Dr. Agarwal's Textbook on Corneal Topography (Including Pentacam and Anterior Segment OCT), 2 E

397 Pages·2010·223.06 MB·English

by  Agarwal

2nd Edition
Dr Agarwal's Textbook on
CORNEAL
TOPOGRAPHY
Including Pentacam and Anterior Segment OCT
SECOND EDITION
Editors
Amar Agarwal
Athiya Agarwal
Soosan Jacob
Dr Agarwal's Group of Eye Hospitals
and Eye Research Centre
India
Foreword
Parag A Majmudar
® 4-
J
AY PEE - HIGHLIGHTS
• MEDICAL PUBLISHERS, INC.
Published by
Jitendar P Vij
Jaypee Brothers Medical Publishers (P) Ltd
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Dr Agarwal's Textbook on Corneal Topography Including Pentacam and Anterior Segment OCT
© 2010, Jaypee Brothers Medical Publishers (P) Ltd.
All rights reserved. No part of this publication should be reproduced, stored in a retrieval system, or transmitted in any form
or by any means: electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the
editors and the publisher.
This book has been published in good faith that the material provided by contributors is original. Every effort is made
to ensure accuracy of material, but the publisher, printer and editors will not be held responsible for any inadvertent
error(s). In case of any dispute, all legal matters are to be settled under Delhi jurisdiction only.
First Edition: 2006
Second Edition: 2010
ISBN 978-81-8448-861-6
Typeset at JPBMP typesetting unit
Printed at Ajanta Offset & Packagings Ltd., New Delhi
PREFACE TO THE SECOND EDITION
When we wrote the first edition of the corneal topography book, we did not believe it would become a best
seller so fast. So when Shri Jitendar P Vij, President of Mis Jaypee Highlights Medical Publishers, Inc.
contacted us asking for us to work on the second edition of the book we were pleasantly surprised.
To write a book on corneal topography is extremely difficult. The reason is to explain every topic whether
it is post-LASIK ectasia or decentered ablation is a challenge by itself. In this book we have covered various
machines like the orbscan and the pentacam. We have also covered related topics like the anterior segment
OCT and the aberrometers as they are complementary to the topography machine.
We would like to thank all the contributors who are big names but more important have become now part
of our family. We would also like to thank Shri Jitendar P Vij and the whole team of Mis Jaypee Highlights
Medical Publishers, Inc. for bringing out this book.
Amar Agarwal
Athiya Agarwal
Soosan Jacob
•
CONTENTS
SECTION ONE: INTRODUCTION TO CORNEAL TOPOGRAPHY AND ORBSCAN
1. Fundamentals on Corneal Topography ........................................................................................................... 3
Guillermo L Simon-Castellvi, Sarabel Simon-Castellvi, Jose Maria Simon-Castellvi, Cristina "Simon-Castellvi (Spain)
2. Topographic Machines .................................................... :. ................................................................................ 29
Guillermo L Simon-Castellvi, Sarabel Simon-CastelIvi, Jose Maria Simon-Castellvi, Cristina Simon-Castellvi (Spain)
3. Corneal Topography and the Orbscan .......................................................................................................... 47
Amar Agarwal, Athiya Agarwal (India)
4. The Orbscan lIz Diagnostic System and Zywave Wavefront Analysis ................................................. 55
Gregg Feinerman, N Timothy Peters, Kim Nguyen, Marcus Solorzano, Shiela Scott (USA)
SECTION TWO : ORBSCAN AND REFRACTIVE SURGERY
5. Orbscan Corneal Mapping in Refractive Surgery ....................................................................................... 75
Francisco Sanchez Leon (Mexico)
6. Anterior Keratoconus ......................................................................................................................................... 87
Amar Agarwal, Athiya Agarwal (India)
7. Posterior Corneal Changes in Refractive Surgery ....................................................................................... 93
Amar Agarwal, Soosan Jacob, Athiya Agarwal (India)
8. Corneal Ectasia Post-LASIK: The Orbscan Advantage ........................................................................... 103
Erik L. Mertens, Arun C Gulani, Paul Karpecki (USA)
SECTION THREE: PENTACAM AND ANTERIOR SEGMENT OCT
9. Pentacam ............................................................................................................ :. ................................................ 117
Tracy Schroeder Swartz (USA)
10. Evaluation of Patients for Refractive Surgery with Visante Anterior Segment OCT
and the Combined Datalink with Atlas Corneal Topographer ............................................................ 137
Amin Ashrajzadeh, Roger-Steinert (USA)
SECTION FOUR: ABERROPIA, ABERRATIONS AND TOPOGRAPHY
11. Corneal Topographers and Wavefront Aberrometers: Complementary Tools ................................... 161
Tracy Schroeder Swartz, Ming Wang, Arun C Gulani (l!SA)
12. Aberrometry and Topography in the Vector Analysis of Refractive Laser Surgery ......................... 175
NoeLA Alpins, Gemma Walsh (Australia)
13. Aberropia: A New Refractive Entity ............................................................................................................ 185
Amar Agarwal, Athiya Agarwal (India)
