Editors Melania Cigales MD
Instituto Oftalmológico Hoyos
Sabadell—Barcelona—Spain
Jairo E Hoyos MD PhD
Instituto Oftalmológico Hoyos
Sabadell—Barcelona—Spain
Jitendar P Vij
Jaypee Brothers Medical Publishers (P) Ltd
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Dr. Hoyos' Step by Step Astigmatic Ablation
© 2006, Melania Cigales and Jairo E Hoyos
All rights reserved. No part of this publication and Photo CD ROM 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.
First Edition: 2006
9788180615894
Typeset at JPBMP typesetting unit
Printed at Paras Offset Press
This book is dedicated to the Father of Refractive
Surgery, who devoted his life to investigating how we should modify the cornea to correct refractive errors.
The knowledge transmitted by
Professor Jose I Barraquer forms the foundations of today's corneal refractive surgery.
67CONTRIBUTORS
- Carmen Barraquer C md
- Instituto Barraquer de America
- Bogota—Colombia
- Claudia Blanco md
- Universidad del Valle
- Clinica de Oftalmológia de Cali
- Cali—Colombia
- Fabrizio I Camesasca md
- Instituto Clinico Humanitas
- Rozzano—Milano—Italy
- Melania Cigales md
- Instituto Oftalmológico Hoyos
- Sabadell—Barcelona—Spain
- Alejandro De la Torre md
- Universidad del Valle
- Clinica de Oftalmológia de Cali
- Cali—Colombia
- Jairo E Hoyos md phd
- Instituto Oftalmológico Hoyos
- Sabadell—Barcelona—Spain
- Jairo Hoyos—Chacón md
- Instituto Oftalmológico Hoyos
- Sabadell—Barcelona—Spain
- M Teresa Iradier md
- Iradier Eye Clinic
- San Carlos University Hospital
- Madrid—Spain
- M Ximena Nuñez md
- Universidad del Valle
- Clinica de Oftalmológia de Cali
- Cali—Colombia
- José Miguel Varas—Prieto md
- Centro Oftalmico Varas Samaniego
- Guayaquil—Ecuador
- José Miguel Varas—Torres md
- Centro Oftalmico Varas Samaniego
- Guayaquil—Ecuador
- Paolo Vinciguerra md
- Instituto Clinico Humanitas
- Rozzano—Milano—Italy
For many years now, the correction of astigmatism has been a challenge for the ophthalmologist, and ideas for combating this defect have been constantly emerging and put into practice. We all accept that before confronting the problem, we need to understand what astigmatism really is. This book was created to help arm ourselves with the definitions and descriptions we will need to tackle the management of astigmatism. It is for this task that we will need to understand the classification of astigmatism, the different ways of approaching its treatment and the importance of correcting not only the difference in curvature between the two main axes of the cornea but also its spherical zone, whether we are dealing with myopia or hyperopia. The effect the correction of astigmatism has on the spherical component of refraction, has proved to be a difficult point to define, calibrate and, even more so, to treat.
The many attempts initially made by means of incisions have taught us several lessons, yet the effect persisting 10over the years achieved by the incision procedure and the many factors influencing this effect—such as length, depth, small differences between the problem axis and the intervened axis, along with the patient's scarring response—makes it impossible to predict what will happen in the long-term to the operated eye. Today, the technological advances that have given way to the new methods of treating astigmatism provide a much safer and predictable way to achieve our goal. Thus, laser ablation allows us to work on the surface of the cornea and with greater precision because of the small amount of tissue removed, and provides the starting point on which to base new calculations and nomograms. However, we all understand that these treatments concentrate on the optical zone with slight variations in transition zones, yet hardly consider the corneal periphery. For many years, we have been pointing out the importance of the peripheral zone for the patient's refraction and therefore treatment. It is in this area that developments including the advent of aberrometry gain importance, since besides being of great help as a diagnostic tool, this device is also very useful for both surgical treatment and elaborating other forms of correction (glasses, contact lenses) based on wave-front analysis of the eye, rather than on only its inner and outer features.11
We thus hope to enjoy and learn from the knowledge recompiled in this book with the aim of benefiting by far the most important component of our clinical practice—the patient.
Luis A Ruiz md
Scientific Director at the
Centro Oftalmologico Colombiano
Ophthalmology trained at the
Instituto Barraquer de America
Specialist in Anterior Segment and Refractive Surgery
ASCRS—CD Kelman Innovator's Lecture (1997)
KMSG—Honorific Lecture JI Barraquer (2000)
Bogota—Colombia
1213PREFACE
To correctly understand astigmatism, we should start by imagining refraction, not at the surface of corrective glasses, but at the two main meridians of the cornea. If to treat an astigmatism defect we are to modify the curvature of the cornea, then we need to know the refractive error of each of the two meridians. We will then know if we need to flatten the meridian (when its error is myopic) or steepen it (when its error is hyperopic) or even when not to modify the meridian because it is emmetropic.
In preparing this text, we have tried to transmit to the reader the idea that astigmatism is really the dioptric difference between the two corneal meridians. Thus, astigmatism is not a given number of diopters, rather it is defined by two dioptric values. If we imagine the patient's refraction at the cornea separated into its two main meridians, this number of diopters of astigmatism of our refractive formula becomes two different dioptric values. These are the values we really need to treat with the laser.
This book analyzes laser ablations to treat myopic, hyperopic and mixed astigmatism. Methods are described for optimizing the treatment of astigmatism through the combined use of positive and negative cylinders. Customized ablation, directed towards not only correcting 14the refractive error but also towards achieving a good quality of vision, is not forgotten. The correction of astigmatism in cataract surgery in which the surgeon increasingly tries to achieve emmetropy is also reviewed.
Following the book's chapters, we have included two appendices explaining the basic refraction and refractive surgery concepts such as the cylinder transposition and spherical equivalent.
We hope that the concepts analyzed in this compilation prove useful to anyone wishing to gain insight into the subject of astigmatism and its treatment.
Melania Cigales
Jairo E Hoyos