Fundamentals of Clinical Ophthalmology - part 1 ppsx

1 Teaching and learning phacoemulsification 12 Incision planning and construction for phacoemulsification 11 4 Phacoemulsification equipment and applied phacodynamics 36 6 Biometry and l

Fundamentals of Clinical Ophthalmology:

Cataract Surgery

Fundamentals of Clinical Ophthalmology series

Edited by Anthony Moore

Plastic and Orbital Surgery

Edited by Richard Collin and Geoffrey Rose

Fundamentals of Clinical Ophthalmology:

Department of Clinical Ophthalmology, Institute of Ophthalmology/Moorfields Eye Hospital,

London, UK

© BMJ Publishing Group 2003 BMJ Books is an imprint of the BMJ Publishing Group All rights reserved No part of this publication may be reproduced, stored in a retrieval system, or transmitted,

in any form or by any means, electronic, mechanical, photocopying, recording and/or otherwise,

without the prior written permission of the publishers.

First published in 2003

by BMJ Books, BMA House, Tavistock Square,

London WC1H 9JR www.bmjbooks.com

British Library Cataloguing in Publication Data

A catalogue record for this book is available from the British Library

ISBN 0 7279 1201 1 Typeset by SIVA Math Setters, Chennai, India Printed and bound in Malaysia by Times Offset

1 Teaching and learning phacoemulsification 1

2 Incision planning and construction for phacoemulsification 11

4 Phacoemulsification equipment and applied phacodynamics 36

6 Biometry and lens implant power calculation 66

7 Foldable intraocular lenses and viscoelastics 84

8 Non-phacoemulsification cataract surgery 102

14 Cataract surgery: the next frontier 200

Chairman of the Department of Ophthalmology

Manhattan Eye, Ear and Throat Hospital

New York, USA

Marie Restori

Consultant Medical PhysicistMoorfields Eye HospitalLondon, UK

Paul Rosen

Consultant OphthalmologistThe Radcliffe InfirmaryOxford, UK

Helen Seward

Consultant OphthalmologistCroydon Eye Unit

Surrey, UK

Hamish Towler

Consultant OphthalmologistWhipps Cross HospitalLondon, UK

Preface to the

Fundamentals of Clinical Ophthalmology series

This book is part of a series of ophthalmic monographs, written for ophthalmologists in training andgeneral ophthalmologists wishing to update their knowledge in specialised areas The emphasis ofeach is to combine clinical experience with the current knowledge of the underlying disease processes.Each monograph provides an up to date, very clinical and practical approach to the subject so thatthe reader can readily use the information in everyday clinical practice There are excellentillustrations throughout each text in order to make it easier to relate the subject matter to the patient.The inspiration for the series came from the growth in communication and training opportunitiesfor ophthalmologists all over the world and a desire to provide clinical books that we can all use Thisaim is well reflected in the international panels of contributors who have so generously contributedtheir time and expertise

Susan Lightman

Preface

Cataract surgery is a dynamic and complex field and is, without doubt, a fundamental part ofophthalmology This book aims to cover the subject comprehensively, particularly the technicalaspects of learning, performing, and teaching phacoemulsification The inclusion of chapters on theThird World and the future of cataract surgery provide the reader with a broader perspective.The structure of the text, cross-referencing between chapters, and a detailed index minimiserepetition For example, intraoperative complications are discussed within the relevant individualchapters on technique (although vitreous loss and the dropped nucleus have a chapter devoted tothem), whereas postoperative complications are grouped together For those who would like moredetail, the text has been thoroughly referenced

Inevitably, some knowledge has been assumed and some detail omitted, but we hope that this bookwill be useful to both trainees and established cataract surgeons

Andrew Coombes and David Gartry

Acknowledgements

We must first acknowledge the contributing authors, without whom this book would not exist.Professor Susan Lightman and all at BMJ Books, particularly Mary Banks, must also be thanked fortheir part (and patience)

Many individuals have contributed photographs and their help has been very much appreciated Theseinclude David Anderson (Figures 2.14, 3.3, 3.5, 5.3, 5.6, 5.14, and 7.20), Bill Aylward (Figure 10.21),Caroline Carr (Figure 9.2a–f), Emma Hollick (Figures 7.4, and 12.21), Alex Ionides (Figure 10.29), JamesKirwan (Figure 8.13b, 10.23, 10.24, 10.26, 12.13, and 12.22b), Frank Larkin (Figure 12.14),Graham Lee (Figure 7.3a,b), Ordan Lehmann (Figures 8.14, 12.12, 12.15, 12.18, 12.22a, 12.24,and 12.26), Martin Leyland (Figure 10.16), and Chris Liu and Babis Eleftheriadis (Figure 7.13) Thestaff in the day surgery unit at Chelsea and Westminster Hospital should also be thanked for their helpwith many of the photographs