14. Differences Between Various Aberrometer Systems ................................................................................ 195
Ronald R Kreuger (USA)
15. Corneal Wavefront-guided Excimer Laser Surgery for the
Correction of Ocular Aberrations .................................................................................................................. 201
Jorge L Alio, David P Pinero, Mohamad Rosman (Spain)
xvi Textbook on Corneal Topography Including Pentacam and Anterior Segment OCT
16. Ocular Higher Order Aberration Induced Decrease in Vision (Aberropia):
Characteristics and Classification ................................................................................................................. 219
Amar Agarwal, Soosan Jacob, Dhivya A Kumar, Rahul Tiwari, Athiya Agarwal (India)
17. Topographic and Aberrometer Guided Laser ........................................................................................... 231
Amar Agarwal, Athiya Agarwal (India)
18. NAV wave: Nidek Technique for Customized Ablation ....................................................................... 239
Masanao Fujieda, Mukesh Jain (Japan), Peter Kellar (Australia)
SECTION FIVE: REFRACTIVE PROCEDURES AND CONDITIONS
19. Post-LASIK Iatrogenic Ectasia ....................................................................................................................... 251
Melania Cigales, Jairo-Hoyos-Chacan, Jairo E Hoyos (Spain)
20. Decentered Ablations ...................................................................................................................................... 271
Helen Boerman, Ming Wang, Tracy Schroeder Swartz (USA)
21. Irregular Astigmatism: Lasik as a Correcting Tool ................................................................................... 287
Jorge L Alia, Jose I. Belda Sanchis, Ahmad MM Shalaby (Spain)
22. Presbyopic LASIK ............................................................................................................................................. 307
Amar Agarwal, Athiya Agarwal (India), Guillermo Avalos (Mexico)
23. Phototherapeutic Keratectomy (PTK) .......................................................................................................... 315
Jes Mortenson (Sweden)
24. Conductive Keratoplasty for Changing Corneal Curvature ................................................................... 321
Roberto Pinelli (Italy)
25. Intacs TM: Refractive Correction with an Intracorneal Device ................................................................ 333
Terry E Burris, Debby Holmes-Higgin (USA)
26. Posterior Chamber Implantable Collamer Lens: ICL and Toric ICL .................................................... 343
Mohamed Alaa EI-Danasoury (Saudi Arabia)
27. Nidek OPD Scan in Clinical Practice .......................................................................................................... 369
Gregg Feinerman, N Timothy Peters, Kim Nguyen, Marcus Solorzano, Shiela Scott (USA)
SECTION SIX: CATARACT
28. Corneal Topography in Cataract Surgery .................................................................................................... 379
Athiya Agarwal, Amar Agarwal (India)
29. Corneal Topography in Phakonit with a 5 mm Optic Rollable IOL. .................................................. 389
Amar Agarwal, Athiya Agarwal (India)
Index ...................................................................................................................................................................... 399
f f f
Section One
Introduction to
Corneal Topography
and Orbscan
Fundamentals on Corneal Topography
~
)- Topographic Machines
)- Corneal Topography and the Orbscan
)- The Orbscan liZ Diagnostic System and Zywave
Wavefront Analysis
One
FUNDAMENTALS ON CORNEAL
TOPOGRAPHY
Guillermo L Sim6n-Castellvi
Spain
Sarabel Sim6n-Castellvi
Spain
Jose Maria Sim6n-Castellvi
Spain
Cristina Sim6n-Castellvi
Spain
4 Introduction to Corneal Topography and Orbscan
INTRODUCTION: HUMAN OPTICS AND THE NORMAL CORNEA
The cornea is the highest diopter of human eye, accounting alone for about 43-44 diopters at corneal apex
(about two thirds of the total dioptric power of the eye). It has an average radius of curvature of 7.8 mm. A
healthy cornea is not absolutely transparent: It scatters almost 10% of the incident light, primarily due to the
scattering at the stroma.
The corneal geography can be divided into four geographical zones from apex to limbus, which can be
easily differentiated in color corneal videokeratoscopy:
1. The central zone (4 central millimeters): It overlies the pupil and is responsible for the high definition
vision. The central part is almost spherical and called apex.
2. The paracentral zone: Where the cornea begins to flatten
3. The peripheral zone
4. The limbal zone
Refractive surgery refers to a surgical or laser procedure performed on the cornea, to alter its refractive power.
The major refractive component of the cornea being its front surface, it is not difficult to understand that most
refractive techniques have involved this frontal surface (PRK, radial keratotomies, ... ). Nevertheless, posterior
surface of the cornea also accounts, and that is the reason why a "posterior surface corneal topographer" like the
Orbscan™ - Bausch and Lomb® was developed by Orbtek®, in the race for a more precise refractive surgery.
