or may be attributed to the chronic use of toxictopical antiamoeba agents.

Severe glaucoma is another complication in cases ofprolonged Acanthamoeba keratitis, with a reportedincidence of 30 percent, and may require drainageprocedures to control the intraocular pressure.16

Scleral Involvement

Acanthamoeba keratitis may be associated with aprominent scleritis, which may be responsible for theboring, severe pain in the later stages of the disease. Itis characterized by deep scleral vascular engorgementand scleral nodules, the frequency of which ranges from11 to 42 percent depending on the stage of infection.13

Most patients have sectional areas of anterior scleritiscontiguous with areas of keratitis (Fig. 10.6). In mostcases, scleritis is a secondary immunologic response,rather than a true scleral infection of Acanthamoeba.13,14

Unexpectedly, prolonged ocular inflammation andinfection with deep corneal abscesses have been recentlyshown to result in a new syndrome of retinal ischemiathrough severe reactive posterior segment inflamma-tion.13

DIFFERENTIAL DIAGNOSIS

Acanthamoeba infection can mimic several other typesof keratitis, including viral bacterial or fungal keratitis.Parmar et al recently showed that 26 (41%) of 63 patientsconfirmed to have Acanthamoeba keratitis by culture orconfocal microscopy were initially diagnosed and

Figure 10.6: Acanthamoeba keratitis with sectoral scleritis

treated as having herpes keratitis, whereas 43 percentwere misdiagnosed as bacterial keratitis.17

Herpes Keratitis

Acanthamoeba keratitis is frequently misdiagnosed asherpes simplex keratitis. It has been reported that herpeskeratitis was misdiagnosed in 70% cases of Acantha-moeba keratitis in one study.18 Minor trauma may beassociated with both, that is, the herpes simplex keratitisand Acanthamoeba keratitis. However, trauma as apredisposing factor for Acanthamoeba keratitis is morecommon as there is also concomitant contamination withsoil or water. Nevertheless, contact lens wear is not afrequent predisposing factor in herpes simplex keratitis.

Clinically, in early stages of infection with herpessimplex the dendritic lesion is ulcerated, whereas inAcanthamoeba keratitis, the pseudodendrite is elevatedat the center of the cornea, and the epithelium has agelatinous appearance. The stromal infiltrates in herpessimplex infection tend to be smaller as compared toAcanthamoeba infection. However, the more advancedstages of the disease, are accompanied by ulceration andloss of stromal tissue and the keratitis may resembleherpes simplex infection.

Fungal Keratitis

Acanthamoeba keratitis can also mimic fungal keratitisand this has been particularly reported from the Indiansubcontinent.6 This may occur due to the presence of

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stromal infiltrates and endothelial plaques. Severe pain,annular infiltrates and radial keratoneuritis arefrequently absent in cases of fungal keratitis.

Laboratory DiagnosisAcanthamoeba keratitis should be diagnosed as early aspossible, because therapy is most effective when initiatedearly and requires prolonged treatment.

CORNEAL SCRAPING

Corneal scraping should be taken from the area ofabnormal epithelium and ulceration. It may fail to revealthe presence of Acanthamoeba in early cases, whenepithelium is intact or in cases in which superficialcornea is unaffected.

WET SMEAR

Fresh wet mount specimens can also be used. The useof a spray fixture to avoid trophozoite disruption by airdrying has been recommended.

STAINING

Trophozoites and cysts can be identified in the cornealscrapings or smears by staining with hematoxylin andeosin, Gram (Fig. 10.7), Giemsa-Wright, Calcofluor,methylene blue, congo red, Janus green, Lugol solution,acridine orange or wheatly trichrome stains. Lightmicroscopy of cysts and motile trophozoites is facilitatedusing Nomarski optics. The staining characters withvarious stains are described in Table 10.3.

A study performed on corneal histopathologicspecimens showed that hematoxylin and eosin isadequate to highlight the Acanthamoeba trophozoites and

cysts for an experienced ophthalmic pathologist;followed by periodic acid Schiff staining.19 The lattertwo stains should be used routinely when screening forAcanthamoeba in corneal tissue, whereas Gomorimethenamine silver should be done whenever there isappreciable inflammation in tissue structures, becausethe amoeba can sometimes resemble inflammatory cells(macrophages), and hematoxylin and eosin would thennot be adequate to make the distinction.20

The trophozoite is characterized by a large singlenucleus and spindle like pseudopodia. It is easier torecognize the cysts, which are double walled, with theinner wall having a variety of polygonal shapes.

Calcofluor white is a relatively simple and reliablemethod for detection of Acanthamoeba, even in cases inwhich Gram and Giemsa fail to reveal organisms.Calcofluor white is a fabric brightener and has an affinityfor chitin and cellulose, which are components of cellwalls of Acanthamoeba cysts and fungi but notAcanthamoeba trophozoites.

A solution containing 0.1 percent cell calcofluor whiteand 0.1 percent Evans blue counter stain is applied tothe specimen for 5 minutes. The specimen is thanexamined under fluorescence microscope. Acanthamoebacysts appear as apple green structures 10-25 μm indiameter. Trophozoites are considerably more difficultto detect with this method because they do not absorbcalcofluor white. However, Evans blue counter stainshows the trophozoites as red brown, irregularly shapedstructures 15 to 20 μm in length.

Table 10.3Staining characteristics of Acanthamoeba trophozoitesand cysts

Type of stain Staining of Staining of cysttrophozoite

Giemsa-Wright Purple PurpleWheatly trichrome GreenKaryosome Red GreenCalcofluor white Red-Brown Apple-Green(counter stained withEvan’s blue)

Figure 10.7: Gram stain sclerosing Acanthamoeba cysts (Courtesy:Dr H Sheorey, Dept. of Microbiology, St. Vincent Hospital, Melbourne)

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Fluorescein–conjugated lectins such as ConcavalinA and wheat gram agglutinin stain both trophozoitesand cyst. Under fluorescent microscopy, the cyst wallsstain green and the trophozoites stain red. In addition,the more specialized technique of indirect fluorescentantibody staining is thought to be more sensitive andspecific.

CULTURE MEDIA

The scraped material should be directly inoculated on aconfluent lawn of Escherichia coli (monoaxonic culture)plated on non-nutrient agar. The laboratories haverecommended a temperature of 35°C, possibly with asecond plate at 30°C or even 25°C. The culture platesshould be sealed with adhesive tape to preventevaporation and loss of Acanthamoeba organisms fromdrying.

Organisms such as Escherichia coli, Aerobacteraerogenes, Enterobacter species, Klebsiella pneumoniae orXanthomonas maltophilia are used as a source ofnutrition for Acanthamoeba on nutrient agar medium.Acanthamoeba trophozoites track through the lawn of thebacteria. The bacteria do not fill in these paths as thereis absence of nutrition for bacteria in the non-nutrientagar. The path depicts the ingestion of bacteria bytrophozoites; the bacteria are unable to reproduce fastenough to fill in the defect in the nutrient poor medium.Large numbers of trophozoites are usually seen by 3days of incubation but may appear as early as 1 day.

At least one serial transfer should be done to confirmthe amoebic isolation, as both macrophages and poly-morphonuclear leukocytes can produce “pseudotrials”on primary isolation. Macrophages and polymorpho-nuclear cells become non viable rapidly, and on serialtransfer do not form trails.

The cultures may require more than 9 days torecover the organism and should be maintained for morethan 2 weeks. The success rate of culturing Acantham-oeba from corneal scrapings is 44-74 percent.20

Method for Examining Contact Lens

An excised fragment of the contact lens is placed on amicroscope slide with a cover slip and examinedunstained or after staining with 0.1 percent CalcofluorWhite. Evans blue counter stain should not be used asit stains the contact lens intensely. The anterior andposterior surfaces of the lens are examined with X200to X400 magnification for the presence of Acanthamoeba.

A fragment of the contact lens may be placed directlyon the non-nutrient agar with an E.coli overlay. IfAcanthamoeba are present, its trophozoites will migrateonto the culture plate.

For wet mount preparation contact lens solution isbest centrifuged at 250 revolutions per minute and thesediment is transferred to a slide and covered with acover slip. The slide should be kept in a covered Petridish and can be examined using phase microscopy.Alternatively, large volumes of contact lens solutionscan be filtered through a 5μm polycarbonate membranefilter, which is than placed upside down on the cultureplate.

POLYMERASE CHAIN REACTION

Polymerase chain reaction testing may be applied onepithelial scrapings to improve the yield, but it is stillexperimental, appears to be highly strain-specific, andrequires the use of numerous screening probes

CORNEAL BIOPSY

A corneal biopsy should be considered if the epitheliumis intact but the stromal lesion is active. It is particularlyvaluable in cases in which the infiltrate is deep in thecornea. A 1.5 to 2.0 mm corneal trephine may be usedto obtain biopsy specimen from an area of infiltrationperipheral to the visual axis.

Non-nutrient agar plates can be used to culture theorganisms in biopsy specimens. Other stainingprocedures such as hematoxylin and eosin, periodic acidSchiff, methenamine silver, calcofluor white, orfluorescein labeled antibodies against Acanthamoeba canbe used to stain organisms in biopsy specimens.Moreover, electron microscopy techniques can beapplied to identify the parasite in the corneal tissues.

By contrast, corneal biopsy is performed masked andis limited by its anterior location and yield. It is believedthat Acanthamoeba trophozoites and cysts are found inthe anterior stroma initially and move deeper into thestroma with prolonged infection. Topical drugs will acton the more superficially positioned amoebas, whereasthe deeper organisms, particularly in large confluentabscesses, are not susceptible to eradication byantiamoeba medications.

CONFOCAL MICROSCOPY

Confocal microscopy has been used in the diagnosis andmanagement of Acanthamoeba keratitis because of the

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ability to detect the organism in the cornea in vivo.21

This technique can also be used to monitor patients whohave been treated for Acanthamoeba keratitis. It can alsobe used to assess if any cysts or trophozoites are presentprior to transplantation surgery. One major advantageof this method is that it is essentially non-invasive,although it requires a cooperative patient and a skilledoperator. In addition, it seems quite likely that thismethod is more sensitive in identifying Acanthamoebaorganisms in early infections, which should improveoutcomes in these cases. In more advanced cases, it alsoaids in differentiating epithelial drug toxicity frompersistent disease. Using the confocal microscope, onecan visualize high-contrast, real-time images of coronalcorneal sections at magnifications of x 240-380 on a videomonitor.

The cystic form of Acanthamoeba is more distinct andappears as a double-walled, hexagonal, hyperreflectivestructure that is 10-25 microns in diameter (Fig. 10.5).The trophozoite form is more difficult to discern, as itappears similar to normal corneal keratocyte nuclei: anovoid, S-shaped, structure within the corneal stroma.20

Other ovoid objects may be observed during confocalmicroscopy of patients with Acanthamoeba keratitis andmay represent inflammatory cells, trophozoites andaltered keratocytes. Confocal microscopy also helps torule out any concomitant infection with fungalorganisms.

The sensitivity of this test for the diagnosis ofsuspected Acanthamoeba keratitis in experienced handshas been reported to be 98 percent, whereas its specificityis yet to be determined.17 Such a powerful tool, however,requires a skilled operator, a qualified and experiencedreader, and a compliant patient. It is also a relativelyexpensive technology available only in select referralcenters.

OTHER TESTS

Although Acanthamoeba can be identified because of itscystic structure and acanthopodia, species identificationis difficult. Morphologic characteristics of cyst stage andisoenzyme analysis have been used to identify differentspecies of Acanthamoeba. More recently, restrictionenzyme analysis of either mitochondrial DNA orcellular DNA were applied to differentiate species ofparasites. However, these characteristics were notcorrelated with morphologic identification of differentspecies.

TREATMENT

The treatment of Acanthamoeba keratitis is difficult, asthe cystic form is highly resistant and may persist foryears.

The drugs which have been found to be effectiveagainst Acanthamoeba include propamidine 0.1 percent(Brolene), neomycin 1 percent and cationic antisepticagents such as chlorhexidine (0.02%) and polyhexa-methylene biguanide (PHMB, 0.02%).21,22 However,most of these medications are not commercially avail-able and must be obtained through compoundingpharmacies.

Most clinicians advocate a combination therapy andtreatment with PHMB or chlorhexidine which isgenerally given in combination with a diamidine, eitherpropamidine (Brolene) or hexamidine (Desmodine).

COMBINATION THERAPY

Therapy is effective if definitive treatment starts withinone month of onset. Combination therapy consists ofuse of two or three medications simultaneously. Thisincludes use of topical PHMB (0.02%) or chlorhexidine(0.02% or 0.04%) without propamidine 0.1 percent. Theyshould be given every hour around the clock for theinitial 72 to 96 hours ,2 hourly for 2-4 weeks and thentapered to to qid dose for 6-12 months.

Topical cycloplegic therapy and oral nonsteroidaldrugs are helpful in the management of pain.

The later the treatment is started, the deeper theAcanthamoeba cysts are in the corneal stroma and it ismore difficult to eradicate the large abscesses . Littledata are available in the literature about the penetrationof antiamoeba agents, but the deeper cysts, especiallyin large abscesses, are shielded from the cysticidalconcentrations, necessitating longer exposure Thishowever may be associated with tissue toxicity from thetreating agents. It has been found helpful to reduceantiamoeba eyedrops abruptly to four times a day andobserve. If there is any reactivation, the eyedrops areincreased to hourly or every 2 hours, and tapered slowlyonce again. This mode of treatment may catch theresistant cysts, especially the deeper ones, in the processof converting to the more drug-vulnerable trophozoites(pulse therapy).13

According to Awwad et al, following the initialtreatment , the clinical picture may worsen during thefirst weeks in terms of infiltrate density, stromal scarring,conjunctival injection, and pain, especially if topical

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steroids or nonsteroidal agents have been used beforediagnosis and are stopped abruptly.13 However, clinicalworsening that develops after the first month can bedue to the worsening of the infection or cumulative drugtoxicity. In the absence of confocal microscopy, it maybe hard to differentiate these two entities, which requiretotally different treatment approaches. The authorsadvise tapering the medications and evaluating closely.13

Subsequent improvement denotes drug toxicity,whereas further deterioration indicates an underlyingintractable infection, which should be treated with morefrequent regimen and possibly higher drug concentra-tions.

The possibility of a coinfection with bacteria or fungishould be constantly borne in mind, and repeat cornealculturing and confocal examination should beperformed when in doubt.

Resistance to antiamoeba agents, such aschlorhexidine and PHMB, has not been documented,and treatment failure is due to lack of cornealpenetration and failure to reach cysticidal concentrationin deeper stroma in conditions in which the entire corneamay be involved. Hence, in vitro sensitivity testing isnot routinely performed.

IMIDAZOLES

Topical imidazoles, when used in a 1 percent solution,are effective against trophozoites, but not against cysts.23

They should never be used as monotherapy. Oralketoconazole and, to a lesser extent, itraconazole pene-trate into the cornea and are used by some practitionersas adjunctive therapy to PHMB and chlorhexidine. Thepenetration of these drugs into cornea is inappropriatefor them to act as trophozoiticidal agents and henceshould not be used alone.21

NEOMYCIN

Most cysts are resistant to neomycin which also has ahigh hypersensitivity rate and hence the use of neomycinis no longer recommended.23

ROLE OF CORTICOSTEROIDS

Corticosteroids suppress the activity of the macrophage,which is essential in scavenging and destroying theamoeba Thus, in general, it is recommended to delayand limit steroid use as much as possible. They are usedin only those patients with severe pain, stromal lysis,

scleritis, chronic ulcers or severe anterior-chamberinflammation under the cover of anti-amoebic drugs.24

Systemic immunosuppression with steroidscombined with antiamoeba therapy has also beendescribed to control pain and tissue destruction forintractable Acanthamoeba sclerokeratitis. In one study,20 eyes of 19 patients received systemic immunosup-pression with steroids during a mean period of7 months, with two eyes remaining in severe pain andnecessitating enucleation.14

SURGICAL TREATMENT

Various surgical procedures for Acanthamoeba keratitiswhich have been tried include penetrating keratoplasty,lamellar keratectomy with conjunctival flap and evenamniotic membrane transplantation.

PENETRATING KERATOPLASTY

The results of therapeutic keratoplasty in eliminatingthe infection in Acanthamoeba keratitis is variable. A curerate of 50 percent and a functional success rate of50 percent have been reported.25

The rate of recurrence of the infection in the graftafter therapeutic keratoplasty varies from 30-50percent.25 Ficker et al reported a recurrence rate of morethan 50 percent with poor graft survival.26 Due to a highrecurrence rate of Acanthamoeba in therapeutic graftsmedical control of infection has been recommended first.There should be a minimum gap of 3 months betweenthe complete resolution of Acanthamoeba keratitis onmedical therapy and optical penetrating keratoplasty.27

Meticulous management and frequent follow up ofcases after penetrating keratoplasty for upto 1 year isrequired as Acanthamoeba can recur in a graft.

LAMELLAR KERATOPLASTY

Lamellar keratoplasty with a conjunctival flap has beenused successfully in some patients.28

AMNIOTIC MEMBRANE TRANSPLANTATIONAmniotic membrane transplantation for progressivestromal lesions with persistent epithelial defects mayalso be effective in controlling inflammation anddelaying penetrating keratoplasty with good success.29

It is sometimes necessary to repeat the amniotic memb-rane transplantation to ensure complete re-epitheliali-zation.

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References1. Seal DV. Acanthamoeba keratitis update: incidence,

molecular epidemiology and new drugs for treatment.Eye 2003;17:893-905.

2. Hammersmith KM. Diagnosis and management ofAcanthamoeba keratitis.Curr Opin Ophthalmol 2006;17:327-31.

3. Butler TK, Males JJ, Robinson LP, et al. Six-year reviewof Acanthamoeba keratitis in New South Wales,Australia: 1997–2002. Clin Exp Ophthalmol 2005;33:41-6.

4. Claerhout I, Goegebuer A, Van Den Broecke C, et al.Delay in diagnosis and outcome of Acanthamoebakeratitis. Graefe’s Arch Clin Exp Ophthalmol 2004;242:648-53.

5. Radford CF, Minassian DC, Dart JK. Acanthamoebakeratitis in England and Wales: incidence, outcome, andrisk factors. Br J Ophthalmol 2002;86:536-42.

6. Sharma S, Garg P, Rao GN. Patient characteristics,diagnosis, and treatment of noncontact lens relatedAcanthamoeba keratitis. Br J Ophthalmol 2000;84:1103-8.

7. Hargrave SL, McCulley JP, Husseini Z. Results of a trialof combined propamidine isethionate and neomycintherapy for Acanthamoeba keratitis. Brolene StudyGroup. Ophthalmology 1999;106:952-7.

8. Beattie TK, Tomlinson A, MyFayden AK, et al. Enhancedattachment of Acanthamoeba to extended-wear siliconehydrogel contact lenses: a new risk factor? Ophthalmo-logy 2003;110:765-71.

9. Beattie TK, Tomlinson A, McFayden AK. Attachmentof Acanthamoeba to first and second-generation siliconehydrogel contact lenses. Ophthalmology 2006;113:117-25.

10. Hiti K, Walochnik J, Haller-Schober EM, et al. Viabilityof Acanthamoeba after exposure to a multipurposedisinfecting contact lens solution and two hydrogenperoxide systems. Br J Ophthalmol 2002;86:144-6.

11. Saviola JF. The current FDA view on overnight ortho-keratology: how we got here and where we are going.Cornea 2005;24:770-1.

12. Moore MB, McCulley JP, Kaufman HE, Robin JB. Radialkeratoneuritis as a presenting sign in Acanthamoebakeratitis. Ophthalmology 1986;93:1310-5.

13. Awwad ST, Petroll WM, McCulley JP, Cavanagh HD.Updates in Acanthamoeba keratitis. Eye Contact Lens2007;33:1-8.

14. Lee GA, Gray TB, Dart JK, Pavesio CE, Ficker LA, LarkinDF, et al. Acanthamoeba sclerokeratitis: treatment withsystemic immunosuppression. Ophthalmology 2002;109:1178-82.

15. Ehlers N, Hjortdal J. Are cataract and iris atrophy toxiccomplications of medical treatment of acanthamoebakeratitis? Acta Ophthalmol Scand 2004;82:228-31.

16. Kelley PS, Dossey AP, Patel D, et al. Secondary glaucomaassociated with advanced Acanthamoeba keratitis. EyeContact Lens 2006;32:178-82.

17. Parmar DN, Awwad ST, Petroll WM, et al. Tandemscanning confocal corneal microscopy in the diagnosisof suspected acanthamoeba keratitis. Ophthalmology2006;113:538-47.

18. Thebpatiphat N, Hammersmith KM, Rocha FN,Rapuano CJ, Ayres BD, Laibson PR, et al. Acanthamoebakeratitis: a parasite on the rise. Cornea 2007;26:701-6.

19. Grossniklaus HE, Waring GO IV, Akor C, et al.Evaluation of hematoxylin and eosin and special stainsfor the detection of acanthamoeba keratitis in penetrat-ing keratoplasties. Am J Ophthalmol 2003;136:520-6.

20. Wilhelmus KR, Liesegang TJ, Osato MS, et al. Laboratorydiagnosis of ocular infections. In: Specter SC, (Ed).Cumitech 13A. Washington DC, American Society ofMicrobiology, 1994;17.

21. Kaufman SC, Musch DC, Belin MW, et al. Confocalmicroscopy: A report by the American Academy ofOphthalmology. Ophthalmology 2004;111:396-406.

22. Larkin DF, Kilvington S, Dart JK. Treatment ofAcanthamoeba keratitis with polyhexamethylenebiguanide. Ophthalmol 1992;99:185-91.

23. Seal DV, Hayt J, Kirkness CM, et al. Successful medicaltherapy of Acanthamoeba keratitis with topicalchlorhexidine and propamidine. Eye 1996;10:413-21.

24. Seal DV. Acanthamoeba keratitis update: incidence,molecular epidemiology and new drugs for treatment.Eye 2003;17:893-905.

25. Park DH, Palay DA, Daya SM, et al. The role ofcorticosteroids in the management of Acanthamoebakeratitis. Cornea 1997;16:277-83.

26. Sony P, Sharma N, Vajpayee RB, Ray M. CLAO J.Therapeutic keratoplasty for infectious keratitis: Areview of the literature 2002;28:111-8.

27. Ficker LA, Kirkness C, Wright P. Prognosis for kerato-plasty in Acanthamoeba keratitis. Ophthalmology 1993;100:105-10.

28. Awwad ST, Parmar DN, Heilman M, et al. Results ofpenetrating keratoplasty for visual rehabilitation afterAcanthamoeba keratitis. Am J Ophthalmol 2005;140:1080-4.

29. Cremona G, Carrasco MA, Tytium A, et al. Treatmentof advanced Acanthamoeba keratitis with deep lamellarkeratectomy and conjunctival flap. Cornea 2002;21:705-8.

30. Bourcier T, Patteau F, Borderie V, et al. Amniotic memb-rane transplantation for the treatment of severe Acantha-moeba keratitis. Can J Ophthalmol 2004;39:621-31.

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4Pediatric Keratitis

Pediatric Keratitis11

IntroductionMicrobial keratitis is an important cause of ocularmorbidity and blindness in children. Children and theirfamilies are frequently unable to provide a completehistory of important risk factors such as previoustrauma, duration of symptoms and contact lens cleaningregimes. Older children may give incomplete or falseinformation because of fear of possible parental reprisalsfor circumstances surrounding the cause of keratitis.Poor co-operation may make the results of slit-lampexamination less reliable.

Epidemiology

PREVALENCE

In general children account for 11 percent of the casesaccording to a review of microbial keratitis in SouthernCalifornia.4 Recent figures of World Health Organizationsuggest that there are 1.5 million children blind world-wide and that 70,000 children annually have activecorneal involvement.2 It is of a greater concern in thedeveloping world; 22 percent of 201 patients admitted ata referral center in South Africa were under 16 years ofage.4

Most studies have described microbial keratitis inthe age group 16 years or younger.1,4,5,9,10 It is generallybelieved that corneal ulceration is not very common inchildren younger than 5 years. However, it has beenreported in children younger than 5 years in one studyfrom Northern India9 (Table 11.1).

There is no predilection for any eye and an almostequal number of right and left eye involvement has beennoted1, 4,10 (Table 11.1). Bilateral affections may alsooccur and have been attributed to systemic illness1,4,10

(Table 11.1).

REGIONAL DIFFERENCES

Just like the prevalence of different organisms respon-sible for adult microbial keratitis varies in differentregions in the world, the organisms responsible forchildhood keratitis also vary.

Gram-positive cocci are the commonest isolates inpediatric keratitis in Southern California (83%),4 NewOrleans / Philadelphia (54.6%)5 and India 751 and 85.5percent.9 However, in Florida,8 gram-negative bacilli(43.2%) are the most prevalent10.

In India, fungal infections were found to be relativelymore (17.2%)1 as compared to California (4%).4

Filamentous fungi are particularly more in Indiansubcontinent (14.1%)1 as compared to the Western world(2%).4

Predisposing FactorsRisk factors for the occurrence of pediatric keratitisinclude trauma, severe systemic illness, contact lenswear and pre-existing external eye disease.6

TRAUMA

Trauma is the leading predisposing factor of microbialkeratitis regardless of age and has been reported in24-44 percent cases (Table 11.2). The introduction of theorganism is through an epithelial defect or gap inepithelial bridges or is concurrent with penetrating orperforating corneal injury.10

SYSTEMIC FACTORS

Systemic illnesses associated with corneal ulcerationvary from region to region. These include eruptive feverssuch as measles, diarrhea and fever in India.1, 9 There isa high prevalence of Vitamin A deficiency leading to

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Specific Types of Keratitis

keratomalacia in Indian subcontinent (58.8% ofsystemic cases)1 and is especially important in cases withbilateral affection. Lower socio-economic status may besignificantly associated with the occurrence of cornealulceration.9

Measles associated corneal ulceration is also animportant cause of viral keratitis in the developingcountries unlike the developed countries.11 In a studyfrom Tanzania 25 percent of the unilateral cases and 57percent of the bilateral corneal ulcers occurred withinone month of the measles infection.11 Keratitis in measlesmay occur due to superadded herpetic infection. Ulcersassociated with measles are varying from typical measlesinduced superficial keratitis to frank ulceration, whichare generally epithelial and accentuated by desiccationdue to exposure.11

In the Western countries, systemic aspergillosis,bronchopulmonary dysplasia, Werdnig-Hoffmann’sdisease, neurofibromatosis, hydrocephalous and mal-development of brain have been reported as the risk

factors for the occurrence of pediatric microbial keratitis.5

In a study by Ormerod et al, systemic infections andmalignancies with orbital involvement were the mainsystemic associations of pediatric microbial keratitis.4

CONTACT LENS WEAR

Contact lens wear as a pre-disposing factor for microbialkeratitis has been reported in various western studiesand varies from 6.4 to 24.1 percent.4,5,10 However, contactlens wear is not an important predisposing factor inIndia1,5 (Table 11.1). Contact lenses are not routinelyprescribed in Indian subcontinent because of tropicalenvironment and socioeconomic constraints.9

Contact lenses predispose to keratitis especially inaphakic children . Orthokeratology is also an importantrisk factor for contact lens induced infection.

The extended wear lenses are more prone to contactkeratitis especially if the contact lens hygiene anddisinfection is not adhered to.

TABLE 11.1Demographic features of microbial keratitis in children

S. Author/ (Year) No. of eyes/ Age group Male/Female Right eye Bilateral SeasonalNo. No. of Children (%) Left eye (%) (%) affection (%) pattern

1. Ormerod et al4 47/44 <16 years 67/33 49/51 6.8 July to(1986) December

2. Cruz et al10 (1993) 51/50 <16 years 68/32 51/49 1.9 —3. Clinch et al5 (1994) 29/28 <16 years 64/36 — — —4. Kunimoto et al1 113/107 <16 years 56/44 51/49 5.6 May, June,

(1998) November5. Vajpayee et al9 50/50 <12 years 68/32 — 0 —

(1999)

TABLE 11.2Predisposing factors for microbial keratitis in children

Predisposing Factor (%) Ormerod4 Cruz10 Clinch5 Kunimoto1 Vajpayee9

Trauma 29.7 44 34.5 24 38Severe systemic illness 6.3 14 27.6 18 24Contact lens wear 6.4 12 24.1 0 0Exposure 25.5 — 24.1 — —Ocular surgery 4.2 24 20.7 10 —Congenital anterior segment 27.6 6 — — 12diseaseAcquired anterior segment 6 20 12diseaseOthers 17 12

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PRE-EXISTING EXTERNAL EYEDISEASE/SURGERY

Exposure keratitis4, 9 trichiasis,4 dry eye4 are importantin infancy and trauma and acquired external diseaseare more common in the school age group.4 Otherprevious eye diseases include spring catarrh, dacryo-cystitis, and conjunctivitis.9

Prior anterior segment surgery performed on thesame eye has also been reported as a risk factor in 8.8 to20.7 percent cases.1,5,10

OTHERS

Use of traditional eye medicines is common in develop-ing countries and has been shown to be associated withcorneal ulceration in 14 percent cases in a study fromTanzania.11

Etiology

MICROBIAL KERATITIS

Just like in adults, infectious microbial keratitis inchildren may be caused by bacteria, fungi, viruses orparasites.

Bacteria

Gram-positive cocci are the most frequently isolatedorganisms in cases of non-viral microbial keratitis inchildren (34-75%).5,9 However, in a series by Cruz et almore Gram-negative bacilli (43.2%) were identified ascompared to the gram-positive cocci.10

Staphylococcal species and Pseudomonas species havebeen isolated most commonly in cases of pediatriccorneal ulceration [Table 11.3]. Indigenous bacteria suchas non- coagulase positive Staphylococcus have also beenincreasingly reported in the recent times particularlyfrom the Indian subcontinent.9 This occurs especially ineyes, which have already been compromised by trauma,previous eye disease or systemic illness. Functional andmorphologic disturbances of the ocular surface in theseeyes facilitate infection by indigenous bacteria.

Pseudomonas aeruginosa infections are more commonin younger children as compared to older children. Inchildren under 3 years of age more than 50 percent ofcases have been reported to occur due to Pseudomonasunlike adults where 19 percent of the cases occurreddue to the same.4

Apart from these, there are myriad of other orga-nisms, which may be isolated from cases of microbialkeratitis in children (Table 11.3).

Childhood microbial keratitis may also be caused bypolymicrobial infections, which varies from 6.9 to 27percent (Table 11.4).

Viruses

Viral keratitis may also occur in children. Herpessimplex virus infection is the most common. Primaryherpetic infections as well as recurrences of the samemay occur.12 Herpes simplex infection has beenassociated in over one third of all cases of cornealulceration in children in one study.12 Primary herpesmanifests as typical vesiculated herpetic skin lesions,preauricular lymphadenopathy and follicular conjunc-tivitis with or without corneal involvement.

Those with recurrences have a previous episode oftypical primary herpes and are characterized by herpeticepithelial involvement alone, stromal keratitis or both.Epithelial involvement varies from punctuate epithelialkeratitis, areolar-stellate, linear dendritic or ameboid.

Fungus

In children the incidence of fungal keratitis is less ascompared to bacterial keratitis. Fungal infections mayoccur in 175 to 18.2 percent10 of the cases (Table 11.3).Aspergillus and Fusarium species are the most frequentlyidentified organisms (Table 11.3).