A large number of companies have allowed their equipment, instruments, and lenses to bephotographed, and we are grateful for their involvement This book was originally developed from theMoorfields Eye Hospital phacoemulsification courses, and Alcon (and their wet laboratory facilities)deserve particular mention for their support of these courses over many years

We should like to take this opportunity to thank those cataract surgeons who have taught us in thepast and those who continue to inspire us Finally, we thank our families (especially Sarah) for thesupport and tolerance that has been essential in completing this book

The change in cataract surgery to

phacoemulsification over the past 10 years has

been well documented by Leaming,1 who has

conducted an annual survey of the practice styles

and preferences of US cataract surgeons In the

UK a similar shift toward phacoemulsification

has occurred2and is likely to continue For the

surgeon in training, phacoemulsification is no

longer an option but an essential surgical skill

to acquire For the trained surgeon the ability

to teach phacoemulsification in a structured

manner has also become necessary

Structured training and

phacoemulsification courses

Phacoemulsification acquired an undeservedly

poor reputation in the past Surgeons did not

spend sufficient time on structured training

programmes and there was a lack of suitably

qualified surgeons to supervise Complications

during the learning curve have been reported,3

but with better training and a wider availability of

simulated surgery these can be reduced

Structured training for phacoemulsification

requires time that may not be readily available in

a busy eye department, but provision must be

made for both trainer and trainee if safe surgery

is to be provided for our patients Teaching and

learning phacoemulsification should be an

enjoyable, if challenging, experience and should

not increase morbidity

The success of the structured training plan

described below depends on the trainee having

already mastered microscope skills, includingthe ability to use the microscope foot controlwith the non-dominant foot It also assumesknowledge of instrument handling and theability to carry out delicate procedures using amicroscope For the teacher it is easy to forgetwhat learning phacoemulsification was like.Teaching is a skill like any other; it requirespatience and insight into the learning process.Courses designed to teach the trainer to teachare becoming more widespread, and these canhelp to improve the effectiveness of teaching andminimise the stress it can involve

Teaching and learning phacoemulsificationcan be divided into three sections:

● Phacoemulsification theory (see Chapter 4)

● Simulated surgery practice (wet lab)

● Surgical learning programme (in vivo)

Where possible the trainer should be involved

at each stage For the trainee, each section should

be mastered before progressing to the next A wellorganised course that combines theory with anintroduction to phacoemulsification surgery using

a wet lab is an interesting and effective entrypoint An introductory course should consist ofseveral key lectures, including the following:

● The physics of phacoemulsification

● Phacoemulsification incisions (corneal andscleral)

● Capsulorhexis

1

1 Teaching and learning

phacoemulsification

● Principles of nuclear sculpting

All trainees should leave a phacoemulsification

course with a training plan based on their existing

surgical skills

Simulated surgery practice

Equipment

A well equipped surgical wet laboratory (wet

lab) (Figure 1.1) is an ideal environment in which

to practice phacoemulsification, and this should

be supervised by an experienced surgeon A wet

lab station should consist of the follwing items:

● Microscope

● Phacoemulsification machine with phaco, and

irrigation and aspiration hand pieces

● A mannequin’s head, for example the

Maloney head or a polystyrene head

● Plastic eyes with disposable cataracts and

corneas (Figure 1.2), or fresh animal eyes

● Irrigating solutions

● Disposable knives

● Cystotome and forceps for capsulorhexis

● Spatula to use in the non-dominant hand

● Rigid, folding, or injectable intraocular lenses

and instruments

Neither postmortem animal eyes nor plastic

model eyes are able to simulate all the attributes

of the human cataractous eye Each represents

a compromise, and their advantages and

disadvantages are summarised in Table 1.1

Although postmortem human eyes can be used,

ethical and legal restrictions exist

Animal eyes (most commonly from the pig)are ideal for practicing incisions and suturing, butbecause the anterior capsule is thick and elasticthey do not always simulate capsulorhexis well.Also, the lens is soft and not ideal for practicingnuclear fracture techniques Attempts have beenmade to harden the pig lens by injecting the eyewith a mixture of formalin and alcohol,4 using amicrowave oven,5 or replacing the lens withvegetable matter.6 Animal eyes have thedisadvantage that they are not always availableand need to be refrigerated for storage They are2

Figure 1.1 A typical wet lab Note the use of the Maloney head (latrotech) to hold the artificial eyes.

