New Investigations in OphthalmOlOgy

Editors

tanuj Dada MD MAMS

ProfessorDr Rajendra Prasad Centre for Ophthalmic Sciences

All India Institute of Medical SciencesNew Delhi, India

Neha midha MD DNB FICO

Senior ResidentDr Rajendra Prasad Centre for Ophthalmic Sciences

All India Institute of Medical SciencesNew Delhi, India

tarun arora MD DNB FICO

Senior ResidentDr Rajendra Prasad Centre for Ophthalmic Sciences

All India Institute of Medical SciencesNew Delhi, India

New Delhi | London | PanamaThe Health Sciences Publisher

Second Edition

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Jaypee Brothers Medical Publishers (P) Ltd

HeadquartersJaypee Brothers Medical Publishers (P) Ltd4838/24, Ansari Road, DaryaganjNew Delhi 110 002, IndiaPhone: +91-11-43574357Fax: +91-11-43574314Email: jaypee@jaypeebrothers.comOverseas OfficesJ.P. Medical Ltd Jaypee-Highlights Medical Publishers Inc83 Victoria Street, London City of Knowledge, Bld. 235, 2nd Floor, ClaytonSW1H 0HW (UK) Panama City, PanamaPhone: +44 20 3170 8910 Phone: +1 507-301-0496Fax: +44 (0)20 3008 6180 Fax: +1 507-301-0499Email: info@jpmedpub.com Email: cservice@jphmedical.comJaypee Brothers Medical Publishers (P) Ltd Jaypee Brothers Medical Publishers (P) Ltd17/1-B Babar Road, Block-B, Shaymali Bhotahity, KathmanduMohammadpur, Dhaka-1207 NepalBangladesh Phone: +977-9741283608Mobile: +08801912003485 Email: kathmandu@jaypeebrothers.comEmail: jaypeedhaka@gmail.comWebsite: www.jaypeebrothers.comWebsite: www.jaypeedigital.com© 2017, Jaypee Brothers Medical PublishersThe views and opinions expressed in this book are solely those of the original contributor(s)/author(s) and do not necessarily represent those of editor(s) of the book.All rights reserved. No part of this publication may be reproduced, stored or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission in writing of the publishers. All brand names and product names used in this book are trade names, service marks, trademarks or registered trademarks of their respective owners. The publisher is not associated with any product or vendor mentioned in this book.Medical knowledge and practice change constantly. This book is designed to provide accurate, authoritative information about the subject matter in question. However, readers are advised to check the most current information available on procedures included and check information from the manufacturer of each product to be administered, to verify the recommended dose, formula, method and duration of administration, adverse effects and contraindications. It is the responsibility of the practitioner to take all appropriate safety precautions. Neither the publisher nor the author(s)/editor(s) assume any liability for any injury and/or damage to persons or property arising from or related to use of material in this book.This book is sold on the understanding that the publisher is not engaged in providing professional medical services. If such advice or services are required, the services of a competent medical professional should be sought.Every effort has been made where necessary to contact holders of copyright to obtain permission to reproduce copyright material. If any have been inadvertently overlooked, the publisher will be pleased to make the necessary arrangements at the first opportunity.Inquiries for bulk sales may be solicited at: jaypee@jaypeebrothers.comNew Investigations in OphthalmologyFirst Edition: 2006Second Edition: 2017ISBN: 978-93-86150-99-8Printed at

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Dedicated toOur dear Alma Mater

Dr Rajendra Prasad Centre for Ophthalmic Scienceson its Golden Jubilee (1967–2017)

The entire author royalty of this book and its subsequent editions is being donated to the Indian Army Welfare Fund Battle Casualties

JAI HIND

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Contributors

Abanti Das MDSenior ResidentDepartment of Radiology All India Institute of Medical SciencesNew Delhi, India

Abhishek Dave MDConsultant Cornea, Cataract and Refractive SurgeryDr Shroff’s Charity Eye HospitalNew Delhi, India

Aditya Modi DNB FICO FRCSConsultant Vitreoretinal ServicesNarayana NethralayaBengaluru, Karnataka, India

Ajay Sharma MScSenior Technical OfficerDr Rajendra Prasad Centre for Ophthalmic SciencesAll India Institute of Medical SciencesNew Delhi, India

Ankit Singh Tomar MBBSJunior ResidentDr Rajendra Prasad Centre for Ophthalmic SciencesAll India Institute of Medical SciencesNew Delhi, India

Archita Singh MD FICOSenior ResidentDr Rajendra Prasad Centre for Ophthalmic SciencesAll India Institute of Medical SciencesNew Delhi, India

Devanshi Bhanushali DNBVitreo Retina Fellowship Narayana NethralayaBengaluru, Karnataka, India

Dewang Angmo MD DNB FICO FRCSAssistant Professor of OphthalmologyDr Rajendra Prasad Centre for Ophthalmic SciencesAll India Institute of Medical SciencesNew Delhi, India

Elisa D’Alessandro MDGlaucoma Research CenterMontchoisi ClinicSwiss Vision NetworkLausanne, Switzerland

Jeewan S Titiyal MDProfessor of OphthalmologyDr Rajendra Prasad Centre for Ophthalmic SciencesAll India Institute of Medical SciencesNew Delhi, India