NON-MICROBIAL KERATITIS

Nutritional

Malnourished children are more prone to vitamin Adeficiency and measles induced corneal ulceration.Vitamin A deficiency leading to keratomalacia is themost important cause of bilateral corneal ulceration. Theulcers vary from small punched out, round, or ovalulcers involving corneal stroma to complete necrosis ofthe cornea.14

Vernal KeratoconjunctivitisThe abnormalities of ocular immune mechanisms foundin vernal keratoconjunctivitis predispose these patientsto microbial keratitis.14 Vernal keratoconjunctivitis maybe rarely associated with secondary bacterial infec-tion14,15 and fungal keratitis.16,17

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TABLE 11.3Non-viral microbes identified from cases of microbial keratitis in children

Organism Ormerod4 Cruz10 Clinch5 Kunimoto1 Vajpayee9

Total Bacteria 89.1Total Gram-positive cocci 34.1 54 75.0Staphylococcus epidermidis 17 2.3 5 23.4 60Staphylococcus aureus 17 20.5 1 20.3 8Streptococcus pneumoniae 20 6.8 2 18.8Streptococci species 29 4.5 12.5Total Gram positive bacilli 2.3 10.9Corynebacterium species 2.3 1 6.3Bacillus species 4.7Total gram-negative cocci 0 6.8 21 0.0Total gram-negative bacilli 43.2 21.9Pseudomonas aeruginosa 24 34.1 2 9.4 14.5Pseudomonas species 4.7Enterobacter species 2 4.5 1 3.1 3Proteus species 4.5 3.1Aeromonas species 1.6Hemophilus species 2 2.3 2Shigella species Klebsiella species 4.5Branhamella species 4.5

2.3Total Gram-negative bacilli-Non-fermenting 7 6.3Moraxella species 2.3 4.7Moraxella lacunata 1.6Total parasites 8 1.6Acanthamoeba species 2 1.6Total fungus 18.2 17 17.2Total filamentous fungi 14.1Aspergillus species 2 4.5 1 6.3 8.6Fusarium species 2 11.4 3.1 5.7Unidentified species 2.3 1 4.7Curvularia species 1Total yeast like fungiCandida species 1 3.1

DiagnosisThe child with suspected microbial keratitis shouldpreferably be immediately hospitalized. A detailedhistory should be taken and a meticulous clinicalexamination should not only include a detailed ocularexamination but also a relevant systemic evaluation.

HISTORYThe history may be elicited from the patient if the childis older or the parent if the child is younger. History

should be taken regarding the onset, duration and thepossible predisposing factors of corneal ulceration.History of prior treatment with topical medications(including antimicrobial and corticosteroids) should alsobe sought.

Apart from this, history should also be obtainedregarding any fever, rash or diarrhea prior to the onsetof or during the occurrence of corneal ulceration. Theimmunization status of the child should also be foundout especially against measles.

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In cases of contact lens wear, specific history shouldbe taken regarding the indication type and duration(daily wear or extended wear) of contact lens wear andthe contact lens hygiene including the cleaning anddisinfection regime.

CLINICAL EXAMINATION

Clinical examination of the child should not only includea detailed ocular examination but also relevant systemicexamination.

Systemic Examination

The systemic examination of the child should be donewith special reference to the nutritional status of thechild. Features suggestive of malnutrition or Vitamin Adeficiency should be evaluated and the child may alsobe examined by a pediatrician in such cases.

In suspected herpetic keratitis systemic features suchas typical vesiculated skin lesions and preauricularlymphadenopathy should also be evaluated.11

Ocular Examination

Standard protocol should be followed and daily slit lampbiomicroscopic examination should be undertaken.Children are difficult to examine with the slit lamp, asthey are uncomfortable, fearful and photophobic.Attempts to ameliorate their anxiety with toys andgames should be made. In case they do not allow aroutine examination, alternative examination undersedation and examination under anesthesia may alsobe considered, the details of which are described later.

Slit-lamp Biomicroscopy

A slit-lamp biomicroscopy is performed using a routineslit lamp microscope or a portable slit lamp microscope(Fig. 11.3). There are several useful aids for the routineslit lamp examination, which have been recommended:12

The base plate for Hruby lens of the Haag Streit slit lampshould be removed because it tends to press into theprotuberant abdomen of the thrusting or the strugglingchild. Technicians or nurses should not be allowed tohold the infant. The mother of the child should beencouraged to hold the child in her lap. The head of thechild should be steadied but extremely forceful pressingis discouraged since respiratory distress may occur dueto the compression of the laryngeal structures againstthe chin rest.

The size, extent and depth of the corneal ulcer,including the epithelial defect as well as the infiltrationshould be noted and documented (Figs 11.1 and 11.2).Fluorescein or Rose Bengal may directly be administeredrather than by controlled small drops from a glass rodor applicator stick to avoid injury. An associatedhypopyon or uveitis and involvement of the sclera, ifany should also be documented.

Ulcer characteristics of microbial keratitis in variousstudies is shown in Table 11.4.

INVESTIGATIONS

Investigation in a case of pediatric keratitis include theusual laboratory investigations for microbiologicaldiagnosis and relevant systemic investigations inselected cases.

Figure 11.1: Bacterial keratitis in a child Figure 11.2: Perforated corneal ulcer in a child

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not adhere to the standard protocol for obtaining aspecimen before starting antibiotic therapy. In childrenlack of patient co-operation should not preclude cornealscraping. Corneal scraping is feasible provided it is doneunder appropriate anesthesia.

Corneal scrapings may be obtained either undertopical anesthesia, topical anesthesia and sedation orgeneral anesthesia depending on the age of the childand his/her co-operation.

Topical Anesthesia

For topical anesthesia either 4 percent xylocaine or 0.5percent proparacaine is used. The latter is preferred asit is least epitheliotoxic.

Topical Anesthesia and Sedation

In most cases of pediatric keratitis, an additionalsedation is required. Chloral hydrate (50-100 mg/kg-body weight) is very commonly used for sedation.5

Sedation may also be achieved by a single intramuscularinjection of meperidine (2 mg/kg), promethazine (2 mg/kg) and chlorpromazine (1 mg/kg). Injection diazepam0.1 mg/kg has also been used for sedation.10

General Anesthesia

In unco-operative children general anesthesia should beused to obtain scraping.

Corneal scrapings should be obtained either with theplatinum spatula,3 Bard Parker blade1 or with the bent26-gauze needle9 from the base as well as the leadingedge of the ulcer. Routine Gram’s staining and KOH

Systemic Investigations

Nutritional status has been evaluated by comparingweight for age against Harvard standards in westernliterature11 and deficit in weight for height in Indianliterature.7

Serum Vitamin A levels may be measured by usinghigh-performance liquid chromatography, although thisinvestigation is not mandatory routinely.11

For herpes simplex keratitis enzyme-linked immuno-sorbent assay cultures may be obtained, although theseare not mandatory and should be only undertaken incase of a diagnostic dilemma.12

Laboratory Investigations

Many ophthalmologists assume that it is difficult toobtain a corneal specimen of a child and therefore do

TABLE 11.4Ulcer characteristics of Microbial keratitis in children

Ulcer characteristics Ormerod4 Cruz10 Clinch5 Kunimoto1 Vajpayee9

(%)

1. Hypopyon 32 - - - 322. Location

Central 47 63 52 52 58Paracentral 49 33 31 23 24Peripheral 4 4 14 25 2

3. Size of ulcer< 2 mm 30 25 31 31 512-6 mm 49 61 52 51 16>6 mm 21 14 14 19

Figure 11.3: Hand-held slit lamp biomicroscope

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wet mount preparation is done to examine the smearsof corneal scrapings.

The specimens obtained should be sent for inocula-tion onto sheep blood agar, chocolate agar and thio-glycolate broth, all incubated at 37 deg C. Sabouraud’sagar plates supplemented with yeast extract and50 micrograms/ml gentamicin sulphate (withoutcyclohexamide) should also be inoculated at 200C tocheck for fungal infection. In suspected cases forAcanthamoeba, non-nutrient agar overlaid withEscherichia Coli should be inoculated.

The culture positivity and polymicrobial involve-ment in pediatric microbial keratitis is shown inTable 11.5.

Management

The management of a case of pediatric keratitis shouldinclude not only the standard medical therapy for ocularaffection but also for systemic diseases.

Attention should be particularly given to thenutrition and vitamin A therapy especially in cases ofkeratomalacia. All children with keratomalacia shouldreceive vitamin A supplement as per the WHOrecommendation.13

Vitamin A supplementation can be given orally,parenterally or both. The initial dose is 200,000IU in oil(110 mg of retinal palmitate or 66mg retinal acetate) or,if necessary, 200,000 IU of water soluble vitamin Aintramuscularly. The next day an additional 200,000 IUof vitamin A should be given. For children less thanone year of age half of these doses are given. Childrenwho are at high risk may require a repeat dose of vitaminA at 4 to 6 months.

TABLE 11.6Therapy in cases of microbial keratitis in children

Ormerod4 Cruz10 Clinch5 Kunimoto1 Vajpayee9

Medical 72% 86% 79% 84% 94%therapySurgical 28% 14% 21% 16% 4%intervention

TABLE 11.7Safe Anti-microbials in pediatric age group

Antibacterial agents1. Ciprofloxacin eye drops 3 mg/ml2. Ofloxacin eye drops 3 mg/ml3. Tobramycin 14 mg/ml4. Gentamicin 14 mg/ml5. Amikacin 20 mg/ml6. Cefazolin 50 mg/ml7. Ceftazidime 50 mg/ml8. Chloramphenicol 3 mg/ml9. Vancomycin 50 mg/ml

Antifungal agents10. Natamycin 50 mg/ml11. Amphotericin B 0.1-0.25%

Antiviral agents12. Vidarabine 3 mg/ml13. Acyclovir 3 mg/ml

MEDICAL THERAPY

Most ulcers respond to medical therapy alone, althoughpenetrating keratoplasty may be required in some eyes5,9

(Tables 11.6 and 11.7). Concern for maintenance ofadequate corneal antibiotic levels by topical applicationin crying, unco-operative children has led someresearchers to advocate repeated sub-conjunctivalinjections under chloral hydrate sedation3. However, wedo not generally recommend the use of sub-conjunctivalantibiotics to treat microbial keratitis.

Bacterial Keratitis

We advocate that initial medical therapy should includea combination of fortified antibiotic drops of cefazolinsodium (5%) and tobramycin sulphate (1.3%) at frequentintervals which may vary initially from half hourly totwo hourly intervals for the initial 48 hours. Subsequent

TABLE 11.5Culture positivity and polymicrobial involvement inpediatric microbial keratitis

S. Author Culture PolymicrobialNo. (Year) positivity involvement

(%) (%)

1. Ormerod et al4 (1986) 87 272. Cruz et al10 (1993) 86.3 11.73. Clinch et al5 (1994) 75.8 6.94. Kunimoto et al1 (1998) 56.6 15.95. Vajpayee et al9 (1999) 70 —

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modifications in the choice of antibiotics and theirdosage depend on the results of culture and sensitivitypattern and clinical response. Alternatively, mono-therapy with ciprofloxacin eye drops 0.3 percent mayalso be used if the ulcers are small and do not involvepupillary axis.1

Fungal Keratitis

In case of identification of fungus in a smear, 5 percentnatamycin drops should be instilled at 5 times a dayalong with the antibacterial medications.

Tablet ketoconazole (200 mg) may be administeredtwice daily (after liver function tests) in patients inwhom the fungal corneal ulcer is greater than 6 mm indiameter, deeper than anterior half of stroma or ifanterior chamber exudates are present.1

Herpetic Keratitis

For herpetic keratitis in children, topical application ofacyclovir ointment five times a day is given. However,in crying and unco-operative children this may be aproblem and so debridement alone as an alternative maybe tried (especially in clinics where out patientanesthesia is available).12 Debridement should be doneunder the microscope, and a cycloplegic agent and theeye is patched.12 Oral Acyclovir in children < 8 years ofage should be used as an adjunct in addition to topicaltherapy in the dose of 12-20 mg/kg body weight. It iseffective in treating active infectious epithelial keratitis,in prophylaxis of children prone to recurrent infectiousepithelial disease and for prevention of infectious diseasein children being treated with topical corticosteroidsmedications for immune stromal keratitis.18

Topical steroids are rarely necessary, but parentsshould be alerted to the symptoms of recurrent stromalkeratitis such as photophobia. Recurrences should betreated promptly with assessment of the severity of thestromal keratitis. Corticosteroids should be employedwhen the lesions are central and severe and selectivelyin cases of marginal stromal keratitis as this may induceirregular astigmatism without their use. With the use ofcorticosteroids, attention should be given to the possibleside effects, which should include ocular hypertensionand possible subcapsular cataracts. Their use requiresslit lamp examination, frequent observation of the opticdiscs through dilated pupils and evaluation of intra-ocular pressure on a regular basis.12

Acanthamoeba Keratitis

Cases of Acanthamoeba keratitis are treated with topicalpolyhexamethylene biguanide (0.02%) drops and 0.1%propamidine isoethionate every hour for 3 days. Thetherapy is subsequently tapered Improvement is seenwithin 2-3 weeks following which qid doses of drugsare given.

Apart from the antimicrobial agents, supportivetherapy should include cycloplegics, antiglaucoma drugsand lubricants.

FOLLOW-UP

Follow-up and monitoring of these patients should bedone daily and sedatives and general anesthesia shouldbe used whenever and wherever it is deemed necessaryfor such examinations.

Absence of symptoms, disappearance of circum-corneal congestion, absence of infiltration and lack offluorescien staining are criteria for healed corneal ulcer.

SURGICAL THERAPY

Surgery for the management of pediatric cornealulceration may also be required in some cases. Surgicalintervention may be required in 4 to 28 percent of theeyes as highlighted in various studies (Table 11.6). In astudy from our center the pediatric keratoplasty wasdone for infectious keratitis and keratomalacia in nearlytwo-thirds of the eyes.19

Apart from penetrating keratoplasty, lamellar kerato-plasty, cyanoacrylate glue application, conjunctival flapand enucleation may be undertaken in these cases, asdeemed necessary. The visual prognosis after penetrat-ing keratoplasty in children for microbial keratitis isgenerally poor. Clear grafts have been reported in only12.5 percent of the cases requiring keratoplasty in onestudy.1

POST-RESOLUTION MANAGEMENT

The various outcomes following microbial keratitis inchildren include corneal scars, adherent leukomas,glaucoma, anterior staphyloma, and disorganizedglobe.1,5,9 However, the most frequent outcome is thepresence of a corneal scar.1,9

The visual acuity after resolution/treatment ofpediatric keratitis depends on the severity of the cornealulcer and the promptness of therapy. Poorer visual

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acuities may be obtained, which does not commensuratewith the extent of the corneal involvement. This has beenattributed to the anisometropic or stimulus deprivationamblyopia and permanent failure to develop stereopsisespecially if the corneal opacification occurs in the earlyyears. Hence, the ophthalmologist should be vigilant inthe postoperative period to institute anti-amblyopiatherapy as and when required.

PREVENTION

In general accidents and injuries in children should beavoided and precautions should be undertaken toprevent the same. Likewise Vitamin A deficiency shouldbe prevented. Sufficient Vitamin A should be availablein the diet and supplementation should be donewhenever required as per the WHO guidelines. Earlydiagnosis and treatment of Vitamin A should be apriority in areas where protein energy malnutrition isprevalent.11 Complete immunization protocol forchildren should be followed and children should beespecially immunized against measles. Use of traditionaleye medications for minor eye ailments should bediscouraged.11 Any eyes with prior ocular surfacedisease or anterior segment surgery should be undervigilance and an early diagnosis and prompt treatmentof corneal ulcers in these cases is mandatory.

In cases of contact lens wear the parents and thechildren should be educated about the contact lenshygiene and proper handling. The pediatrician and theneonatologist should be made aware of the predisposingfactors of keratitis.

References

1. Kunimoto DY, Sharma S, Reddy MK, Gopinathan U,Jyothi J, Miller Rao GN. Microbial keratitis in Children.Ophthalmology 1998;105:252-7.

2. Underwood BA. Update: Xerophthalmia, keratomalaciaand child mortality including measles. In: Kupfer C,Gillen T (Eds): World Blindness and its Prevention . Vol.4. Oxford.

3. Coster DJ, Wilhelmus K, Peacock J, Jones BR. Suppu-rative keratitis in London. In: Trevor Roper PD (Ed):With Congress of the European Society of Ophthalmo-

logy; The cornea in health and disease. LondonAcademic Press, 1981;395-8.

4. Ormerod DL, Murphree AL, Gomez DS, Schanzlin DJ,Smith RE. Microbial keratitis in Children. Ophthal-mology 1986;449-55.

5. Clinch TE, Palmon FE, Robinson MJ, Cohen EJ, BarronBA, Laibson PR. Microbial keratitis in Children. Am JOphthalmol 1994;17:65-71.

6. Gudmundsson OG, Ormerod LD, Kenyon KR, GlynnRJ, Baker AS, Haaf J, et al. Factors influencing predilec-tion and outcome in bacterial keratitis. Cornea 1989;8:115-21.

7. Ormerod LD, Hertzmark E, Gomez DS, Stabiner RG,Schanzlin DJ, Smith RE. Epidemiology of microbialkeratitis in southern California. A multivariate analysis.Ophthalmology 1987;94:1322-33.

8. Alexandrakis G, Alfonso EC, Miller D. Shifting trendsin bacterial keratitis in South Florida and emergingresistance to fluoroquinolones. Ophthalmology 2000;107:1497-502.


10. Cruz OA, Sabir SM, Capo H, Alfonso EC. Microbialkeratitis in childhood. Ophthalmology 1993;100:192-6.

11. Foster A, Sommer A. Corneal ulceration, measles, andchildhood blindness in Tanzania. Br J Ophthalmol1987;71:331-43.

12. Poirier RH. Herpetic ocular infections of childhood. ArchOphthalmol 1980;98:704-6.

13. Sandford-Smith JH, Whittle HC. Corneal ulcerationfollowing measles in Nigerian children. Br J Ophthalmol1979;63:720-4.

14. Cameron JA. Shield ulcers and plaques of the cornea invernal kerato conjunctivitis. Ophthalmology 1995;102:985-93.

15. Kerr N, Stern GA. Bacterial keratitis associated withvernal kerato conjunctivitis. Cornea 1992;11:355-9.

16. Sridhar MS, Gopinathan U, Rao GN. Fungal keratitisassociated with vernal keratoconjunctivitis. Cornea 2003;22:80-1.

17. Gupta A, Sharma A, Mohan K, Gupta A. Mycotickeratitis in non-steroid exposed vernal keratoconjunc-tivitis. Acta Ophthalmol Scand 1999;77:229-31.

18. Schwartz GS, Holland EJ. Oral acyclovir for the manage-ment of herpes simplex virus keratitis in children.Ophthalmology 2000;107:278-82.

19. Dada T, Sharma N, Vajpayee RB. Indications for pediat-ric keratoplasty in India. Cornea 1999;18:296-8.

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Contact Lens Related Keratitis12

IntroductionContact lens induced keratitis is an ocular emergencythat requires immediate and appropriate treatment tolimit corneal morbidity and vision loss. Contact lenswear is the most common predisposing factor forinfectious keratitis in patients with previously healthyeyes.

EpidemiologyThe incidence rates for bacterial microbial keratitis rangefrom approximately 2/10,000 per year for rigid contactlens, 2.2-4.1/10,000 per year for daily-wear soft contactlens, to 13.3-20.9/10,000 per year for extended-wear softcontact lenses. The risk with therapeutic contact lensesis much higher: 52/10,000 per year.1

Risk FactorsThe major risk factors in the development of contact lensrelated infectious keratitis include corneal trauma,exposure to polluted water, use of home made salinefor disinfection, improper lens care and poor compliancewith contact lens cleaning solutions, overnight wear andextended wear schedules.2,3

Overnight usage for soft contact lenses is associatedwith a higher risk and this increases with increasingnumber of nights of continuous wear.4

Higher risks of contact lens induced keratitis havealso been related to lower socioeconomic status, smokingand patients with the acquired immunodeficiency virus.

PathogenesisThe pathogenesis of the contact lens induced keratitis isrelated to the factors related to the alterations producedin the dynamics of the tear film and the ocular surface

due to contact lenses, contact lenses per se and thecontact lens care systems.

ALTERED TEAR DYNAMICS DUE TOCONTACT LENSES

Contact lenses have significant effect on the tear film,resulting in increased tear evaporation, stimulation ofreflex tearing, a decreased blink rate, alteration in tear-film osmolarity and trapped debris with tear stagnationunder the lens. Epithelial erosions from corneal desicca-tion manifest as coarse punctate erosion in the centralor paracentral cornea or with nasal and temporalperipheral staining of the cornea adjacent to the edge ofthe lens.

The normal cornea obtains oxygen by diffusion fromair when the eye is open and from the tarsal and bulbarconjunctiva when the eye is closed. Contact lens wearcauses a wide spectrum of changes in the cornea andconjunctiva such as an induced hypoxia and hyper-capnia.5 This causes a reduction in the corneal epithelialmetabolic rate and accumulation of stromal lactic acidwhich leads to a compromised epithelial junctional inte-grity, resulting in epithelial fragility, abrasion,6 punctatekeratitis and susceptibility to microbial invasion.7 Amore permanent effect of stromal acidosis is endothelialpolymegathism, characterized by an increased variationin corneal endothelial cell size. More severe changes ofpolymegathism occur with increased duration of contactlens wear.8,9

Additionally, allergic or toxic responses can occurrelated to deposits that form on the lens surface or toreactions against sensitizing preservative solutions.

CONTACT LENSES

The presence of contact lenses and the contact lensdeposits increases bacterial adherence. Multiple factorsplay a role in mediating bacterial adherence to the

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4Contact Lens Related Keratitis

contact lens including net surface charge of bacteria,carbohydrate adhesions, the biofilm, exotoxins andendotoxins. Bacteria have mechanisms to adhere tocontact lens surfaces, especially worn lenses withcomponents of mucin and proteins from the tear film.10

The rapid production of a biofilm on the lens furtherincreases the bacterial attachment. The adherence ofbacteria on the lens surface allows the development ofa glycocalyx and biofilm to form and convert adheringbacteria into replicating bacteria colonizing the lenssurface with a stronger attachment. The glycocalyx is apolysaccharide (slime) containing structure lying outsidethe outer membranes of Gram-positive and Gram-negative organisms.11,12 Organisms can also reach thecontact lens from the conjunctival flora or other environ-mental sources.13 These biofilms may explain howcomplaint patients or patients with uncontaminatedcontact lens cases can have a source of organisms.

The insertion and removal process can injure thecornea by lens deposits or defects, by chemical toxicityof contact lens disinfectants, or by lens-induced hypoxia.Oxygen transmissibility is also an important factor incontact lens associated ulcerative keratitis. The chancesof visually significant infections with overnight wearingof contact lenses are always significant.

CONTAMINATION OF CONTACT LENS CARESYSTEMS

Contact lens case contamination results from a combi-nation of poor hygiene and the failure of currentdisinfection systems.14-18 Disinfection by chlorine isassociated with a higher contamination rate comparedwith chemical, hydrogen peroxide, chlorhexidine, orheat.19 Contamination of rigid gas permeable lens casesis associated with increasing age of the contact lens. Theuse of contaminated tap water or home made salinesolutions may also cause keratitis.17,20 Other featureswhich influence the contamination of the lens caseinclude the patient’s hygiene and the surroundingsocioeconomic environment.21

Biofilm formation has been demonstrated on contactlenses and contact lens cases even after appropriatesterilization.13, 20

OrganismsAlthough the bacterial infections are most prevalent,fungi, parasites and viruses can also cause the infec-tions.5 Approximately one third of contact lens related

microbial keratitis is associated with Gram-positivecocci, such as Staphylococci and Streptococci, but twothirds is associated with gram-negative rods, especiallyPseudomonas aeruginosa.5-7,14,15 Fungi are relativelyinfrequent and account for 3 percent of infections,occurring more commonly following the usage oftherapeutic contact lenses as compared to the cosmeticor aphakic contact lenses. Acanthamoeba keratitis hasbeen associated with both hard and soft contact lenses,although daily wear soft contact lens wearers are morefrequently involved.14-18

CLINICAL FEATURES

Patients usually present with symptoms of progressivediscomfort, limbal or conjunctival hyperemia, photo-phobia, muco-purulent exudates and decreased vision.The contact lens induced keratitis may manifest as aninfiltrative keratitis or an ulcerative keratitis. Theinfiltrates associated with contact lens wear may or maynot be clinically significant Sweeney et al have classifiedthe events related to contact lens wear into seriousevents, clinically significant events and clinically nonsignificant events22 (Table 12.1).

Microbial Keratitis

The symptoms in cases of microbial keratitis includesevere limbal and bulbar redness, rapid onset ofmoderate to severe pain, decreased visual acuity, muco-purulent or purulent discharge, tearing, photophobia,and lid edema.

Microbial keratitis in a contact lens wearer ischaracterized by excavation of the corneal epithelium,Bowman’s layer, and stroma with infiltration andnecrosis of tissue. Focal infiltrates are usually large(> 1 mm) and irregular with small satellite lesions andsignificant diffuse infiltration. Infiltrates are mainlyfound in the central or paracentral region.

TABLE 12.1Events related to contact lens wear

I. Clinically non-significantAsymptomatic infiltrative keratitisAsymptomatic infiltrates

II. Clinically significantContact lens related peripheral ulcer (CLPU)Contact lens related acute red eye (CLARE)Infiltrative keratitis

III. Serious: Microbial keratitis

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Contact Lens Induced Peripheral Ulcer

The symptoms of a case of contact lens induced peri-pheral ulcer (CLPU) include limbal and bulbar rednessand tearing. Patients experience severe to moderate pain,foreign body sensation, or irritation or could even beasymptomatic.

It is associated with an inflammatory reaction of thecornea characterized in its active stage by focal excava-tion of the epithelium, infiltration, and necrosis of theanterior stroma. Small (up to 2 mm), single, circular focalinfiltrates with slight diffuse infiltration surrounding thefocal infiltrates are present in the midperiphery toperiphery of the cornea (Figs 12.1 and 12.2).

Contact Lens Induced Red EyeThe symptoms in a case of contact lens induced red eyeinclude moderate to severe circumferential redness,irritation to moderate pain, tearing, and photophobia.Patients are awakened by their symptoms or notice themsoon after waking.

There is an inflammatory reaction of the cornea andthe conjunctiva immediately following eye closure. Smallmultiple focal infiltrates and diffuse infiltration in themidperiphery to periphery of the cornea are present,generally without punctate staining overlying theinfiltrate.

Infiltrative KeratitisThe symptoms in a case of infiltrative keratitis includemild to moderate irritation, redness, and occasionaldischarge.

In infiltrative keratitis there is an inflammatoryreaction of the cornea characterized by anterior stromalinfiltration, with or without epithelial involvement, inthe mid periphery to periphery of the cornea. Infiltratesare small, possibly multiple, with or withoutaccompanying mild to moderate diffuse infiltration.

Asymptomatic Infiltrative Keratitis

Asymptomatic infiltrative keratitis is defined as aninflammatory event characterized by infiltration of thecornea without patient symptoms.

There are small focal infiltrates (up to 0.4 mm) withor without mild to moderate diffuse infiltration in theperiphery of the cornea. It is associated with punctatestaining after instillation of fluorescein and may beassociated with mild to moderate limbal and bulbarredness.

Asymptomatic Infiltrates

There are very small focal infiltrates (0.2 mm) and/ormild, diffuse infiltration with no staining overlying theinfiltrates after instillation of fluorescein. Infiltrates werecommonly peripheral but could be found across thecornea (Fig. 12.3).

Management

The management of contact lens induced keratitisconsists of management of microbial keratitis andinfiltrates.

Figure 12.1: Contact lens induced peripheral ulcerFigure 12.2: Contact lens induced peripheral ulcer in a full thicknessgraft

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MICROBIAL KERATITIS

Corneal scrapings for smears and culture should beobtained prior to initiation of antimicrobial therapy forinfectious keratitis. Specimens should be directlyinoculated onto standard media – blood, chocolate, andSabouraud dextrose agar and thioglycolate broth. KOHand Gram-stained smears of corneal scrapings help inthe identification of pathogens such as Staphylococcus(Fig. 12.4) Pseudomonas (Fig. 12.5) and Acanthamoeba(Fig. 12.6) as well as fungal elements. In contact lenswearers, culturing lens care solutions and the contactlens care may be helpful in establishing the diagnosis.

Although Acanthamoeba cysts and trophozoitesobtained from corneal scrapings can be stained withGram stain, as well as with giemsa, trichrome, periodicacid – Schiff (PAS), Gomori methenamine silver (GMS),and hematoxylin and eosin stain, calcofluor white achemofluorescent vital stain, is also very useful. It bindsto chitin and cellulose in the cell walls of fungi andAcanthamoeba cysts. Yeast, fungal elements andAcanthamoeba cysts show bright apple-greenfluorescence against a reddish-orange background. Anindirect immunofluorescent staining technique andfluorescien-conjugated lectins may also be usedfor Acanthamoeba species identification, but these

Figure 12.3: Asymptomatic infiltrateFigure 12.4: Microbial keratitis (Staphylococcus) in a contact lenswearer

Figure 12.5: Microbial keratitis (Pseudomonas) in a contact lenswearer

Figure 12.6: Microbial keratitis (Acanthamoeba) in a contact lenswearer

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techniques require a fluorescent microscope forvisualization.

Corneal scrapings inoculated on a non-nutrient agarwith an overlay of Escherichia coli or other Gram-negativeorganism enhances the recovery of Acanthamoeba. Thepresence of Acanthamoeba trophozoites is indicated bya snail-tract clearing through the layer of bacteria.

Antibiotic therapy is instituted according to theisolated organism. Fortified cefazolin sodium 5 percentand tobramycin 1.3 percent is initiated after preliminarycorneal scraping is done. Topical antibiotic therapy isaltered in accordance to the culture sensitivity reportsand clinical progress. They are given at one hourlyfrequency for the initial 48 hours. Following a clinicalresponse the fortified antibiotics are tapered to 2 hourlypregnancy and subsequently 4 hourly. Anti-acantha-moeba treatment is initiated in cases with positiveAcanthamoeba cysts. The long-term maintenance ofanti-acanthamoeba therapy is important along with closeand regular follow-up.

STERILE INFILTRATES

If a sterile infiltrate is suspected, the contact lens shouldbe removed immediately. A topical antibiotic such as afluoroquidone (0.3% ofloxacin) or 0.3% ciprofloxain qicshould be used which is effective against Pseudomonasand the eye should be re-examined after 24 hours. Inour experience, discomfort is substantially reducedwithin 24 hours of removing the contact lens, if theinfiltrate is sterile.

Withholding antibiotic therapy for 24 hours after thecontact lens is removed is an alternative approach. Thisapproach, without the addition of other therapy shouldbe undertaken only when the ophthalmologist is verysure that the patient will return 12-24 hours after theinitial examination. If, by this time, the patient discom-fort increases as does fluorescien staining, stromaledema, and infiltration, therapy for bacterial infectionis initiated.

However, if symptoms diminish or abate after theinitial 12-24 hours and if the corneal signs decrease,therapy is again withheld and the patient is asked toreturn again in 24 hours for further observation. After48 hours of observation without therapy, a sterileinfiltrate typically becomes more translucent and, overthe next several days, will continue to improve orresolve. In such instances, when the patient is symptom-free (especially if the infiltrate is outside the visual axis),

there is no need for further treatment. However, ifdiscomfort or disturbed vision continues to persist, thepatient may demand a more rapid resolution ofsymptoms. In these rare situations, topical corticosteroidtherapy may be administered. We suggest commencingtopical corticosteroid treatment, usually two to threedrops of 1 percent prednisolone acetate daily, only afterocular symptoms have diminished spontaneously afterremoval of the contact lens and there is no increase influorescein staining, stromal edema, or infiltrate size ordensity over the course of 2-3 days after the initialdiagnosis. It is mandatory to attempt this approach onlyin those patients who can be confided to comply withfollow-up schedules and who can be seen daily for thefirst few days.

PREVENTIONDisinfection resistant biofilms must be disruptedregularly by scrubbing all internal surfaces of the contactlens case with a cotton ball or Q-tip moistened with thecontact lens cleaner. The contact lens case should be heatdisinfected with hot water exposure periodically,followed by air-drying and the case should be replacedperiodically. We recommend the use of daily disposablecontact lenses as they are associated with decreasedchances of infection.