Figure 1.2 Artificial eyes (bottom) with disposable cataract (top left) and cornea (top right; Karlheinz Hannig Microsurgical Training Systems Company).

non-sterile and may potentially be infected with,

for example, prions In the absence of a dedicated

wet lab, the operating theatre, with its microscope

and phaco machine, is often used to provide a wet

lab facility out of hours Unlike plastic model

eyes, animal tissue should not be used in this

environment Plastic model eyes consistently

simulate the human cataract during sculpting,7

and some systems have the facility to vary the

density of the “nucleus” In contrast, rotating and

cracking the lens are less like they are in surgery

in vivo The artifical cataract is contained within

a capsule (that may be supplied as coloured) that

allows capsulorhexis and intraocular lens

implantation to be practised Unfortunately, the

thin plastic cornea of the model eye does not

behave like the human eye when attempting

incisions and is prone to trapping air bubbles

Wet lab training

The set up sequence for the machine and

equipment should be understood before

commencing simulated surgery practice in the

wet lab The following is a suggested programme

for wet lab learning and teaching

Foot pedal control

Trainees should spend time familiarising

themselves with foot pedal function and control

(also see Chapter 4)

● Foot position 1 engages irrigation only

● Foot position 2 engages irrigation togetherwith aspiration (the sound of aspiration can

be heard from the machine)

● Foot position 3 engages phacoemulsification

as well as irrigation and aspiration (the handpiece emits a high pitched sound)

Additional audible cues may be generated bysome machines, which act as a guide to thesurgeon’s foot position The trainee should beable to move comfortably from one foot position

to the next without watching the screen andshould know which foot pedal position has beenengaged It is important to explain andunderstand the need to remain consistently infoot position 1 while the phaco tip is in the eye.This maintains the anterior chamber depththroughout the procedure When the three footpositions have been mastered, the use of refluxshould be taught (usually a kick to the left oncethe foot is taken off the pedal) The use of thevitrectomy foot position should also beexplained, as should the use of the bipolar pedal.Before moving to the next step, it is essentialthat the trainer observe the trainee using the footpedal The trainee needs to be able to simulatesculpting by engaging foot position 3 for a fewseconds and then move comfortably back to footposition 1 or 2 The use of complex pedal

3

Table 1.1 Comparison of plastic model and animal eyes

Plastic model eyes Relative sterility (can be used in the Plastic cornea poorly simulates incision

operating theatre) Consistent nucleus density (stimulates Air bubbles are trapped within the sculpting well) anterior chamber during phacoemulsification Capsular bag for practising capsulorhexis/ Lens cannot easily be rotated

intraocular lens implantation Readily available Nucleus difficult to crack Animal eyes Excellent for incision and suturing practice Non-sterile (cannot be used in operating

theatre)

“Normal” lens capsule for capsulorhexis, Soft nucleus, which is mainly aspirated hydrodissection and nucleus rotation Variable availabilty and require refrigrated

storage

movements, such as those required for dual

linear control, is best reserved for the more

accomplished surgeon

Holding the phacoemulsification

hand piece

The hand piece should be held like a pencil,

and it is important to bring the index finger quite

close to the tip (Figure 1.3) This gives good

control of the phacoemulsification hand piece in

the eye (in the USA many surgeons hold a

phaco hand piece like a screwdriver) It is

important that the tubing and lead rest over the

arm to prevent kinking of the irrigation and

aspiration lines The trainer should emphasise

the importance of relaxing the hand and

maintaining the horizontal position of the wrist

at this stage

Balancing infusion and aspiration

Before inserting the phacoemulsification tip

into the eye, the trainee should check that the

hand piece is working and that the level of the

infusion is matched to the rate of aspiration This

is achieved by putting the plastic test chamber

(the “condom”) over the phacoemulsification

needle and filling it with irrigation fluid using

foot position 1 The hand piece is then held

horizontally and foot position 2 is engaged whilethe hand piece is raised The chamber shouldcollapse at approximately the level of themicroscope eyepiece (Figure 1.4) If it collapses

at the level of the patient’s eye, then theaspiration rate is too high for that level ofinfusion or the infusion bottle is too low.Conversely, if the chamber does not collapseuntil well above the level of the microscopeeyepiece, then either the infusion bottle is toohigh or the aspiration level is too low and thisshould be rectified The sound of thephacoemulsification hand piece should be heardand should be vigorous when the foot pedal isfully depressed If, for example, the needle isloose, then the sound will not be normal Thisprocess is a quality control procedure that

Figure 1.3 Holding the phacoemulsification hand

piece.

before inserting the phacoemulsification tip into the eye (the plastic test chamber should collapse at approximately the level of the microscope eyepieces).