Kaweh Mansouri MD MPHGlaucoma Research CenterMontchoisi Clinic, Swiss Vision NetworkLausanne, SwitzerlandDepartment of OphthalmologyUniversity of ColoradoDenver, Colorado, USA

Kirsten Hoskens MDGlaucoma Research CenterMontchoisi Clinic, Swiss Vision NetworkLausanne, Switzerland

Krishna Poojita Vunnava DNBConsultant OphthalmologyNarayana Nethralaya Bengaluru, Karnataka, India

Luci Kaweri MDConsultant OphthalmologyNarayana NethralayaBengaluru, Karnataka, India

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viii New Investigations in Ophthalmology

Manpreet Kaur MDSenior ResidentDr Rajendra Prasad Centre for Ophthalmic SciencesAll India Institute of Medical SciencesNew Delhi, India

Monisha E Nongpiur MDConsultant OphthalmologySingapore Eye Research InstituteSingapore

Natasha Gautam MDSenior ResidentDepartment of OphthalmologyAdvanced Eye Care CentrePGIMERChandigarh, India

Neha Midha MD DNB FICOSenior ResidentDr Rajendra Prasad Centre for Ophthalmic SciencesAll India Institute of Medical SciencesNew Delhi, India

Parul Ichhpujani MDAssociate Professor of OphthalmologyGovernment Medical CollegeChandigarh, India

Prafulla K Maharana MDAssistant Professor of OphthalmologyDr Rajendra Prasad Centre for Ophthalmic SciencesAll India Institute of Medical SciencesNew Delhi, India

Rajesh Sinha MD DNB FRCSProfessor of OphthalmologyDr Rajendra Prasad Centre for Ophthalmic SciencesAll India Institute of Medical SciencesNew Delhi, India

Ramanjit Sihota MD FRCS FRCOphthProfessor and Head Glaucoma ServicesAll India Institute of Medical SciencesNew Delhi, India

Reetika Sharma MDConsultant OphthalmologyASG Eye Hospital, Hazipur, Bihar, India

Rohit Shetty DNB FRCS PhDVice ChairmanNarayana NethralayaBengaluru, Karnataka, India

Ronnie Jacob George DO DNB MS Research DirectorSankara NethralayaChennai, Tamil Nadu, India

Roshan T MDFellow, Lens and Refractive SurgeryNarayana NethralayaBengaluru, Karnataka, India

Sanjay Sharma MDProfessor of RadiologyAll India Institute of Medical SciencesNew Delhi, India

Sathi Devi AV MDConsultant Glaucoma ServicesNarayana NethralayaBengaluru, Karnataka, India

Saurabh Verma MBBSJunior ResidentDr Rajendra Prasad Centre for Ophthalmic Sciences.All India Institute of Medical SciencesNew Delhi, India

Shibal Bhartiya MDConsultant OphthalmologyFortis Memorial Research InstituteGurugram, Haryana, India

SS Pandav MDProfessor of ophthalmologyAdvanced Eye Care Centre, PGIMERChandigarh, India

Sushmita Kaushik MSProfessor of OphthalmologyAdvanced Eye Care Centre, PGIMERChandigarh, India

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ixContributors

Sushmitha S MS FICOAssociate ConsultantSankara NethralayaChennai, Tamil Nadu, India

Talvir Sidhu MD Senior ResidentDr Rajendra Prasad Centre for Ophthalmic SciencesAll India Institute of Medical SciencesNew Delhi, India

Tanuj Dada MDProfessor of OphthalmologyDr Rajendra Prasad Centre for Ophthalmic SciencesAll India Institute of Medical SciencesNew Delhi, India

Tarun Arora MD DNB FICOSenior ResidentCornea, Lens and Refractive surgery servicesDr Rajendra Prasad Centre for Ophthalmic SciencesAll India Institute of Medical SciencesNew Delhi, India

Vasanth TM BS Opto M PhilResearch Associate Sankara NethralayaChennai, Tamil Nadu, India

Vaishali G Rai DNBSenior ResidentDepartment of OphthalmologyAll India Institute of Medical SciencesBhopal, Madhya Pradesh, India

Vijay Sharma MSAssistant Professor Army Hospital Research and ReferralNew Delhi, India

Vinay Nangia MDChairmanConsultant Glaucoma and RetinaSuraj Eye InstituteNagpur, Maharashtra, India

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Preface to the Second Edition

Clinical investigations for anterior segment disorders have a vital role in the diagnosis and management of various ocular disorders. Recent introduction of optical coherence tomography, including angiography, adaptive optics and wavefront imaging has brought in a revolution in diagnostics.

The main utility of these investigations is to improve the diagnostic capability such that the disease can be picked up at a relatively early stage and to detect any progression of the disease, which is not yet evident by clinical examination (e.g. in glaucoma). Another important aspect of these investigations is their ability to image and outline the exact pathogenesis of the disease at the cellular level (e.g. confocal microscopy). An understanding of these investigations gives the clinician a powerful tool which can aid in situations of diagnostic dilemma.