References1. Liesegang TJ. Contact Lens - Related Microbial Keratitis:

Part-I: Epidemiology Cornea 1997;16:125-31.2. Lisegang, Dart JK, Stapleton F, Minassian D. Contact

lenses and other risk factors in microbial keratitis. Lancet1991;338:650-3.

3. Poggio EC, Glynn RJ, Schein OD, et al. The incidence ofulcerative keratitis among users of daily - wears andextended - wear soft contact lenses. N Engl J Med 1989;321:779-83.

4. Schein OD, Buehler PO, Stamler JF, et al. The impact ofovernight wear on the risk of contact lens-associatedulcerative keratitis. Arch Ophthalmol 1994;112:186-90.

5. Bruce AS, Brennan NA. Corneal pathophysiology withcontact lens wear, sur. Opthalmol 1990;35:25-58.

6. Madigan MC, Holden BA, K wok LS. Extended wear ofcontact lenses can compromise corneal epithelialadhesion. Curr Eye Res 1987;6:1257-60.

7. Holden BA, Sweeney DF, Vannas A, Nilsson KT, EfronN. Effects of long-term extended contact lens wear onthe human cornea. Invest Opthalmol Vis Sci 1985;26:1489-501.

8. Carlson KH, Bourne WM, Brubarker RF. Effect of longterm contact lens wear on corneal endothelial cell

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morphology and function. Invest Opthalmol Vis Sci1988;29:185-93.

9. Mac Rae SM, Matsuda M, Shellans S, Rich LF. The effectof hard and soft contact lenses on the cornealendothelium. Am J Opthalmol 1986;102:50-7

10. Aswad MI, John T, Barza M, Kenyon K, Baum J. Bacterialadherence to extended wear soft contact lenses.Ophthalmology 1990;296-302.

11. Costerton JW, Irvin RT, Cheng KJ. The bacterialglycocalyx in nature and disease. Annu Rev Microbiol1981;35:299-324.

12. Elder MJ, Stapleton F, Evans E, Dart JK. Biofilm relatedinfections in ophthalmology. Eye 1995;9:105-9.

13. Sulsher MM, Myrvik QN, Lewis JC, Gristina AG.Extended wear lenses, biofilm and bacterial adhesion.Arch Ophthalmol 1987;105:110-5.

14. Collinus MJ, Carney LG. Patient compliance and itsinfluence on contact lens wearing problems. Am JOptom Physiol Opt 1986;63:952-6.

15. Chun MW, Weissman BA. Compliance in contact lenscare. Am J Optom Physiol Opt 1987;64:274-6.

16. Sokol JL, Mier MG, Bloom S, Asbell PA. A study ofpatient compliance in contact lens wearing populationCONTACT LENSAO J 1990;16:209-13.

17. Donzis PB, Mondino BJ, Weissman BA, Bruckner DA.Microbial contamination of contact lens care systems.Am J Ophthalmol 1987;104:325-33.

18. Bowden FW, Cohen EJ, Arentsen JJ, Laibson PR. Patternsof lens care practices and lens product contaminationin contact lens associated microbial keratitis. CONTACTLENSAO J 1989;15:49.

19. Contact lensark BJ, Harkins LS, Munro FA, DevonshireP. Microbial contamination of cases used for storingcontact lenses. J Infect 1994;28:293-304.

20. Devonshire P, Munro FA, Abernethy C. Contact lensarkBJ. Micorbial contamination of contact lens cases in thewest of Scotland. Br J Opthalmol 1993;77:41-5.

21. Dart J. Contamination of contact lens storage cases. Br JOphthalmol 1990;74:129-30.

22. Sweeney DF, Jalbert I, Covey M, Sankaridurg PR, VajdicC, Holden BA, et al. Clinical characterization of cornealinfiltrative events observed with soft contact lens wear.Cornea 2003;22:435-42.

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Infectious CrystallineKeratopathy

13

IntroductionInfectious crystalline keratopathy is a specific entity seenmost frequently following keratoplasty. It manifests asan indolent corneal infection with needle-like branchingcrystalline opacities.1,2 Although there are no actualdeposition of crystals, the term “crystalline” refers tothe characteristic appearance of these lesions.2

Risk FactorsThe most common risk factor responsible for theoccurrence of ICK is prior ocular surgery and steroiduse. ICK never occurs as a primary disease in apreviously healthy cornea. It occurs most often followingpenetrating keratoplasty4 although it has also beenreported after other surgeries such as epikeratoplasty,5

corneal relaxing incisions,6 LASIK7 and followingglaucoma filtering surgery with postoperative sub-conjunctival 5-fluorouracil (Table 13.1).8

ICK may also occur in eyes with post-herpeticpersistent epithelial defects treated with bandage softcontact lenses,2,4 and topical anesthetic abuse.9 One ormore of these factors may also co-exist. In cases ofpenetrating keratoplasty, acute herpes simplex keratitis,Acanthamoeba keratitis and topical anesthetic abuse,persistent epithelial damage occurs, which acts as aportal of entry for bacteria.9

Systemic and topical immunosuppression have alsobeen known to be predisposing factors for the develop-ment of ICK.10 Eyes, which have been previously treatedwith long-term topical corticosteroids, and topical anti-microbials are also predisposed.

EtiologyICK is usually caused by an alpha-hemolytic strepto-coccus in majority of cases (Table 13.2). Other causativebacteria which have been reported include peptostrepto-coccus,11 nutritionally variant Streptococci,12 haemophilus

TABLE 13.1Factors associated with ICK

Ocular factorsOcular surgery

1. Corneal transplant (most common)2. Epikeratophakia3. Relaxing incisions4. Glaucoma filtering surgery with postoperative

subconjunctival 5-fluorouracil5. Laser in situ keratomileusis

Ocular surface disorders1. Persistent epithelial defect2. Chronic herpetic keratitis3. Ocular cicatricial pemphigoid4. Corneal scars5. Acanthamoeba keratitis6. Exposure keratitis

Topical drugs1. Corticosteroids (Prednisolone acetate, betamethasone,

dexamethasone)2. Antibiotics (Bacitracin eye ointment, neo-poly B.,

Sulphacetamide, gramacidine, gentamicin, tobramycin,ciprofloxacin, cefazolin)

3. Anesthetic abuse-Proparacaine HCl4. Antiglaucoma-timolol maleate, apraclonidine5. Antivirals-Trifluridine6. Others-atropine, cyclosporin, NaCl ointment, unpreser-

ved tears, chlorhexidine.

Systemic factor1. Systemic immunosuppression

aphrophilus,13 coagulase-negative staphylococci14

pseudomonasi15 propionibacterium acnes16and mixedinfection with Mycobacterium fortuitum and pseudomonasaeruginosa15 and streptococcus pneumoniae (Table 13.3).3

Fungal organisms may also cause ICK. These includeCandida albicans (mixed with Staphylococcus epidermidis

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4Infectious Crystalline Keratopathy

and Staphylococcus hemolyticus),17 and Candida tropicalis18

(Table 13.2). Other rare organisms which have beenreported are Stenotrophomonas19 and enterococcalinfections.20 Recurrent ICK caused by two differentorganisms in two successive grafts in the same patienthave also been reported due to Streptococcus viridans andCandida albicans.21 ICK has also been reported to occurdue to non-tuberculous mycobacteria after LASIK.22

PathogenesisPredilection for alpha-hemolytic streptococci to causeinfection in ICK is unknown. These bacteria are thepredominant inhabitants of the oral cavity and upperairway and may rarely inhabit the normal flora of the

eyelids or conjunctiva. Access to the corneal stromaappears to occur via breaks in the corneal surface orthrough sutures.

It is unclear whether this is due to intrinsic propertiesof the organisms or whether the corneal stroma providesa marginal environment for bacterial replication.Glycocalyx production which is characteristically seenin these cases may shield the organisms from immunerecognition, decreasing the inflammatory response,which is suppressed further by the chronic use of topicalcorticosteroids.23

Although the reason for the crystalline growthpattern of the lesions is not known, it is possibly relatedto the criss-cross lamellar architecture of the cornealstroma and represents the path of least resistance to theexpanding bacterial colonies.

Characteristically intralamellar pockets of bacteriawithin the corneal stroma are isolated in a single lamellarplane. There is a distinct paucity of inflammatory cellsof any type. The overlying epithelium is often intact, ifan accompanying disease process has not altered it.Collagen lamellae adjacent to the collections of bacteriaare undisturbed with no evidence of necrosis or cornealthinning. The crystalline deposits, which are composedof bacterial aggregates, are most often in the anteriorand less commonly in a mid-stromal location or inposterior stroma. Intraocular spread of organisms mayoccur rarely.

Clinical FeaturesICK has been reported worldwide, with no predilectionfor any race. Primarily, it is a disease of the adults andis rare in patients under 20 years of age. Usually itpresents unilaterally, although anecdotal reports ofbilateral presentation are also there.

ICK occurs most often following a keratoplasty andthe lesions often originate at the site of a suture track,

TABLE 13.2Microbial organisms isolated from eyes with ICK

I. Bacteria1. Gram-positive aerobic.

Streptococcus (42%)Streptococcus viridans and variants (mitis,sangius)Enterococcus (Streptococcus fecalis)Staphylococcus spp. (12%) (aureus, hemolyticus,Epidermidis)Micrococci

2. Gram-positive aerobic bacilli Mycobacterium fortuitumBacillis spp

3. Gram-positive anaerobic cocciPeptostreptococcus

4. Gram-positive anaerobic bacilliDiphtheroidsCornybacterium SppPropionibacterium acne

5. Gram-negative aerobic rods Stenotrophomonas maltophilia

6. Gram-negative bacilliPseudomonas aeruginosaPseudomonas maltophilia Pseudomonas stutzeri

II. Fungus (8%)1. Yeast like Fungi

Candida tropicalisCandida albicansCandida parapsilosis

2. Filamentous fungi (dematiaceous)Alternaria

III. Acanthamoeba species

TABLE 13.3Co-infections in ICK

1. Candida albicans and Streptococcus haemolyticus2. Candida albicans and Streptococcus epidermidis3. Staphylococcus aureus and Corynebacteria4. Micrococci and Staphylococcus epidermidis5. Diphtheroids and Staphylococcus albus6. Bacillus and Staphylococcus spp7. Mycobacterium fortuitum and Pseudomonas aeruginosa

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epithelial defects, or at a location from which loosesuture has been removed or replaced.

It is characterized by the presence of insidiously pro-gressive gray white branching opacities within thecorneal stroma (Fig. 13.1). These may vary in appearancefrom small, round stellate opacities to lesions in whichlarge, branching needle-like opacities extend across theentire cornea. The opacities may occur at any depthwithin the corneal stroma but tend to be isolated withina single lamellar plane. The overlying epithelium is oftenintact and, despite the infectious nature of the lesions,the eyes exhibit minimal signs of anterior segmentinflammation. It may also show a multifocal presenta-tion (Fig. 13.2).

Other rare forms of presentations include annularinfiltration confluent with progressive melting andendothelial plaque formation and satellite lesions.Epithelial integrity is usually maintained but thepresence of microcystic edema with marked stromalthickening may occur.

Epithelial crystalline keratopathy has also beenreported which is characterized by minimal inflam-mation and plaque like lesion at the level of the cornealepithelium, which has fine crystalline appearance.24

In addition, ICK may also be mimicked by thedeposition of calcium in the corneal stroma.18 Threecases have been described where eyes developed whitecrystalline anterior stromal deposits in their grafts whilereceiving long term topical corticosteroids.18

LABORATORY DIAGNOSIS

The causative organisms in cases of superficial lesionsmay be isolated from the cultures of corneal scrapings,which should be undertaken in all cases. The identifica-tion of offending organisms is generally made fromcultures and histopathological analysis of cornealbuttons obtained at the time of repeat cornealtransplantation in most cases.

Microbiological Investigations

Corneal scrapings should be obtained and culturesshould be sent for routine bacterial and fungalorganisms. Routine culture methods are often unsuccess-ful due to the depth of the lesions, and corneal biopsiesare necessary to confirm the diagnosis.

Histopathology

Light Microscopy

Characteristically intra-lamellar pockets of bacteriawithin the corneal stroma are isolated in a single lamellarplane with a pauci-inflammatory type of reaction.Collagen lamellae adjacent to the collections of bacteriaare undisturbed with no evidence of necrosis or cornealthinning. The crystalline deposits, which are composedof bacterial aggregates, are most often in the anteriorand less commonly in a mid-stromal location or inposterior stroma.

Figure 13.1: Infectious crystalline keratopathy after lamellarkeratoplasty

Figure 13.2: Multifocal Infectious crystalline keratopathy afterpenetrating keratoplasty

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Electron Microscopy

Electron microscopy analysis of corneal specimenconfirms the findings revealed on light microscopy. Inaddition, bacteria are often seen in varying stages ofviability or degeneration. Transmission electronmicroscopy shows bacterial organisms with a distinctlaminated cell wall.25 The crystalline appearance isprobably due to bacterial masses between the corneallamellae. Samples and coworkers26 observed electrondense bodies with needle-like projections and suggestedthat these may be responsible for the crystalline appear-ance. Amorphous material consistent with bacterialbiofilm (glycocalyx) has also been observed surroundingthe bacteria in these cases.

Confocal Microscopy

Confocal microscopic evaluation of patients with ICKshows, two basic patterns of crystal morphology distinctneedle-like deposits at varying depths in the stroma andamorphous deposits grouped at different levels in thestroma.16

TreatmentICK responds poorly to treatment with antibiotics. It isdifficult to manage a case of ICK due to the followingfactors:1. Antibiotics, which interfere with cell wall synthesis,

require active bacterial replication for their effect andare therefore less effective against slowly replicating

Figure 13.3: Fungal crystalline keratopathy after LASIK required penetrating keratoplasty

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organisms, which are usually the causativeorganisms of these lesions. The nutritionally variantstreptococci are relatively resistant when comparedto other streptococci.

2. The encasement of the bacteria with biofilms limitsthe bioavailability of topically administeredantibiotics.Discontinuation of the topical corticosteroids coupled

with aggressive therapy with appropriate antibiotics isthe mainstay of the treatment of ICK.

Medical Therapy

The initial treatment of ICK consists of discontinuationof topical corticosteroids therapy and intensive topicalapplication of fortified antibiotics that are effectiveagainst the causative organisms. These include use ofaqueous Penicillin G 100,000 units /mL, cefazolinsodium 50 mg/mL or vancomycin 10 to 20 mg/mL foralpha-hemolytic streptococci. These are given at 1-2hourly frequency for 1 week and are subsequentlytapered. Other antibiotics may be considered whendifferent organisms are identified as the cause ofinfection.

Medical treatment has however been generallydisappointing. Most cases cured by medical treatmenthave required prolonged use of antibiotics and visualresults have been poor. In some cases prolonged use oftopical antibiotics may have caused the emergence ofresistant strains of organisms. Additionally, slowreplication rate of organisms may impair the effective-ness of antibiotics that block cell wall synthesis.

Surgical Therapy

More than 50 percent of cases of ICK fail to respond tomedical treatment and require therapeutic penetratingkeratoplasty (Fig. 13.3). Due to minimal inflammation,the results of therapeutic keratoplasty are generallyfavorable.

Lamellar keratectomy in some cases has also beentried due to the infection by virulent organisms such asPseudomonas aeruginosa and Mycobacterium fortuitum.15

Excimer Laser Ablation

Excimer laser ablation of the infectious lesions may alsobe done especially if the infection is superficial.27, 28 A25 mm myopic ablation followed by 25 mm hyperopicablation is performed using a maximum diameter of5.8 mm.27

YAG Laser Application

Recently YAG laser is also being used by some cornealsurgeons to break the protective biofilm of microorga-nisms of ICK. This helps in achieving a better responseto antimicrobial therapy.

References

1. Gorovoy MS, Stern GA, Hood CI, Allen C. Intrastromalnoninflammatory bacterial colonization of a cornealgraft. Arch Ophthalmol 1983;101:1749-52.

2. Stern GA. Infectious crystalline keratopathy. IntOphthalmol Clin 1993;33:1-7.

3. Meisler DM, Langston RH, Naab TJ, Aaby AA,McMahon JT, Tubbs RR. Infectious crystalline kerato-pathy. Am J Ophthalmol 1984;97:337-43.

4. Zabel RW, Mintsioulis G, MacDonald I, Tuft S. Infectiouscrystalline keratopathy. Can J Ophthalmol 1988;23:311-4.

5. Brooks SB, Bruce-Lyle L, Rao NA, Wright KW. Crystal-line keratopathy and epikeratophakia. Am J Ophthalmol1992;113:337-9.

6. Kincaid MC, Fouraker BD, Schanzlin DJ. Infectiouscrystalline keratopathy after relaxing incisions. Am JOphthalmol 1991;111:374-5.

7. Verma K, Vajpayee RB, Titiyal JS, Sharma N, Nayak N.Post-LASIK infectious crystalline keratopathy caused byAlternaria. Cornea 2005;24:1018-20.

8. Patitsas C, Rockwood EJ, Meisler DM, McMahon JT.Infectious crystalline keratopathy occurring in an eyesubsequent to glaucoma filtering surgery with post-operative subconjunctival 5-fluorouracil. OphthalmicSurg 1991;22:412-3.

9. Kintner JC, Grossniklaus HE, Lass JH, Jacobs G.Infectious crystalline keratopathy associated with topicalanesthetic abuse. Cornea 1990;9:77-80.

10. Sridhar MS, Laibson PR, Rapuano CJ, Cohen EJ.Infectious crystalline keratopathy in an immunosuppres-sed patient. CLAO J 2001;27:108-10.

11. Eiferman RA, Ogden LL, Snyder J. Anaerobic pepto-streptococcal keratitis. Am J Ophthalmol 1985;100:335-6.

12. Ormerod LD, Ruoff KL, Meisler DM, Wasson PJ, KintnerJC, Dunn SP, et al. Infectious crystalline keratopathy.Role of nutritionally variant streptococci and otherbacterial factors. Ophthalmology 1991;98:159-69.

13. Groden LR, Pascucci SE, Brinser JH. Haemophilusaphrophilus as a cause of crystalline keratopathy. Am JOphthalmol 1987;104:89-90.

14. Lubniewski AJ, Houchin KW, Holland EJ, Weeks DA,Wessels IF, McNeill JI, et al. Posterior infectious crystal-line keratopathy with Staphylococcus epidermidis.Ophthalmology 1990;97:1454-9.

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15. Hu FR. Infectious crystalline keratopathy caused byMycobacterium fortuitum and Pseudomonas aerugi-nosa. Am J Ophthalmol 1990;109:738-9.

16. Sharma N, Vajpayee RB, Pushker N, Vajpayee M. Infec-tious crystalline keratopathy. CLAO J 2000;26:40-3.

17. Wilhelmus KR, Robinson NM. Infectious crystallinekeratopathy caused by Candida albicans. Am J Ophthal-mol 1991;112:322-5.

18. Weisenthal RW, Krachmer JH, Folberg R, Dunn SP,Whitson WE. Crystalline deposits mimicking bacterialinfectious crystalline keratopathy. Am J Ophthalmol1988;105:70-4.

19. Penland RL, Wilhelmus KR. Stenotrophomonas malto-philia ocular infections. Arch Ophthalmol 1996;114:433-6.

20. Lam S, Meisler DM, Krachmer JH. Enterococcal infec-tious crystalline keratopathy. Cornea 1993;12:273-6.

21. Touzeau O, Bourcier T, Borderie VM, Laroche L.Recurrent infectious crystalline keratopathy caused bydifferent organisms in two successive corneal grafts inthe same patient. Br J Ophthalmol 2003;87:1053.

22. Umapathy T, Singh R, Dua HS, Donald F. Non-tuberculous mycobacteria related infectious crystallinekeratopathy. Br J Ophthalmol 2005;89:1374-5.

23. Fulcher TP, Dart JK, McLaughlin-Borlace L, Howes R,Matheson M, Cree I. Demonstration of biofilm ininfectious crystalline keratopathy using ruthenium redand electron microscopy. Ophthalmology 2001;108:1088-92.

24. Sridhar MS, Sharma S, Garg P, Rao GN. Epithelialinfectious crystalline keratopathy. Am J Ophthalmol2001;131:255-7

25. Reiss GR, Campbell RJ, Bourne WM. Infectious crystal-line keratopathy. Surv Ophthalmol 1986;31:69-72.

26. Samples JR, Baumgartner SD, Binder PS. Infectiouscrystalline keratopathy: An electron microscope analysis.Cornea 1985-1986;4:118-26.

27. Eiferman RA, Forgey DR, Cook YD. Excimer laserablation of infectious crystalline keratopathy. ArchOphthalmol 1992;110:18

28. Daneshvar H, MacInnis B, Hodge WG. Nd:YAG lasercorneal disruption as adjuvant treatment for infectiouscrystalline keratopathy. Am J Ophthalmol 2000;129:800-1.

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Post-surgical Microbial Keratitis14

Corneal infections are known to occur after variousextraocular surgeries such as pterygium surgery and alsoafter intraocular surgeries such as cataract surgery,corneal transplantation, refractive surgery, excimer lasersurgery, trabeculectomy and vitreoretinal surgery.

Keratitis after Pterygium SurgeryCorneal ulceration is known to occur after Pterygiumsurgery. Many cases of Scedosporium corneoscleralinfection have been seen following Pterygium surgerywith beta radiation. They may be amenable to topicalmedications if the associated keratitis is mild or mayrequire a large corneoscleral graft in severe cases ofmelting (Fig. 14.1A and B).

Keratitis After Cataract SurgeryInfectious keratitis can occur after cataract surgery whichincludes the extracapsular cataract extraction (Fig. 14.2)and the phacoemulsification surgery. The infection

generally begins at the incision site which in cases ofphacoemulsification may be the scleral tunnel, cornealtunnel or the side port.

The infection in the tunnels is related to the woundarchitecture with imperfect apposition which creates apotential space between the roof and the floor of thetunnel. In cases of the scleral tunnel, it may commenceas scleritis and in cases of clear corneal incisions itmanifests as keratitis.1 Clear corneal wound infection(Fig. 14.3) may be associated with scleritis andendophthalmitis.2 Simultaneous infection of the mainwound and the side port has also been reported (Fig.14.4).


The important predisposing factors in a case of woundinfection include the presence of wound leak aftersurgery or the occurence of infection in the adnexalareas.

Figures 14.1A and B: Corneoscleral melting (A) in a case following pterygium surgery which was managed by (B) corneoscleral graft

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4Post-surgical Microbial Keratitis

The sources of microorganisms include the patient’sown eyelids and conjunctiva, contaminated instruments,lenses or irrigating solutions, airborne infections, andbreaches in the sterile technique. Another importantpredisposing factor with cases is the use of cortico-steroids without antibiotics.1,2

CLINICAL EXAMINATION

The diagnostic criteria in cases of keratitis followingphacoemulsification surgery is the presence of anepithelial defect with or without infiltrates in thesurrounding stroma along the tunnel incision, i.e.,

external wound, tunnel, or internal wound, andassociated anterior chamber reaction (Fig. 14.3). At times,the epithelial defect may not be present. It is imperativeto examine the wound, adjoining sclera, size and depthof the infiltrate, and anterior chamber reaction. Inaddition, Seidel’s test and irrigation of the lacrimaldrainage system should also be performed to rule outwound leak and dacryocystitis, respectively.

MICROBIOLOGIC EXAMINATIONAll patients should be subjected to a detailed micro-biology workup. Specimens should be collected throughcorneal or scleral scraping by using a no. 15 surgicalblade, corneal or scleral biopsy, and anterior chamberparacentesis. The material should be examinedmicroscopically by using Gram stain, Giemsa stain, andpotassium hydroxide and inoculated on various culturemedia that facilitate the growth of fungi, bacteria, andparasites (blood agar, chocolate agar, Sabouraud’sdextrose agar, non-nutrient agar, thioglycolate broth,and brain heart infusion broth).

At times scrapings from the corneal surface overlyingthe infiltrate may not reveal any organisms on micro-scopy or culture and keratitis may be present in theposterior part of the tunnel. Hence, it may be necessaryto a make a flap at the incision site like a trap door andbiopsy may be taken from the visibly infected part ofthe posterior aspect of the tunnel. In cases where scleritisis present corneoscleral biopsy may be required and incases of thick exudates associated with hypopyonanterior chamber paracentesis may be undertaken.

Figure 14.3: Tunnel infection in a case of phacoemulsification

Figure 14.4: Simultaneous tunnel and side port infection in a casefollowing phacoemulsification surgery

Figure 14.2: Corneal ulcer after extracapsular cataract extraction

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Figure 14.5A: Pseudomonas infection in a full thickness graftFigure 14.5B: Graft infection (Staphylococcal) in a case of penetratingkeratoplasty

TREATMENTThe initial treatment should be based on the smearresults and is subsequently modified after the culturereport. In cases of bacterial ulcers fortified cefazolinsodium 50 mg/ml may be given with tobramycinsulphate eye drops 1.3 mg/ml every hour initially.Alternatively in cases which are not responding totreatment and in cases where resistance is seen to thesedrugs, vancomycin 50 mg/ml may be given. The topicalantibiotics are then tapered and topical steroids such asprednisolone acetate 1% eyedrop in qid doses may beadded depending on the healing response of the ulcer.

Patients who had filamentous fungal infectionshould be treated with topical natamycin 5 percent onehourly and cycloplegics. Additionally oral ketoconazole400 mg/day or itraconazole 200 mg/day may be givenin suspected cases of scleritis or endophthalmitis. Incases of yeast infection, topical fluconazole 2 percent oramphotericin B 0.05 percent are given hourly alongwithcycloplegics.

Microbial Keratitis After KeratoplastyGraft infection is the most devastating complicationfollowing corneal transplant surgery and may causegraft failure if not managed promptly and appropriately(Figs 14.5A and B). The immunity of ocular surface of acorneal graft is suboptimal due to altered tear filmdynamics, loss of corneal sensations and frequent

instillation of topical corticosteroids in the postoperativeperiod.

The incidence of infectious keratitis after cornealtransplantation surgery varies from 1.7 to 11.9 percentin various studies.1-7 The incidence of infectious keratitisfollowing lamellar keratoplasty has been reported to be11.11 percent.8 Most infections present in the first yearof corneal transplantation surgery.4-6


Various factors that can predispose to infection in a caseof corneal graft include type of corneal pathology of therecipient, donor tissue contamination and ocular surfaceproblems.

Indication for KeratoplastyCorneal grafts performed for bullous keratopathy9 andcorneo-iridic scars10 have an increased risk of keratitisas compared to corneal grafts done for keratoconus,Fuch’s endothelial dystrophy and stromal cornealdystrophies.

Donor FactorsCertain causes of donor death like malignancy, cardiacdiseases and septicemia are more prone to graftinfection.11 Preservative media for tissue storage mayalso be a potential source of graft infection due toinadvertent contamination during the processing andstorage of the donor tissue.12

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Recurrence of Host Infection

Recurrence of infection is usually seen when there isincomplete excision of infected tissue of the host corneaespecially in cases of therapeutic grafts (Figs 14.6A andB). This occurs in cases of grafts performed for herpessimplex keratitis and may occur in 23 percent oftransplanted corneas (Fig. 14.7).6

Persistent Epithelial Defect

Persistent epithelial defect acts as a breach in the cornealprotection and in such a situation there are increasedchances of microbial invasion (Fig. 14.8). This has been

reported to occur in 14 to 74 percent cases in variousseries.3,6,8,10 Lid abnormalities like trichiasis, poor qualityand inadvertent damage of the donor tissue, tightsuturing (Fig. 14.8), loose suturing (Fig. 14.9) and preser-vative toxicity can delay epithelialization leading to theoccurrence of persistent epithelial defects.

Contact Lens

Bandage contact lenses, when used to promote healingof the epithelial defect may induce corneal hypoxia,reduces local immunity and can cause increasedmicrobial adherence and a subsequent keratitis.9

Figure 14.6A: Recurrence of bacterial keratitis after penetratingkeratoplasty

Figure 14.6B: Recurrence of fungal keratitis after lamellar kerato-plasty

Figure 14.7: Herpes simplex keratitis in a graftFigure 14.8: Persistent epithelial defect and tight suture in a case ofgraft infection

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Dry Eye and Ocular Surface Problems

Ocular surface disorders like dry eye and dellen resultin altered tear film dynamics and decreased tear filmcoating which increases the chances of adherence of themicrobes to the transplanted corneas.

Suture Related Problems

Suture related problems are the most importantpredisposing factors for graft infection in 14 to 60 percentcases.8,13-17 Loose or exposed sutures attract mucin (Fig.14.9) and act as a nidus for microbial invasion andproliferation and can cause graft infection. Sutureabscesses may also lead to graft infection (Figs 14.10A

and B). A continuous suture has a higher chance ofpredisposing a graft to the occurrence of infection ascompared to interrupted sutures.

Systemic Associations

It has been reported that patients with diabetes mellitusmay have more chances of graft infection.9,10 Indeveloping countries graft infection is associated withlow socioeconomic status of the patient.10,18,19 In ourstudy there was 2.5 times higher chances of infection inthe lower socioeconomic status as compared to higherstrata and was attributed to poor living conditions andinadequate hygiene.18

Microbiology of Graft InfectionThe most common cause of graft infection is herpessimplex virus followed by bacterial organisms. Morecases with Gram-positive cocci (coagulase-negativestaphylococci, Streptococcus pneumoniae and Staphylo-coccus aureus)3,4,20 have been reported as compared toGram-negative organisms (Pseudomonas aeruginosa andSerratia marcescens). Mycotic keratitis after cornealtransplantation has also been known to occur and fungiof Aspergillus and Mucoraceae species21 are mostcommonly isolated fungal organisms from these cases.

Clinical Features

Patients of graft infection in the early post-operativeperiod present with non-specific symptoms of redness,

Figure 14.9: Loose suture acts as a nidus for infection

Figure 14.10B: Sutures abscess leading to graft infectionFigure 14.10A: Suture infiltrates in a graft

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photophobia, foreign body sensation and purulentdischarge. There may be a sudden or gradual decreasein the visual acuity depending on the location of thelesion. Infections involving the central part of corneacause a sudden decrease in visual acuity. Some patientswith infection at the graft host junction or with infectionlocalized to the periphery of the graft may present witha normal visual acuity.

There may be a delay in diagnosis of infection inlamellar grafts, especially in the early stages, becausean infiltrate may develop in the interface and hence maynot be visualized earlier.8

The ulcer should be examined under slit lamp anddocumented with a careful detailed drawing and photo-graphs (if possible). The size of the epithelial defect,infiltrate and hypopyon, if present should be measuredand recorded at each follow-up.

The ulcers may be either peripheral or central inlocation. The former are usually associated with suturerelated problems whereas the latter are related toexposure and tear film abnormalities. Advanced casesmay present with frank graft dehiscence or melting.

InvestigationsGenerally, culture swabs are taken from the donorcorneoscleral rim and the media. This may aid inidentification of the micro-organism especially if theinfection has occurred in the early post-operative period.The corneal scraping should be done under topicalanesthesia using a slit lamp biomicroscope. Smears for

Gram’s stain and potassium hydroxide (KOH) wetmount should be prepared. In cases of suture relatedproblems, the offending suture should be removed andsent for bacterial and fungal culture examinations. If acontact lens is in place, it should be removed and placedon a separate culture plate. Initially the cultures shouldbe done on blood agar, chocolate agar and Sabourauddextrose agar. Special culture media like LowensteinJensen media, non-nutrient agar with Escherichia coli andthioglycolate broth should be used if there is clinicalsuspicion of infection by unusual pathogens.

ManagementCorneal graft infection requires a prompt and judiciousmanagement, which depends on a good clinicaljudgment and an early microbiological diagnosis of theulcer.

