usion is the sense of simultaneous single binocular vision. It occurs when the two eyes fix the same object at the same time, and the two ocular images occupy corresponding parts of the two retinae (p. 186).
The cause [of imbalance] may be anatomical . . . physiological or pathological, there being (1) deficiency of nerve force or paresis, (2) spasm of a muscle, (3) excessive or deficient innervation of some muscles, or excessive or deficient resistance of opposing muscles (p. 187).
The imbalance varies if tests be made on different occa- sions (p. 203).
More people suffer from this defect than is ordinarily recognised. It may be due to many causes, as we see from the above quotation. One marked feature is that the degree varies if tests are made on different occasions, and it is this peculiarity that gives discomfort in the wearing of corrective glasses, for sometimes the glasses `fit’ the defect, and at other times they do not. Perhaps for this reason we are told that “Low degrees of insufficiency generally require no treatment or correction; high ones require rather exercise or operation than prismatic aid” (p. 206).
With this defect, the `fusion’ of the images from each eye does not take place because the eyes are not held in a position with regard to the object looked at where the images occupy corresponding parts of the two retinae. People find it difficult to talk with one another, and they often look fast at one eye of the friend and then at the other, or look at the friend through their right eye and then through the left, so that the eyes are constantly moving. This is an endeavour to avoid the fusion of the images, but the result is a severe headache, and the dread of tea parties! Incidentally it is a very irritating habit to watch. This movement of the eyes should not’ be confused with nystagmus.
Imbalance is often the cause of migraine, and always the cause of discomfort, but if the degree of the defect varies from time to time, there must be a reason for this difference. Nothing ever just happens; what comes about is always an effect, for which there must be a cause. Once we take this attitude towards bodily defects we will remedy them by striking at the root cause. Glasses strike at the effects only.
The causes are quoted in the above extract, and therefore each case must be judged from one or other standpoint. It is no use exercising muscles if the defect is due to nerves or paresis, but muscular defects can be treated by exercise. Many of the exercises used are those advocated by orthodoxy, and are adaptations of the principle of focus. If a pencil is held on a level with the tip of the nose, pointing to the nose, about five or seven inches from it, and then moved slowly, very, very slowly, upwards and downwards, it will be found that the sufferer sees two points or a blurred point. When the eyes are turned upwards, and sometimes when turned far downwards, one point is seen, but when the eyes look at the point held just above the top of the nose two points are seen. If the pencil is moved up and down and the endeavour is made to see only one point, the faculty to do so will grow. Sometimes the point is seen as two points crossing over, making the pencil like open scissors; sometimes the points are seen at the ends of separate pencils. But as all these are wrong, the pencil should not be looked at in that way. Some position should be found where it is correctly seen, and then it should be moved up and down or nearer or farther away.
The ordinary eye muscle exercises must also be used, i.e. the muscles that enable the eyes to turn sideways, up and down, and diagonally, should be well exercised many times a day, turning them each way as far as possible, equally so with each eye. These exercises should be done with a swing, not lazily or as if it did not matter. If the muscles are very strong in resistance or too weak to comply with the will, it is hard work at first to get them to respond, and as Laurance points out, much depends upon the personality of the practitioner, as well as on the will of the patient.
There have been many attempts to bring into practice the principle of movement, in a circular form, for the eyes. The latest was by Dr. N.A. Stutterheim* whose machine was a moving circular board with a dull red spot in one place. The patient is fitted with prisms, the room is darkened, and he is told to watch the moving red light. The only difficulty with this is that its author states that it must be used daily for some weeks before it effects a cure, and anything which necessitates this is bound to fail these days, added to which, the use of the prisms would have to be in the hands of a very skilled operator.
But an adaptation of this principle yields vastly benficial results. One of the difficulties in eye muscular movement is’ that the sense of sight is not employed. We advocate that in turning. the eyes, some object is seen as far to each side, or up and down or diagonally, as possible. If a pencil or knitting needle is held about. twelve to twenty-four inches from the nose and moved in a circle (the eyes following the point) far enough outward to make each eye work, the brain has to use each eye, for the nose gets in the way of one eye when the other is far outward, while at the top and bottom of the circle fusion takes place. The best effect is gained when the eyes are coaxed over the difficult places. The circles need not always be perfect circles, but the motion adapted to the defect. It is not always necessary to move the eyes right round to the limit, as the imbalance or jerkiness of movement can be helped by smaller circles or ovals.
Many young children suffer slightly from this defect. In fact, when a child is normally bright, but very backward in reading, it is well to look for a slight imbalance, as that is often the cause behind the inability to separate the letters of words or to see them as parts of syllables.
As Laurance points out, patience is needed by the instructor, and will by the instructed, but the difficulty can be got over quickly when both help.
* Ophthalmic surgeon to the Johannesburg School Clinic, Transvaal Education Department; late Assistant, Eye Clinic University, Leyden.
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