Although majority of ophthalmic institutions do not have all of these new technologies, it is important to understand their basic principle, indications and interpretation. It is a common situation to see a patient walking into your outpatient department, carrying the printout of a new investigation done elsewhere for review. The chapters in this book, contributed by various authors working at the best centers in India, provide the reader with the basic information about the recent investigations in the field of corneal diseases, glaucoma, cataract surgery, and radiological imaging modalities. The text has been simplified to include the indications of the new tests, optical principle, interpretations of the printout, advantages, disadvantages, available clinical studies and patient examples with a self assessment quiz. Numerous clinical photographs have been added related to each investigation to aid the reader in grasping the clinical utility of these tests.

We hope that the text will provide useful practical information for the residents and practitioners and help them in understanding and interpreting these new investigations and incorporating them into their routine clinical practice.

tanuj DadaNeha midhatarun arora

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Preface to the First Edition

Clinical diagnosis and management of various ocular disorders has undergone a sea change in the last decade with the introduction of new investigations and imaging modalities. There are two broad principles of these investigations: evaluation of structure and an assessment of the function of a particular part of the eye. The main utility of these investigations is to improve the diagnostic capability, such that the disease can be picked up at a relatively early stage, thereby preventing visual loss and to detect any progression of the disease, which is not yet evident by clinical examination (e.g. in glaucoma). Another important aspect of these investigations is their ability to image and outline the exact pathogenesis of the disease at the cellular level (e.g. confocal microscopy).

An understanding of these investigations gives the clinician a powerful tool, which can aid in situations of diagnostic dilemma. The main limitation of these new technologies is their prohibitive cost, especially for developing countries which makes their availability very restricted. The second problem is the frequent upgrades of hardware and software, which makes it difficult for the practitioners to keep pace with the new developments. In addition, there are very few texts that elucidate on these varied technologies and the reader has to search numerous journals to get any useful information on this subject.

Although majority of ophthalmic institutions do not have all of these new technologies, it is important to understand their basic principle, indications and interpretation. It is a common situation to see a patient walking into your outpatient department, carrying the printout of a new investigation done elsewhere for review. The current monograph compiled by two of the leading institutes of ophthalmology in Asia, provides the reader with the basic information about the recent investigations in the field of corneal diseases, glaucoma, cataract surgery, retinal disorders, ocular blood flow and radiological imaging modalities. The text has been simplified to include the indications of the new test, optical principle, interpretation of the printout, advantages, disadvantages, available clinical studies and patient examples. Numerous clinical photographs have been added related to each investigation, to aid the reader in grasping the clinical utility of these tests. We hope that the text will provide useful practical information for the residents and practitioners and help them in understanding and interpreting these new investigations and incorporating them into routine clinical practice.

tanuj DadaSubrata mandal

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Acknowledgments

I would like to thank Professor Atul Kumar, Chief of Dr Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, India, for his constant inspiration and encouragement.

I am greatly indebted to Dr Tarun Arora, one of the most exceptional Senior Residents of Dr Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, India. This edition of the book was only possible due to his energy and enthusiasm. I am thankful to Dr Neha Midha, Senior Resident of Dr Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, India, in the glaucoma services for her dedication and hard work.

I wish to thank my colleagues Professor Ramanjit Sihota, Dr Viney Gupta, Dr Sunil Choudhary and our optometrists Mr Ajay Sharma and Mrs Amisha Gupta for helping to create one of the best glaucoma clinical and research facilities in the world.

I especially wish to thank Dr Subrata Mandal (Ex-Senior Resident of Dr Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, India), who was my co-author in the first edition and Dr Saurabh Verma, Junior Resident of Dr Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, India, who is currently working with me for his time and effort in our academic projects.

I wish to thank Brigadier Dr Sagarika Patyal and Col Dr Sanjay K Mishra (Army Research and Referral Hospital, New Delhi) and Brigadier Anil Hooda (Deputy Director General (Ceremonial and Welfare Directorate Indian Army) for facilitating the donation of the author royalty to the Army Welfare Fund Battle Casualties.

No success in life and beyond is possible without a “Guru”. Words are not enough to thank my spiritual teacher.His Holiness Saint Dr Gurmeet Ram Rahim Singh ji Insan, Dera Sacha Sauda

Ashram, Sirsa, Haryana, India, from whom I learnt about the art and science of meditation.

My “charansparsh” to my parents Drs Kamlesh and Vijay Kumar Dada who have been my lifelong loving mentors, and I extend my humble heartfelt gratitude to my soulmate Geeta and little darling Josya.

Tanuj Dada

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Contents

Section 1: Cornea and Ocular Surface

1. Dry Eye Evaluation 3Rohit Shetty, Luci Kaweri, Krishna Poojita Vunnava

� Tests for Tear Film Analysis 3 � History and Symptoms 4

2. anterior Segment Optical Coherence tomography in Cornea and Refractive Surgery 15Tarun Arora, Vijay Sharma, Rajesh Sinha, Jeewan S Titiyal

� Principle 15 � Procedure 16 � Indications 16 � Advantages 21 � Limitations 23

3. Corneal topography: Newer horizons 25Vijay Sharma, Tarun Arora, Saurabh Verma, Rajesh Sinha

� Pentacam 26

4. Specular microscopy 40Tarun Arora, Vijay Sharma, Neha Midha, Rajesh Sinha

� Principle 40 � Procedure 41 � Analysis 41 � Indications 42 � Advantages 43 � Interpretation of Readings 43 � Limitations 44

