Corneal Edema

Presented by: Dr. Omar Abdulrazzak

Supervised by: Dr. Buraa kubaisi

Thickness of the cornea in the center 0.52 mm while at periphery is 0.67 mm

Epithelium is 50-90 micrometer

thick BM is 8-14 Mcirometer

Stroma is 0.5 mm thick and

constitute most of the cornea DM is 10-12 Micrometer

Endothelium is 18-20

Micrometer with 2400-3000 cells/mm2

Cornea

To perform its primary function of refraction of light the cornea must be relatively thin and dehydrated with smooth anterior surface

In normal cornea, optical transparency is directly related to the state of hydration of the tissue

If cornea swells, it increases its thickness, its surface becomes irregular both changes downgrades its optic properties.

Corneal hydration

Cornea is relatively in dehydrated state for its transperancy.

Water content of cornea is 80% which is highest of any connective tissue in the body

thickness increases and % its central 80 aboveIf hydration becomes transperancy reduces

Cornea swells only in the direction of its thickness therefore, corneal thickness and hydration are linearly related

hydration

Factors draw water into the cornea

swelling pressure of sromal matrix

intraocular pressure

Factors prevent water to flow into the cornea

Mechanical barriers

Na+/ K+ pump of Endothelium

Stromal swelling pressure A.

Pressure exerted by corneal stroma mainly GAGs is stromal pressure (SP) SP is 60 mmhg, is a keystone of corneal biophysics Anionic charges on GAGs molecule expands the tissue, draws fluid with

equal but negative pressure called imbibation pressure. In vivo imbibation pressure is reduced by IOP, so IP = IOP – SP IP = 17-60 = -43 mmhg In vitro IP=SP SP generates interfibrillar tension may be biophysical mechanism to

maintain fibrils normal arrangement Cornea has an swelling pressure, which is maintained by endothelial

metabolic pump

B. barrier mechanism

Both epithelium and endothelium acts as a barrier for excessive flow of water and diffusion of electrolytes into stroma

As compare to endothelium, epithelium offers twice resistance Endothelium allows diffusion of small solutes like Nacl and urea, while

epithelium produces hypertonicity of the solution bathing the cornea Endothelial cells are attached to each other by discontinuous tight

junction i.e maculae occludentes Endothelial barrier function is mainly calcium dependent A calcium free solution will reduce the barrier function and cause

stromal edema

C. NA+/ k+ pump

Present in endothelium, several fold more active than its epithelium counterparts

Activated ATPase mediates active extrusion of NA from stroma to the aqueous

It causes diffusion gradient for water NA conc. in aqueous is more compare to stroma, which draws water from

the stroma

Bicarbonate dependent ATPase has also been reported in the endothelial cells

Depletion of bicarbonates induces swelling

Carbonic anhydrase enzyme has also been implicated in fluid transport, CAE inhibitors decreases flow of fluid from stroma to aqueous (found only in the endothelium)

D. Evaporation

Evaporation of water from precorneal tearfilm increases its osmolarity relative to cornea

Hypertonicity of tear film could draw water from cornea However this water loss is readily replaced by aqueous, it results in only a

little corneal dehydration

E. intra ocular pressure

Most of early writers assume corneal edema is due to mechanical forcing of aqueous into the cornea

But exoerimental event found out that to achieve this effect pressure required is 200 mmhg

More likely explanation is that the determining factors is endothelial damage

Edema

Word edema is derived from Greek word means swelling Formerly known as dropsy or hydropsy which means

accumulation of excessive fluid Etiology of corneal edema: Primary causes Secondary causes

Secondary causes A. Mechanical trauma

1. blunt non penetrating injury causes edema by injury to endothelium,

mostly it is reversible 2. Perforating injuries cause direct damage to the cornea, intra ocular FB

in AC can cause edema in inferior periphery where FB mainly settles 3. Forceps delivery cause pressure on globe, may cause edema due to DM

tear

4. Noxious chemicals mainly alkalies which penetrates cornea cause endothelium damage

5. Brown McLEAN syndrome : peripheral edema with brown black

discolouration of underlying endothelium seen in ICCE, ECCE, CCPE, pars plana vitrectomy

6. Cold induced reversible corneal edema has been reported trigeminal nerve dysfunction

7. Certain systemic medications like amantadine and cefaclor can cause

edema 8. Lasers used for iridotomy can cause focal corneal edema 9. High altitude corneal decompensation has been reported causing

hypoxia induced corneal edema

B. Glaucoma

Acute rise in IOP which exceeds swelling pressure of stroma causes epithelial edema

Hypoxic endothelial decompensation occurs due to diminished aqueous flow

When corneal endothelium is compromised, edema occurs even at lower level of IOP

Chronic elevation of IOP permanently damages the endothelium Irreversible corneal edema may occur.