MEDICAL MANAGEMENT

We prefer to hospitalize all cases with corneal graftinfection. In all cases of suppurative infectious keratitisof corneal graft topical corticosteroids should be stoppedimmediately and an intensive regimen of broad-spectrum combination therapy with fortified cefazolinsodium 50 mg/ml and fortified tobramycin 14 mg/mlshould be instituted every 30 minutes round the clockin the first 24 hours. Alternatively, fortified cefazolin50 mg/ml and gatifloxacin 3 mg/ml may be started inthe same frequency.

Antifungal medications such as 5 percent natamycineye drops one hourly are added only if there ismicrobiological evidence of presence of fungus (i.e. onGram’s smear, KOH wet mount or culture examination).

Supportive topical medical therapy is given in theform of cycloplegics, lubricants and antiglaucomamedications (if required). Topical corticosteroid may bere-started in cases of bacterial infections only if theoffending organism has been identified and there is asignificant positive response to the antimicrobialtherapy. Systemic antibiotics are indicated in cases withfrank/impending scleral involvement, graft melting,perforation or dehiscence.

The patient should be examined daily to monitor theclinical response for progression of the ulcer. Once theclinical improvement occurs, the topical medicationsshould be tapered.

However, if the medical management fails, surgicaloptions for the management of post-keratoplasty

Figure 14.11: Mycotic keratitis in a graft (Aspergillus)

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infections should be resorted to. If the cultures arenegative and the keratitis worsens despite medicaltherapy, a diagnostic biopsy is indicated.

SURGICAL MANAGEMENT

If a loose suture is noted in the early post-operativeperiod, it should be removed and replaced immediately,taking care that the exposed part of the suture does nottraverse the corneal stroma. If a suture is the cause ofinfection during the late postoperative period i. e. after3 months it should be immediately removed and sentfor cultures. During the late postoperative periodremoval of a single interrupted suture does not adverselyaffect the wound stability. However, if infection occursdue to a loose continuous suture, it should be imme-diately removed and replaced with interrupted sutures.

The indications for a graft exchange include non-resolving graft ulcers, deep-seated abscess nonresponsive to treatment, wound dehiscence, perforationor graft melting. A graft exchange using the same sizegraft as the one used in the prior surgery may be donein cases where the infection has not spread to the hostcornea or a larger sized graft may be used in cases wherethe infection spreads to the host cornea.

Associated Endophthalmitis

Endophthalmitis may occur early or late after penetrat-ing keratoplasty, often with disastrous consequences. Itmay occur in 4 to 13 percent of the cases of graftinfection.2,3,8,13 The sources of infection are contaminateddonor tissue or corneal storage media or irrigatingsolutions. Ulcerative keratitis at the graft host junctionmay progress to perforation and subsequent endoph-thalmitis. Anterior vitrectomy performed at the time ofpenetrating keratoplasty may increase the chance ofendophthalmitis by 1.5 times. In cases of corneal graftinfection associated with endophthalmitis intravitrealinjection of vancomycin 1 mg in 0.1 ml and ceftazidime2.25 mg in 0.1 ml should be given along with topicaltherapy for corneal ulcer.

HERPETIC GRAFT INFECTIONS

Herpes simplex virus keratitis may recur in cases ofpenetrating keratoplasty performed for herpetic scarsor may develop following keratoplasty without a clinicalhistory of herpes keratitis in the host.23 The incidence ofrecurrence of herpetic infection after penetrating

keratoplasty varies from 10 to 25 percent during the firstyear of follow-up.23,24

Herpetic keratitis in a corneal graft may have avariable presentation and may present as a classicdendritic ulcer (Figs 14.12A and B), persistent epithelialdefect, graft rejection, or a herpetic stromal infiltrationof the graft (Figs 14.12A and B).25 A geographicalherpetic ulcer has to be differentiated from a neurotro-phic ulcer by slit lamp biomicroscopy using Rose BengalStaining. The risk of recurrence of herpetic infectionincreases specially if the corticosteroids are used afterpenetrating keratoplasty without the concomitant useof antiviral drugs as this enhances viral multiplication.Hence a prophylactic dose of systemic acyclovir 800 mgper day is recommended for up to year in cases ofpenetrating keratoplasty done for herpetic scars.24-26

Graft Survival and Visual OutcomeVisual prognosis in eyes with post-keratoplasty graftinfection is poor even after a successful medical therapydue to corneal scarring after resolution of keratitis anda high rate of graft decompensation. A repeat kerato-plasty is required in almost half of the cases.4,10 Cleargrafts following graft infection has been reported in23 to 67 percent cases in various studies.5,6,15,20 A bestcorrected visual acuity (BCVA) of better than6/60 on Snellen’s acuity chart is seen in only 14 to30 percent of the eyes and only 6 percent of patientsachieved a best corrected visual acuity of > 6/18 at thefinal follow up in one study.10 Infections after lamellarkeratoplasty are associated with grave prognosis andmay not be amenable to antimicrobial therapy.8 Thismay necessitate the removal of the graft or a therapeuticpenetrating keratoplasty.8

MICROBIAL KERATITIS AFTERREFRACTIVE SURGERYMicrobial keratitis has been reported after radialkeratotomy, photorefractive keratectomy, laser in situkeratomileusis and laser subepithelial keratectomy.

Microbial Keratitis After LASIK

Microbial keratitis following LASIK is a rare compli-cation but can be sight-threatening and can lead todevastating consequences. The incidence of microbialkeratitis varies between 1:1000 and 1:5000.22 Most casespresent within the first week after surgery; howevercases have been reported even after 1 month.

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Infectious keratitis following LASIK may be earlyonset (occurring within the first 2 weeks of surgery) orlate onset (occurring 2 weeks to 3 months after surgery).The organisms seen in early-onset infectious keratitisare common bacterial pathogens such as staphylococcalstreptococcal and Pseudomonas (Figs 14.3A and B)species. Gram-negative organisms are rare. Theorganisms seen in late-onset infectious keratitis areusually opportunistic such as fungi (Fig. 14.4), nocardia,and atypical mycobacteria.

Infectious keratitis following LASIK often presentswith inflammation in the corneal interface, which canmimic diffuse lamellar keratitis (DLK). Because of this,

many cases are typically treated with frequent topicalcorticosteroid therapy that may obscure the clinicalpicture with transient improvement in the inflammation.However, unlike DLK, the inflammation associated withLASIK-associated infections usually persists despitetopical corticosteroids, and the underlying infections canpotentially worsen with corticosteroid tapering.

The appearance of an interface inflammation morethan 1 week after LASIK should be presumed to be ofan infectious etiology until proven otherwise. Diffuselamellar keratitis characteristically has a diffuseappearance , while infectious keratitis has a focal areaof infiltration surrounded by diffuse inflammation

Figures 14.12A and B: Dandrities due to herpes simplex keratitis following penetrating keratoplasty stained with Rose Bengal dye (A) andflorescien (B)

Figures 14.13A and B: Post LASIK keratitis due to Pseudomonas (A) healed on topical therapy (B)

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(Figs 14.13A and B) or even focal inflammation limitedto the area of the infiltrate. Any focal infiltratesurrounded by inflammation should be presumedinfectious until proven otherwise.

Microbiologic Examination

Any focal infiltrate following LASIK should beconsidered infectious, and the practice of empiricalantibiotic treatment without performing cultures ofmicroorganisms should be avoided.

Scraping should be sent for Gram-stain, Gomori-methenamine silver stain, and Ziehl-Neelsen stain torule out unusual pathogens such as nocardia, atypicalmycobacteria, and fungi.The culture media whichshould be inoculated include blood agar, chocolate agar,Sabouraud’s agar, and thioglycolate broth andLowenstein-Jensen or Middlebrook 7H-9 agar. If thesespecial media are unavailable, blood agar may be usedas atypical media. Mycobacteria grow quite well in thismedia also. In cases in which cultures are negative andthe infection continues to worsen, a corneal biopsy orpolymerase chain reaction should be contemplated.

Treatment

The topical corticosteroids should be discontinued. Incases of Post LASIK keratitis fortified cefazolin sodium5% eyedrops along with tobramycin sulphate 1.3% eyedrops are instilled hourly. In cases where there is noresponse to above therapy and where the flap isedematous irrigation of the flap interface with an appro-priate antibiotic solution (fortified vancomycin 50 mg/mL for rapid-onset keratitis and fortified amikacin35 mg/mL for delayed-onset keratitis) may be helpful.

In patients who work in a hospital environment,there is an added risk for methicillin-resistantStaphylococcus aureus (MRSA). In these patients, fortifiedvancomycin 50 mg/mL may be given instead ofcefazolin every 30 minutes to provide more effectivetherapy against MRSA. In addition, oral doxycycline 100mg twice a day may be used to inhibit collagenaseproduction.

For delayed-onset keratitis, which is commonly dueto atypical mycobacteria,22 nocardia, and fungi, therapyshould be commenced with amikacin 35 mg/mL everyhour, alternating with a fourth-generation fluoroquino-lone (gatifloxacin 0.3% or moxifloxacin 0.5%).Clarithromycin 1 percent and Oral Clarithromycin mayalso be tried in cases which do not respond to amikacin.

Topical medications are generally given for 4 monthsand systemic medications are given for 2 months.

In cases where total melting of the cornea occursdespite amputation of the flap and maximal medicaltherapy, a therapeutic keratoplasty may be required tosave the eye.

References1. Garg P, Mahesh S, Bansal AK, Gopinathan U, Rao GN.

Fungal infection of sutureless self-sealing incision forcataract surgery. Ophthalmology 2003;110:2173-7.

2. Cosar CB, Cohen EJ, Rapuano CJ, Laibson PR. Clearcorneal wound infection after phacoemulsification. ArchOphthalmol 2001;119:1755-9.

3. Al-hazzaa SAF, Tabbara KF. Bacterial keratitis afterpenetrating keratoplasty. Ophthalmology 1988;95:1504-8.

4. Akova YA, Onat M, Koc F, Nurozler A, Duman S.Microbial keratitis following penetrating keratoplasty.Ophthalmic Surg Lasers 1999;30:449-55.

5. Tavakkoli H, Sugar J. Microbial keratitis followingkeratoplasty. Ophthalmic Surg 1994;25:350-60.

6. Bates AK, Kirkness CM, Ficker LA, Steele AD, Rice NSC.Microbial keratitis after penetrating keratoplasty. Eye1990;4:74-8.

7. Lamensdorf M, Wilson LA, Waring GO III, CavanaghHD. Microbial keratitis after penetrating keratoplasty.Ophthalmology 1982;89:124.

8. Sharma N, Gupta V, Vanathi M, Agarwal T, VajpayeeRB, Satpathy G. Microbial keratitis following lamellarkeratoplasty. Cornea 2004;23:472-8.

9. Saini JS, Rao GN, Aquavella JV. Post-keratoplastycorneal ulcers and bandage lenses. Acta Ophthalmo-logica 1988;66:99-103.

10. Vajpayee RB, Boral SK, Dada T, Murthy GVS, PandeyRM, Satpathy G. Risk factors for graft infection in India:A case control study. Br J Ophthalmol 2002;86:261-5.

11. Rehany U, Balut G, Lefler E, Rumelt S. The prevalenceand risk factors for donor corneal button contaminationand its association with ocular infection after trans-plantation. Cornea 2004;23:649-54.

12. Chittum ME, Grutzmacher RD, Oiland DM, Kalina RE.Contamination of corneal tissue from infected donors.Arch Ophthalmol 1985;103:802-5.

13. Driebe WT, Stern GA. Microbial keratitis followingcorneal transplantation. Cornea 1983;2:41.

14. Dana MR, Goren MB, Gomes AP, Laibson PR, RapuanoCJ, Cohen EJ. Suture Erosion after penetrating kerato-plasty. Cornea 1995;14:243-8.

15. Harris DJ Jr, Stulting RD, Waring GO 3rd, Wilson LA.Late bacterial and fungal keratitis after cornealtransplantation. Spectrum of pathogens, graft survival,and visual prognosis. Ophthalmology 1988;95:1450-7.

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16. Leahey AB, Avery RL, Gottsch JD, Mallette RA, StarkWJ. Suture abscesses after penetrating keratoplasty.Cornea 1993;12:489-92.

17. Christo CG, van Rooij J, Geerards AJ, Remeijer L,Beekhuis WH. Suture-related complications followingkeratoplasty: A 5-year retrospective study. Cornea 2001;20:816-9.

18. Dandona L, Naduviath TJ, Janarthanan H, et al. Causesof corneal graft failure in India. Indian J Ophthalmol1998;46:149-52.

19. Dandona L, Naduvilath TJ, Janarthanan M, et al. Survi-val analysis and visual outcome in a large series of

corneal transplants in India. Br J Ophthalmol 1997;81:726-31.

20. Tseng SH, Ling KC. Late microbial keratitis after cornealtransplantation. Cornea 1995;14:591-4.

21. Satpathy G, Vishalakshi P. Microbial profile andsensitivity pattern – a five-year study. Ann Ophthalmol1995;27:301-6.

22. Daines BS, Vroman DT, Sandoval HP, Steed LL,Solomon KD. Rapid diagnosis and treatment ofmycobacterial keratitis after laser in situ keratomileusis.J Cataract Refract Surg 2003;29:1014-8.

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Keratitis and Endophthalmitis15

IntroductionEndophthalmitis is secondary to infectious keratitisalthough rare is a serious ocular infection that can resultin blindness. Keratitis with endophthalmitis has beenreported in 6.3 percent of cases.1 Considerable vitreousinflammation can occur with microbial keratitis in theabsence of histologically demonstrable micro-organismsin the vitreous. Microbial keratitis associated withsuppurative endophthalmitis is usually caused by viru-lent (coagulase-negative staphylococci, streptococci, andGram-negative organisms) organisms.2,3

PathogenesisOnce endophthalmitis occurs, damage to ocular tissuesoccurs due to direct effect of microbial replication aswell as initiation of a fulminant cascade of inflammatorymediators. Endotoxins cause direct cellular injury andcytokines attract neutrophils which enhance theinflammatory effect.

Predisposing Factors

Patients in whom keratitis is associated with endoph-thalmitis give a history of frequent corticosteroid use.They may also have a concomitant systemic disorderassociated with relative immune dysfunction. Patientsin whom there is absence of an intact posterior capsule,presence of wound abnormalities (in post surgical cases),or occurence of corneal perforation are also at a greaterrisk of having endophthalmitis.3

Clinical Features

SYMPTOMS

Most patients complain of a sudden onset and a rapidworsening of pain accompanied by a significant decrease

in vision. Other symptoms that may be present aredischarge, excessive tearing, increased sensitivity tonormal light (photophobia), increase in redness of theeye and blepharospasm (Table 15.1).

SIGNSOn examination, the visual acuity is decreased and maybe hand motions or only light perception in fulminantcases. There is marked conjunctival hyperemia, chemosisand circumcorneal congestion. There is presence of acorneal ulcer and the adjacent cornea is grosslyedematous. A limbal ring abscess or corneal melting mayalso be present. The underlying findings in the anteriorchamber and the posterior segment are not visible dueto the presence of the overlying keratitis. The anteriorchamber shows a significant degree of flare and cells,the reaction sometimes being frankly fibrinous. The irispattern is lost, appears muddy and boggy and isresistant to dilation. There may be presence of posteriorsynechiae. Pupillary response to light is absent orsluggish. In more severe cases, a dense discrete orconfluent, yellowish vitreous exudation is evident (Figs15.1 and 15.2). The intraocular pressure may be elevatedin the early stages of endophthalmitis. The fundus glowmay be dull or absent.

InvestigationsThe investigations in a case of keratitis with endoph-thalmitis include clinical investigations such asultrasonography and microbiological evaluation.

TABLE 15.1Symptoms and signs of keratitis with endophthalmitis

1. Increasing pain2. Sudden and rapid diminution of vision3. Poor or absent fundus glow4. Disproportionate anterior chamber reaction5. Exudates in anterior chamber/ Pupillary membrane

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ULTRASONOGRAPHY

The presence of a corneal ulcer prevents the properassessment of the posterior segment and hence ultra-sonography A and B scan in these cases is mandatoryto detect the involvement of vitreous and for monitoringthe course of infective process.5

In a patient with suspected endophthalmitis whereretinal details are not visible it is mandatory to undertakeultrasonography whenever it is available, beforeinstituting any form of invasive, diagnostic ortherapeutic interventions. This is to detect the presenceof a choroidal detachment, retinal detachment, thedegree of vitreous exudation and the presence ofposterior vitreous detachment. Ultrasonography is auseful aid in establishing the diagnosis, prognostication,of the case planning the surgery and sometimes infollow-up.

CORNEAL SCRAPINGS

Corneal scrapings should be obtained as is done in aroutine case of corneal ulcer. The scrapings should besent for smear (Grams, Giemsa and KOH wet mountpreparation) as well as culture examination (Blood Agar,Chocolate Agar and Sabrouad’s dextrose agar).

AQUEOUS AND VITREOUS TAP

The most important samples to culture are aspiratesfrom the aqueous and vitreous cavity. The possibility ofisolating an organism in vitreous tap is 56-70 percent

and in aqueous sample is 36-40 percent Hence it isnecessary to culture specimens obtained from bothaqueous and vitreous samples.

Aqueous Tap

Aqueous tap is obtained by a paracentesis using a 25-27gauge, half inch needle mounted on a tuberculin syringewith its plunger on. About 0.1ml of fluid is aspirated ina controlled manner by gently withdrawing the plunger.The needle may be directly inoculated into the culturemedia. A part of the aspirate is ideally plated directlyon to the culture media while any remaining aspirate isused to prepare slides for Gram stain and Giemsa stain.

Vitreous TapIf there is no underlying rhegmatogenous retinal detach-ment, an intravitreal antibiotic injection (Vancomycin1 mg in 0.1 ml with Ceftazidime 2.25 mg in 0.1 ml) isthe treatment of choice in cases with bacterial endo-phthalmitis.

In cases of fungal endophthalmitis 10 μg ofamphotericin B is given intravitreally.

Our technique for performing vitreous tap andgiving intravitreal antibiotics is as follows:1. Place a drop of topical anesthesia (0.5% propara-

caine) on the affected eye.2. Culture the conjunctival surface with a conjunctival

swab.3. Prepare the globe with a 5 percent povidone iodine

(Betadine) solution. Insert a sterile lid speculumbetween the lids.

Fig. 15.1: Anterior chamber exudates with endophthalmitis Fig. 15.2: Corneal melting with endophthalmitis

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4. Perform a vitreous tap with a 23-gauge needle on atuberculin (TB) syringe, removing 0.2 ml of vitreousfor cultures.

5. Choose an injection site 3-4 mm posterior to thelimbus, depending on the lenticular status. Toanesthetize this site, hold an anesthetic-soaked cottonswab at the site for one to two minutes. If the patientis extremely uncomfortable, as is often the case, usea subconjunctival injection of lidocaine in additionto the topical anesthesia. ‘

6. Enter the globe at the injection site, using a ½ inch26-gauge needle on a TB syringe. The needle shouldpoint towards the optic nerve. Avoid entering deeperthan 1 cm, ensuring entry into vitreous cavity andnot in the suprachoroidal space.

7. Inject the antibiotic, and then withdraw the needle.Re-enter the globe in the same site with each of thetwo intravitreal antibiotics in TB syringes with 30-gauge needles. Inject 0.1 cc of each antibiotic slowlyand separately. The bevel of the needle should befacing anteriorly, in order to minimize contactbetween the drug and the macula. In suspected casesof fungal endophthalmitis Amphotericin B isinjected.

8. Remove the lid speculum. Measure the intraocularpressure after the procedure.

The inocula from the AC tap as well as the vitreoustap ideal is plated on the following:1. Blood agar plate at 37 degree C2. Chocolate agar plate at 37 degree C in a 4-10 percent

CO2 enriched environment3. Sabourauds medium without any inhibitors at room

temperature4. Thioglycolate broth at 37 degree C .5. Two clean glass slides for Gram and Giemsa stain6. Brain-heart infusion or cooked meat broth.

TREATMENT

The treatment of keratitis with endophthalmitis consistsof medical and surgical therapy.

Topical TherapyThe medical therapy consists of the treatment of cornealulcer as described previously using a combination offortified antibiotics in frequent doses. Topical fortifiedcefazolin sodium 5% along with tobramycin sulphate1.3% are given in hourly dosage for the initial 48 hours.Topical cycloplegics such as homatropine eye drops 2%

is given thrice a day. In the event of raised intraocularpressure, anti-glaucoma medications such as timololmaleate 0.5% is given twice a day. Topical steroids arewithheld till the corneal healing begins.

Intravitreal Antibiotics

Intravitreal injection of antibiotics (i.e vancomycin 1 mgin 0.1 ml with ceftazidine 2.25 mg in 0.1 ml) is given incases of bacterial endophthalmitis, following whichresponse is monitored untill 36 to 72 hours. In case thereis no response, a repeat injection may be given again.Likewise following intravitreal injection of antifungals(i.e. 10 μg of amphotericin B) in cases of fungalendophthalmitis, one waits for one week and a repeatinjection of amphotericin B may be given if there is noresponse.

Systemic Therapy

We recommend the routine use of systemic steroids inall cases except when contraindicated systemically ordue to fungal infections. Tab prednisolone 1.5 mg/kgbody weight is given for the initial 2 weeks which istapered after the inflammation decreases. Systemicsteroids are helpful in controlling and inhibiting theinflammatory effects of endotoxins and subsequent opticnerve damage.

Systemic antibiotics consists of intravenousvancomycin 1 gm bd, intravenous amikacin orgentamicin 80 mg tds and intravenous metronidazole500 mg tds (in case where anaerobic infections aresuspected) which are given in cases of bacterialendophthalmitis. Systemic antifungal agents consist ofuse of oral ketoconazole 600 mg per day. Fluconazole200 mg bd or more recently voriconazole 100 mg bdmay be given in recalcitrant cases. Liver function testhave to be repeated after every 2 weeks in these cases.

The patients should be examined twice daily duringthe initial treatment period to assess adequate sterili-zation of the vitreous cavity, control of intraocularinflammation, and identification of the need foradditional intervention.

The overlying corneal ulcer and edema preventsimmediate surgical intervention for the vitreousinfection.

SURGICAL THERAPY

Earlier, the surgical intervention was not carried out incases of endophthalmitis associated with corneal ulcer

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due to poor prognosis. More recently, a trial of vitreoussurgery (vitrectomy) may be given in which one of thetemporary kerato-prostheses is used. A team approachof an anterior segment and posterior segment surgeonis required. Though the results are not as good as incases with either corneal ulcer or endophthalmitis alone,yet the patient may obtain ambulatory vision.

An early vitreous surgery should be planned in caseswith endophthalmitis and keratitis before the cornealinvolvement becomes so extensive so as to prevent thefeasibility of vitreous surgery. This occurs as a temporarykeratoprosthesis may not hold in place due to cornealmelting. The vitreous surgery can usually be performedif the corneal involvement is not complete. Sometimes,it is required to perform a near complete vitrectomyespecially when an associated retinal detachment ispresent. In such cases the vitreous surgery is done,internal subretinal fluid drainage and silicone oiltamponade is given to flatten the retina. A 360º retinalendophotocoagulation is usually not possible (becauseof overlying corneal involvement) and should not beperformed, as the retina is inflamed and therefore morelikely to develop secondary retinal tears. In such cases,

if the patient recovers from the disease process and hasvisual potential, a 360º retinopexy by cryotherapy in aphased gradual manner can be done over 2-3 weeksfollowing which removal of silicone oil is done.

References1. Malov VM, Stepanov VK, Ivanov DV, Nikolaeva GA.

Effectiveness of present-day therapy of purulent lesionsof the cornea. Vestn Oftalmol 2003;119:22-4.

2. Margo CE. Eyes removed for primary ulcerative keratitiswith endophthalmitis: Microbial and histological find-ings. Ophthalmic Surg Lasers 1999;30:535-9.

3. Scott IU, Flynn HW Jr, Feuer W, Pflugfelder SC, AlfonsoEC, Forster RK, et al. Endophthalmitis associated withmicrobial keratitis. Ophthalmology 1996;103:1864-70.

4. Tsai YY, Tseng SH. Risk factors in endophthalmitisleading to evisceration or enucleation. Ophthalmic SurgLasers 2001;32:208-12.

5. Marchini G, Pagliarusco A, Tosi R, Castagna G.Ultrasonographic findings in endophthalmitis. ActaOphthalmol Scand 1995;73:446-9.

6. Wilson LA. Acute bacterial infection of the eye: Bacterialkeratitis and endophthalmitis. Trans Ophthalmol Soc UK 1986;105:43-60.

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Neurotrophic Keratitis16

IntroductionNeurotrophic keratitis involves various degrees ofdegenerative corneal and conjunctival changes1

secondary to loss of sensory function in the pathway ofthe nasociliary branch of the trigeminal nerve with orwithout decreased tear production.2

The characteristic features of neurotrophic kerato-pathy includes breakdown of the corneal epithelium inthe absence of desiccation, infection, or trauma. Thispersistent epithelial defect if left untreated extends intothe deeper layers of the stroma and may result in cornealperforation and melting.

EtiologyThe neurotrophic keratitis may occur due to ocularfactors, systemic factors or a combination of the ocularand the systemic factors (Table 16.1).

OCULAR CAUSESThe most common ocular cause of occurrence ofneurotrophic keratitis is herpes virus infection. Bothherpes zoster ophthalmicus and herpes simplex keratitiscan cause loss of corneal sensations subsequent to lossof corneal sensations is herpes virus infection of theocular surface. Neurotrophic ulcers are seen in up to 25percent of the patients with herpes zoster ophthal-micus.3,4 While herpes zoster ophthalmicus involves theophthalmic division of the trigeminal nerve, the herpessimplex infection of the cornea effects the terminaldistribution of the trigeminal nerve5 Other causesinclude corneal dystrophies, local trauma to the cornealnerves and topical medications. The topical anestheticagents may also cause neurotrophic keratitis when theseagents are used for relief of eye pain.

SYSTEMIC CAUSESSystemic disorders can also cause damage to thetrigeminal nerve and reduce corneal sensations. The

most common systemic causes of neurotrophic keratitisinclude tumors and surgeries, which may damage thetrigeminal nucleus, root, ganglion or any segment ofophthalmic branch of the trigeminal nerve.6 This

TABLE 16.1Causes of decreased corneal sensations

Ocular CausesHerpes Zoster OphthalmicusHerpes Simplex KeratitisLyme DiseaseContact Lens WearTrauma to ciliary nerves by diathermy, laser, cryotherapy orscleral buckling, corneal surgery, cataract surgery, lamellarkeratoplasty, penetrating keratoplasty, refractive surgery,epikeratophakiaTopical drugs e.g. anesthetic agents, Timolol maleate (usuallytemporary), Betaxolol, Sulfacetamide 30 percent, Atropine,Diclofenac sodiumOcular surface toxicity e.g. chemical burns, carbon disulfideexposure, hydrogen sulfide.Corneal dystrophies e.g. lattice, granular (rare)Adie’s syndrome

Systemic causesDiabetesLeprosyVitamin A deficiency

Fifth Nerve palsyTrigeminal nerve palsy e.g. surgical (as for trigeminalneuralgia) aneurysm, tumor (e.g. acoustic neuroma) facialtraumaCongenital causes, e.g Familial dysautonomia, Goldenhar’ssyndrome, Mobius syndrome, Parry-Romberg syndrome,Bassen-Kornzweig syndrome

ToxinsCarbon di sulfide exposureHydrogen sulfide exposure

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specially occurs during any ablative procedure fortrigeminal neuralgia. Following resection of the acousticneuroma, both the fifth and the seventh nerves may bedamaged.

Diabetics may have generalized peripheral neuro-pathy including that of trigeminal nerve especially inlong standing cases and a pan-retinal photocoagulationmay deepen the corneal hypesthesia already present.7

Further, these patients may require surgical interventionfor proliferative vitreo-retinopathy and vitreoushemorrhage and are at a risk of developing persistentepithelial defects postoperatively.

Leprosy is also known to cause corneal hypesthesia(8.1 to 59.2% of cases) and neurotrophic keratitis.8

PATHOGENESIS

The corneal epithelial proliferation is regulated by thesensory and the sympathetic nerves and their neuro-transmitters. These sensory neurons directly affect theintegrity of the corneal epithelial cell mitosis and causean epithelial defect. This defect occurs centrally as thecorneal epithelium is persistently regenerated centri-petally from the periphery and sheds old cells at its apexas described by Thoft “X, Y, Z hypothesis.”

Corneal anesthesia due to lack of afferent limb ofthe reflex, also cause reduction in reflex tearing andblinking. Tear mucus secretions increase and abnor-malities of corneal epithelial surface makes it more proneto injury.

Diagnosis

Determination of the primary etiology of neurotrophickeratopathy is extremely important. The history of thepresent illness should include a thorough medical andsurgical workup of the patient.

HISTORY

Patients with neurotrophic keratitis are usually asympto-matic and may only complain of blurring of vision. Adetailed ocular history should include prior episodes ofrecurrent pain, watering and presence of blisters on theface or the eyelids.

One should also enquire regarding the prior historyof any ocular trauma (chemical burns) or any otherocular pathology. Any history of use of contact lens orocular surgery such as cryotherapy,9 diathermy, cataractor corneal surgery should be taken. The patients should

also be enquired about the use of topical NSAIDs (Non-steroidal anti-inflammatory drugs) and topicalanesthetic agents which may predispose an eye toneurotrophic keratitis.10

A detailed systemic history should include historyof diabetes mellitus, leprosy, or history of any surgeryor facial/ head trauma or tumors.

OCULAR EXAMINATIONA detailed external examination as well as slit lampbiomicroscopy should be done. The eyelids should beexamined carefully for any defects, scarring, ectropionor lagophthalmos.

Absence of nasal –lacrimal tearing reflex along withipsilateral loss of sensations in the nasal mucosa is ahigh risk for the occurrence of neurotrophic cornealulceration.

Slit-lamp Biomicroscopy

The tear film should be examined carefully . Mackie hasclassified the characteristic stages of neurotrophickeratitis as follows (Table 16.2):

Stage IIn this stage the earliest sign of sensory denervation isthe development of rose Bengal staining of the inferior

TABLE 16.2Clinical stages of neurotrophic keratitis

Stage IRose Bengal staining of the palpebral conjunctivaDecreased tear break-up timeIncreased viscosity of tear mucusPunctate epithelial staining with fluorescienScattered small facets of dried epithelium (Gaule spots)

Stage IIAcute loss of epithelium, usually under the upper lidSurrounding rim of loose epitheliumStromal edemaAqueous cell and flareEdges of the defect become smooth and rolled with time

Stage IIIStromal lysis, sometimes resulting in corneal perforation

Adapted from Mackie IA: Neuroparalytic (neurotrophickeratitis) In Symposium on contact lens: Transactions of theNew Orleans Academy of Ophthalmology, St. Louis, 1973,Mosby; mackie IA: Trans Ophthalmol Soc UK 93 : 343, 1978

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palpebral conjunctival surface. The tear break up timeis also decreased and the viscosity of the tears increases.Punctate epithelial staining with fluorescein may alsobe present. Small facets or depressions of dryingepithelium also known as Gaule spots may be seen onretro-illumination.

Stage IIIn this stage the superficial punctate defects, which mayprogress to large epithelial defects surrounded by a rimof loose epithelium. Gradually the edges of the epithe-lium get rolled up with surrounding stromal edema. Ifallowed to progress further, a neurotrophic ulcerdevelops with characteristic features of a punched-outulcer (Figs 16.1 and 16.2). Such an ulcer is usuallyhorizontally oval or circular in shape with thickenedborders formed by heaped up epithelial cells. Due tostromal edema, descemet’s folds may develop and thismay be accompanied by flare and cells in the anteriorchamber. This may or may not be associated with asterile hypopyon. Following this, collagenase enzymesstart acting and lead to stromal lysis, necrosis, andperforation. Secondary infection may occur at any stageof development of the ulcer. The ulcer usually heals withepithelial hyperplasia and irregularity, stromal scarring,and neovascularization.11

Stage IIIStromal lysis is the feature of this stage and may lead tostromal necrosis, perforation and secondary bacterialinfection.