5. Confocal microscopy 46Abhishek Dave, Ankit Singh Tomar, Tarun Arora

� Principle 46 � Confocal Systems for Clinical Use 48 � Procedure of Confocal Microscopy 49 � Confocal Microscopy of Normal Cornea 49 � Clinical Confocal Microscopy 53

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xviii New Investigations in Ophthalmology

� Infective Keratitis 53 � Corneal Dystrophies 54 � Refractive Surgery 55 � Keratoconus and Collagen Cross Linking 56 � Ocular Surface Disorders 56 � Corneal Grafts 57 � Other Corneal Diseases 57 � Corneal Deposits 58 � Other Clinical Uses 58

6. Corneal Biomechanics: Ocular Response analyzer and Dynamic Scheimpflug Imaging 61Prafulla K Maharana, Vaishali G Rai

� Principle 62 � Indications 68 � Contraindications 68 � Advantage 68 � Disadvantages 69 � Review of Literature 69

Section 2: lens

7. Biometry 79Manpreet Kaur, Archita Singh, Saurabh Verma, Talvir Sidhu

� Axial Length 79 � Keratometry 85

8. Wavefront analysis Systems 92Manpreet Kaur, Roshan T, Saurabh Verma, Jeewan S Titiyal

� Principle 92 � Specifications of iTrace 94 � Procedure 95 � Data Graphs with iTrace 96

Section 3: glaucoma

9. Scanning laser polarimetry 107Tanuj Dada, Reetika Sharma, Talvir Sidhu, Neha Midha

� Principle of Scanning Laser Polarimetry 107 � Generations of Scanning Laser Polarimetry and Calculation of

Birefringence 108 � Special Scenarios 113 � Limitations 115

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xixContents

10. Role of OCt in glaucoma Diagnosis and progression (Cirrus SDOCt) 120Sushmita Kaushik, Natasha Gautam, SS Pandav

� Time Domain OCT 122 � Spectral Domain OCT 123 � Cirrus OCT 124 � OCT and Glaucoma Detection 125 � Detection of Glaucoma Progression 126

11. Imaging the Retinal Nerve Fiber layer with Spectralis SDOCt 140Vinay Nangia

� Spectralis OCT 140 � Imaging the RNFL 141 � Appearance of the Retinal Nerve Fiber Layer 142 � Clinical Cases 146

12. Dynamic applanation procedures 156Sathi Devi AV

� Ocular Response Analyzer 157 � Corneal Visualization Scheimpflug Technology 163

13. Frequency Doubling perimetry and Short Wavelength automated perimetry 170Sushmitha S, Vasanth TM , Ronnie Jacob George

Frequency Doubling Perimetry 170 � Principle 170 � Frequency Doubling Technology Perimetry 170 � Screening Strategy 171 � Full Threshold Strategy 172 � Effect of Cataract on FDT 173 � Interpretation of FDP with Screening Strategy 173 � Advantages of FDT Perimetry 173 � Disadvantages of FDT Perimetry 174 � Humphrey Matrix Perimetry 174 � Screening Strategy 174 � Threshold Strategy 174

Short Wavelength Automated Perimetry (SWAP) 178 � Principle 178 � Full Threshold SWAP 179 � SITA SWAP 179 � Comparison of Full Threshold SWAP and SITA SWAP 180 � Learning Effect 181 � Effect of Cataract on SWAP 182

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xx New Investigations in Ophthalmology

� SWAP in Other Ocular Disorders 182 � Advantages 182 � Disadvantages 183

14. Ultrasound Biomicroscopy in glaucoma 186Tanuj Dada, Dewang Angmo, Ankit Singh Tomar, Talvir Sidhu

� Principle 186 � Technique 187 � Normal Ocular Structures 187 � Clinical Uses in Glaucoma 189 � Quantitative Ultrasound Biomicroscopy 204 � Quantification of the Anterior Chamber Angle 206 � Effects of Drugs 207 � Effects of Surgery 208 � Comparison with Anterior Segment OCT 209 � Limitations 209

15. OCt—angiography and glaucoma 215Elisa D’Alessandro, Kirsten Hoskens, Kaweh Mansouri

16. Contact lens Sensor for IOp monitoring 222Shibal Bhartiya, Parul Ichhpujani, Talvir Sidhu

� Principle 222 � Limitation 225 � Review of Literature 226

17. anterior Segment OCt in glaucoma 229Dewang Angmo, Monisha E Nongpiur, Talvir Sidhu, Ankit Singh Tomar, Tanuj Dada

� Clinical Uses 230 � Technique 231 � ASOCT (Visante and CASIA) Measurement and Analysis 231 � Applications of ASOCT in 237 � Limitations 244 � Future/Upcoming Technologies 244

18. heidelberg Retinal tomography 247Tanuj Dada, Neha Midha, Ajay Sharma, Ramanjit Sihota

� Principle 247 � Operation of the Heidelberg Retinal Tomograph II 250 � Moorfield’s Regression Analysis and Other Discriminant Formulas 253 � Current Role in Diagnosis 255 � Advantages 255 � Disadvantages 256 � Types of Printout 256 � Interpretation of the Printout 258

