Understanding Strabismus Sameera Irfan
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1UNDERSTANDING STRABISMUS2
3UNDERSTANDING STRABISMUS
Sameera Irfan FRCS (Edin) Consultant Oculoplastic Surgeon and Strabismologist Mughal Eye Trust Hospital Lahore, Pakistan Foreword Amjad Akram
4
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Understanding Strabismus
First Edition: 2014
9789350909904
Printed at
5To
My Papa Ji,
Prof. Daljit Singh6
7FOREWORD
Plenty of comprehensive books are available on strabismus in the market which are read by ophthalmology residents and junior ophthalmologists. But when a patient with strabismus walks into the ophthalmic outpatients department, the resident has a blackout as to where to start and how to proceed.
The good thing about Dr Sameera's book is that it describes the management of such patients in a way that is concise, to the point and easy to understand; rather than being comprehensive, it provides a stepwise approach to the target audience, i.e. the ophthalmologist in training.
Amjad Akram fcps frcs (edin) frcs (glasgow)
Consultant Ophthalmologist
Armed Forces Institute of Ophthalmology
Pakistan8
9PREFACE
The subject of strabismus is like a vast ocean; standing by its shores, one cannot assess its full expanse but only by taking a deep plunge into it does one realize its true depth and dimension. I have been a practicing strabismologist for more than 20 years and have been giving lectures to postgraduate trainees and general ophthalmologists, during which I realized a lack of basic understanding of the pathogenesis of strabismus. This formed the foundation of this book. I wanted to develop an insight into this complex problem and to develop a stepwise approach in the treating ophthalmologist.
Eyes are the organs that receive and reflect the intelligence of thought and the warmth of sensibility. According to JC Lavater, Physiognomist (London, 1826), “The images of our secret agitations are particularly painted in the eyes. The eye at once receives and reflects the intelligence of thought, and the warmth of sensibility. It is the sense of the mind, the tongue of the understanding.” Hence, it is our duty and responsibility as strabismologists to ensure equal vision in both eyes, which are, therefore, locked into equal and simultaneous movement in all directions.
Strabismus (squint) is a sign; it is Nature's way of telling us that something is wrong with the eye itself, either structurally or functionally, or with the visual pathways and higher centers controlling the ocular motility. It has a multifactorial etiology. In order to plan the correct management, it is important to find the causative factors and an attempt should be made to rectify them first before embarking on strabismus surgery. A clear conceptual knowledge of refractive errors is mandatory to understand it completely. About 80–85% cases of strabismus are due to mismanaged refractive errors. A sound understanding of refractive errors is the backbone of strabismus management.
It is also very important to realize that except the truly Essential Infantile Esotropia, all other kinds of strabismus have defective vision in either one or both eyes as a contributory factor. Normally, equal visual acuity in both eyes causes a state of sensory fusion that locks the two eyes to move together. If this locking mechanism does not occur due to poor vision in one eye, that eye either turns inwards (esotropia) in an infant or a toddler or it turns outwards (exotropia) if visual loss occurs after the age when accommodation is less active.
Although a strabismus surgeon is mainly concerned with “How” to correct the misalignment, it is important to understand “Why” a particular procedure works. This is discussed in detail in Chapter 10, “Basic Surgical Principles”. There is always a choice of surgical options for correcting a particular ocular misalignment and the procedure that gives an easy solution without compromising any other ocular movement should be opted for.
There are certain Laws governing the ocular movement, which should be kept in mind while assessing a strabismus patient. Listing's Law describes how a fixed ocular movement takes place around an equatorial plane going through the center of rotation of the eye; hence, the strabismic surgeon should not disturb this plane by too much recession/resection of the recti. According to the Hering's Law, there is an equal and simultaneous innervation of the yoke muscles in both eyes 10for any direction of gaze (while assessing ocular motility, both yoke muscles should act to the same extent without any under-action/over-action of either member of the group). Sherrington's Law describes reciprocal innervation of the agonist and the antagonist, so when one muscle contracts, its direct antagonist relaxes. Hence, the strabismologist must understand these basic concepts to interpret complex ocular motility patterns, particularly in paralytic strabismus where secondary muscle changes commonly occur in longstanding cases.
Finally, always remember, “Vision before Surgery”; only equal vision in both eyes allows sensory fusion to Lock the ocular alignment in all directions of gaze. However, if the vision is poor in one eye, absence of sensory fusion will not allow the eyes to Lock even after an excellent squint surgery, and the eye with poor vision will drift outwards under the influence of active divergence in adults.
Sameera Irfan