Penetrating keratoplasty is the only treatment of choice in irreversible corneal edema, but IOP must be first controlled

In hypotony, AC is shallow or flat Mechanical trauma by cornea iris or

iris cornea touch leads to edema Normal human volunteers experiment study can be explained by

hypotony induced edema, (Corneal edema occurs in tightly patched eye)

C. Contact lenses

Most common cause of corneal edema is prolonged use of contact lens It is mainly due to insufficient supply of oxygen to eithelium Edema presents as microcystic epithelial edema near the center of

resting position of the lens If allowed to continue, it will cause stromal edema, descemet’s

membrane folds Edema easily clears if contact lens is removed Even altering the fit of contact lens is also successful in reducing edema

if it provides sufficient oxygen to the epithelium The response and recovery from edema is independent of age

D. ICE Syndrome

Iridocorneal endothelial syndrome is basically spectrum of disorders that includes : 1. progressive iris atrophy 2. chandler’s syndrome 3. iris nevus syndrome (Cogan Reese)

1. Iris atrophy: Essential iris atrophy

characterised by distortion of pupil, peripheral anterior synechie and iris atrophy with full thickness holes

Glaucoma commonly present in

the involved eye Unilateral, occurs in 4th and 5th

decades of life in Caucasians

2. Chandler Syndrome: Corneal endothelial abnormalities (hammered silver) Presents with blurred vision and haloes due to corneal

edema Corectopia may be mild to moderate Glaucoma may be less severe but at presentation IOP

may be normal Chandler syndrome have more severe edema

3. Cogan resse syndrome: Characterised by diffuse naevus which

covers iris or iris nodule Iris atrophy may be absent in 50% of

patients but corectopia and glaucoma may be severe

E. Essential corneal edema Idiopathic, episodic and often cyclic may be unilateral Presents with typical features of corneal edema like FB sensation,

diminished vision and haloes which persists for months then disappears Recurrent erosions on cornea may be noted It may be progress to the formation of bullae with ciliary injection and

urgent symptoms of pain and photophobia Pupils may be semidilated and sluggishy reacting to light If secondary infection does not set up attack passes of and the condition

eventually cleans up Some of these cases may be early presentation of dystrophic changes like

Fuch’s dystrophy

F. Metabolic disorders

Some vague concepts suggested by corneal edema occuring in some metabolic conditions like myxedema

It has also seen in hypercholesterolemia In malaria mainly in patients taking mepacrine for its treatment, in this

condition edema is limited to basal layer of epithelium and superficial layer of stroma

Primary Causes

Primary endothelial dystrophy : dystrophies involving endothelium and descemet’s membrane causes symmetrical marked stromal edema which is gradually progressive over a period of years, Congenital hereditary endothelial dystrophy Posterior polymorphous dystrophy

Primary endothelial dystrophy which develop later in life Fuch’s dystrophy

1. Congenital hereditary endothelial dystrophy: characterised by diffuse edema at birth or soon thereafter, without

significant anterior segment abnormalities

2. Posterior polymorphous dystrophy: B/L vesicular or linear lesions at the level of descemet’s membrane and

endothelium is present, it presents with congenital corneal edema

3. Fuch’s dystrophy: AD pattern of inheritance, earliest changes are limited to posterior cornea and presents with central bilateral asymmetrical corneal guttata

In Fuch’s dystrophy endothelial cells transform into fibroblast like cells capable of secreting collagen fibrils

Contribute to BM thickening

Progressive endothelial decompensation leads to stromal and epithelial edema Fluid in the stroma permeates the epithelial layer causes microcystic epithelial edema Individual epithelial cells burst, intercellular edema occurs and typical blisters or bullae formed These changes are confined to centre of cornea initially

Bullous keratopathy it represents the terminal stage of severe or prolonged epithelial

edema.

In the affected area the epithelium is steamy irregular and on its surface one or more large bullae appears, raised in the form of blebs.