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xxiContents

� Interpretation of a Single Printout 263 � Monitoring Progression 266 � Summary of HRT Literature 268 � Literature Summary on HRT III 271

Section 4: Imaging

19. Orbital Imaging: Newer perspectives 281Sanjay Sharma, Abanti Das

� Intraconal 282 � Muscle Cone 286 � Extraconal Space 288 � Globe 294 � Choroidal Hemangioma 299 � Congenital Anomalies 300

20. adaptive Optics 303Devanshi Bhanushali, Aditya Modi, Rohit Shetty

� Principle of Adaptive Optics 303 � Image Acquisition 305 � Applications 307

Self-assessment Quiz 311Index 333

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IntroductIon Wavefront analysis provides a detailed evaluation of the aberrations in the optical system of the eye. Various visual imperfections, referred to as lower and higher-order aberrations, exist within the eye and can affect both visual acuity and the quality of vision. Higher-order aberrations are often linked to glare and halos that may cause night vision problems. Wavefront analyzers map both the lower and higher-order aberrations and provide an estimation of the optical quality of the eye. Aberrometry devices that perform wavefront analysis are based on one of the three different wavefront measuring principles: (1) Hartmann-Shack, (2) Tscherning or ray tracing, and (3) Automated retinoscopy.

The iTrace System (Tracey Technologies, Houston, Texas) integrates ray tracing wavefront aberrometry analysis with advanced corneal topography analysis and is considered one of the best methods for analyzing visual function. It is a multifunctional instrument that combines ray tracing wavefront aberrometry, pupillometry, keratometry, auto-refraction and corneal topography.

PrIncIPle iTraceTM combines the principles of ray tracing aberrometry and placido disk topography to measure quality of vision in a patient. In the ray tracing method, a laser beam parallel to the line of sight is projected through the pupil. The exact point where the laser beam reaches the retina is located by means of the retro-reflected light captured by reference lineal sensors. Local aberrations in the path of the laser beam through the cornea and the internal structures cause a shift in the location on the retina. Once the position of the initial beam on the retina has been determined, the laser beam is shifted to another position, which is then located in the retina. This process continues until several separated points are projected into the entrance pupil. This helps in obtaining a connection between the direction that the light beams have taken

Wavefront Analysis Systems

8Chapter

Manpreet Kaur, Roshan T, Saurabh Verma, Jeewan S Titiyal

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93Wavefront Analysis Systems

while entering and leaving and allows a reconstruction of the real wavefront error. This principle measures forward aberrations of the light that goes through the eye. The pattern of rays that can be used in ray tracing is rectilinear, polar and concentric rings.1

The iTrace is based on this principle of Ray Tracing and a sequential series of infrared beams of the order of 100 microns and 785 nm wavelength each are projected into the entrance pupil parallel to the eye’s line of sight. The exact location where the laser beam reaches the retina is recorded in x, y axis by retroreflected light collected on linear sensors. A total of 64 laser beams are projected through the entrance pupil 4 times each (256 points) at a high speed (approximately 250 milliseconds). These 256 rays would sequentially focus at a single point on the fovea in an emmetropic eye.2 The iTrace uses a pattern of concentric rings.

Using this data from 256 points, a retinal spot diagram is created (RSD) which contains all the information of refraction, aberration and point spread function of the eye (Fig. 1, bottom left). Point spread function shows the image obtained in the retina when the patient sees a point source of light (Fig. 2). Modulation transfer function describes how the optical system reproduces detail from the object to the image produced by the lens (Fig. 2).

The iTrace uses a Placido design called Vista based on the hardware developed by Eyesys Vision Inc. (Houston, Texas). A set of concentric rings is projected onto the anterior corneal surface and the pattern of the image formed on the cornea is captured using a camera (Fig. 3). It covers an area spanning 0.6 mm from the center to 10 mm of the peripheral cornea. Data is collected along a fixed number of radial lines across the concentric rings and this data is used to calculate corneal topography. The placido disk contains 26 concentric rings and collects data across 9,360 points.

Fig. 1: Wavefront verification display screen. Upper left figure displays the iTrace projection pattern. 64 thin, parallel light beams are projected through the pupil. Bottom left figure displays the retinal spot diagram of a patient with high myopia. The two graphs on the right hand side display the horizontal point profile and the vertical point profile diagrams that indicate the quality of the laser’s signal captured during measurement

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94 Section 2: Lens

The Eyesys Vista provides the standard keratometric readings in the zone of 3 mm, the reading of the refractive power of the cornea in the central 3 mm zone, corneal indices and topographic maps.

SPecIfIcatIonS of Itrace iTrace has an internal optometer which acts as a fixation target and aligns the laser beams to the patient’s line of sight. Fogging can be done in the instrument by adding spherical equivalent from +7D to – 5D to relax accommodation. Accommodation can be measured both objectively and subjectively.