Corneal Sensations

Corneal sensations are checked for the pattern anddegree of corneal anesthesia gives a clue regarding localor systemic pathology. Patchy loss of corneal sensationindicates a local condition such as herpes zosterkeratitis.3, 12 Segmental evaluation of corneal sensationis therefore important compared to a simple measure-ment of central corneal sensation. Prominence andbeading of the corneal nerves may be a subtle sign oflepromatous corneal involvement. Decreased cornealsensations may also occur in advanced lattice andgranular dystrophies.

Corneal sensations are checked for the pattern (fourquadrants and central area) and degree . Following twomethods are employed to test the corneal sensations:

Cotton Wisp Method

This technique is performed using the slit-lampbiomicroscope.10 A cotton wisp is lightly touched firstat the central cornea and then at different quadrants.Sensitivity varies in the different parts of the cornea,the central area and horizontal meridian being the leastsensitive. If the touching of the cotton wisp incites ablink reflex and is felt by the patient, corneal sensitivityis graded as normal. If the corneal blink reflex is absentand forceful application is required for subjectivesensation, corneal sensitivity is graded as diminished.An absent blink reflex and the absence of subjectivetouch sensation to the cotton wisp application isinterpreted as complete corneal anesthesia.

Figure 16.1: Neurotrophic keratitis Figure 16.2: Neurotrophic keratitis in tattooed cornea

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Cochet and Bonnet Aesthesiometer

This instrument is more accurate than the cotton wispmethod and helps in the quantitative assessment of thepattern and severity of corneal anesthesia.13 It consists ofa standardized nylon filament 0.12 mm in diametercontained in a calibrated holder (Fig. 16.3). For the quanti-tative measurement of corneal sensations, the length ofthe monofilament is changed according to the scalereading (60.5 mm) along the holder. A conversion tableis provided with the instrument, which converts thelength of the filament into pressure in grams per squaremillimeter (11 mg to 200 mg/0.0113 mm2) (Table 16.3).

The severity of corneal hyposensitivity may begraded as follows: A mean corneal sensitivity of 55 mmor more, measured in five separate quadrants of thecornea is considered normal corneal sensitivity. A valueof 50-54 mm indicates severe hyposensitivity, and avalue of 30 mm or lower depicts advanced cornealhyposensitivity. This test helps us to define thosepatients who are at a risk for development of neuro-trophic keratopathy.

Associated ocular findings may help to elicit theetiology of corneal hypesthesia. Iris atrophy with orwithout anterior chamber reaction is present with herpeszoster and simplex keratouveitis and leprosy.

Dilated Fundus Examination

Dilated fundus examination should be done in all casesas optic nerve swelling or pallor may indicate an orbitalor retro-orbital lesion. Diabetic retinopathy couldindicate the likelihood of diabetic neuropathy and laserscars from pan-retinal photocoagulation, which mayindicate ciliary nerve damage and hence decreasedcorneal sensations.

Systemic Examination

Systemic examination, especially neurological examina-tion, is of particular importance. The presence of otherneurologic deficits helps to localize the neoplasms,injuries, vascular accidents that may include the fifthcranial nerve or its brain stem nucleus. Seventh andeighth nerves may be involved especially in acousticneuromas. Ocular motility may also indicate malfunc-tioning of the cranial nerves III, IV and VI, which maylocalize an aneurysm or cavernous sinus pathology.

Pupillary abnormalities are related to the dysfunctionof the cranial nerve II and defects in the sympatheticinnervation of the iris. The presence of an afferentpapillary defect with corneal hypesthesia indicates theintraconal lesion of the orbit. Abnormal pupil reactionsassociated with Adie’s pupil is a cause of neurotrophickeratitis.

Sensations of the skin and the nasal mucosa shouldalso be checked. Immunological and connective tissuesystem work-up should also be performed and thyroidophthalmopathy should also be ruled out.

Differential DiagnosisNeurotrophic keratitis must be differentiated fromherpetic epithelial keratitis (Table 16.4). The latter mayoccur at any site and is due to active viral infection. Itusually presents as a dendritic ulcer with branchingpattern and terminal bulbs with swollen epithelium atthe borders. However, a geographic ulcer may mimicneurotrophic keratitis.

The neurotrophic keratitis on the other hand, is seenmost often in the interpalpebral area. It presents as apersistent epithelial defect with boggy epithelium andmay have sometimes a dendritic shape. A classicalneurotrophic ulcer is usually smooth, typically roundor oval in shape with heaped epithelium at the border.

Rose Bengal staining may conclusively help inmaking a clinical diagnosis. In herpetic cornealulceration the epithelial cells present at the margins aredead and stain heavily. In neurotrophic keratitis, the

Figure 16.3: Cochet and bonnet aesthesiometer

TABLE 16.3Conversion table used with Cochet and Bonnet aesthesiometer

Nylon length (mm) 60 55 50 45 40 35 30 25 20 15 10 5Mean value of pressure in 11 12 13 16 21 27 36 52 75 100 145 200mm HgMean value of pressure in 0.96 1.08 1.16 1.4 1.84 2.4 3.2 4.6 6.64 8.84 12.84 17.68gm/sq/mm

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epithelial cells at the margin are healthy and do not stainwith Rose Bengal.

InvestigationsThe investigations in a case of neurotrophic keratitisshould include ocular and systemic investigations.Although neurotrophic ulcers are sterile by definition,this should not be presumed clinically. Bacterial superinfections are common and an active herpes keratitismay simulate a neurotrophic ulcer. If a super-infectionis suspected in a patient with a neurotrophic ulcer,scrapings should be taken from the leading edge andbase of the ulcer and sent for culture and sensitivitytesting before initiation of therapy. The specimenobtained from the scraping should be directly inoculatedonto blood agar, chocolate agar, Sabouraud agar plate,and viral culture medium. Multiple smears should bemade for examination under Gram’s, Giemsa, andGrocott’s methenamine silver stain. Direct immuno-fluorescence staining should be done for herpes virus.

A magnetic resonance imaging of the brain and orbitsshould be done when neurotrophic keratitis is associatedneurologic deficit or the etiology of corneal hypesthesiais in doubt.12

TreatmentSelection of the treatment modality depends on the stageof the ulcer which is being treated.

STAGE I

The treatment of Stage I of neurotrophic keratitis consistsof withdrawal of all epitheliotoxic drugs, use of ocularlubricants (preferably preservative free) and bandagesoft contact lenses. In some cases, one may also considerthe application of the punctual plugs, if the tears aredeficient.

Oral tetracycline 250 mg twice a day or doxycycline100 mg every other day may be used as it reduces theamount of mucus produced and may be used as anadjunct to above therapy.

STAGE II

Ocular Lubricants

Just like in stage 1, copious preservative free artificialtears and ointment should be used to protect the vulner-able epithelium until it adheres tightly to the stroma.

Growth Factors and Cell Attachment Factors

There are various reports available on the use of variousgrowth factors and cell attachment factors, whichstimulate the proliferation and differentiation of cornealepithelial cells and prevent recurrent epithelial erosions.The various growth factors, which have been used,include nerve growth factor,21 epidermal growthfactor,22 laminin23 Fibronectin and albumin.24

Transpore Tape or Patching

Eyelid closure with transpore tape or pressure patchingmay be done which is a temporary measure.

Tarsorrhaphy

Lateral or a complete tarsorrhaphy should be performedto protect loosely attached or non-adherent regeneratingepithelium from the windshield wiper action of theeyelids. Tarsorrhaphy is an easy and reversible processand is preferred in patients who are bedridden or thosewho require lid closure for short duration. In many cases,tarsorrhaphy may be maintained for 1 year as thepremature opening of tarsorrhaphy may result inrecurrence of corneal epithelial disruption.

STAGE III

Despite every effort, the corneal epithelial defect mayprogress to corneal ulcer with stromal lysis resulting in

TABLE 16.4Differential diagnosis of neurotrophic keratitis

Parameters Neurotrophic ulcer Herpetic EpithelialKeratitis

Cause Impaired corneal Active viralsensations replicationDamaged basementmembrane of epithelium

Location Interpalpebral area Any siteShape Oval or with heaped Dendritic ulcer,

epithelium at the border. branching patternSlow/ no change in size with terminal bulbsof ulcer over a period with swollenof time epithelium. Rapid

changes in thesize of the ulcer.

Staining Margins of the ulcer not Margins of thestained with Rose ulcer stained withBengal Rose Bengal

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corneal thinning and perforation. During this stage it isimportant to maintain the integrity of the cornealsurface.

Collagenase Inhibitors

Proteolytic enzymes play a major role in the formationand progression of ulcer. Topical cysteine, acetyl-cysteine 20 percent,13-15 ethylene-diaminetetra-acetic acid0.2 mol/L, or tetracycline16 inhibit collagenase activityand decrease stromal meltdown. These collagenaseinhibitors are relatively nontoxic, although their efficacyin humans has not yet been conclusively demonstrated.

Tetracycline has also been reported to protect thecornea against proteolytic degradation after chemicalburns by inhibiting matrix metalloproteinases (MMPs).Initially it was believed that tetracycline acts by inhibit-ing MMPs after binding with cations, i.e. Zn and Ca but

it is now thought to act primarily through restriction ofthe gene expression of neutrophil collagenase andepithelial gelatinase.16

Tetracycline is given in the dose of 250 mg 4 times aday or doxycycline 100 mg twice a day for 4 to 6 weeks.

Tissue Adhesive

Tissue adhesive, particularly isobutyl cyanoacrylate(histoacryl) along with a bandage contact lens is usedas an adjunctive treatment for filling the corneal ulcerand perforation (< 2 mm) and providing tectonic supportto the cornea. Tissue adhesives also aid in the following:1. Exclusion of polymorphonuclear leukocytes from the

involved stroma (possibly by creating a hypoxicenvironment which is not favorable to polymorpho-nuclear leukocytes

2. Antibacterial action

Figures 16.4A to D: Neurotrophic keratitis healed after multi-layered amniotic membrane transplantation

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Figures 16.5A to D: Neurotrophic keratitis healed after multi-layered amniotic membrane transplantation

3. Promotion of neovascularization and postponingkeratoplasty in an acutely inflamed eye.

Conjunctival Flap

Despite the prompt use of non-surgical modalities, theulcer may progress, requiring surgical intervention. Aconjunctival flap halts the inflammatory process,eliminates frequent medications, improves cosmesis, andprovides an alternative to invasive surgery orenucleation.17 Several studies have been done on the useof the conjunctival flap for persistent ocular surfacedisease and its role is well established.18, 22

A total conjunctival flap or partial or bridgeconjunctival flap is indicated to prevent progression ofthe ulcer to perforation. Total conjunctival flap(Gunderson flap) is indicated for patients with extensive

stromal destruction with a poor visual prognosis.21,22 Fora peripheral or small ulcer, a partial or bridge conjunc-tival flap, particularly of vertical orientation, isperformed. Along with structural support, the partialconjunctival flap maintains good vision for the patientby not involving the central area.

Amniotic Membrane Transplantation

Multi-layered amniotic membrane is used for filling thecavity of the ulcer and restoring the stromal thicknessand integrity of the corneal epithelium.23,24 For thisprocedure cryo-preserved amniotic membrane isemployed. Small pieces are cut from the membrane andcarefully placed into the base of the ulcer. Dependingon the depth and the configuration of the ulcer, two ormore of these pieces are stacked one above the other to

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fill the cavity of the ulcer (Figs 16.4A to 16.5D). Finally,a larger piece of membrane is trimmed to cover the ulcerand the de-epithelialized zone surrounding the ulcer.The membrane is then secured to maintain itsphysiologic orientation (epithelium up and stromafacing the ulcer) with six or more interrupted 10-0 nylonsutures. The knots of the sutures are cut short but notburied. On completion of the surgery, the eye is coveredby a soft bandage contact lens.

The advantages of using a multi-layered amnioticmembrane are:1. Stromal thickness is maintained even after the

amniotic membrane dissolves (perhaps because theamniotic membrane modifies the proliferative andmigratory behavior of stromal keratocytes).

2. It allows rapid epithelial wound healing and long-term stability of the corneal surface.

3. It provides an effective barrier for inflammatory cellentry.

4. It downregulates the synthesis of chemotactic factorsand thereby reduces corneal inflammation.

Penetrating Keratoplasty

For large corneal perforations (>2 mm) an emergencysmall lamellar (blow-out) or full thickness graft isrequired in an acutely inflamed eye.25 However, graftsdo poorly in such anesthetic corneas.

References1. Lambiase A, Rama P, Aloe L, Bonini S. Management of

neurotrophic keratopathy. Curr Opin Ophthalmol 1999;10:270-6.

2. Heigle TJ, Pflugfelder SC. Aqueous tear production inpatients with neurotrophic keratitis. Cornea 1996; 15:135-8.

3. Liesegang TJ. Corneal complications from herpes zosterophthalmicus. Ophthalmology 1985;92:316-24.

4. Cavanagh HD, Pihlaja D, Thoft RA, Dohlman CH. Thepathogenesis and treatment of persistent epithelialdefects. Trans Am Acad Ophthalmol Otolaryngol 1976;81:754-69.

5. Liesegang TJ. Ocular herpes simplex infection:Pathogenesis and current therapy. Mayo Clin Proc 1988;63:1092-105.

6. Paton L. The Trigeminal and its ocular lesion. Br JOphthalmol 1926;10:305-42.

7. Schultz RO, Peters MA, Sobocinski K, Nassif K, SchultzKJ. Diabetic keratopathy as a manifestation of peripheralneuropathy. Am J Ophthalmol 1983;96:368-71.

8. Karacorlu MA, Cakiner T, Saylan T. Corneal sensitivityand correlations between decreased sensitivity andanterior segment pathology in ocular leprosy. Br JOphthalmol 1991;75:117-9.

9. Mackie IA. Neuroparalytic (neurotrophic) keratitis insymposium on contact lenses. Transactions of the NewOrleans Academy of Ophthalmology, St. Louis, Mosby,1973.

10. Van Buskirk EM. Corneal anesthesia after timololmaleate therapy. Am J Ophthalmol 1979;88:739-43.

11. Holland EJ, Schwartz GS. Classification of herpessimplex virus keratitis. Cornea 1999;18:144-54.

12. Foster CS. Ocular surface manifestations of neurologicaland systemic disease. Int Ophthalmol Clin 1979 Summer;19:207-42.

13. Cochet P, Bonnet R. [Corneal esthesiometry. Perform-ance and practical importance] Bull Soc Ophtalmol Fr1961;6:541-50. French.

14. Brown SI, Weller CA. The pathogenesis and treatmentof collagenase-induced diseases of the cornea. Trans AmAcad Ophthalmol Otolaryngol 1970;74:375-83.

15. Berman MB. Collagenase inhibitor: Rationale for theiruse in treating corneal ulceration. Int Ophthalmol Clin1975;15:49-58.

16. Ralpf RA. Tetracyclines and the treatment of cornealstromal ulceration: A review. Cornea 2000;19:274-7.

17. Thoft RA. Conjunctival surgery for corneal diseases. In:SmolinG, Thoft RA (Eds). The Cornea: Scientific founda-tion and clinical practice. Boston, Little Brown, 1983;465-76.

18. Lugo M, Arentsen JJ. Treatment of neurotrophic ulcerswith conjunctival flaps. Am J Ophthalmol 1987;103:711-2.

19. Alino AM, Perry HD, Kandellopaulos AJ, et al. Conjunc-tival flaps. Ophthalmology 1998;105:1120-3.

20. Lesher MP, Lohman LE, Yeakley W, et al. Recurrenceof herpetic stromal keratitis after a conjunctival flapsurgical procedure (letter). Am J Ophthalmol 1992;114:231-3.

21. Rosenfeld SI, Alfoso EC, Gollamudi S. Recurrent herpessimplex infection in conjunctival flap. Am J Ophthalmol1993;116:242-4.

22. Buxton JN. Therapeutic conjunctival flaps and tarsor-raphy. Contact Intraocular Lens Med J 1981;7:150-2.

23. Kruse FE, Rohrschneider K, Volcker HE. Multilayeramniotic membrane transplantation for reconstructionof deep corneal ulcers. Ophthalmology 1999;106:1504-11.

24. Khokhar S, Natung T, Sony P, Sharma N, Agarwal N,Vajpayee RB. Amniotic membrane transplantation inrefractory neurotrophic corneal ulcers: a randomized,controlled clinical trial. Cornea 2005;24:654-60.

25. Langston RHS, Pavan-Langston D. Penetrating kerato-plasty for herpetic keratitis: Decision making andmanagement. Int Ophthalmol Clin 1975;15:125-33.

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Peripheral Ulcerative Keratitis17

Introduction

Peripheral corneal ulceration or peripheral ulcerativekeratitis (PUK) is usually characterized by crescent-shaped destructive inflammation of the juxtalimbalcorneal stroma which is associated with an epithelialdefect, presence of stromal inflammatory cells, andprogressive stromal degradation and thinning. Conjunc-tival, episcleral and scleral inflammation are usuallypresent. It leads to progressive necrosis of the cornealstroma, leading to perforation and blindness.

Epidemiology

Collagen vascular diseases are responsible for approxi-mately half of the non-infectious cases of PUK.Rheumatoid arthritis (RA) is the most common collagenvascular disorder that causes PUK and is responsiblefor 34 percent of cases of noninfectious PUK.1 It mayalso be the initial manifestation of Wegener’s granula-matosis2 (WG) and polyarteritis nodosa (PAN).

It is rarely reported after relapsing polychondritis(RP) and systemic lupus erythematosis (SLE). Mooren’sulcer is a rare local autoimmune disease associated withPUK and is a diagnosis made by exclusion. It is believedthat some of these cases may have been the presentingmanifestation of an occult systemic disease rather thana true Mooren’s ulcer.

There is no predilection for any age for a case of PUK.Since PUK is more common in people with collagenvascular disorders (especially RA), it is more commonin females than in males. However, Mooren’s ulcer ismore common in males than females.

Etiology

First and foremost, an infectious origin of the PUK mustbe excluded. In any case of limbal thinning associated

with corneal infiltrate, it is mandatory to assume aninfectious etiology until proved otherwise.

Although most bacterial organisms affect the centralcornea, all are capable of producing limbal ulceration.The most likely microbial organisms, which can causePUK, include Staphylococcus (Fig. 17.1) fungal organisms(Fig. 17.2), and herpes simplex virus (Figs 17.3A and B).

The major risk factors of PUK are the connectivetissue and vasculitic diseases (Table 17.1).1,2 Otherdisorders that can cause PUK include systemic and localinfectious conditions, as well as local degenerativedisorders (Table 17.1).

PathogenesisThe peripheral cornea has distinct morphologic andimmunologic characteristics, which make it prone toinflammatory reactions. Unlike the avascular centralcornea, the peripheral cornea is closer to limbalconjunctiva and derives its blood supply and lymphaticsfrom the limbal capillary vessels, which extendapproximately 0.5 mm into the clear cornea. This is asource of immunocompetent cells, such as macrophages,Langerhan’s cells, lymphocytes, and plasma cells.Immune complexes circulating in the blood of thepatients with collagen vascular disease can lodge at theends of the limbal vessels by virtue of their size and therestrictive molecular sieving characteristics of the cornea.The peripheral cornea contains five times higher levelsof the first component of the complement (C1) than doesthe central cornea which stimulates chemotaxis of theneutrophils to the area.3 The concentration of Ig M whichis a large molecule directed against Ig G (rheumatoidfactor) is also greater at this site.4 Immune complexes ofrheumatoid factor and Ig G can deposit in the peripheralcornea and produce inflammation and cornealulceration. Langerhans’ cells, which are the pre-eminentantigen-presenting cell, are also concentrated moredensely in the peripheral cornea.

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4Peripheral Ulcerative Keratitis

Any inflammatory stimulus in the peripheral corneathat is caused by invasion of microbial organisms(bacteria, virus, fungi, and parasites), immune complexdeposition (in systemic immune diseases), trauma,malignancy, or dermatologic conditions may producelocal and systemic immune responses, resulting inneutrophil recruitment and complement activation atthe limbus.

Activated complement components increase vascularpermeability and further generate chemotactic factorsfor neutrophils (e.g. C3a, C5a), which infiltrate the peri-pheral cornea and release proteolytic and collagenolyticenzymes, reactive oxygen metabolites, and proinflam-matory substances (such as platelet-activating factor,

leukotrienes, prostaglandins), causing dissolution anddegradation of the corneal stroma. The inflamed limbalconjunctiva itself is capable of producing collagenase,which also causes stromal degradation.

Systemic diseases that may cause immune complexdeposition at the peripheral cornea and cause PUKinclude collagen vascular diseases such as rheumatoidarthritis (RA), Wegener’s granulomatosis (WG),polyarteritis nodosa (PAN), relapsing polychondritis(RP), and systemic lupus erythematosus (SLE).5

Infectious conditions, whether systemic (hepatitis,syphilis) or local (herpes simplex keratitis, fungalkeratitis), and noninfectious local disorders (Mooren’sulcer, marginal keratitis) also may cause PUK.

Figure 17.1: Peripheral ulcerative keratitis due to Staphylococci Figure 17.2: Peripheral ulcerative keratitis due to Aspergillus

Figures 17.3A and B: Peripheral ulcerative keratitis due to Herpes simplex virus

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CLINICAL PICTUREA careful history, physical and systemic evaluation alongwith appropriate laboratory studies will establish aprecise diagnosis.

HISTORYThe ocular symptoms vary, but patients may complaintof a nonspecific foreign body sensation with or withoutpain, tearing, photophobia, and reduced visual acuity.The decrease in the visual acuity may be gradual or asudden loss of vision may occur when PUK progresses. PUK is frequently a manifestation of an occult systemicdisease. Thus, a thorough systemic history is veryimportant and should include chief complaints, charac-teristics of present illness, past medical history, familyhistory, and a meticulous systemic history. Sometimesan underlying systemic disease may be diagnosed bythe presence of PUK.

PUK associated with RA, WG, PAN, and RP isassociated with scleritis, and may also be associated withsignificant pain.6,7 PUK in patients with Mooren’s ulcermay also present with pain, although there is no scleralinvolvement.

The onset of ulceration should be noted as acute(onset of symptoms within 2 weeks of presentation),subacute (within 3 months) or chronic (> 3 months).

Past medical history should be sought especially inrelation to a systemic disease such as RA, SLE, PAN,WG and RP. History should be taken for constitutionalsymptoms, such as chills, fever, decreased appetite,recent weight loss, and fatigue, any problems related toskin disorders, respiratory, cardiac, gastrointestinal andneurologic symptoms. This may elicit the presence ofsystemic disease, which may cause PUK.

ExaminationExamination should include a complete systemic and athorough ocular examination.

SYSTEMIC

Any lesion on the skin, face, trunk, joints, and extremitiesshould be noted. Diagnosis of PUK in a patient of colla-gen vascular disease may require multiple evaluationsby a rheumatologist or clinical immunologist as clinicallydetectable manifestations of these systemic diseases mayevolve slowly.8

OCULAR

A complete ocular examination should be performedwith special emphasis on the conjunctiva, sclera, andcornea. Visual acuity, laterality, intraocular pressure and

TABLE 17.1Etiology of peripheral ulcerative keratitis

Infections Non-infections

Ocular • Bacterial • Mooren’s ulcer(Staphylococcus, • Terrien’s marginalStreptococcus, degenerationMoraxella, • Pellucid marginalHaemophilus degenerationGonococcus) • Blepharitis

• Keratoconjunctivitissicca

• Viral (Herpes • Neurotrophic andsimplex, herpes Neuroparalyticzoster) • Nutritional deficiency

• Acanthamoeba • Ocular chemical injury• Fungal organisms • Contact lens

• Trauma • Post-surgical

Systemic • Tuberculosis • Rheumatoid arthritis• Syphilis • Giant cell arthritis• Varicella zoster • Wegener’s

granulomatosis• Gonorrhea • Systemic lupus

erythematosis,• Sjögren’s syndrome• Relapsing polychondritis• Progressive systemic

sclerosis• Churg-Strauss

syndrome• Crohn’s disease• Ulcerative colitis• Rosacea • Steven Johnson’s

syndrome• Sarcoidosis • Behçet’s disease• Psoriasis• Malignancy• Cryoglobulinemia• Schönlein-Henoch

purpura• Serum sickness• Pyoderma

gangrenosum • Erythema devatum

diutinum

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detailed results of biomicroscopic slit-lamp examinationshould be recorded. Corneal sensations and lacrimalfunction by Schirmer test should also be recorded. Apartfrom this the details of anterior chamber (for thepresence of any inflammation), vitreous, and fundusshould also be noted.

Slit-lamp examination generally reveals a presenceof a crescent-shaped lesion of the juxtalimbal cornealstroma associated with an epithelial defect, stromalyellow-white infiltrates composed of inflammatory cells,and varying degrees of corneal stromal thinning(minimal to full thickness) adjacent to the limbus. Insevere cases, the peripheral cornea is progressivelythinned out both circumferentially and centrally. Theleading edge of the ulcer is infiltrated and untreatedPUK will eventually progress towards the visual axis.

Corneal ulceration should be graded as follows:< 25 percent depth of ulceration = 1, 25-50 percent = 2,50-75 percent = 3 and 75-100 percent = 4.

Scleral invovement should be characterized asdiffuse, nodular or necrotizing. PUK when accompaniedby a necrotizing scleritis indicates the presence of anunderlying systemic disease (Fig. 17.4).6

InvestigationsThe various investigations in a case of PUK includessystemic as well as ocular investigations. The tests forsystemic evaluation should be done, wherever available.The various laboratory tests should focus on thesuspected underlying systemic disease and include thefollowing:

1. Complete blood cell count2. Erythrocyte sedimentation rate3. Serum creatinine, blood urea nitrogen4. Rheumatoid factor (RF) in cases of RA (80% positive

in RA)5. Angiotensin-converting enzyme (ACE) which may

be elevated in sarcoidosis6. Antinuclear antibodies (ANA) which are positive

in patients with SLE and RA7. Antineutrophil cytoplasmic antibodies (ANCA);

C-ANCA sensitivity of 96 percent for active genera-lized WG, 67 percent for active regional disease,and 32 percent for WG in full remission after initialregional symptoms9

8. Anti-type II antibodies (positive in RP)9. Complement - C3 and C4, CH50; in patients with

SLE10. Hepatitis B surface antigen (HBsAg); present in

40 percent of patients with PAN.

Imaging StudiesChest X-ray and sinus CT scan to rule out WG, sarcoi-dosis, and tuberculosis should be done and otherradiographic studies of the affected joints should alsobe undertaken.

Microbiology Work UpRoutine scraping and culture of the ulcer arerecommended in all cases (as described for microbialkeratitis).10-12 PUK can be caused by microbial organismssuch as bacteria, fungus or herpes. Hence in all casescorneal scraping should be done and smears should beprepared and cultures should be sent.

BiopsyThe conjunctival resection/biopsy is helpful inestablishing an etiologic diagnosis in some cases andalso helps in removing the limbal source of collagenasesand other factors causing progressive ulceration.Biopsies are taken from the bulbar conjunctiva adjacentto the ulcerating cornea. In selected cases, episcleral ,scleral and /or corneal tissue may also be excised andanalyzed.

HISTOLOGIC FINDINGS

In cases of biopsied specimens any evidence of vasculitis,perivasculitis, granulomas, eosinophils, mast cells and

Figure 17.4: PUK with necrotizing scleritis

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neutrophil and lymphocyte infiltrate should bedocumented to corroborate the diagnosis of collagenvascular disease. However, vasculitis may be segmentaland focal and hence a single negative biopsy does notrule it out.

In Mooren’s ulcer, corneal thickening occurs at themargin of the ulcer where inflammatory cells haveinvaded the anterior stromal layers. However, theinflammation is nonspecific, and no etiologic agent canbe identified. Necrosis of the involved epithelium andstroma is seen.

TreatmentThe treatment is aimed towards promoting epithelialwound repair and limiting ulceration and supportingthe repair process.

Medical TherapyThe local treatment is aimed at preventing or reducingthe epithelial defect, while systemic treatment is givento treat the underlying disease. One of the aims oftreatment is epithelization of the ulcer, which will haltthe progression of the corneal ulceration.

Topical Therapy

In cases where a microbial organism is suspected tocause PUK, antimicrobial therapy is started dependingon the organism. However, in cases where microbialcause is ruled out, topical corticosteroids are themainstay for treatment of PUK. Topical prednisoloneacetate 1% eye drops four to six times a day are givenwhich are tapered after the inflammation settles down.

Topical 1 percent medroxyprogesterone (whichinhibits collagenase synthesis) is given in qid doses.Alternatively, topical 20 percent N-acetylcysteine (acompetitive inhibitor of collagenase) may also be givenin similar doses. Copious lubricants and ointments(preferably preservative free) in aiding re-epitheliali-zation. Prophylactic topical antibiotics such aschloramphenicol 0.3 percent may be given in qid doses.

Systemic Therapy

Antibiotics

Systemic collagenase inhibitors such as tetracycline 250-mg tab qid or doxycycline 100 mg tab bid for the initialone month followed by tapering dose may help inslowing the progression of the pathology.

Immunosuppressive Therapy

It is generally seen that in cases of PUK associated withsystemic diseases, recurrences following symptomatictreatment are common.

The systemic immunosuppression therapy isindicated in cases of PUK in the following situations:14

1. PUK unresponsive to aggressive conventionalmedical and surgical therapy

2. Bilateral and/or progressive Mooren’s ulcer3. PUK associated with potentially lethal systemic

vasculitic syndromes, such as PAN, RA, SLE, RP,WG, PSS, Sjögren’s syndrome, allergic angiitis ofChurg-Strauss, and giant cell arteritis

4. PUK associated with necrotizing scleritis withvasculitis based on histopathologic analysis.

Corticosteroids

High dose oral prednisone is started, as the chemo-therapeutic agents begin to act optimally only after4-6 weeks. Prednisone is given 1-1.5 mg/kg/d initially(not to exceed 60-80 mg/d) (Table 17.2). The dose isadjusted on the basis of the clinical response and adverseeffects.

Cyclophosphamide

Cyclophosphamide is the drug of choice for almost allPUK associated with connective tissue disorders.Cyclophosphamide is used in the oral dose of 1 to2 mg/kg /day or as pulsed intravenous therapy every3 to 4 weeks under rheumatologist or internal medicineguidance (Table 17.2). The dose is adjusted to maintainthe total blood count between 3000 and 4000 permicroliter for optimal efficacy and safety.

Methotrexate

Methotrexate is preferred as the initial drug by someophthalmologists over cyclophosphamide, as it is lesstoxic. Oral methotrexate 10 to 25 mg/week is given forthe treatment of scleritis and PUK, which is unrespon-sive to corticosteroids.

Cyclosporine

In cases of recalcitrant disease, oral cyclosporin A is usedin the dose of 2.5 to 5.0 mg/kg/day with frequent moni-toring of blood pressure and renal functions (Table 17.2).The doses are adjusted so that the trough levels of wholeblood cyclosporin are in the range of 150-200 ng/ml.

