CHAPTER VIII

Amblyopia

AMBLYOPIA is a term applied to a condition of the eyesight in which there is a lowering of visual power which can not be relieved by glasses and is not dependent on any visible changes in the organ of vision. It has been facetiously defined as a condition in which neither the patient nor the doctor can see. The patient suffers from poor vision, while the doctor can find nothing wrong with his eyes. The condition usually affects only one eye, and is so often associated with squint that it has been erroneously supposed to be both the cause and the effect of that condition.

The text books enumerate many different types of amblyopia. The one known as amblyopia exanopsia was so named because it was supposed to result from a suppression of the sight of the affected eye during early youth, owing to some defect, such as a squint or error of refraction. Such defects were supposed to prevent the retina from attaining the functional capacity of normal eyes, and the literature of the subject is full of the impossibility of cure. "The function of the retina never again becomes perfectly normal," says Fuchs, "even when the cause of the trouble has been removed."

There are, nevertheless, many cases of spontaneous cures on record, these usually occurring when the perfect eye has been lost by accident. In such cases the amblyopic eye in the course of time frequently becomes normal.

It is gratifying to be able to state that the ailment is a purely functional one, and that the authorities are quite wrong in supposing that it can not be cured. All cases have been relieved by eye training, and complete cures have been effected when the exercises were faithfully practiced. The progress has sometimes been very rapid, the sight occasionally improving in a few minutes from one-fiftieth of the normal to one-tenth.

In order that patients may understand the condition, they are taught how to produce amblyopia in the better eye and how to increase it in the amblyopic eye by improper efforts to see. After they have learned to lower their vision voluntarily they become better able to improve it. The following case illustrates the method: A girl of fifteen had had amblyopia and squint since childhood. The vision of the right eye was 1/40 (of normal), while that of the left was 2/3. Glasses did not improve either eye. The patient was seated twenty feet from a Snellen test card and the right or poorer eye was covered with an opaque screen. She was then directed to look with her better eye at the large letter on the card and to note its clearness. Next she was told to look at a point three feet to one side of the card, and her attention was called to the fact that then she did not see the large letter so well. The point of fixation was brought closer and closer to the letter until she appreciated the fact that her vision was lowered even when she looked only a few inches to one side of it. When she looked at a small letter she readily recognized that an eccentric fixation of less than an inch lowered the vision.

After she had learned to increase the amblyopia of the better eye this eye was covered, while she was taught how to lower the vision of the other or poorer eye by increasing its eccentric fixation. This was accomplished in a few minutes. She was told that the cause of her defective sight was her habit of looking at objects with a part of the retina to one side of the true center of sight. She was advised to see by looking straight at the letters she wished to see. In less than half an hour the vision of the left eye became normal, while the right improved from 1/40 to 1/10. The cure was complete in two weeks.

Unconscious of the fact that they were looking at objects with their eyes turned to one side, many amblyopic patients had difficulty in realizing that this was the case. When they did come to understand it, it helped them to secure central fixation, and their sight immediately improved.

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