Fig. 2: Wavefront summary display screen displaying the modulation transfer function and point spread function of a patient with high myopia. The upper two graphs display the total MTF and PSF for the entire eye, and the bottom two graphs display the MTF and PSF for higher order aberrations of the eye, which are minimal

Fig. 3: The iTrace uses a Placido design and a set of 26 concentric rings are projected onto the anterior corneal surface

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95Wavefront Analysis Systems

The fixation target can be used to determine aberrations in different viewing distances.3 Using the data from the RSD, the Zernike coefficients are calculated from which the refractive error of the eye at different pupil sizes are calculated and displayed (multizone refraction analysis). The measurement range of iTrace is ± 15D sphere and ± 10D cylinder, with an accuracy and reproducibility of ± 0.10D. Measurements can be taken accurately even at pupil size as low as 2.5 mm. The iTrace takes the measurement on the real pupil of the patient with a range of pupil size between 2.5 and 8.0 mm. A laser of 655 nm is used to align the system and prevent errors due to tilt and auto corrects alignment. iTrace gives measurements of both total and internal aberrations.

Procedure The patient details are entered in the user interface on the computer. The patient is explained the procedure and asked to relax. Procedure is carried out on an undilated patient in a dim room. The patient places his chin on the chin rest with the forehead stabilized against the forehead support, and looks through the device. The eye of the patient is focused using four infrared tracking spots on the cornea before starting the data acquisition. The aberrometry data of the eye is provided by the system within seconds and the results are displayed on three screens: Wavefront (WF) screen, Corneal Tomography (CT) screen and combined screen. The higher order aberrations should be evaluated in an undilated pupil as pupil decentration caused by dilatation causes calculation error. Cycloplegia also has effect on ocular aberrations and hence should be avoided.4 Small shifts of pupil center causes change in HOA and refractive components measured.5 Higher order aberrations are to be measured in the primary position, as there is a small but significant change noted with the change in gaze from the primary position.6

Verifying the Quality of the Measurement in the Wavefront examThe WF Verification Display shows the entire patient’s data on limbal diameter, pupil size and scan diameter (Fig. 1). The examiner can manually select the analyzed pupil diameter to determine where certain aberrations occur and their effect on vision. The WV verification display also shows the number of nonmeasured or rejected points. If they are less than nine they are displayed in yellow and if they are more than nine they appear in red and the exam is invalid. The Horizontal Point Profile and the Vertical Point Profile diagrams show the position of each point that reflects on the retina, taking the center of each profile in the X and Y-axis. They give an image of the quality of the laser’s signal captured during measurement; if the profile is irregular the measurement is incorrect.

The Retinal Spot Diagram (RSD) is also shown in this screen, and a distorted RSD indicates an error in the measurement or an eye with many aberrations.

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96 Section 2: Lens

data graPhS WIth Itrace Six basic graphs are obtained with the iTrace measurements.7 Combinations of these 6 basic graphs appear in the different screens or displays.

Wavefront Map Total and High-order Aberrations (HOA) These maps display the color-coded wavefront aberrations of the eye as measured in microns of error. The error can be positive or negative. Warm colors indicate that the wavefront is in front of the reference plane (positive aberrations) and blue colors indicate that the wavefront is retarded in relation to this plane (negative aberrations).

RMS (Root Mean Square) It is the measurement of the magnitude of the aberration. A total RMS value for the total aberration of the eye and a specific RMS value for each Zernike term of the eye aberrations can be obtained.

Total Refractive and HOA Refractive MapsThese maps display the refractive power of the whole eye in diopters.

Emmetropia is represented in green, myopia in red and hypermetropia in blue. This map in combination with the topographic map can indicate if the astigmatism is purely corneal or if it has a lenticular component. The objective measurement of accommodation is done comparing these maps taken at different distances and analyzing the refractive change.

PSF Total and HOA PSF PSF (Point Spread Function) represents the quality of the image of an optic system, determined by the aberrations to a single point of light. The more aberrations, the higher the defocus effect obtained.

Snellen Letter Total and High-order Aberrations (HOA)The Snellen Letter (E) is a simulation of the iTrace system and provides an estimate of how the eye would see the letter E projected in different sizes. This virtual optotype allows the examiner to see what the patient sees and to clinically determine the visual discomforts reported by the patient.

Zernike PolynomialsIt is a bar graph and a table of the terms or polynomials of Zernike, which show a detailed analysis of the specific aberrations in an eye. The iTrace shows the Zernike polynomials up to the 6th order (27 terms) and can show the total for the eye (Total), only the corneal and the difference between the corneal and the total (internal optics).

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97Wavefront Analysis Systems

itrace displays (Screens) for analysisThe topographic and aberrometric data is displayed in different ‘screens’ or ‘Displays’ for analysis.7

A. Wavefront Analysis � Visual Function Analysis (VFA Summary Display) (Fig. 4) shows the

Refraction Map HO Total or the Wavefront HO Total. Refraction in different diameters, the RMS, PSF, Snellen letter and Potential Visual Complaints (nocturnal myopia, halos, glare, defocus, double vision) is displayed. These symptoms are quantified with 1 to 3 crosses depending on their intensity and they are marked in red or yellow depending on their grade. The size of the entrance pupil can be altered by the pupil size regulator.

� Wavefront comparison map: It compares two wavefront maps in one patient. This map is used to compare the status of the aberrations before and after refractive surgery and to measure the accommodation.

