Eyes and Education PDF
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Eyes and Education Vernon H. Smith, MA MB BChir FRCS FRCSE DO Consultant Surgeon, Birmingham and Midland Eye Hospital, Senior Clinical Tutor in Ophthalmology, Birmingham University, Visiting Ophthalmologist, National Childrens Home F. E. James, MB BS (Lond) MRCS LRCP DCH Principal School Medical Officer, City of Nottingham William Heinemann Medical Books Limited London First published 1968 © Vernon Smith and F. E. James, 1968 Printed in Great Britain by The Whitefriars Press Ltd London and Tonbridge FOREWORD 9 EYES AND EDUCATION was written primarily for teachers school nurses and students training to be teachers. Both Mr. Vernon Smith, an ophthalmic surgeon, and Dr. F. E. James, the principal school medical officer for Nottingham, and formerly a busy general medical practitioner who was also a school doctor working part-time for the Oxfordshire Education Authority, have long experience of, and concern for, children with visual defects and the effect these defects have on their education and development. Mr. Smith and Dr. James regard the teacher and school nurse as essential partners in their work. The main purpose of their small but very practical book is to give teachers, school nurses and students the basic facts about eye defects in childhood and so enlist their help both in the early de tection of these defects and in the treatment and manage ment of the children whilst at school. All books can be criticised and no doubt this one will be no exception; but, it would be an unusually captious critic who asserted that it failed in its purpose. It will be of much help to teachers and nurses in all types of school and de serves a wide readership. P. HENDERSON, CB MD DPH Senior Principal Medical Officer Department of Education and Science PREFACE The purpose of this small book is to describe some of the ways in which abnormalities of vision may cause difficulty in children learning to read and write, and how in some cases these visual defects can have a profound effect on their subsequent career. This is not a small problem. Apart from dental disease there are more children with defective vision than with any other complaint. At the present time, in England and Wales alone, 160,000 children a year are found to require treatment for defective vision. The vast majority have simple refractive errors, that is, their vision can be corrected by spectacles, but 25,000 have squints, a more serious problem, and in others the defect is graver still. Although many visual defects are obvious there are some that do not show up readily with the standard methods of testing, and yet which can be recognised by an astute and informed observer of the child in the more normal environment of the schoolroom, rather than the fairly alarming and slightly strange world of the medical examina tion room. Indeed, it might be claimed that the major hurdle is to send the child to his doctor and alert him to the possibility of an eye defect that has not been noticed on routine examination. In addition to this, the teacher should play a part in the treatment of visual defects. Just because a child has been given a pair of glasses, or diagnosed as suffering from some visual defect it does not absolve his teacher from all further responsibility, e.g. it may be necessary for the pupil, or patient, however you may regard him to sit in a parti cular seat in the classroom, and it is the teacher's duty to see that he does so constantly. Another example is the child who has difficulty in learning to read, or word blindness as it is called. Unhappily a very viii common finding in these cases is that the child dislikes school. This antagonism acts as a barrier to progress in a field in which the pupil is poorly equipped by nature in the first place. If the diagnosis can be made early, patience and understanding by the teacher may well result in such improvement in the condition that special treatment is unnecessary. We hope that this short account of the common visual defects found in children will promote a better under standing which can only result in improving the lot of the child. V. H. S. F. E. J. iz SCLERA (WHITE) UPPER in \ RETINA LENSS IRIS I (BY WHICH THE COLOUR>> OF THE EYE IS KNOWN)^ PUPIL(NORMALLY A—- ROUND BLACK HOLE) CORNEA • (TRANSPARENT) t CONJUNCTIVA Fig. 1. Chapter I THE STRUCTURE AND FUNCTION OF THE VISUAL ORGANS To understand how visual defects of different types may affect the vision, some knowledge of the structure and function of the eye and its connections with the brain is essential. The eye itself is roughly spherical in shape and its internal structure is, in many ways, similar to that of a camera. It is protected by its position in the orbit where it is surrounded by the bones of the nose, cheek, temple and forehead, and by the lids. The lids have two functions; by narrowing or closing your lids you can reduce or prevent the light entering your eye; and by blinking you ensure that the front of the eye is constantly kept clean and moist because the inner surface of the lids, which is called the conjunctiva, is lubricated by the tears. The front of the eye proper is called the cornea, and is completely transparent. It projects forward from the rest of the eyeball because it is more sharply curved than the rest of the eye. Rays of light can pass through the cornea until they meet the lens. The lens focuses the light rays that pass through it so that they form a clear picture on a structure that lines the back of the eye called the retina. Like a camera