After 2-3 days the Bullae rupture only to

reappear, the cycle associated with considerable irritation and pain

Treatment is extremely difficult, retrobulbar injection of alcohol, removal of endothelium by scraping, cauterisation of cornea by tincture iodine, trichloro-acetic acid

Bandage contact lens to relieve pain Lamellar grafting, if measures of therapy fails and if

recurrence persists treatment is enucleation

Manifestation of edema Depends upon cause and degree of the condition:

Mild discomfort in conditions like Fuch’s dystrophy Severe neuralgic pain is seen in Bullous Keratopathy Colour haloes Severe visual loss

Visual acuity

Small amount of epithelial edema can result in substantial reduction in visual acuity Although 70% stromal edema is compatible with normal visual acuity Decreased acuity is more severe in early morning IOP, iritis glaucoma and optic nerve changes may be contribute to reduced acuity

Pain and discomfort

As edema increases epithelium is detached from basement membrane to form bullae This rupture of bullae causes severe pain, photophobia, epiphora and narrowing of palpebral fissure Photophobia is due to light scattering in the edematous cornea Coloured haloes

Evaluation of corneal morphology

Slit lamp examination

Specular biomicroscopy

Pachymetry

Optical coherence

Scheimpflug camera

orbscan

1. Slit lamp examination

Examination reveals cornea guttata, stromal density, descemet’s membrane folds Bullae are easily observed by slit lamp In case of chronic corneal edema neovascularization, pannus formation or dystrophies are visible In case of stromal edema thickness exceeds 0.6 mm

2. Specular biomicroscopy Measures cell density Normal endothelial cells count is 3000-2000 cells/mm2

cell count less than 1000 poorly tolerate ocular surgery

Used in assesing cells in corneal grafting, LASIK, dystrophies corneal edema

3. Pachymetry: is the process of measuring the thickness of the cornea . It can be done using contact methods, such as ultrasound and confocal microscopy (CONFOSCAN), or noncontact methods such as optical biometry with a single Scheimpflugcamera (such as SIRIUS or PENTACAM), or optical coherence tomography (OCT), and online optical coherence pachymetry (OCP, such as ORBSCAN)

4. Optical coherence tomography: Is an established medical imaging technique It is widely used to obtain high resolution images of the retina and the anterior segment of the eye Corneal thickness can also be measured

5. Scheimpflug camera: Pentacam trade name, is a diagnostic unit able to perform five functions: Images of AS

3D anterior chamber analyzer

Pachymetry

Corneal topography

Cataract analyzer

6. Orbscan II : It analyses the physical shape/ contours of cornea and allows the surgeon to decide if it has suitable shape, is healthy and thick enough for treatment It is the only topographer currently available that measures the shape of both the front and back surface of the entire cornea (other systems only measure the front surface) and can therefore provide acomplete picture of the thickness of cornea

Management

o In all cases of corneal edema if documented IOP is high, its control with topical anti glaucoma drugs or systemic CAE inhibitors are given

o Even in moderately elevated IOP patients control may significantly

reduces epithelial edema o If IOP remains elevated despite maximum tolerated medical therapy

surgical intervention must be considered o Cyclocryotherapy / trabeculectomy are considered

Local therapy

o Early morning reduced vision can be improved by exposing eyes to warm air E.g: hair dryer

o Topical application of hyperosmotic agents like 5% NACL solution or

ointment can reduce edema to a little extend o If inflammation is a contributory cause of corneal edema, topical

application steroids may be very helpful o If the etiology of edema is not apparent 10 days course of topical

steroids can serve as diagnostic as well as therapeutic purpose o In patients with early corneal decompensation and mild edema a careful

refraction may improve vision o Therapeutic hydrophilic contact lens can be used

o Thin hydrophilic lens fitted flat on cornea allow maximum contact between lens and irregular cornea

o Application of radiodiathermy or other forms of electrocautery on

Bowman’s membrane o This produces adhesion between stroma and basal layer of epithelium

preventing formation of Bullae

Management

o Gunderson conjunctival flap with or without lamellar keratectomy can be performed to relieve pain

o Retrobulbar alcohol injection or tarsorrhaphy also may relieve pain o In painful blind eye or in absolute glaucoma enucleation may

represent the optimal procedure

Penetrating keratoplasty

o If visual recovery exists penetrating keratoplasty is performed before cauterisation of BM or conjunctival flap procedure

o In case of multiple graft failure and corneal thickness exceeds 1.5 mm,

the use of keratoprosthesis has been advocated o Keratoprosthesis is considered as an last ditch effort for visual

rehabilitation

Keratoprosthesis

o It causes high rate of failure and complications

o In case of bilateral corneal edema

keratoprosthesis in worst eye and keratoplasty in fellow is performed