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TABLE 17.2Drugs given in a case of PUK

Prednisone Adult dose 1 mg/kg/d PO initially; not to exceed 60-80 mg/d Mechanism of action Provides prompt suppression of inflammatory and immunologic reaction

Immunosuppressive agents—Inhibit key factors that mediate immune response

Methotrexate (Folex PFS, A folic acid analog which acts on the enzyme dihydrofolate reductase, which catalyses the reductionRheumatrex) of folate to tetrahydrofolate, a compound necessary for DNA synthesis. Actively replicating cells,

such as the leukocyte, are affected and their functions suppressed Adult dose 7.5-12.5 mg/wk PO/IM/SC single dose initially; not to exceed 40 mg/wk Contraindications Hypersensitivity,hepatic insufficiency, immunodeficiency syndromes, pre-existing blood dyscrasias,

renal insufficiency Precautions Monitor complete blood counts monthly and liver and renal function 1 to 3 monthly. Fatal reactions

reported when administered concurrently with NSAIDsAzathioprine (Imuran) Purine nucleoside analog which is activated in the liver producing metabolites, which interfere with

purine metabolism. T- and B-cell functions are suppressed. Adult dose 1-3 mg/kg/d PO initially Contraindications Hypersensitivity reactionsPrecautions Increases risk of neoplasia,

May cause liver and kidney toxicityHematologic toxicities may occurCheck liver function tests, kidney function tests and complete blood counts level prior to therapyMonitor liver, renal, and hematologic function

Cyclosporin A An amino acid cyclic peptide which acts on T-cell replication and activity (Sandimmune, Neoral,SangCyA) Adult dose 2.5-5 mg/kg/d PO divided bid initially; not to exceed 10 mg/kg/d Contraindications Documented hypersensitivity; uncontrolled hypertension or malignancies. Precautions Evaluate renal and liver functions 3 monthly by measuring BUN, serum creatinine, serum bilirubin,

and liver enzymes may increase risk of infection and lymphoma Cyclophosphamide Nitrogen mustard derivative, which affects cell replication by alkylating purines in DNA and RNA (Cytoxan) Adult dose Initial dose is 2 mg/kg/d PO; not to exceed 3 mg/kg/d Contraindications Hypersensitivity reactions; breastfeeding; immunosuppression; leukopenia or thrombocytopenia Precautions Bone marrow depression may occur requiring regular blood count monitoring

Long-term oral therapy may lead to myelodysplasiaUrinalysis required, malignancy, ovarian and testicular atrophy, lLymphopenia with opportunistic infections may occur

TNF Alpha BlockersRecently, Infliximab (Remicade™, Centacor, Malvern,PA) a chimeric antibody against the proinflammatorycytokine tumor necrosis factor alpha (TNFα) has alsobeen used (Table 17.2).15 It is effective for treatment ofRA that was refractory to conventional disease-modifying drugs. Sterile corneal ulceration developswhen there is an imbalance between MMPs and theirphysiological inhibitors, such as tissue inhibitors of

matrix metalloproteinases (TIMPs), that may occur onthe ocular surface of patients with RA. The target ofinfliximab, TNFα, is recognized to stimulate theproduction of the matrix metalloproteinases (MMPs)that are responsible for the dissolution of the cornealepithelial basement membrane and stroma in PUK.

Infliximab is given in three doses of 3 mg/kg IVinitially and then at weeks 2 and 6 and then every 8weeks for a period of 8 to 18 months.

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Another systemically administered TNFα inhibitor,etanercept, which is a soluble TNF receptor, has alsobeen observed to be effective for treatment of necrotizingscleritis and keratitis.5 Both of these anti-TNF agents canbe used synergistically with methotrexate, which mayenhance their effect. They have a much better safetyprofile than cyclophosphamide but do carry an increasedrisk of opportunistic infections.

When local or systemic infectious causes aresuspected, therapy must be aimed at eliminating theinfectious organism using the appropriate antibioticmedications based on clinical presentation or culture.

Referral to an appropriate specialist may be neces-sary. In patients with connective tissue diseases, co-management with a rheumatologist is necessary toaddress the systemic disease. Pulmonary, nephrology,cardiac, hematology, and infectious disease consulta-tions may be sought depending on the patient’ssymptoms and laboratory findings. Regular consultationwith an oncologist may be necessary for those patientswho are receiving chemotherapy.

SURGICAL TREATMENT

Tissue AdhesivesTissue adhesives, such as cyanoacrylate glue, arerecommended for use in impending perforation andperforation size smaller than 1-2 mm. Adhesiveapplication follows keratectomy and conjunctivalresection to remove sources of collagenase, cytokines,and inflammatory cells from the ulcerated cornea,temporarily preventing further stromal loss. Applicationof a bandage contact lens prevents discomfort anddislodging of the adhesive.

Tectonic procedures, including lamellar keratoplasty,penetrating keratoplasty, and corneoscleral patch grafts,are performed as needed to maintain the integrity ofthe globe when corneoscleral perforation is imminentor has occurred. A single stage or a multi-stage proce-dure may be undertaken for optimal visual rehabili-tation.

FOLLOW-UP

Continued, possibly lifelong, follow-up care is necessaryeven after complete resolution since relapses may occur.Furthermore, many patients may require prolongedsystemic steroid, non-steroidal anti-inflammatory, and/or chemotherapeutic medications for the systemicdisease despite a quiet eye.

COMPLICATIONS

Ocular complications include corneal scarring andneovascularization with irregular astigmatism, cornealthinning and perforation, loss of vision, and evenblindness.

PROGNOSISIn patients with collagen vascular diseases, PUK withnecrotizing scleritis is associated with poor lifeexpectancy because of the presence of subclinicalsystemic vasculitis.

Specific Diseases

RHEUMATOID ARTHRITIS

Rheumatoid arthritis (RA) is a chronic systemicinflammatory disease, which produces the arthritis ofthe hands, wrists, knees and feet. It is diagnosed on thebasis of the diagnostic criteria followed by the AmericanCollege of Rheumatology.

Keratoconjunctivitis sicca (KCS) is the most commonocular manifestation of the disease and is due to meibo-mian gland dysfunction. PUK is a common occurrencein RA and associated scleritis is a distinguishing feature.Marked peripheral thinning or marginal furrows rapidlyprogressive in nature can occur.1 No (Fig. 17.5) asso-ciated vascularization or epithelial defect is seen.

The patient’s clinical profile and positive serologicstudies help in establishing the diagnosis.4 The 5 yearsmortality rate for untreated RA with either PUK or

Figure 17.5: Rheumatoid melt

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scleritis is approximately 50 percent. Appropriatesystemic therapy in addition to topical treatment helpsin effective management of the disease.

WEGENER’S GRANULOMATOSIS

This is a rare multi-system granulomatous necrotizingvasculitis characterized by respiratory and renalinvolvement. Ocular involvement occurs in upto 50 to60 percent.2 The associated conjunctivitis and scleritismay progress to PUK or PUK may be present as anisolated finding. The sclera is usually involved in thesecases and this differentiates it from Mooren’s ulcer inwhich sclera is generally not involved.

A laboratory test, which helps in the diagnosis ofWegener’s granulomatosis, is the serum anti-neutrophilcytoplasmic antibody (ANCA) test.9 ANCA titerscorrelate with the severity and extent of the disease andtend to decrease in remission of the disease. Twopatterns of staining are associated with this test –the C-ANCA (cytoplasmic anti-neutrophil cytoplasmicantibody) and the P-ANCA (perinuclear anti-neutrophilcytoplasmic antibody). The C-ANCA test has 99 percentspecificity and 96 percent sensitivity. This test also helpsto follow the clinical response to therapy and chancesof recurrence of PUK are more if these values have notnormalized, despite apparent clinical remission whentherapy has been tapered or discontinued.3

POLYARTERITIS NODOSA

PAN is a rare multi-system disease with necrotizingvasculitis of the small and medium sized arteries.Histopathological identification of the vascular changesis diagnostic of PAN. The various ophthalmic manifes-tations include choroidal vasculitis (most commonophthalmic manifestation), PUK, conjunctival lesions,scleritis, choroiditis, central retinal artery occlusion arethe various ophthalmic manifestations. The clinicalcharacteristics of PUK in this disease are similar to thoseof Mooren’s ulcer. Hepatitis B surface antigen is positivein about 50 percent patients with PAN. Systemicimmunosuppressive therapy is the key to retard theprogression of PUK.

OTHER COLLAGEN VASCULAR DISEASES (CVD)

PUK is rarely seen in other CVD such as systemicsclerosis, SLE and RP. The clinical profile and thelaboratory tests help in confirming the diagnosis. The

detection of antibodies to double stranded (dsDNA) isspecific for SLE. No laboratory test is specific forrelapsing polychondritis. Dry eye is seen in about 70percent of systemic sclerosis patients. PUK may occurunrelated to the KCS.

STAPHYLOCOCCAL MARGINAL KERATITIS

Staphylococcal marginal keratitis occurs in a patient withchronic blepharitis. This presents as a peripheralinfiltrate with breakdown of the overlying epithelium(Fig. 17.6). There is a clear zone between the infiltrateand limbus. Pain is not a significant feature as in a caseMooren’s ulcer. Immune complex mediated reactionsagainst the microbial antigens have been attributed tocause the ulceration.

TERRIEN’S MARGINAL DEGENERATION (TMD)

TMD is usually non-inflammatory and does showfeatures of corneal ulceration. It is more common inmales and is asymmetrical. TMD begins superiorly asfine punctate stromal opacities and a clear zone existsbetween the limbus and the infiltrate. Superficialvascularization is also present. However, the epitheliumoverlying is intact. The peripheral thinned zone isdetermined by a white lipid line at its central edge (Fig.17.7). Slowly progressive thinning spreads circum-ferentially and causes irregular astigmatism. An obliquepseudopterygium is associated in about 20 percent ofcases and perforation may occur due to trivial trauma.Recurrent inflammation, scleritis/episcleritis is rarelyseen.

Figure 17.6: Staphylococcal marginal keratitis

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Figure 17.8: Rosacea keratitisFigure 17.7: Terrien’s marginal degeneration

SENILE FURROW DEGENERATION (SFD)

SFD is thinning of the interval between the limbus andthe arcus senilis and occurs in the elderly.

ROSACEA KERATITIS

Ocular rosacea is a relatively common disorder. Thediagnosis largely rests on its association with thecutaneous disease characterized by persistent erythema,telangiectasia, papules and pustules and hypertrophicsebaceous glands of the face and neck. Ocular involve-ment is seen in upto 58 percent of cases and ranges fromchronic blepharoconjunctivitis to neovascularization andthinning. PUK is rarely associated with ocular rosacea.The lesion begins as vascularized marginal subepithelialinfiltrates, which are initially small and round. Untrea-ted cases progress to ulcers spreading towards the centerof the cornea (Fig. 17.8). Oral tetracycline (250 mg4 times/day) or doxycycline (100 mg bd) is effectivealong with topical corticosteroids which is given for 4to 6 weeks duration.

MOOREN’S ULCER

Definition

Mooren’s is a chronic. It is characterized by the presenceof an overhanging edge overlying central and leadingedge that starts in the periphery and may progresscentrally or circumferentially to involve the entire cornea(Fig. 17.9).

Males have a greater predilection for this disorder(1.6 times).16

Types of Mooren’s Ulcer

Mooren’s ulcer has been classified into 2 groups accord-ing to the age of onset and the clinical characteristics.17

Type I is benign and usually unilateral with mild tomoderate symptoms. It occurs in older people (over 35years) and usually responds well to medical and surgicaltreatment (Fig. 17.9). Type II is malignant and occurs inyounger patients (< 35 years) and is more likely to bebilateral (in 75% cases) with relatively more pain andpoor response to therapy (Fig. 17.10).

Pathogenesis

Autoimmunity is suspected to be involved in thepathogenesis of Mooren’s ulcer based on evidence ofcirculating antibodies18,19 to the corneal stroma andspecific cell mediated immune reaction toward apartially purified corneal antigen (Co-Ag). Reports havedescribed the presence of inflammatory cells,immunoglobulin and increased expression of HLA classII molecules in the cornea and conjunctiva, adjacent tothe ulcers.20

The triggering factor instigating this autoimmuneresponse is not clearly known. Privileged cornealantigens may become the target of the patient’s immunesystem by local exposure of these antigens due to cornealtrauma, surgery or infection.21,22 It has been proposedthat organisms such as a helminth23 stimulate the

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production of antibodies that cross-react with cornealantigens and cause ulcer. Mooren’s ulcer has occurredfollowing corneal trauma and eye surgery.22

Histopathology

Pathological examination of the specimens of involvedcorneal tissue have shown presence of plasma cells,neutrophils, mast cells and eosinophils in the involvedregions.24 There was destruction of the collagen matrix.Epithelium and Bowman’s layer were absent. Midtromashowed hyperactivity of fibroblasts with disorganizationof the collagen lamellae. The deep stroma was intactbut contained heavy macrophage infiltration. Heavyneutrophil infiltration and dissolution of the superficialstroma were present at the leading edge of the ulcer.Adjacent conjunctiva shows epithelial hyperplasia anda subconjunctival lymphocytic and plasma cellinfiltration.

Clinical FeaturesPatients with Mooren’s ulcer will complain of rednessof the eye, tearing and photophobia, but pain is typicallythe outstanding feature. The pain is excruciating andmay seem well out of proportion the corneal inflam-mation. Decreased visual acuity may be secondary toassociated iritis irregular astigmatism due to theperipheral corneal thinning.

The disease may begin as several patchy peripheralstromal infiltrates that then coalesce, commonly in theregion of the palpebral fissure. Generally there isinvolvement upto the limbus. The ulcerative process

spreads circumferentially and then centrally to involvethe entire cornea eventually. The anterior 1/3 to 1/2 ofthe stroma is involved characteristically with a steepoverlying central and leading edge. Healing andvascularization occurs slowly over 4-18 months. Partsof the ulcer may be quiescent while the remaining maybe active (Fig. 17.11). The end stage is a typical scarred,vascularized thinned cornea with the patient experienc-ing sudden relief from the excruciating pain.

Adjacent conjunctiva may be inflamed and viritis issometimes associated with Mooren’s ulcer. Hypopyonis rare unless secondary infection is present. Sometimesthere may be associated glaucoma and cataract.Perforation is rare, though it can occur, especially follow-ing trivial trauma due to the presence of weakenedcornea (Fig. 17.12).

Diagnosis

Investigations include laboratory investigations to ruleout several systemic diseases leading to PUK. Theseinclude immunology and dermatology workup, X-raychest and sinus X-ray, Mantoux, hemogram, liver andrenal function tests, rheumatoid factor, autinuclearantibody (ANA), antineutrophil cytoplasmic antibody(ANCA), complement fixation, angiotensin convertingenzyme, VDRL, hepatitis B, hepatitis C and HIV antigendetection, serum protein electrophoresis and stoolexamination. Scrapings should be done to rule outinfectious pathology per se or secondary infection dueto Mooren’s ulcer.

Figure 17.10: Mooren’s ulcer malignant preoperativelyFigure 17.9: Mooren’s ulcer

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Treatment

The management of Mooren’s ulcer depends on thepresentation of the disease and can be done both bymedical or surgical means depending on the severity ofthe disease.

MEDICAL MANAGEMENT

The mainstay for medical management of Mooren’sulcer is topical corticosteroids. These are given in 4 to 6hourly dosage initially. However, if healing is notsatisfactory the dose may be increased to 1 hourlyfrequency. Generally 1% prednisolone acetate eyedropsare used.

Gradual tapering of topical steroids over a period isdone during the healing phase of the disease. It isimperative to maintain the patient on topical dilutesteroids over a prolonged period. Use of oral pulsesteroids (60-100 mg of oral prednisolone) has also beenadvocated where topical therapy is ineffective for over10 days or in cases of deep ulcers.25 Topical tetracycline,medroxy progesterone 1 percent may be used becauseof their acute collagenolytic properties. A therapeuticbandage contact lens may be used in conjunctiva alongwith topical therapy. Prophylactic topical chlorom-phenicol eyedrops are also given in qid doses.

Some people also give topical cyclosporin A 2%eyedrops in qid doses. However, this is not found to bevery effective.26

In malignant cases systemic corticosteroid should beadded. Systemic prednisolone is given in the dose of1.5 mg/per/kg body weight.

Systemic immunosuppression is indicated in casesof bilateral relentlessly progressive Mooren’s ulcer notresponding to previous therapeutic modalities. Thedrugs which can be used in cases of Mooren’s ulcerinclude: cyclophosphamide(2 mg/kg/d), Methotrexate(7.5-15 mg weekly), Azothioprine (2 mg/kg/d) andCyclosporine A (loading dose of 8 mg/kg in two divideddoses for 2 days, thereafter being reduced to 3-4 mg/kg/d to maintain serum level of 200-400 ng/ml).27

SURGICAL MANAGEMENT

The surgical management of Mooren’s ulcer includelimbal conjunctivectomy, keratoepithelioplasty andkeratoplasty.

Limbal Conjunctivectomy/Resection

Conjunctival resection may be done if the ulcerprogresses despite steroid therapy.28 The excision andrecession of the adjacent limbal conjunctiva aids in theremoval of proteolytic conjunctival enzymes or theinflammatory cells that produce antibodies against thecornea. A wide conjunctival resection to bare the sclera,extending at least 2 clock hours on either side of theulcer and 4 mm posteriorly has been recommended .

Keratoepithelioplasty

In keratoepithelioplasty several fresh donor corneallenticules with intact epithelium are placed near thedistal side of the ulcerated area and securely suturedon the bare sclera with 10.0 nylon interrupted sutures.29

Figure 17.11: Healing Mooren’s ulcer Figure 17.12: Mooren’s ulcer with perforation

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The lenticules form a biological barrier between the hostcornea and the conjunctiva which is the source ofimmunological mediators. This procedure can becombined with a corneoscleral lamellar graft.

Superficial Keratectomy

Superficial lamellar keratectomy along with conjunctivalresection including the resection of the overhanging lipof the ulcerating cornea and application of tissueadhesive with bandage soft contact lens application oramniotic membrane has been described.

Keratoplasty

In advanced cases surgery may be done in two stages,that is initial lamellar tectonic grafting followed bycentral penetrating keratoplasty. Lamellar keratoplastyremoves antigenic targets of the cornea, preventsimmunological reactions, reconstructs the anatomicalstructure, prevents perforation and improves vision (Figs17.13A and B).

References1. Brown SI, Grayson M. Marginal furrows. A characteristic

corneal lesion of rheumatoid arthritis. Arch Ophthalmol1968;79:563-7.

2. Bullen CL, Liesegang TJ, McDonald TJ, DeRemee RA.Ocular complications of Wegener’s granulomatosis.Ophthalmology 1983;90:279-90.

3. Foster CS, Sainz de la Maza M. Immunological consi-derations of the sclera. In: Foster CS (Ed): The Sclera.1st ed. New York: Springer-Verlag 1993;33-58.

4. Carson DA. Rheumatoid factor. In: Kelley WN, HarrisED Jr, Ruddy S, Sledge CB (Eds): Textbook of Rheuma-tology. 3rd ed. Philadelphia: WB Saunders Co; 1989;664-79.

5. Foster CS, Forstot SL, Wilson LA. Mortality rate inrheumatoid arthritis patients developing necrotizingscleritis or peripheral ulcerative keratitis. Effects ofsystemic immunosuppression. Ophthalmology 1984;91:1253-63.

6. Gregory JK, Foster CS. Peripheral ulcerative keratitis inthe collagen vascular diseases. Int Ophthalmol Clin 1996;36:21-30.

7. Hoang-Xaun T, Foster CS, Rice BA. Scleritis in relapsingpolychondritis. Response to therapy. Ophthalmology1990;97:892-8.

8. Jabs DA, Rosenbaum JT, Foster CS, et al. Guidelines forthe use of immunosuppressive drugs in patients withocular inflammatory disorders: Recommendations of anexpert panel. Am J Ophthalmol 2000;130:492-513.

9. Ludemann G, Gross WL. Autoantibodies againstcytoplasmic structures of neutrophil granulocytes inWegener’s granulomatosis. Clin Exp Immunol 1987;69:350-7.

10. Messmer EM, Foster CS. Vasculitic peripheral ulcerativekeratitis. Surv Ophthalmol 1999;43:379-96.

11. Mondino BJ. Inflammatory diseases of the peripheralcornea. Ophthalmology 1988;95:463-72.

12. Robin JB, Schanzlin DJ, Verity SM, et al. Peripheralcorneal disorders. Surv Ophthalmol 1986;31:1-36.

13. Shiuey Y, Foster CS. Peripheral ulcerative keratitis andcollagen vascular disease. Int Ophthalmol Clin 1998;38:21-32.

14. Tauber J, Sainz de la Maza M, Hoang-Xuan T, FosterCS. An analysis of therapeutic decision making regard-ing immunosuppressive chemotherapy for peripheralulcerative keratitis. Cornea 1990;9:66-73.

Figure 17.13A: Mooren’s ulcer preoperatively Figure 17.13B: Mooren’s ulcer after crescentic patch graft

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15. Atchia II, Kidd CE, Bell RW. Rheumatoid arthritis-associated necrotizing scleritis and peripheral ulcerativekeratitis treated successfully with infliximab. J ClinRheumatol 2006;12:291-3.

16. Lewallen S, Courtright P. Problems with currentconcepts of the epidemiology of Mooren’s corneal ulcer.Ann Ophthalmol 1990;22:52-5.

17. Wood TO, Kaufman HE. Mooren’s ulcer. Am JOpthalmol 1971;71:417-22.

18. Brown SI, Mondino BI, Rabin BS. Autoimmune pheno-menon in Mooren’s ulcer. Am J Ophthalmol 1976; 82:835-40.

19. Gottsch ID, Liu’SH, Minkovitz IB, et al. Autoimmunityto a cornea-associated stromal antigen in patients withMooren’s ulcer Invest Ophthalmol Vis Sci 1995;36:1541-7.

20. Zhao JC, Jin XY. Immunological analysis and treatmentof Mooren’s ulcer with cyclosporin A. Cornea 1993;12:481-8.

21. Wilson SE, Lee WM, Murakami C, Weng J, MoningerGA. Mooren’s corneal ulcers and hepatitis C virusinfection. N Engl J Med 1993;329:62.

22. Mondino BJ, Hofbouer JD, Foos RY. Mooren’s ulcer afterpenetrating keratoplasty. Am J Ophthalmol 1987;103:53-6.

23. Zelefsky JR, Srinivasan M, Kundu A, Lietman T,Whitcher JP, Wang K, et al. Hookworm Infestation as aRisk Factor for Mooren’s Ulcer in South India.Ophthalmology 2006.

24. Young R, Watson P. Light and electron microscopy ofcorneal melting syndrome (Mooren’s Ulcer). Br JOphthalmol 1982;66:341-56.

25. Wakefield D, McCluskey P, Penny R. Intravenous pulsemethylprednisolone therapy in severe inflammatory eyedisease. Arch Ophthalmol 1986;104:847-51.

26. Zhao J, Jin X. Immunological analysis and treatment of,Mooren’s ulcer with cyclosporine A applied topically.Cornea 1993;12:481-8.

27. Wakefield D, Robinson LP. Cyclosporin therapy inMooren’s ulcer. Br J Ophthalmol 1987;71:415-7.

28. Agrawal V, Kumar A, Sangwan V, Rao GN. Cyanoacry-late adhesive with conjunctival resection and superficialkeratectomy in Mooren’s ulcer.Indian J Ophthalmol1996;44:23-7.

29. Kinoshita S, Ohashi Y, Ohji M, Manabe R. Long-termresults of keratoepithelioplasty in Mooren’s ulcer.Ophthalmology 1991;98:438-45.

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5Intracameral Antibiotics

Intracameral Antibiotics18

IntroductionIntracameral route of drug administration is graduallyemerging as a new modality for the management of deepkeratitis particularly those due to fungal etiology. Insevere cases of fungal keratitis, hyphae may penetratean intact Descemet’s membrane and colonize in theanterior chamber.1 The hypopyon in these cases of deepkeratomycosis usually contains fungal elements (unlikebacterial corneal ulcers with perforation where thehypopyon is sterile).2 Fungal hypopyon is particularlydifficult to treat because corneal penetration of mosttopically applied anti-fungal drugs is poor and improvesonly marginally even with repeated scraping of thecorneal epithelium.3

Thus in these cases of deep keratitis with retro-corneal involvement or anterior chamber involvement,adequate drug levels may not be achieved at the site ofthe infection.4 Both, the antibiotics as well as anti-fungalagents have been used intracamerally in various studies.However, with the advent of the newer generationantibiotics such as fluoroquinolones, which haveexcellent ocular penetration, the intracameral mode ofanti-bacterials is not indicated. Presently, the use of intra-cameral antimicrobials as a modality for the manage-ment of infectious keratitis is limited to treat fungalkeratitis.

Indications of Intracameral AntimicrobialsOnly amphotericin B has been used to treat fungalkeratitis caused by yeasts and natamycin-resistantfilamentous fungi, notably Aspergillus.5-8 Intracameralamphotericin B is given in addition to the topical andsystemic antimicrobial therapy. In experimental studiesit has been demonstrated that anterior chamber injection

of as much as 50 micrograms of amphotericin B doesnot cause any lenticular or corneal toxicity.9

TECHNIQUE

Preparation of Intracameral Amphotericin B Injection

Commercial preparations of amphotericin B (50 mgpowder, Fungizone, Sarabhai Chemicals, Vadodara,India) for intravenous administration is diluted forintracameral injection. To achieve the desired concen-tration, the drug is diluted aseptically in preservative-free sterile water for injection.

Dosage

Amphotericin B is constituted in 5 percent dextrose. Tenmilliliters of dextrose is added to the vial, giving amixture containing 5.0 mg/mL; 1.0 mL of this is addedto 4.0 mL of dextrose to further dilute it to 1.0 mg/mL.Of this concentration, 1.0 mL is then diluted with9.0 mL of dextrose, thus making a concentration of100 μg/mL; 0.1 mL of this contains 10 μg. Similarly,0.75 and 1.25 mL of this diluted drug contains 7.5 and12.5 μg, respectively.

Surgical Technique

Anterior chamber paracentesis for instillation of theintracameral drugs should be performed under theoperating microscope in the operating room understerile conditions.

Topical anesthesia is used and 0.5 percent propara-caine is instilled at 5 minutes intervals three times priorto injection. The anterior chamber entry is made fromthe superior or the temporal limbus as these are mostaccessible areas, and preferably from a site where clear

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Figure 18.1: Case of fungal keratitis (Aspergillus)Figure 18.2: Fungal keratitis treated with Intracameral ampho-tericin B (same case as Figure 18.1)

TABLE 18.1Summary of cases who received intracameral amphotericin B for mycotic keratitis

Author, year No. Age/ Initial Ulcer size Dose of No. of Final VA Organism Outcomesex VA (mm) amphotericin injec-

B (μg) tions

Kuriakose et al, 1 50/F CFFC 3 × 4 5 4 CF 1 m Fungus Healed2002

2 55/M PL,PR 5 × 6 5 13 CF 2 m Fusarium Healed3 53/M CF 1/2 m 2.4 × 2.2 5 3 20/200 No growth Healed4 27/M PL, PR 6 × 8 5 4 - Fusarium Eviscerated

Kaushik et al, 5 35/M CFCF 6 × 8 7.5, 10 2 20/200 Aspergillus Healed2001 flavus

6 42/M HMCF 2.5 × 3.5 10 2 - Aspergillus Healedflavus

7 28/M HMCF 5.5 × 5.0 10 1 20/80 Aspergillusflavus

Sridhar et al, 8 45/M CF 3 m 3.4 × 4.4 5 1 20/70 Aspergillus Ulcer healed.2002 Cataract

surgery done9 28/M 20/400 Abscess 5 2 20/50 Fungus Ulcer healed.

with endo- Cataractthelial surgery doneexudate

cornea is seen which aids in visualization of the track ofthe needle. A 22 gauge needle is usually used.Viscoelastic such as hydroxypropyl methylcellulose maybe used for viscoexpression of the anterior chamberexudates. If the exudate cannot be removed, the anteriorchamber may be entered with no. 11 surgical blade andthe exudate removed with forceps or a Simcoe cannulamay be used to aspirate the exudate. Care should be

taken not to damage the corneal endothelium, especiallywhen endothelial plaque is being aspirated. Further,sometimes it may become necessary to leave a part ofthe exudate, especially if the anterior capsule is involved,as this may injure the lens and cause cataract.

Smears should be prepared for KOH wet mountpreparation, Gram’s and Giemsa stains and culturemedia such as blood agar, chocolate agar, non-nutrient

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agar, and thioglycollate broth should be inoculated.Intracameral injection of amphotericin B 7.5 mg in0.1 ml is prepared as described previously and injected.The wound is then closed with a 10-0 monofilamentnylon suture.

Repeat Injections

Repeat injections are given based on the clinicalresponse. In cases of non-responding cases, a repeatinjection may be considered after a time interval of 1 to5 days.

Generally the response to intracameral amphotericinB is monitored by the following parameters: A clinicalresponse is present when the size of the epithelial defect,ulcer infiltrates and hypopyon decreases. The cornealinfiltrates become rounded, there is visible shrinking ofthe endothelial plaque and pigmentation on the surfaceof the endothelial plaque (Figs 18.1 and 18.2). Althougha maximum of 13 injections have been reported, weprefer not to give more than 4 injections. These injectionsare given from the site of the first injection.

RESULTS

In the various studies in literature as well as in ourexperience intracameral amphotericin B is safe andefficacious in treating deep keratomycosis and non-responsive mycotic keratitis (Table 18.1). The patientsmay complain of pain immediately after the injectionand there may be transient uveitis and an exudativemembrane during the first 24 hours. The time from thefirst injection to the complete resolution of theendothelial plaque ranges from 13 to 52 days. Thevarious organisms, which have been isolated from theanterior chamber tap, include Cladosporium species,

Acanthamoeba, Aspergillus species and Cryptococcusspecies.

SummaryPresently, the intracameral injection of antimicrobials isused only to treat some cases of deep mycotic keratitis.

References1. Naumann G, Green WR, Zimmerman LE. A histo-

pathologic study of 73 cases. Am J Ophthalmol1967;64:668-82.

2. Abad JC, Foster CS. Fungal keratitis. Int OphthalmolClin 1996 Summer;36:1-15.

3. O’Day DM, Head WS, Robinson RD, Clanton JA.Corneal penetration of topical amphotericin B andnatamycin. Curr Eye Res 1986;5:877-82.

4. Kaushik S, Ram J, Brar GS, Jain AK, Chakraborti A,Gupta A. Intracameral amphotericin B: initial experiencein severe keratomycosis. Cornea 2001;20:715-9.

5. Kuriakose T, Kothari M, Paul P, Jacob P, Thomas R.Intracameral amphotericin B injection in the manage-ment of deep keratomycosis. Cornea 2002;21:653-6.

6. Sridhar MS, Sharma S, Gopinathan U, Rao GN. Anteriorchamber tap: Diagnostic and therapeutic indications inthe management of ocular infections. Cornea 2002;21:718-22.

7. Bharadwaj PC, Shrivastava KN, Lall K, Varma V.Intracameral injections of framycetin sulphate(Soframycin) in fulminating corneal infections. A clinicaltrial. Br J Ophthalmol 1969;53:185-7.

8. Agarwal LP, Malik SR, Dhir SP. Intracameral injectionof Framycetin (soframycin). Ophthalmologica 1962;144:311-5.

9. Foster JB, Almeda E, Littman ML, Wilson ME. Someintraocular and conjunctival effects of amphotericin Bin man and in the rabbit. AMA Arch Ophthalmol 1958;60:555-64.

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Glue Application19

IntroductionTissue adhesives such as cyanoacrylate glue has beenused in various ophthalmic conditions.1-4 These includerepair of frank or impending corneal perforations,closure of leaking filtering blebs, occlusion of lacrimalpuncta, skin closure in oculoplastics (e.g. skin grafts)and fixing of hard/rigid contact lenses in severe ocularsurface disease (e.g. chemical burns).

Chemical Composition and CharacteristicsThere are two types of tissue adhesives—the synthetic(in the form of cyanoacrylate derivatives) and thebiologic (in the form of fibrin glue). Of the variouscyanoacrylate derivatives, butyl monomers withoptimum adhesive strength and rate of polymerizationhave been reported to be effective in the treatment ofcorneal perforations up to 3 mm in diameter. Cyano-acrylates are esters (alkyl side chains) of cyanoacrylicacid and the polymerization (hardening) of the glue isdue to the active double bond with oxygen.