Fig. 4: Visual function analysis summary display shows the Refraction Map HO Total or Refraction in different diameters, the RMS, PSF, Snellen letter and potential visual complaints for both eyes

B. Corneal Topographic Analysis (CT Summary Display) (Fig. 5)The iTrace shows 5 different screens in CT Summary Display depending on the topographic maps that we want. The five topographic maps are the standard axial map, local or tangential curvature map, refractive map, elevation map and the corneal wavefront map. The corneal wavefront map gives us the information on the corneal aberrometry. The iTrace makes the calculations based on the data obtained through the Placido Eyesys Vista. By means of the refractive map a transformation in Zernike polynomials is made and the corneal aberrometry is obtained. By subtracting the corneal aberrations from

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the total aberrations, we obtain the aberrations of the internal optics, mainly caused by those produced by the crystalline lens.

C. Wavefront (WF) and Topographic (CT) Analysis (WF/CT Summary Display) (Figures 6 and 7)It analyses the aberrations of the internal optics. Through corneal topography the corneal aberrations map can be mathematically generated. The difference obtained by subtracting the corneal aberrations from the total aberrations represents the aberrations of the internal optics. Most of the aberrations of the internal optics are induced by the crystalline lens.

Clinical Applications � Measurement of accommodation8-10 � The accommodation measurement is based on a far stimulus (0 D of

accommodative demand), measuring its refractive map and subsequently observing its difference with the refractive maps resulting from stimulus at different specific distances

� In a patient undergoing cataract surgery with IOL implantation, the aberrations (induced or compensated) introduced by the IOL can be studied by analyzing the preoperative and postoperative map displaying the aberrations of the internal optics, cornea and total.

� Different types of IOL can also be analyzed. � A preoperative iTrace can help analyze if a patient’s optics will support

a multifocal IOL. The iTrace gives the “Angle Alpha”. If the Angle Alpha is significant, a multifocal will be misaligned and cause high order aberrations producing poor results. In these cases, the patient could achieve more optimal results with a monofocal lens

Fig. 5: CT Summary display screen showing the axial map, local curvature map, Z elevation map and refractive map and the information on the corneal aberrometry

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Fig. 6: WF/CT summary display screen displaying the aberrations of the internal optics, corneal aberrations and the total aberrations of the eye

Fig. 7: WV/CT summary display showing the point spread function of the internal optics, cornea and the entire eye. The majority of aberrations are contributed by the internal optics. This is a case of cataract

� iTrace’s integrated toric calculator, surgically induced astigmatism analysis and the Zaldivar Toric Caliper helps improve the precision of toric power selection and placement (Fig. 8). The integrated toric calculator presents several toric power options and predicted results, so that an optimal power can be selected. After selecting the lens, the incision site can be virtually adjusted on screen to observe its effect on the residual astigmatism. It also allows in precisely determining the location of the placement axis in relation to actual landmarks or surgical ink marks

� Postoperative toric enhancement to analyze the toric lens orientation and the deviation of the toric IOL from the target axis (Fig. 9)

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Fig. 8: iTrace’s integrated toric calculator, surgically-induced astigmatism analysis and the Zaldivar Toric Caliper helps improve the precision of toric power selection and placement

Fig. 9: Postoperative toric enhancement to analyze the toric lens orientation and the deviation of the toric IOL from the target axis

� The aberrations induced by a cataractous lens can be analysed (Fig. 7) � It helps in differentiating corneal pathologies from lenticular pathologies

(Figs 10 and 11). In a patient with high total aberrations planned for a refractive procedure, an analysis of the corneal aberrations and the internal optics can help in deciding between a corneal or lens-based refractive procedure. It helps improve treatment outcomes by determining the origin of aberrations (cornea vs. lens) and selecting the proper procedure (LASIK/Refractive lensectomy/Wavefront-guided contacts)

� Achieve better auto-refraction by eliminating instrument accommodation through natural, open-field evaluation of the total visual function

� Analyze refractions on a multizone basis and analyze complaints about night and day vision fluctuations and postoperative dissatisfaction

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Fig. 10: WF/CT summary display of a patient with keratoconus. As seen in the image, RMS value of entire eye is mainly contributed by the corneal aberrations and axial map shows typical skewed bow-tie appearance with mean keratometry of more than 49D at 1 mm diameter. CT summary shows keratometry of 52.61 D/44.47 D (122°/33°) with astigmatism of 8.14D (122°) and I-S asymmetry of 9.90 D

Fig. 11: WV/CT summary display of a patient with lenticonus. In contrast to the case in Figure 10, it is seen that most of the aberrations are contributed by the internal eye and very little by cornea. This indicates pathology in the internal optics. The patient was planned for phacoemulsification with intraocular lens implantation

� Become a better patient educator by illustrating your patient’s vision to your patient with the iTrace’s true point spread function analysis and the simulated Snellen Letter acuity display.

advantages over other aberrometersRay tracing aberrometry has the advantage of avoiding overlapping of points due to sequential capturing. Overlapping of points can hinder wavefront reconstruction.11

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The pattern of laser beams projected through the entrance pupil adapts to the pupil’s size. Compared to Hartmann-Shack aberrometers, ray tracing system enables more beams to pass through small pupil and give reliable measurement of aberrations.12 Since each point is measured separately using linear detectors, the accuracy of measuring the center of each point increases in comparison to other aberrometric systems.