the eye has a mechanism that controls the amount of light passing through the lens. This is called the iris. The iris is a circular diaphragm that has a hole at its centre. This is the pupil. When the iris contracts the pupil becomes smaller and the amount of light passing into the back of the eye is reduced. The iris is situated immediately in front of the lens, which it conceals, and the pupil itself appears as a black circular hole. In contrast the iris is coloured: blue, grey, or brown are the commonest colours, 1 2 Eyes and Education and it is because of this that one says that a person has blue, grey or brown eyes. While the lens performs the same function as the lens in a camera, the human lens has one big advantage over that in a camera in that we can alter its shape. We can make it a fatter or stronger lens at will, by contracting certain muscles inside the eye. This means that the lens can do its own focusing without altering position. When you focus a camera you have to alter the distance between the lens and the photographic plate. The mechanism in the eye is much more elegant and efficient. We have followed the rays of light from the moment they touched the cornea to the point where they are brought into focus on the retina, which is the photographic plate of the eye. The picture of the object that we are looking at is then transformed into a nerve impulse which passes from the back of the eye to the brain by a nerve tract called the optic nerve. When it reaches the brain it is turned into a mental picture that is appreciated and acted upon—rather like closed circuit television. We must now go into slightly more detail. Because of the laws of optics, rays of light coming from an object on the right of the midline, after passing through the lens will fall on the left side of the retina, and this will apply to both eyes. The nerve pathways behind the eye are so arranged that all the nerve impulses from the left side of both retinae are transported to the left side of the brain. Thus, an object on the right of the midline results in nerve impulses passing to the left hand side of the brain. To return to our earlier simile, it is as though there were two closed circuit television cameras each photographing one half of everything we see, the impulses from which are fused together into a single picture by the brain. In addition to this, our eyes are capable of a further refinement. Con sider once more the example of an object situated to the right of the midline. The right eye will be a little nearer to this object than the left, and the angle at which the rays of light enter the two eyes will also be slightly different. This The Structure and Function of the Visual Organs 3 (R) Fig. 2. Objects on the (R) are "seen" with the (L) side of the brain will result in two slightly different pictures being produced on the retinae of the two eyes. These two pictures are both relayed back to the brain which fuses them together and so receives a binocular or stereoscopic image of the object concerned. By this means we are able to appreciate how far away from us the object is and thus to judge the distance and the relationship of one object to another. So far we have assumed that it is a simple matter for the eye to identify whether an object is on the right or the left, and while this may be true for objects seen at the very fringe of the field of vision a little reflection will show that 4 Eyes and Education this may not be so with objects more centrally placed. The eye has to have a point of reference at its centre and this central region is called the macula. In addition to being the central point of the retina the macula is its most sensitive part. When we see an object with the macula we see it more clearly and in much greater detail than with the peripheral parts of the retina. Furthermore, colour vision is much better developed at the macula than in other parts of the retina. When you think about it this is obvious, you see an object in front of you with greater clarity and appreciate its colour much more readily than you do when you see it out of the corner of your eye. Finally, we must consider what happens after the message conveying a visual picture reaches the brain. We will assume once more that the impulse is caused by rays of light passing from an object on the right of the midline to the left side of the brain. At this stage the brain is presented with a mental photograph of the object. Close to the part of the brain that receives this mental picture are certain regions called association areas. They are concerned with visual memory and are concerned with such functions as reading, writing, and adding up. The simple mental picture is then analysed and appreciated, remembered if necessary, and action taken as required. Should action be required the areas of the brain that control the right arm and leg are nearby. If need be, the right arm or leg is moved to take defensive or offen sive action. Thus objects seen on one side of the midline are ap preciated on the opposite side of the brain which can relay back messages to the arm and leg on the side of the body near the object in question. In addition to this, the eyes turn towards the object to see it more clearly. The move ments of each eye are controlled by six muscles, again controlled by nerve impulses from the brain. This account of the primitive eye and limb reflexes must not of course be interpreted as being a description of what happens every time a fresh object comes into view. All these
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