The histotoxicity of the cyanoacrylates depends onthe length of the alkyl side chains and the vascularity ofthe tissues on which it is being applied. It is greater whenthe alkyl side chains are short and when the glue is beingused in the well-vascularized soft tissues.5

The accumulation of the degradation products in thetissues leads to significant tissue toxicity characterizedby both acute and chronic inflammation. The currentlyavailable glues (e.g. N-butyl-2-cyanoacrylate) havelonger alkyl chains and hence degrade slowly therebylimiting the accumulation of byproducts to amounts thatcan be effectively eliminated by tissues.6 The polymeri-zation (hardening) of cyanoacrylates occur throughcontact with water or a weak base (such as cellmembranes/tissue pH) and the hydroxylation occursthrough the exclusion of oxygen from the substancesbeing bonded.

Fibrin glue is a highly concentrated fibrinogenaprotinin solution, which also contains Factor XIII.Asolution of thrombin and calcium chloride are appliedto the ulcerated area, where the mixture coagulates. Thepresence of Factor XIII causes the fibrin to crosslinkwhich gives the coagulum additional resilience.

Biological EffectsIt was shown that direct early application of cyano-acrylate adhesive to the ulcer bed and adjacent basementmembrane along with a bandage contact lens waseffective in preventing progression of the corneal stromalmelting . The corneal epithelium and its interaction withsubjacent keratocytes stimulate the infiltration of thecorneal stroma by polymorphonuclear neutrophils andsubsequent release of collagenolytic enzymes in cornealulcerations. Cyanoacrylate glue prevents re-epitheliali-zation into the zone of damaged stroma and henceinhibits polymorphonuclear leukocytes, which are thesource of collagenolytic and proteolytic enzymes.Interruption of the melting process is most successfulwhen applied early in the course before overwhelmingnumbers of polymorphonuclear neutrophils haveaccumulated.7

Cyanoacrylate glue also possesses antibacterialproperties both in vitro and in vivo.8 It has significantbacteriostatic activity against gram-positive organisms(Staphylococcus aureus, Streptococcus pneumoniae, andgroup A streptococci).

Application of the Glue

PATIENT SELECTION

The indications for using cyanoacrylate glue includetemporary repair procedure of small corneal perfora-tions (less than 2 mm diameter), descemetoceles andcorneal melts (Fig. 19.1).

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5Glue Application

METHOD OF APPLICATIONThe cyanoacrylate glue may be applied with variousdevices, which include tuberculin syringe, applicatorsand aerosol application.9-12

Materials RequiredHistoacryl glue1 mL syringe and 26 gauge needleWeckcel sponges

Direct Application method:• The glue is loaded in a 1ml tuberculin syringe with

a fresh 26 G needle.• Topical anesthesia with 0.5 percent proparacaine

eye drops is instilled.• The lid speculum is inserted gently as the eye is

perforated and soft.• The surface is dried completely.• The adjacent epithelium is scraped.• If the anterior chamber is flat and the defect is large

(>2 mm), the anterior chamber may be reformedwith air or viscoelastic to enable easier applicationof the glue.

• The syringe is then gently screwed in small turns(for controlled release) to express the glue onto the26 G needle tip. Alternatively the bead of the gluemay be dripped on to a fresh 26 G needle tip forbetter results.

• The region to be treated is touched with the tip ofthe needle containing the glue drop.

• After waiting for 2 minutes, a bandage contact lensis applied.

MODIFICATION OF THE TECHNIQUEThe adherence of the glue is limited by the size of thedefect and the condition of the surrounding tissue towhich the glue is bonding (Fig 19.2). Reapplication maybe required in case of continued corneal stroma meltingor persistent wound leak. Various modifications havebeen made in the application of the glue. These includethe following:

Overlapped ApplicationsLarger defects can be treated with multiple applicationsoverlapped if necessary.

Using a SutureA running 10/0 nylon suture is used to create areticulum over the defect on which the glue is appliedin case of larger defects (> 3 mm).13 This is followed bythe application of the bandage contact lens.

ViscoelasticsThe sodium hyaluronate can be used as a visco-maintainer/retainer prior to application of the cornealglue in situations where anterior chamber is com-promised and/or intraocular contents are tending toprolapse through the perforation site.9 The viscoelasticis useful as it prevents the intraocular structures fromadhering to the glue.

Corneal PatchA dermatological punch is used to cut three or fourcircular patches of the non-stick portion of opsite plastic

Figure 19.1: Glue application in a small perforation (Courtesy:Medical Photographic Imaging Centre, Royal Victorian Eye and EarHospital, Melbourne)

Figure 19.2: Cyanoacrylate glue in perforated corneal ulcer (directapplication)

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or the steridrape. The opsite is picked with a stick, whichis dipped in a K-Y jelly and the cyanoacrylate glue isapplied over the patch with a 26 gauge needle which ismounted on a tuberculin syringe and this patch is thenapplied at the site of the perforation (Figs 19.3A and B).

This procedure is effective in healing of the smallcorneal perforations. In larger perforations such as incases of sterile melts this procedure helps in delayingsurgery which can be performed as an elective proce-dure at a later date under more optimal conditions ofcontrolled inflammation.

POSTOPERATIVE MANAGEMENT

Topical prophylactic antibiotic drops should be used at2 hourly intervals for the first three days followed byfour times daily. Additionally, lubricants should alsobe given. One should monitor the degree and time toepithelialization, vascularization, and corneal thickeness.Any evidence of extrusion of the glue or infection,especially at 3 to 5 weeks should also be be monitored.

ADVERSE EFFECTS

Application of cyanoacrylate glue to the conjunctiva,sclera or skin causes greater tissue reaction than to thecorneal epithelium and stroma. The tissue histotoxicityis generally less with the newer cyanoacrylates. The sideeffects of the glue application include the scarring ofthe conjunctiva and giant papillary conjunctivitis.14,15

Inadvertent instillation of cyanoacrylate glue into theanterior chamber can result in polymerization of thecorneal endothelium and iridocorneal and iridolenti-cular adhesions.16 Close monitoring for infection/cornealinfiltrate is essential when the glue has been present for

more than 6 weeks especially with the therapeuticcontact lenses. Rare report of retinal toxicity, cataractsand granulomatous keratitis are also there.15

References1. Hirst LW, Smiddy WE, Stark WJ. Corneal perforations;

changing methods of treatment, 1960-1980.Ophthalmology 1982;89:630-4.

2. Refojo MF, Dohlman CH. The tensile strength ofadhesive joints between eye tissues and alloplasticmaterials. Am J Ophthalmol 1969;68:248-55.

3. Refojo MF, Dohlman CH, Ahmad B, Carroll JM, AllenJC. Evaluation of adhesives for corneal surgery. ArchOphthalmol 1968;80:645-56.

4. Hirst LW, Stark WJ, Jensen AD. Tissue adhesives: Newperspectives in corneal perforations. Ophthalmic Surg1979;10:58-64.

5. Weiss JL, Williams P, Lindstrom RL, Doughman DJ. Theuse of tissue adhesive in corneal perforations. Ophthal-mology 1983;90:610-15.

6. Kim JC, Bassage SD, Kempski MH, et al. Evaluation oftissue adhesives in closure of scleral tunnel incisions. JCataract Refract Surg 1995;21:320-5.

7. Eiferman RA, Snyder JW. Antibacterial effect ofcyanoacrylate glue. Arch Ophthalmol 1983;101:958-60.

8. Hirst LW, De Juan Jr E. Sodium hyaluronate and tissueadhesive in treating corneal perforations. Ophthal-mology 1982;89:1250-3.

9. Wessels IF, Mcneill JI. Applicator for cyanoacrylatetissue adhesive. Ophthalmic Surg 1989;20:211-4.

10. Quillen DA, Rosenwasser GO. Aerosol application ofcyanoacrylate adhesive. J Refract Corneal Surg 1994;10:149-50.

11. Erdey RA, Lindahl KJ, Temnycky GO, Aquavella JV.Techniques for application of tissue adhesive for cornealperforations. Ophthalmic Surg 1991;22:352-4.

Figures 19.3A and B: Glue application in perforated corneal ulcer (Corneal patch technique) (Courtesy: Medical Photographic ImagingCentre, Royal Victorian Eye and Ear Hospital, Melbourne)

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5Glue Application

12. Vote BJT, Elder MJ. Cyanoacrylate glue for cornealperforations: A description of a surgical technique anda review of literature 2000;28:437-42.

13. Moschos M, Droutsas D, Boussalis P, Tsioulias G.Clinical experience with cyanoacrylate tissue adhesive.Doc Ophthalmol 1996-97;93:237-45.

14. Carlson AN, Wilhelmus KR. Giant papillary conjuncti-vitis associated with cyanoacrylate glue. Am JOphthalmol 1987;104:437-8.

15. Leahey AB, Gottsch JD, Stark WJ. Clinical experiencewith N-butyl cyanoacrylate (Nexacryl) tissue adhesive.Ophthalmology 1993;100:173-80.

16. Markowitz GD, Orlin SE, Frayer WC, Andrews AP,Prince RB. Corneal endothelial polymerisation ofhistoacryl adhesive: A report of a new intraocularcomplication. Ophthalmic Surg 1995;26:256-8.

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Conjunctival Flaps20

IntroductionOver the years, conjunctival flaps have been used to treatrecalcitrant corneal ulcers.1 However, with the adventof better lubrication systems, hydrophilic bandagecontact lens, tissue adhesives, more potent antimicrobialagents, collagen shields and amniotic membranetransplantation, the routine use of conjunctival flaps issteadily diminishing.2

Presently, conjunctival flaps are performed for onlya selected group of patients of corneal ulcers.

IndicationsA conjunctival flap is principally used to treat recalci-trant sterile corneal ulcers.2 Conjunctival flaps providea smooth ocular surface and also help in tectonic supportand nutrition to a chronic, non-healing corneal ulcer.

The major indications of conjunctival flaps are:1. Neurotrophic corneal ulcers3

2. Neuroparalytic keratitis4

3. Exposure keratitis4. Peripheral ulcerative keratitis

Conjunctival flaps may be rarely used in non-responding fungal and bacterial keratitis with damageto epithelial basement membrane damage, whichhinders the surface healing. However, most cornealspecialists do not like to perform conjunctival flaps dueto the following reasons:1. Conjunctival flaps obscure the view of the ulcerated

area hindering the monitoring of the progression ofcorneal ulcer.

2. Penetration of the antimicrobial agents may besuboptimal.

CONTRAINDICATIONS

The contraindications of conjunctival flaps include thefollowing:

1. Corneal perforation2. Infectious corneal ulcers.

TYPES OF CONJUNCTIVAL FLAPS

The conjunctival flaps may be of two types dependingon type of conjunctival closure – partial or total.5 Thepartial conjunctival flaps may be advancement flaps,bipedicle flaps or single-pedicle flaps.

Partial Conjunctival Flaps

Advancement Flaps

An advancement conjunctival flap is be used to cover aperipheral limbal or paralimbal corneal lesion such asfollowing a limbal dermoid excision.2 A limbal incisionwith relaxing incisions is made and the flap is advancedover the peripheral lesion and sutured onto theconjunctiva (Fig. 20.1). Peripheral patch grafts andsclerocorneal grafts may also be covered by theseadvancement flaps. However, such flaps usually retractand gape over a period of time.

Single Pedicle Flaps (Racquet Flaps)

The flaps were advocated for peripheral and paracentrallesions, which are not large enough to require a completeflap. Subconjunctival lidocaine with 1: 100,000epinephrine may be used to balloon the area of theconjunctiva to be undermined.The adjacent pedicle ofconjunctiva is fashioned and is placed on the peripheralcorneal lesion and sutured. Although technically moredifficult than a simple advancement flap, it has theadvantage that the retraction of the flap does not occur.

Bipedicle Flaps (Bucket Handle Flaps)

These are used for small paracentral or limbal corneallesions that do not require the coverage of the wholecornea2. The width of the flap should be 1.3 to 1.5 times

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the width of the lesion. The flap is fashioned with twopedicles from the limbal conjunctiva spanning the widthof the lesion and placed on the lesion and fixed withsutures.

Total Conjunctival Flap (Gunderson Flap)

This is performed for large lesions requiring coverageof the total cornea.6 The superior bulbar conjunctiva isballooned with injection of 2 ml of 2 percent lignocainewith 1 in 100,000 dilution of adrenaline into thesubconjunctival space anterior to the Tenon’s capsule.This aids in easy dissection. The bulblar conjunctivastarting from the superior fornix is dissected free fromthe Tenon’s capsule upto the 10 and 2 O’ clock positions.All tension on the flap is relieved by dissection.

After debridement of the corneal epithelium, thepedicle is placed over the cornea. In cases of irregularcorneal surface a superficial keratectomy may berequired. The cornea is then irrigated meticulously withbalanced salt solution and care is taken to maintain thecorrect orientation of the flap. The flap is then positionedon the cornea and anchored to the limbus or sclera withinterrupted 7-0 silk or other non-absorbable materialsutures (Fig. 20.2). The superior sclera is left bare whichre-epithelialises rapidly. An inferior flap can be similarlyfashioned if required.

Postoperative Therapy

Postoperatively, a broad-spectrum fluoroquinolone suchas 0.3 percent ciprofloxacin or ofloxacin is given four

times a day for one week along with a cycloplegic agent.The suture removal is done at one month.

Complications

The complications may occur intraoperatively or post-operatively.

Intraoperative

Intraoperatively, button-holing of the conjunctiva mayoccur which should be avoided by careful and meti-culous dissection of the conjunctiva. In case a button-hole occurs, it should be sutured with a non-absorbablesuture.

Postoperative

Postoperatively, retention of the conjunctival cyst mayoccur due to in curling of the conjunctival edges.However, these do not cause too much of a problemand may be left alone.

Further, occurrence of the herpetic infection in theconjunctival flap has also been reported.7,8

Summary

Conjunctival flaps have limited usefulness in the modernday era. They may be used in cases of indolent painfulcorneal ulcers. Successful keratoplasty is possible afterperformance of these flaps.

Figure 20.1: Advancement flap (Courtesy: Medical photographicimaging centre, Royal Victorian Eye and Ear Hospital, Melbourne)

Figure 20.2: Gunderson flap (Courtesy: Medical photographic imagingcentre, Royal Victorian Eye and Ear Hospital, Melbourne)

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References

1. Gunderson T. Conjunctival flaps in the treatment ofcorneal disease with reference to a new technique ofapplication. Arch Ophthalmol 1958;60:880-8.

2. Mannis MJ. Conjunctival flaps. Int Ophthalmol Clin1988;28:165-8.

3. Lugo M, Arentsen JJ. Treatment of neurotrophic ulcerswith conjunctival flaps. Am J Ophthalmology 1987;103:711-2.

4. Donzis PB, Mondino BJ. Management of noninfectiouscorneal ulcers. Surv Ophthalmol 1987;94-110.

5. Nichols BD. Conjunctival flaps. In: Krachmer JH, MannisMJ, Holland EJ (Eds): Cornea: Surgery of the Corneaand Conjunctiva. Vol III. Mosby St. Louis 1997 Chapter155;1903-10.

6. Maguire LJ, Shearer DR. A simple method of conjunc-tival dissection for Gunderson flaps. Arch Ophthalmol1991;109:1168-9.

7. Rosenfeld SI, Alfonso EC, Gollamudi S. Recurrent herpessimplex infection in a conjunctival flap. Am J Ophthal-mol 1993;116:242-4.

8. Lesher MP, Lohman LE, Yeakley W, Lass J. Recurrenceof herpetic stromal keratitis after a conjunctival flapsurgical procedure. Am J Ophthalmol 1992;114:231-3.

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5Therapeutic Keratoplasty

Therapeutic Keratoplasty21

IntroductionTherapeutic keratoplasty is usually performed tomanage a corneal perforation in a case of cornealulceration. Sometimes it is used as a modality of treat-ment to debulk the cornea of active infection that is notgetting controlled with maximal medical therapy.1

Despite recent advances in medical management ofinfectious keratitis a sub-group of microbes may notrespond to antimicrobial therapy so that a therapeutickeratoplasty is indicated when the disease progressesin spite of maximum medical therapy and/or theintegrity of the globe is compromised. This procedurehelps by the following methods:1. Excision of the infectious or inflammatory process

by debulking or removing the infectious inoculumso that the organisms in the cornea decreases to alevel at which exogenous infective process terminatesand the host defense becomes active.2

2. It maintains the integrity of the globe integrity.3. It may provide visual rehabilitation in some cases.4. It may also help in diagnosis of the infective

pathology.3

Therapeutic keratoplasty is of great relevanceespecially in developing countries where cases of non-healing microbial keratitis and perforated corneal ulcersare frequent and therapeutic keratoplasty is frequentlyperformed.2,4-7

IndicationsThe primary indication of a therapeutic graft is aperforated corneal ulcer that is not amenable to cornealgluing. It is also performed for uncontrolled microbialinfections particularly the fungal keratitis to debulk thecornea of infectious tissue.

BACTERIAL KERATITIS

Penetrating keratoplasty is required less often for thetreatment of active bacterial keratitis owing to theavailability of specific antibacterial drugs. Indicationsfor keratoplasty in bacterial keratitis include progressiveulceration despite maximum antibacterial medication(Fig. 21.1) , extensive corneal involvement and formationof descemetocele, or perforation (Fig. 21.2).2,5

Figure 21.1: Non-healing corneal ulcer on maximal anti-bacterialtherapy Figure 21.2: Perforated corneal ulcer due to Pseudomonas

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The percentage of cases requiring a therapeutickeratoplasty in cases of bacterial corneal ulcer variesfrom 3-6 percent.2,5 The most common organism isolatedin these cases includes Staphylococcus species.7 The otherorganisms, which have also been isolated in variousstudies, include Proteus species, Streptococci pneumoniae,Moraxella species, and Salmonella species.4 Otherindications of therapeutic keratoplasty are the conditionsthat are resistant to conventional medical treatment likeinfectious crystalline keratopathy and Mycobacterialkeratitis.8-14

FUNGAL KERATITIS

Therapeutic keratoplasty is more often required ascompared to cases bacterial keratitis in the managementof refractory fungal corneal ulcers.3-5,7,10,11,15 Theincidence of cases requiring a therapeutic keratoplastyin fungal keratitis varies from 18-29 percent.3,5,11,15

ACANTHAMOEBA KERATITIS

Due to the availability of effective and newer anti-acanthamoebic medications early and moderatelyadvanced cases may be successfully treated with medicaltreatment alone.16-20 In the management of advancedcases, which are unresponsive to medical therapy atherapeutic corneal transplantation alone or in combi-nation with cryotherapy of the host cornea has beenrecommended.2,16-19 Although some surgeons recom-mend early keratoplasty in cases of Acanthamoebakeratitis to remove the bulk of infiltration and to reducethe risk of scleral extension,17 presently a therapeuticpenetrating keratoplasty in Acanthamoeba keratitis isperformed for advanced cases that are unresponsive tomedical management.18, 20 A review of 38 case reportsof Acanthamoeba keratitis in various studies of differentauthors showed that 29 patients required a transplantsurgery.16-36

HERPES KERATITIS

A therapeutic keratoplasty may need to be performedfor necrotizing herpetic keratitis leading to extensivecorneal melting and perforation37,38 (Figs 21.2 and 21.3).Therapeutic keratoplasty is also performed in patientswho develop corneal perforations secondary topersistent epithelial defect with little or no stromalinflammation.4,37,38

OTHER INDICATIONS

Apart from infectious keratitis, therapeutic keratoplastyis also undertaken in large corneal perforationssecondary to keratoconjuctivitis sicca as in Sjögren’ssyndrome, Rosacea, ocular cicatricial pemphigoid, rileyday syndrome, post-radiation dry eye and collagenvascular diseases such as rheumatoid arthritis4,39,40

(Figs 21.3 and 21.4). It may also be undertaken in casesof perforation secondary to persistent epithelial defect,which may become secondarily infected such as in casesof neurotrophic keratitis, chemical burns, Stevens-Johnson syndrome, neuroparalytic keratitis andrecurrent erosion syndrome.4,40

Timing of SurgeryTiming of the surgery also relates to the success of thetherapeutic graft. A few reports suggest that a delay inthe surgery improves the surgical outcome. Nobe et alobtained a graft clarity rate of 17 percent with emergencysurgery (within 24 hours), 57 percent with intermediatesurgery(within 2-6 days) and 31 percent with a delayedsurgery (1 week-2 months). Failure rate was highest ifthe surgery was an emergent one. In a study by Fosteret al a graft clarity rate of 85 percent was achieved ineyes that were initially managed with lamellarkerato-plasty or glue and bandage contact lens and adelayed penetrating keratoplasty compared to 17 percentin eyes treated with a early penetrating graft for aperforation.38 Polack et al reported clear grafts in all the

Figure 21.3: Perforated corneal ulcer

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eyes with inactive herpes compared to a rate of 45percent in grafts with active disease.37

Preoperative Evaluation

HISTORY TAKING

History taking should include a detailed assessment ofonset of symptoms, duration of symptoms, prior medicaltherapy and /or any surgical intervention, informationabout the type of organism isolated (if the records areavailable) and the response to medical therapy.

OCULAR EXAMINATION

Prior to the surgery a detailed ocular examination ismandatory. Initial assessment includes determinationof best-corrected visual acuity and slit-lamp evaluationto determine the depth and extent of the corneal

involvement and size of the infiltrates particularly inrelation to the limbus.2-4 This facilitates planning ofsurgical details such as size of trephine that has to beused and its optimal placement in the recipient’s bed.

The presence of iris prolapse is diagnostic of a cornealperforation. Topical fluorescein and a positive Seidel’stest should be done to evaluate the size of a smallperforation (Figs 21.5A to C). The amount of anteriorsegment inflammation is assessed carefully and the eyeis examined for other associated conditions like dry eye,exposure, secondary glaucoma and endophthalmitis.39,40

INVESTIGATIONS

A and B scan ultrasonography is mandatory when theintegrity of globe is not compromised by a largeperforation, to assess the posterior segment involvementand to rule out endophthalmitis especially when retinais not visualized adequately.2

PREOPERATIVE TREATMENT

Preoperatively, the patients may be given antibioticagents, antiglaucoma medications and some surgeonseven recommend the use of corticosteroids.

Anti-microbial TherapyBoth systemic and topical anti-microbial treatment isrecommended preoperatively in all the patients2. Thetreatment should be directed against the offendingagent. If preoperatively an etiologic diagnosis has notbeen established, broad-spectrum antibiotic or acombination therapy should be given.2 Donnenfeld etal recommend use of topical ofloxacin at hourlyfrequency in all cases undergoing therapeutic kerato-plasty regardless of the cause of infection to preventbacterial superinfection. They also recommend use ofOfloxacin 400 mg every 12 hours before admission and

Figure 21.4: Peripheral melt with secondary infection in rheumatoidarthritis

Figures 21.5A to C: Seidel’s test reveals presence of perforation (note the dark spot which is the site of the florescien leek)

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intravenous vancomycin and tobramycin afterhospitalization.3

SteroidsMost of the authors2,3, 7,10,11 avoid use of topical steroidsas it worsens the infectious process, though Killings-worth4 and O’Day et al41 recommend use of topical andsystemic steroids even in cases of fungal keratitis.

Hypotensive AgentsMany authors recommend preoperative use of intra-venous mannitol to lower the intraocular pressure.2-3

We routinely use intravenous mannitol in all casespreoperatively. This decreases the problems related topositive vitreous pressure.

Our RegimeWe in our practice start the patients on systemicCiprofloxacin 500 mg twice a day and Acetazolamide250 mg three times a day especially in cases of perforatedcorneal ulcers. Topical treatment includes use ofcefazoline sodium (5%) and tobramycin sulphate (1.3%)at hourly frequency. Alternatively Gatifloxacin (0.3%)eye drops may also be combined with cefazolin sodium(5%) at an hourly frequency. Homatropine (2%) eyedrops are also given thrice a day. We avoid thepreoperative use of topical and systemic steroids.

Surgical Technique

ANESTHESIA

Therapeutic keratoplasty should always be performedunder general anesthesia by experienced cornealsurgeons as local anesthesia carries the danger ofcompromising the integrity of the perforated globe.4 Theanesthetist should be informed about the caution withthe use of depolarizing agents to avoid sudden intra-ocular pressure rise in an open globe.3,42,43

DONOR TISSUE CONSIDERATIONS

A good quality donor cornea should be used as a healthytissue with intact epithelium minimizes the risk ofreinfection in the graft and the presence of clear grafthelps in monitoring the anterior chamber reactionduring the postoperative period.2 If fresh donor isnot available one can also use cryo-preserved and

glycerin-preserved corneas and even sclera has beensuggested.44-46

HOST TISSUE PREPARATION

Exposure

A self-retaining lid speculum or lid sutures are helpfulin preventing the pressure on the globe.3 Killingsworth4

suggested that in most of the cases the scleral fixationrings should be avoided, as in a hypotonous eye thesuturing is difficult, whereas others advocate3,4,7 use ofa Flieringa ring whenever possible to provide scleralsupport. We do not use scleral fixation rings owing totheir difficult suturing in eye with very low tension.

Conjunctival peritomies should be performed incases which require a large or an eccentric graft to avoidpassing sutures through the conjunctiva.2-4 Hemostasisshould be achieved in all cases of conjunctival peritomieswith a wet field cautery.2

Recipient Bed TrephinationThe size of the recipient bed should be determined byplacing the appropriate trephine over the cornea andcreating an indent in the epithelium keeping in mindthe size of graft and the centration. During trephinationof the recipient bed, care should be taken to avoidpressure on the globe which could lead to extrusion ofthe ocular contents. Trephination is difficult in eyes withlarge perforations, which have zero IOP. The recipientcornea is incised using either a hand held or a vacuumtrephine. A comparative study done by John D Ng et alon eyes with both central and peripheral large cornealperforations suggested that the Hessberg-Barron andHanna suction trephines are easier to use as comparedto Franceschetti type free-blade trephine.47

The suction trephines have lesser incidence ofanterior chamber collapse and iris prolapse comparedto the free-blade trephines. In suction trephines peri-pheral suction provides the support and counter-tractioninto the advancing blade whereas the free-blade reliessolely on the inherent structural stability of cornea whichis already weak in cases of perforations. The authorsfound that the Hanna trephine was technically moreeasy to use than the Hessberg- Barron trephines.47 It hasmore peripheral ring of suction that causes less centralcorneal distortion and holds the cornea in a more naturalconfiguration.47

We use disposable handheld trephine in all cases dueto easy availability. Some surgeons advocate initial

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tectonic support with cyanoacrylate glue or a patch graftin cases of eyes with perforation.2 They also recommendfreehand dissection of the host bed after marking witha trephine, in cases of large perforation or with entirecornea involvement.2

Size of the Recipient Bed

The smallest recipient opening is created thatencompasses the ulcerated or infiltrated corneal tissuecompletely. The basic aim is to have a centraltrephination of a standard size of 7 to 8 mm as far aspossible. However, the diameter of host trephinationusually depends on location and size of perforation andsurrounding infected area. If the size of perforation issmall and peripheral, a small patch graft may be suitable.If the perforation is very large reaching up to limbus orinvolving sclera beyond the limbus a 12 to 13 mm graftmay be required. Care should be taken to remove theentire diseased area even if the size of the graft requiredbecomes larger.2,4 Whenever possible, the hosttrephination should include at least 1 mm of healthycorneal tissue.3

Anterior Chamber ReconstructionPurulent and fibrinous material should be irrigated fromthe anterior chamber; the membranes over the iris shouldbe dissected gently by the irrigating cannula and shouldbe removed with the forceps and iris lesions should beexcised.48 Every effort should be made to arrest thebleeding from the iris surface. One or two iridectecomiesis recommended by most of the authors.2-4 Donnenfeldet al2 and Rao et al3 suggest use of intracameral antibioticsor antifungals whenever required. Intracameralvancomycin 0.1 mg/ml and intracameral AmphotericinB 7.5 micrograms/ ml wash may be given.

Lens Surgery

In most cases one should try to preserve the lens as itforms an effective barrier against the spread of infectioninto the vitreous.2-4 Donnenfeld et al recommends useof 2 percent pilocarpine 1 hour preoperatively in allphakics and pseudophakics in an attempt to constrictthe pupil and prevent spontaneous expulsion of thelens.3

Anterior Vitrectomy

If associated endophthalmitis is found at the time ofsurgical procedure, a combination of therapeutic

keratoplasty, crystalline or intraocular lens removal, totalopen sky vitrectomy, and injection of appropriateintraocular antibiotic at the end of the surgery is advoca-ted.2,4 Even in cases of suspected endophthalmitis, if theorganism is known, appropriate antibiotic should beinjected intravitrealy and vitreous tap should be takenfor culture. If the organism is not known intravitrealinjection of vancomycin (1 mg in 0.1 ml) and ceftizidime(2.5 mg in 0.1 ml) should be given.3 Open sky vitrectomyis performed in all aphakics and in cases complicatedby inadvertent crystalline lens extrusion and vitreousloss.2 The anterior chamber is reformed gently with aviscoelastic agent and the peripheral anterior synechiaeare released to open up the anterior chamber angle.2-4

Over more monofilament sutures may be applied toreconstruct the pupil.

DONOR TISSUE PREPARATION

In a case of therapeutic keratoplasty, the donor buttonis trephined always after the recipient’s trephination,as necrosis around the host cut may require additionaltrimming and may alter the size of the graft.2 Carefuldecision regarding the graft size should be made. Witha very small graft and an eccentric graft the sutures maycome into the visual axis resulting in a visual compro-mise. However, a large graft may be associated withthe danger of graft rejection, post-keratoplasty glaucomaand subsequent graft failure.49,50 Hence, carefulassess-ment of the size and centration is mandatory. Theclarity of the graft depends on the size of the graft.Larger grafts give a worse prognosis because of morechances of immunologic graft reactions with vasculariza-tion, development of posterior synechiae and secondaryglaucoma. Du and coworkers reported a clarity rate of89 percent with a graft size of 7 mm or less compared to21 percent where grafts were 8 mm or larger.51

Donor button is punched from the endothelial side,and is usually 0.5-1.0 mm larger than the host bed.2-4

We take 1 mm oversized grafts in cases of perforatedcorneal ulcers as this helps in better maintaining of theanterior chamber postoperatively.48

GRAFT HOST APPOSITION

Donor button is sutured in place with 10-0 monofilamentnylon interrupted. Use of interrupted sutures is prefer-red by us and also by most of the surgeons.2,4 The suturedepth should be 75 percent of the host corneal thicknessand not full thickness as this increases the risk for

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Surgical Management

conduit of the infectious organism from cornea to theanterior chamber.3 Longer sutures bites on the host sidewith moderate tension are preferred to avoid cheesewiring of the suture through a potentially necrotic bed.3

All suture knots should be trimmed and buried on thehost side2 (Figs 21.6A and B). Meticulous wound closureis recommended even if it requires greater number ofsutures.2,3 Care should be taken to avoid any pressureover the globe through out the surgery.

Microbiological and Pathological Examination

In all cases, the corneal specimen is divided into twopieces and sent for microbial and histopathologicalinvestigations. Material should be inoculated on bloodagar, chocolate agar, Sabouraud’s agar withoutcyclohexamide and blood agar coated with E.coli, forplating.3 The corneal specimen should also be sent forhistopathological evaluation for identification of theoffending organisms.

Postoperative Management

The postoperative therapy consists of the use ofantimicrobial agents and cycloplegics.

ANTIMICROBIAL THERAPY

There is a general consensus to give antimicrobialpostoperatively following therapeutic keratoplasty.2-4

The duration of therapy depends on the severity ofinfection and the causative organism and should be

given until the corneal epithelium has healed.3 Fungal,Acanthamoeba and viral keratitis may requireantimicrobial treatment for several months post-operatively.2-4

In cases of bacterial keratitis we give topical fluoro-quinolones such as 0.3 percent ciprofloxacin or 0.3percent ofloxacin eye drops are given 2 to 4 hourlyinitially along with systemic antibiotics.

In cases of fungal keratitis, in addition to the aboveregime, 5 percent natamycin eye drops five times a dayare also added.