The main advantage of Ray Tracing over other aberrometric principles is that the x-y scanner can be programmed to analyze any other rectilinear or polar pattern. iTrace can measure both objective accommodative response and near wavefront aberrometry at same time.3 iTrace has advantage of being able to measure both subjective and objective accommodation. Due to simple robust mechanism of sequential collection of data, it is particularly helpful in assessment of highly aberrated eyes, with ability to give refractive information over a range of 15D.3 Binocular wavefront aberrometry can be used to measure the accommodation and fluctuation in spherical aberrations objectively in cases of accommodative spasm.13

limitations/disadvantagesThe RSD captured in real time is not taken directly for calculation of aberrations but is taken in accordance to the pupil size selected, thus the aberration measurements may not be a true representation of the aberrations present in eye. iTrace aberrometer requires an experienced examiner for data acquisition.14 Fluctuation of accommodative effort causes a change in the defocus measurements and thus can affect repeatability of the measurements. Changes are seen more in spherical aberrations than in other HOA. Pupil size also dynamically affects HOAs.15-17 The measurements given by the aberrometers are static measurements at a particular pupil size at a particular accommodation effort whereas ocular optics has a dynamic component to it. Thus, correction done in according to these measurements by customized refractive surgery may not be suitable in all viewing conditions.18

referenceS 1. Rozema JJ, Dirk EM, Van Dyck PhD, Tassignon MJ. Clinical comparison of 6

aberrometers. Part I: Technical specifications. J Cataract Refract Surg. 2005;31:1114-27.2. Buhren J, Kohnen T. Application of wavefront analysis in clinical and scientific

settings. From irregular astigmatism to aberrations of a higher order—Part II: examples. Der Ophthalmologe: Zeitschrift der Deutschen Ophthalmologischen Gesellschaft. 2007;104(11):991-1006; quiz 7-8.

3. Pinero DP, Sanchez-Perez PJ, Alio JL. Repeatability of measurements obtained with a ray tracing aberrometer. Optometry and vision science : official publication of the American Academy of Optometry. 2011;88(9):1099-105.

4. Hiraoka T, Miyata K, Nakamura Y, Miyai T, Ogata M, Okamoto F, et al. Influences of cycloplegia with topical atropine on ocular higher-order aberrations. Ophthalmology. 2013;120(1):8-13.

5. Atchison DA, Mathur A. Effects of pupil center shift on ocular aberrations. Investigative ophthalmology & visual science. 2014;55(9):5862-70.

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6. Ghosh A, Collins MJ, Read SA, Davis BA, Iskander DR. The influence of downward gaze and accommodation on ocular aberrations over time. Journal of vision. 2011;11(10):17.

7. Gómez AC, Verdejo A, Bautista CP, Ferrándiz AE, González DC, Burgos SC. Principles and Clinical Applications of Ray-Tracing aberrometry (Part I). J Emmetropia. 2012;3:96-110.

8. Win-Hall DM, Glasser A. Objective accommodation measurements in prepresbyopic eyes using an autorefractor and an aberrometer. Journal of cataract and refractive surgery. 2008;34(5):774-84.

9. Win-Hall DM, Glasser A. Objective accommodation measurements in pseudophakic subjects using an autorefractor and an aberrometer. J Cataract Refract Surg. 2009;35:282-90.

10. Planis S, Ginis HS, Pallikaris A. The effect of ocular aberrations on steady-state errors of accommodative response. J Vis. 2005;5:466-77.

11. Molebny VV, Panagopoulou SI, Molebny SV, Wakil YS, Pallikaris IG. Principles of ray tracing aberrometry. Journal of refractive surgery. 2000;16(5):S572-5.

12. Moreno-Barriuso E, Navarro R. Laser Ray Tracing versus Hartmann-Shack sensor for measuring optical aberrations in the human eye. Journal of the Optical Society of America A, Optics, image science, and vision. 2000;17(6):974-85.

13. Kanda H, Kobayashi M, Mihashi T, Morimoto T, Nishida K, Fujikado T. Serial measurements of accommodation by open-field Hartmann-Shack wavefront aberrometer in eyes with accommodative spasm. Japanese journal of ophthalmology. 2012;56(6):617-23.

14. Won JB, Kim SW, Kim EK, Ha BJ, Kim TI. Comparison of internal and total optical aberrations for 2 aberrometers: iTrace and OPD scan. Korean journal of ophthalmology : KJO. 2008;22(4):210-3.

15. Li YJ, Choi JA, Kim H, Yu SY, Joo CK. Changes in ocular wavefront aberrations and retinal image quality with objective accommodation. Journal of cataract and refractive surgery. 2011;37(5):835-41.

16. Lopez-Gil N, Fernandez-Sanchez V, Legras R, Montes-Mico R, Lara F, Nguyen-Khoa JL. Accommodation-related changes in monochromatic aberrations of the human eye as a function of age. Investigative ophthalmology & visual science. 2008;49(4):1736-43.

17. Gabriel C, Klaproth OK, Titke C, Baumeister M, Buhren J, Kohnen T. Repeatability of topographic and aberrometric measurements at different accommodative states using a combined topographer and open-view aberrometer. Journal of cataract and refractive surgery. 2015;41(4):806-11.

18. Artal P, Fernandez EJ, Manzanera S. Are optical aberrations during accommodation a significant problem for refractive surgery? Journal of refractive surgery. 2002;18(5):S563-6.

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