The cornea of an eagle is almost as transparent as glass: There is almost no scattering of incident light.
That alone explains the resolution of an eagle eye being much better than ours. As we are never satisfied, we
are now developing new tools and extremely promising laser surgical techniques that have proven to increase
human being visual acuity by reducing corneal aberrations: we reduce diopters and also improve visual acuity.
The new dream is "supervision". Topographic and aberrometer-linked LASIK are on the way to achieve
this goal of better-than-normal vision. Bausch and Lomb®'s Zywave™ combines topography and wavefront
measurements to achieve customized computer controlled flying spot excimer laser ablation, which appears
to be fundamental in treating irregular astigmatisms or retreating unsatisfied LASIK patients to regularize the
corneal shape. Regularizing the corneal shape has the theoretical advantage of improving the quality of vision
by means of reduction of halos, glare and any other optical aberrations. We are on the way to achieve an
aberration-free visual system, though the influence of all other dioptric surfaces (vitreous, lens, ... ) and interfaces
still has to be ascertained (Table 1.1).
In this chapter we will try to introduce the novice to this interesting new world of instruments recently
developed due to the advent of refractive corneal surgery. We have tried to show different maps from different
systems, trying to make an interesting basic atlas of corneal topography. Corneal maps of rare cases and
Table 1.1: Indications and uses of corneal topographers
The use of computerized corneal topography is indicated in the following conditions:
1. Preoperative and postoperative assessment of the refractive patient
2. Preoperative and postoperative assessment of penetrating keratoplasty
3. Irregular astigmatism
4. Corneal dystrophies, bullous keratopathy
5. Keratoconus (diagnostic and follow-up)
6. Follow-up of corneal ulceration or abscess (Figure 1.3)
7. Post-traumatic corneal scarring
8. Contact lens fitting
9. Evaluation of tear film quality
10. Reference instrument for IOL-implants to see the corneal difference before and after surgery
11. To study unexplained low visual acuity after any surgical procedure (trabeculectomy, extracapsular lens
extraction, ... ).
12. Preoperative and postoperative assessment of Intacs™ corneal rings (intrastromal corneal rings)
Fundamentals on Corneal Topography 5
complications can be found in the different chapters of this book. Please refer to them for better knowledge.
There is no perfect system to assess true corneal surface shape, but we still have to rely on the instruments we
have, waiting for new instruments and methods being developed for better accuracy. With that goal in mind
BioShape AG® has developed the EyeShape™ system, based on a principle called fringe projection. Patterns of
parallel lines are first imaged onto a reference and then onto the surface to be measured. D~tection of the lines
with a digital camera under a tilted angle yields distorted line patterns. The deviation of the detected lines
from the original lines together with the tilt make it possible to calculate the absolute height at any point on the
surface of the cornea (or not).
INSTRUMENTS TO MEASURE THE CORNEAL SURFACE
The normal corneal surface is smooth: A healthy tear film neutralizes corneal irregularities. The cornea, acting
as a convex "almost transparent" mirror, reflects part of the incident light. Different instruments have been
developed to assess and measure this corneal reflex. These non contact instruments use a light target (lamp,
mires, Placido disks, etc.) and a microscope or another optic system to measure corneal reflex of these light
targets (Tables 1.2 and 1.3).
Table 1.2: Advantages and disadvantages of projection-based systems over reflection-based ones
Advantages
Measurement of direct corneal height
Ability to measure:
irregular corneal surfaces
non-reflective surfaces
Higher resolution (theoretical)
Uniform accuracy across the whole cornea
Less operator dependent
Do not suffer from spherical bias
Disadvantages
Not standard instruments (most are still prototypes):
complex to use
need clinical experience validation
nonstandard presentation maps (more difficult to learn)
Longer examination time:
longer image acquisition time
longer image analysis
Fluorescein instillation needed (in some, like the Euclid Systems Corporation® ET-8(X)TM)
Table 1.3: Different methods of measuring corneal surface used by
modern corneal topographers
Placido systems (small cone or large disk) are the most popular
Placido cone with arc-step mapping (Keratron™ from Optikon 2000®)
Placido's disk with arc-step mapping (Zeiss Humphrey®A tlas™)
Slit-lamp topo-pachymetry (Orbscan™ -Bausch and Lomb®)
Fourier profilometry (Euclid Systems Corporation® ET -8(X)TM)
Fringe projection or Moire interference fringes (EyeShape® from BioShape AGTM)
Triangulation ellipsoid topometry (Technomed™ color ellipsoid topometer)
Laser interferometry (experimental method, it records the interference pattern generated on
the corneal surface by the interference of two lasers or coherent wave fronts)