In cases of herpetic keratitis, in addition to theantibiotic, topical acyclovir 3 percent ointment is added5 times a day in cases of keratitis subsequent to herpessimplex and systemic acyclovir is added in case ofkeratitis subsequent to herpes zoster.

In cases of acanthamoeba keratitis, in addition to theantibiotics, polyhexamethyl biguanide or brolene eyedrops are given.

STEROIDSThe use of topical steroids following a therapeutickeratoplasty for infectious keratitis is controversial.Killingsworth et al and O’Day et al suggested that asthe infection is cured by surgery in virtually all thepatients, aggressive use of both topical and systemicsteroids can be considered postoperatively in all casesto decrease the postinflammatory sequel and improvethe visual outcome.4,41

As most of the bacterial corneal infections areresponsive to antibiotics therefore concomitant use ofcorticosteroids may be justified in an inflamed eye.4,41

Figure 21.6A: Total corneal melting Figure 21.6B: Therapeutic graft

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We give topical steroids in cases of bacterial keratitisin reduced frequency (8 hourly doses). However, in casesof recurrence of infection, and in cases of active fungalor Acanthamoeba infection after therapeutickeratoplasty steroids should be avoided.4 In therapeutickeratoplasty for herpetic keratitis, topical corticosteroidsmay be given without significant risk, as long as thepatient is managed with concomitant topical or oralantiviral therapy.41

ComplicationsThe complications seen after therapeutic keratoplastyinclude severe uveal inflammation, and reinfection ofthe graft along with other usual complications seen aftera standard full thickness corneal transplantation surgery.

HEMORRHAGE/HYPHEMA

Postoperative hyphema results from inflamed iris andif associated with raised intraocular tension requiresevacuation2 (Figs 21.7A to C).

UVEITIS

Mild to moderate anterior uveitis is encountered inalmost all cases (40-100%)6,7,51-53 and can be controlledby judicious use of topical corticosteroids and cyloplegics(Figs 21.8A and B). O’Day et al advocates use of steroidseven in fungal corneal ulcers.6,7,41 Severe iritis may leadto formation of pupillary membrane in 3 to 9 percentcases.7,52

SECONDARY GLAUCOMAEarly postoperative increase in IOP(14-20%) occurssecondary to anterior chamber reaction and may requiretopical and systemic anti-glaucoma treatment along withanti-inflammatory therapy.2

Late onset secondary glaucoma results fromextensive peripheral synechiae and may lead to graftfailure. The incidence of secondary glaucoma has beenreported to vary from 3 percent in keratoplasty forPseudomonal keratitis6 to 50 percent after keratoplastyin fungal corneal ulcer.6,52,53 Our study showed a 19.46percent incidence of glaucoma following therapeutickeratoplasty.

Figures 21.7A to C: (A) Hypopyon corneal ulcer (B) No response maximal medical therapy (C) Therapeutic graft associated with hemorrhage

Figure 21.8A: Perforated corneal ulcer due to herpes Figure 21.8B: Postoperative uveitis after therapeutic graft

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Surgical Management

Figures 21.9A and B: (A) Recurrence of infection in a therapeutic graft (B) Uncontrolled infection in the same case

RECURRENCE OF INFECTION

Recurrence of infection is the most undesirablecomplication of therapeutic keratoplasty.

A therapeutic keratoplasty in active herpetic keratitishas been associated with highest reinfection rate(7-75%) compared to the other infectious keratitis.37-54

Polack et al report a recurrence in 15(75%) of the 20patients who underwent keratoplasty for acute viralkeratitis, athough 9 (60%) grafts survived the earlyrecurrence.37 Recurrence rate in keratomycosis variesfrom 7.3-10 percent.53 Acanthamoeba keratitis has beenassociated with a recurrence rate of 40-50 percent.54 Inour study the graft reinfection rate was seen in 9 eyes(7.96%) (Figs 21.9A and B).

It should be considered as an emergency and shouldbe treated intensively with topical antimicrobial therapyand a repeat surgery may be undertaken, if required.3

GRAFT FAILURE

Graft clarity is the most important factor in decidingthe functional outcome of the procedure. Graft failurefollowing therapeutic keratoplasty occurs in 4 to 52percent.7,37,38,52 The status of the graft depends as anumber of factors. These are offending organism, timingof surgery, donor tissue quality and the graft size.

OTHER COMPLICATIONS

Other complications following therapeutic keratoplastyinclude, graft ectasia (7% in early postoperative period

and 16% in late postoperative period), chronic irritableeye (7%) and phthisis bulbi (1%).4,51

SUCCESS OF A THERAPEUTIC GRAFT

The final visual outcome after therapeutic keratoplastydepends on the virulence of the causative organism, itssusceptibility to treatment, the severity of inflammation,the timing of the surgery, the type of donor materialused, the size of the graft, underlying ocular surfacedisorder and the postoperative management of variouscomplications.3

Acanthamoeba keratitis and keratomycosis have aworse prognosis as compared to bacterial keratitis.Therapeutic grafts, which remain clear in cases ofbacterial keratitis, range from 70 to 75 percent,4,51 incomparison to fungal keratitis where it varies from20 to 60 percent54 and Acanthamoeba keratitis whichhas a graft clarity rate upto 50 percent.16,17

SummaryTherapeutic penetrating keratoplasty has a definitiverole in the management of infectious keratitis especiallywhen integrity of the globe is jeopardized. Results ofthe procedure can be improved by concomitant use ofspecific antimicrobial therapy both preoperatively andpostoperatively. It is mandatory to encompass andremove the entire infected area even if a large sized graftis required. Further long-term studies are required toevaluate the outcome of therapeutic keratoplasty with

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a good quality donor, which can replace requirement ofthe second stage optical keratoplasty.

References1. Fine M. Therapeutic keratoplasty. Trans Acad

Ophthalmol and Otolaryngol 1960;64:786-808.2. Rao GN, Garg P, Sridhar MS. Penetrating keratoplasty

in infectious keratitis. In Brightbill FS (Ed): CornealSurgery: Theory, Technique and Tissue. St. Louis,Missouri, Mosby. Third edition 1999;65:518-25.

3. Donnenfeld ED, Kanellopoulos AJ. Therapeutic kerato-plasty. In: Krachmer JH, Mannis MJ, Hollan EJ (Eds):Cornea: Surgery of the Cornea and Conjunctiva.150:1843-5.

4. Killingsworth DW, Stern GA, Driebe WT, et al. Resultsof therapeutic penetrating keratoplasty. Ophthalmology1993;100:534-41.

5. Foster RK. The role of excisional keratoplasty inmicrobial keratitis. In Cavanagh HD (Ed): The Corneatransctions of World congress on the Cornea , New york,Raven. Third Edition 1988.

6. Malik SRK, Singh G. Therapeutic keratoplasty inPseudomonas pyocyaneus corneal ulcers. Br J Ophthalmol1971;55:326-30.

7. Panda A, Khokhar S, Rao V, et al. Therapeutic pene-trating keratoplasty in non-healing corneal ulcer.Ophthalmic Surg Lasers 1995;26(4):325-9.

8. Partnoy SL, Insler MS, Kaufman HE. Surgical manage-ment of corneal ulceration and perforation. Survey ofOphthalmol 1989;34(1):47-58.

9. Ginsberg SP, Brightbill FS. Corneal thinning andperforation. In: Brightbill FS (Ed): Corneal surgery-theory, technique and tissue. St. Louis CV Mosby 1986;396-409.

10. Sanders N. Penetrating keratoplaty in treatment offungal keratitis. Am J Ophthalmol 1970;70(1):24-30.

11. Foster RK, Rebell G. The diagnosis and management ofkeratomycosis II. Medical and surgical management.Arch Ophthalmol 1975;93:1134-6.

12. Dugel PU, Holland GN, Brown HH, et al. Mycobacte-rium fortitium keratitis. Am J Ophthalmol 1988;105:661-9.

13. Sharma N, Vajpayee RB, Pushker N, et al. Infectiouscrystalline keratopathy. CLAO J 2000;26(1):40-3.

14. Stern GA. Infectious crystalline keratopathy. IntOphthalmol Clin 1993;33:1-7.

15. Foster RK, Rebell G. Therapeutic surgery in failures ofmedical treatment for fungal keratitis. Br J Ophthamol1975;59:366-71.

16. Cohen EJ, Parlato CJ, Arentsen JJ, et al. Medical andsurgical treatment of Acanthamoeba keratitis. Am JOphthalmol 1987;103:615-25.

17. Hirst LW, Green WR, Merz W, et al. Management ofAcanthamoeba keratitis. A case report and review ofthe literature. Ophthalmology 1984;91:1105-11.

18. Wright P, Warhurst D, Jones BR. Acanthamoeba keratitissuccessfully treated medically. Br J Ophthalmol 1985;69;778.

19. Binder. Cryotherapy for medically unresponsiveAcanthamoeba keratitis. Cornea 1989;8:106-14.

20. Bacon AS, et al. A review of 72 consecutive cases ofAcanthamoeba keratitis. 1984-1992 Eye 1993;7:719.

21. Jones DB, Visesvara GS, Robinson NM. Acanthamoebapolyphagia keratitis and Acanthamoeba uveitisassociated with fatal meningoencephalitis. Trans.Ophthalmol Soc UK 1975;95:221.

22. Nagington J, Wastson PG, et al. Amoebic infections ofthe eye. Lancet 1974;2:1537.

23. Lund OE, Stefani FH, Dechant W. Amoebic keratitis. Aclinicopathological case report. Br J Ophthalmol 1978;61:373.

24. Ma P, et al. A cases of keratitis due to Acanthamoeba inNew York, and features of 10 cases. J Infect Dis1981;143:622.

25. Key SN, et al. Keratitis due to Acanthamoeba castellani.A clinicopathologic case report. Arch Ophthalmol 1980;98:475.

26. Bos HJ, et al. A case of Acanthamoeba keratitis innetherlands. Trans R Soc Trop Med Hyg 1981;75:86.

27. Hamburg A, De Jonckheere JF. Acanthamoeba keratitis.Ophthalmologica 1980;181:74.

28. Samples JR, et al. acanthamoeba keratitis possiblyacquired from a hot tub. Arch Ophthalmol 1984;102:707.

29. Moore MB, et al. Acanthamoeba keratitis associated withsoft contact lens. Am J Ophthalmol 1985;100:396.

30. Blackman HJ, et al. Acanthamoeba keratitis successfullytreated with penetrating keratoplasty. Suggestedimmunogenic mechanisms of action. Cornea 1984;3:125.

31. Theodore FH, et al. The diagnostic value of ring infiltratein Acanthamoeba keratitis. Ophthalmology 1985;92:1471.

32. Wilhemus KR, et al. Rapid diagnosis of Acanthamoebakeratitis using calcofluor white. Arch Ophthalmol1986;104:1309-12.

33. Mannis MJ, et al. Acanthamoeba sclerokeratitis. ArchOphthalmol 1986;104:1313-7.

34. Epstein RJ, et al. Rapid diagnosis of Acanthamoebakeratitis from corneal scrapings using indirect fluore-scent antibody staining. Arch Ophthalmol 1986;104:1318.

35. Case records of the Massachusetts General hospital.Weekly clinicopathologic exercises(case 10-1985). N EngJ Med 1985;312:634.

36. Moore MB, et al. Radial keratoneuritis as a presentingsign of acanthamoeba keratitis. Ophthalmology 1968;93:1310.

37. Polack FM, Kaufman HE, et al. Penetrating keratoplastyin Herpetic keratitis. Am J Ophthalmol 1972;73:908-13.

38. Foster CS, Duncan J. Penetrating keratoplasty for Herpessimplex keratitis. Am J Ophthalmol 1981;92:336-43.

39. Krachmer JH, Laibson PR. Corneal thinning andperforation in Sjögren syndrome. Am J Ophthalmol1974;78:917-20.

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40. Pfister RR, Murphy GE. Corneal ulceration andperforation in Sjögren‘s syndrome. Arch Ophthalmol1980;98:89-95.

41. O’ Day DM, Moore TE, Jr Aronson SB, et al. Deep fungalcorneal abscess: Combined corticosteroid therapy. ArchOphthalmol 1971;86:414-9.

42. Donlon IV. Succinylcholine and open eye injury II.Anesthesiology 1986;64:525-6.

43. Libonitis MM, Leahy JJ, Ellison N. The use of succinylcholine and open eye injury. Anesthesiology 1985;62:637-40.

44. Capella JA, Kaufman HE, Robbin JE. Preservation ofviable corneal tissue. Arch Ophthalmol 1965;74:669-73.

45. Eastcott HJ, et al. Preservation of corneal graft byfreezing. Lancet 1954;1:327-31.

46. Müeller FO, Casey TA, Trevor-Roper PD. Use of deepfrozen human cornea in full thickness grafts. Br Med J1964;2:473.

47. Ng JD, Nekola M, Parmely VC, et al. Comparison ofthree corneal trephines for use in therapeutic penetrating

keratoplasty for large corneal perforations. OphthalmicSurgery 1995;26(3):209-15.

48. Vajpayee RB, Singhvi A, Sharma N, Sinha R. Penetratingkeratoplasty for perforated corneal ulcers: preservationof iris by corneal debuling. Cornea 2006;25:44-6.

49. Van RG, Cornell FM, Waring GO III, et al. Postopertaiveastigmatism after central or eccentric penetratingkeratoplasty. Trans Am Ophthalmol Soc 1974;72:123-31.

50. Gary N Foulks. Clinical aspects of corneal allograftrejection. In: Krachmer (Ed): 1691-6.

51. Du NZ, Chen JQ, Gong XM, et al. Therapeutic kerato-plasty in the management of purulent corneal ulcer:Report of 100 cases. Jpn J Ophthalmol 1979;23:412-20.

52. Hill JC. Use of penetrating keratoplasty in acute bacterialkeratitis. Br J Ophthalmol 1986;70:502-6.

53. Singh G, Malik SRK. Therapeutic keratoplasty in fungalcorneal ulcer. Br J Ophthalmol 1972;56:41-5.

54. Cohen EJ, Buchanan HW, Laughrea PA, et al. Diagnosisand management of Acanthamoeba keratits. Am JOphthalmol 1985;100:389-95.

197

5Phototherapeutic Keratectomy

Phototherapeutic Keratectomy22

IntroductionPhototherapeutic keratectomy has been done by variousinvestigators in cases of healing keratitis. It may bedifficult to perform surgery in these inflamed andinfected eyes.

Phototherapeutic keratectomy has been evaluatedearlier as a surgical tool to treat superficial cornealpathologies such as recurrent epithelial erosions, cornealdystrophies degenerations and corneal scars involvingthe anterior one-thirds of the stroma.

The ability of 193 nm excimer laser to treat microbialkeratitis was demonstrated initially by Serdaveric et alin rabbit corneas after scratch inoculation with Candidaalbicans.1 It has been shown to be effective in earlylocalized Fusarium, Mycobacterium and Pseudomonaskeratitis in animal models.1-3

MECHANISM OF ACTION

Due to the ultraviolet radiation, tissue sterilizationoccurs and this effect is further enhanced due to ablationor elimination of organisms and the surroundingnecrotic tissue.2 It also provides debulking effect andimproves drug penetration.

CASE SELECTION

Phototherapeutic keratectomy can be undertaken incases of superficial keratomycosis which do not respondto standard antimycotic therapy. There are only a fewtopical and systemic antifungal drugs available for themanagement of keratomycosis which often penetrate theocular barriers poorly. It has been reported that 20 to 50percent cases of keratomycosis require surgicalintervention.4

Phototherapeutic keratectomy may also be done incases of superficial opacities due to herpetic keratitis. Itmay also be done in cases of long standing metaherpetic

ulcers which do not epithelialize on conventionaltreatment. Excimer laser can also be used in selectedpatients having opacities and irregularities due to herpessimplex keratitis.5

CASE WORK UP

Slit-lamp biomicroscopy is mandatory in cases wherephototherapeutic keratectomy is planned. The opticalpachymeter should be used to measure the total cornealthickness and the apparent involvement of the suppu-rative stroma.2 In cases where there is substantial cornealthinning that is more than 50 percent of the cornea,phototherapeutic keratectomy should not be under-taken. It should also be noted that following photothera-peutic keratectomy the eyes become hyperopic andhence the refractive status and vision of the fellow eyeshould also be considered.

LASER CHARACTERISTICS

The ability of 193 nm excimer laser to eradicate a varietyof microorganisms as colonies in agar plates has beenreported.9 Ultrastructural findings in cases treated withthe 193 nm wavelength laser consist of fine basophilicstippling at the epithelial- stromal interface in the treatedarea. The underlying stroma which has not been ablatedis undamaged on light microscopic examination.1

ComplicationsFew complications following phototherapeutic keratec-tomy for treatment of infectious keratitis have beenreported.5,7 Since the corneal thickness in cases ofkeratitis is irregular and the ablation rate of the suppu-rating corneal tissue is not predictable, a conservativeapproach towards excimer laser ablation should beadopted. Usually one-third to one-half of the cornealthickness is considered as a safe margin for ablation.

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Pachymetry may be unreliable in these cases and it maybe difficult to reveal the thinnest point on the cornea.

Astigmatism may occur which occurs due to thedifference in the ablation rates of infected and normaltissues, size and depth of the lesion and involvement ofthe optical axis. A focal lesion in the paracentral areawill be thinner as compared to the adjacent normal tissueand hence induce astigmatism. The initial zone forphototherapeutic keratectomy should be broad enoughto cover the entire optical zone.

Delayed epithelialization may occur in some cases.Corneal haze is more common especially in fungalkeratitis as topical corticosteroids are often not used inthese cases.

ConclusionTopical medical therapy should be continued afterphototherapeutic keratectomy in all cases. Great cautionshould be used in selecting excimer treatment candidatesbecause of high-risk of corneal perforation in advancedinfections. Recurrences have been reported especiallyin cases of herpes simplex keratitis.

References1. Serdaveric O, Darrell RW, Krueger RR, et al. Excimer

laser therapy for experimental Candida keratitis. Am JOphthalmol 1985;99:534-8.

2. Gottsch JD, Gilbert ML, Goodman DF, et al. Excimerlaser ablative treatment for microbial keratitis. Ophthal-mology 1991;98:146-9.

3. Frucht-Pery J, Golan G, Hemo I, et al. Efficiency oftopical gentamicin treatment after 193 nm photo-refractive keratectomy in an experimental Pseudomonaskeratitis model. Graefes Arch Clin Exp Ophthalmol1995;233:532-4.

4. Brooks JG Jr, Coster DJ. Non-ulcerative fungal keratitisdiagnosed by posterior lamellar biopsy. Aust N Z JOphthalmol 1995;21:115-9.

5. Fagerholm P, Ohman L, Orndahl M. Phototherapeutickeratectomy in herpes simplex keratitis. Acta Ophthal-mologica 1994;72:457-60.

6. Trokel S L, Srinivasan R, Braren B. Excimer laser surgeryfor cornea. Am J Ophthalmol 1983;96:710.

7. Chang- Ping Lin, Chi- Wu Chang, Chuan-Yi Su. Photo-therapeutic Keratectomy in treating keratomycosis.Cornea 2005;24:262-8.

Index

AAcanthamoeba 13Acanthamoeba infection 110Acanthamoeba keratitis 107, 126, 188

corneal involvement 108cataract and glaucoma 110iritis and hypopyon 110lids and conjunctiva involvement 110scleral involvement 110

differential diagnosis 110epidemiology 107etiology 107laboratory diagnosis

corneal scraping 111staining 111wet smear 111

risk factors 107contact lens wear 108non-contact lens wearer 108

signs 108symptoms 108treatment 112

combination therapy 112surgical treatment 114

Acetazolamide 31Acquired immunodeficiency syndromes 40Acridine orange 55Actinomycetes 68Acyclovir 30Adenoviral infections 104Adjuvants 31Alpha blockers 167Aminoglycosides 26Amniotic membrane transplantation 114, 160Amphotericin B 28

injection 177Anterior chamber 48Anterior vitrectomy 191Antibacterial agents 25Antibiotic therapy 72Antibiotics 166Antifungal agents 28Antimicrobial susceptibility testing 60Antiviral agents 30Aspergillus 15Asymptomatic infiltrates 130Asymptomatic infiltrative keratitis 130Atropine 31Azoles 29

BBacillus 18Bacterial keratitis 65, 125, 187

clinical featuressigns 69symptoms 69

contact lens use 66etiologic organisms 67microbiologic work up 71regional differences 67risk factors 65specific features

alpha hemolytic streptococci 69anaerobes 71gram-negative organisms 69other gram-negative rods 70

specific organisms 67actinomycetes 68gram-positive aerobic bacilli 68less common organisms 68nonspore-forming anaerobic

organisms 68non-tuberculous mycobacteria 68spore forming anaerobic bacteria 68staphylococcal organisms 67

systemic defense mechanisms 66treatment 71

adjunctive therapy 73medical therapy 72specific drugs 73surgical therapy 74systemic therapy 74

Bacteriology 16Basal cells 4Basement membrane 4Beta lactam antibiotics 25Blood agar 22, 57Bowman’s layer 4Brain-heart infusion 58

broth 23Bullous keratopathy 38

CCalcofluor white 55, 83Cataract surgery 140Cephalosporins 25Chocolate agar 23, 57Chronic corneal inflammation 78Circulating antibodies 99

Clinical investigations 51Clostridium 71Clotrimazole 29Coagulase negative staphylococci 17Cochet and Bonnet aesthesiometer 157Collagen vascular diseases 169Collagenase inhibitors 159Collection of samples 52Confocal microscopy 60, 72, 84, 113, 137Congenital ocular herpes 92Conjunctiva 41Conjunctival flap 160, 184

complications 185contraindications 184indications 184postoperative therapy 185types

advancement flaps 184bipedicle flaps 184Gunderson flap 185single pedicle flaps 184

Connective tissue diseases 40Contact lens 37Contact lens induced keratitis 128

clinical features 129, 135management 130organisms 129pathogenesis

altered tear dynamics 128contact lenses 128contamination of contact lens care

systems 129risk factors 128

Contact lens induced peripheral ulcer 130Contact lens induced red eye 130Contact lens wear 78Cornea 3

applied physiology 6blood supply 5defense mechanism 6innervation 5oxygen and nutritional supply 5structure 3transparency 6

Cornea 41Corneal biopsy 61, 113Corneal injuries 37Corneal scraping 52, 53, 111Corneal sensations 45, 156Corneal stroma 4Corneal surgery 79Corneal thinning/perforation 46

200 Corneal Ulcer: Diagnosis and Management

Corneal trauma 65Corneal ulcer

location 42margins 43shape 43size 43

Corneal ulceration 8corneal fistula 11ectatic cicatrix 11endophthalmitis 12hemorrhage 11perforation 11sequel and complications

corneal opacification 9descemetocele 9

stages 8healing stage 9progressive 8regressive 9

Corneal vascularization 46Corneo-iridic scar 11Corticosteroids 31, 114, 166Corynebacterium diphtheriae 68Cotton wisp method 156Culture examination 56Culture media 22, 113Curvularia lunata 81Cyclophosphamide 166Cycloplegics 31Cyclosporine 166

DDebridement 86Dematiaceae 16Dematiacious fungi 81Dendritic keratitis 93Descemet’s membrane 5Diabetes mellitus 40Diffuse endothelitis 98Dimorphic fungi 15Diphtheroids 18Disciform keratitis 98

EElectron microscopy 137Endophthalmitis 146Endothelium 5Enterococcus 18Epithelial defect 44Epithelial keratitis 95Epithelium 4Examining contact lens 113Eye trauma 78Eyelid disease 65Eyelids 41

FFilamentous fungi 14Fluconazole 29Fluorochromatic stains 21Fluoroquinolones

mechanism of action 26side effects 27spectrum of activity 27

Fungal keratitis 77, 110, 126, 178, 188clinical features

signs 80specific features 81symptoms 80

epidemiologyage distribution 77geographical distribution 77incidence 77seasonal variation 77sex distribution 77

etiopathogenesis 79laboratory diagnosis

direct microscopy 82fungal culture 83newer diagnostic modalities 83

managementmedical therapy 84surgical therapy 86

risk factors 77ocular factors 78systemic factors 79

Fusarium 15, 82

GGeneral anesthesia 124Geographic ulcers 94Giemsa stain 20, 55, 83, 99Glucose fermenters 19Glue application 180

adverse effects 182biological effects 180chemical composition and characteristics

180method of application 181modification of the technique 181patient selection 180postoperative management 182

Glycopeptides 26Graft survival and visual outcome 146Gram’s stain 20, 54, 83Gram-negative bacteria 18Gram-positive bacteria 17Grocott’s methanamine-silver stain 83

HHaemophilus 19Herpes keratitis 110, 188

Herpes simplexiridocyclitis 98stromal keratitis 96trabeculitis 98virus 91

Herpetic endothelitis 97Herpetic graft infections 146Herpetic keratitis 126Homatropine 31

IIdoxuridine 30Imidazoles 29, 114Immune mediated stromal keratitis 96Immune ring of Wessely 96Immune stromal keratitis 101Immunologic disease 101Immunosuppressive 166Infectious crystalline keratopathy

etiology 134histopathology 136laboratory diagnosis 136microbiological investigations 136pathogenesis 135risk factors 134treatment 137

medical therapy 138surgical therapy 138YAG laser application 138

Infectious epithelial keratitis 93, 100Infiltration 45Infiltrative keratitis 130Intracameral antibiotics

dosage 177indications 177

Intracameral therapy 86Intraocular pressure 49, 52Intrastromal therapy 86Iridocyclitis 102Iris 48Itraconazole 30

KKeratectomy/biopsy 84Keratitis 93Keratitis with endophthalmitis

clinical features 150investigations 150

aqueous and vitreous tap 151corneal scrapings 151ultrasonography 151

pathogenesis 150predisposing factors 150treatment

intravitreal antibiotics 152

Index 201

surgical therapy 152systemic therapy 152topical therapy 152

Keratoepithelioplasty 172Keratoplasty 173Ketoconazole 29Kimura’s spatula 52KOH wet mount preparation 82

LLacrimal SAC 41Lactophenol cotton blue 83Lamellar keratoplasty 114Lens surgery 191Lid and adnexal infections 38Light microscopy 136Limbal conjunctivectomy 172Linear endothelitis 98Listeria monocytogenes 71Löwenstein-Jensen media 23, 58

MMacrolides 26Mannitol 31Marginal keratitis 94Methotrexate 166Miconazole 29Micro-antimicrobial removal device 59Microbial keratitis 35, 129, 131

clinical examination and signs 40external ocular examination 41history and symptoms

decreased visual acuity 35discharge 35pain 35redness and photophobia 35

onset of disease 36predisposing factors 36

occupational factors 40ocular factors 37systemic factors 39

record of visual acuity 41slit-lamp biomicroscopy 41

Microbial keratitis after keratoplastypredisposing factors 142

contact lens 143donor factors 142dry eye and ocular surface problems

144indication for keratoplasty 142persistent epithelial defect 143recurrence of host infection 143suture related problems 144systemic associations 144

Microbial keratitis after refractive surgery 146micribiologic examination 148treatment 148

Microbiological investigations 51

Microbiology of graft infection 144clinical features 144investigations 145management 145

medical management 145surgical 146

Micrococcus species 17Microsporidia 13Modified Grocott-Gomori methenamine-silver

nitrate stain 21, 56Moniliaceae 15Monotherapy 72Mooren’s corneal ulcer 44Mooren’s ulcer 170

clinical features 171diagnosis 171pathogenesis 170treatment 172types 170

Moraxella 19Moraxella species 68Moraxella ulcers 70Mycobacterium 18Mycology 14

NNatamycin 28Necrotizing stromal keratitis 102Necrotizing stromal keratitis 97Neomycin 114Neonatal HSV keratitis 92Neurotrophic epithelial keratitis 95Neurotrophic keratitis 154

diagnosis 155differential diagnosis 157etiology 154

ocular causes 154systemic causes 154

investigation 158ocular examination 155

corneal sensations 156dilated fundus examination 157slit-lamp biomicroscopy 155systemic examination 157

pathogenesis 155treatment 158

Neurotrophic keratopathy 100Nocardia 18Non-fermenters 19Nutrient agar 22Nystatin 28

OOcular investigations 51Ocular lubricants 158Ocular surface diseases 38

Ocular surface disorder 66Ophthalmic varicella zoster 104Orthokeratology 108

PPatch grafts 74Pediatric keratitis 119

bacteriafungus 121nutritional 121vernal keratoconjunctivitis 121viruses 121

clinical examination 123diagnosis 122etiology 121investigations 123

laboratory investigations 124systemic investigations 124

managementmedical therapy 125post-resolution management 126surgical therapy 126

predisposing factors 119contact lens wear 120pre-existing external eye disease/

surgery 121systemic factors 119trauma 119

prevalence 119prevention 127regional differences 119

Penetrating keratoplasty 102, 114, 161Peripheral ulcerative keratitis 162

clinical picture 164complications 168epidemiology 162etiology 162examination

ocular 164systemic 164

investigationsbiopsy 165histologic findings 165imaging studies 165microbiology work up 165

pathogenesis 162treatment

medical therapy 166surgical treatment 168

Phototherapeutic keratectomycomplications 197laser characteristics 197mechanism of action 197

Pneumococcal ulcers 69Polyarteritis nodosa 169Polyenes 28Polymerase chain reaction 84, 99, 113Polymicrobial keratitis 59

202 Corneal Ulcer: Diagnosis and Management

Posterior segment 49Post-surgical microbial keratitis 140

clinical examination 141microbiologic examination 141predisposing factors 140treatment 142

Potassium hydro-oxide wet mount 53preparation 20

Pre-corneal tear film 3, 41Pre-reduced anaerobically sterilized media 58Primary ocular herpes 92Prior ocular surgery 39Protozoa 13Pseudomonas aeruginosa 19Pseudomonas species 68Pseudomonas ulcers 69Pterygium surgery 140Punctate keratitis 93Punctate stromal opacities 96Pupil and lens 48

RRecipient bed trephination 190Recurrent ocular herpes 93Rheumatoid arthritis 168Robertson cooked meat medium 23Rosacea keratitis 170

SSabouraud agar 23, 56, 57Senile furrow degeneration 170Serological investigations 60Serratia marcescens 19Signs of healing 74Slit-lamp biomicroscopy 123Staining methods 20Stains and culture media 19Staphylococcal marginal keratitis 169

Staphylococcus aureus 17, 69Sterile infiltrates 132Streptococcus pheumoniae 68Stromal neovascularization 97Superficial keratectomy 173Superficial squamous cells 4Systemic antifungal agents 86Systemic investigation 51

TTarsorrhaphy 158Tear film dysfunction 66Terrien’s marginal degeneration 169Tetracyclines 26Thayer-Martin medium 23, 58Therapeutic keratoplasty 74, 87, 187

complications 193graft failure 194hemorrhage/hyphema 193recurrence of infection 194secondary glaucoma 193success of a therapeutic graft 194

indications 187, 188postoperative management

antimicrobial therapy 192steroids 192

preoperative evaluationhistory taking 189investigations 189ocular examination 189

preoperative treatmentanti-microbial therapy 189hypotensive agents 190steroids 190

surgical managementanesthesia 190anterior chamber reconstruction 191donor tissue considerations 190donor tissue preparation 191

graft host apposition 191host tissue preparation 190

timing of surgery 188Thioglycolate broth 23, 58Tissue adhesive 74, 159, 168Topical anesthesia 124Topical antibiotics 27Topical antifungal agents 84Topical corticosteroids 73, 86Topical medications 38Trabeculitis 102Transpore tape or patching 158Triazoles 29Trifluridine 30

UUltrasonography 49, 52

VValacyclovir 30Varicella zoster virus 103Vidarabine 30Viral culture 99Voriconazole 30

WWegener’s granulomatosis 169Wing cells 4

YYeasts 15, 82

ZZiehl-Neelsen acid-fast stain 21, 55

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