Ординатура / Офтальмология / Английские материалы / Pickwell's Binocular Vision Anomalies 5th edition_Evans_2007

This fifth edition is intended as an update of the previous editions on the

practical and clinical aspects of binocular vision for students and

practitioners. The ‘how to do it’ approach has been retained and in some

cases extended by new tables, flow charts and case studies. The theory of

binocular vision has been kept to the minimum necessary to understand

the investigative and therapeutic procedures.

The first and second editions drew largely on Professor David Pickwell’s

enormous clinical and research experience. This new edition, which is the

third completed by me since Professor Pickwell’s retirement, continues to

contain a great deal of the late Professor Pickwell’s sound advice. Most of the

alterations have been revisions and updates in view of recent research, and

this new edition contains 864 references compared with 565 in the fourth

edition. The fact that contemporary research has not necessitated any major

changes in emphasis is a tribute to Professor Pickwell’s original work. There

has been a gradual evolution of binocular vision tests and treatments from

using artificial instruments that create unnatural viewing conditions

towards more natural methods that are less disruptive to normal binocular

vision. This evolution is desirable, and some of the older techniques that do

not add useful additional clinical information and are not in common use

have been omitted from this edition.

A great many theories and therapies have been suggested concerning

binocular vision anomalies and it can be difficult to sort the wheat from the

chaff. The healthcare disciplines are increasingly tending to cope with this

issue by adopting an evidence-based approach. In this approach, high-quality

scientific research is used to investigate old and new techniques alike.

Investigative approaches and treatments that have been validated in this

way are taken most seriously, and ones that have less rigorous support are

openly acknowledged as unproven. An attempt has been made in Pickwell’s

Binocular Vision Anomalies to rank different methods, especially treatments,

according to an evidence-based approach. Greatest weight is given to

approaches that have been validated with double-masked, randomized,

placebo-controlled trials.

The book is divided into four parts: the general investigation of bino-

cular anomalies, heterophoria, strabismus and incomitant deviations. In the

parts on heterophoria and strabismus the main features of these conditions

are summarized in a general introductory chapter and are then discussed

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in more detail in subsequent chapters.

This book is intended to provide a clinical text on the investigation and

management of binocular vision anomalies by methods other than

medicine and surgery. It is hoped that it will be useful to the student facing

the subject for the first time, and also to the established practitioner seeking

a reference to the binocular anomalies likely to be seen in everyday practice.

The aim has been to produce a ‘how to do it’ book. It is not a textbook on

the theory of binocular vision. There are a number of excellent books which

cover the anatomy, physiology and mechanisms of binocular vision. The

theory has therefore been kept to the minimum necessary for an adequate

appreciation of the anomalies, their investigation and treatment. I have

assumed that the reader has a basic knowledge of normal binocular vision

or is acquiring this simultaneously with clinical studies. I also assume a

knowledge of the general procedures of eye examination and refractive

methods.

The history and past literature of orthoptics seem to be full of descrip-

tions of unsubstantiated methods which have come and gone as it was

found that they did not work. At times it has appeared to have been a

maze of suggested procedures which have varied from ‘cure alls’ to useful

clinical ideas. I cannot claim to have explored all of them. What I have

tried to do is describe the methods which I have found effective, and

where possible provided the references for practical evaluations. I have

tried to write from my own particular experience which has extended over

30 years. In doing so, I am very aware of others whose experience has been

parallel, but not necessarily the same. As far as possible, I have also tried

to reflect some of their views, and acknowledge their contributions to the

ongoing development of clinical practice.

To help the student, I have tried to provide a recognizable pattern in

dealing with the conditions described, and I hope thereby to have pro-

duced a mnemonic approach to the subject which will aid learning and

application in a clinical setting. Each condition is dealt with in the general

order of definition, investigation, evaluation and management. Under the

heading of management, I have considered five non-medical possibilities:

removing any general cause, correcting refractive error, orthoptics,

relieving prisms and referral. These patterns will be obvious in the early

chapters, and are assumed in the later ones.

I wish particularly to acknowledge the work and encouragement given

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to me by my colleagues in the binocular vision clinics at the University of

NATURE OF BINOCULAR VISION ANOMALIES

1

The anatomical, motor and sensory systems must be adequate for normal

binocular vision to be present. The position of the eyes relative to each

other is determined first by their anatomical position. Humans have

forward-looking eyes placed in the front of the skull, and this brings the

visual axes of the two eyes almost parallel to each other. In most cases,

they are slightly divergent when the position is determined only by

anatomical factors, and this is known as the position of anatomical rest.

In normal circumstances, this state seldom exists, as physiological factors

are nearly always operative also. When a person is conscious, muscle

tone and postural reflexes usually make the visual axes less divergent: the

position of physiological rest. Another physiological factor affecting the posi-

tion of the eyes is the accommodation–convergence relationship: the eyes

will converge as accommodation is exerted, and this is known as accom-

modative convergence. The final adjustment of the eyes is made to achieve

single binocular vision. This is known as fusional (disparity) vergence and

positions the retinal images on corresponding points (or within corre-

sponding Panum’s areas). For distance vision, this will produce parallel

visual axes.

If fusional vergence is suspended, for example by covering one eye, the

eyes will adopt a dissociated position. This is slightly deviated from the active

3

position that is maintained when all of the factors are free to operate. This

Ocular deviations can be classified as comitant or incomitant. Comitant

deviations are the same in all directions of gaze for a particular distance of

fixation. Incomitant deviations vary with the direction of gaze; that is, as

the patient moves the eyes to fixate objects in different parts of the field of

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fixation, the degree or the angle of the deviation will vary (Ch. 17). There

may be no deviation in one part of the motor field but a marked deviation