Use Your Own Eyes

by William B. MacCracken, M. D. Use Your Own Eyes was first published in 1937.



CHAPTER IV


THE EYE


Everyone knows that the eye is round. Not many have inquired much further. Some could tell us that the round eye lies cushioned in the soft tissue which lines the cave-like round hollows of bone that carry the eyes; right under the floor of the skull, beneath the brain. There are six muscles attached to the outside covering of the eye. At one end they are attached to the edge of the round hole in the rear of the cavity through which the optic nerve passes on its way back to the brain. Four muscles pass forward and are imbedded in the outer walls of the eye, near the front; one on top, one on the bottom, and one on each side. The other two are attached to the sidewalls of the cavity, and are wrapped around the middle of the eye like belts, one passing over, and the other passing under the eye.


The four muscles called the recd, passing forward on all four aspects of the walls, move the eye in different directions. Working in harmony. they change the position of the eye in the socket, and point it, unconsciously, wherever the mind wants to look. When they are contracted together and sufficiently they chance the shape of the eye and make it flatter on each end. That is, they make the distance shorter between the front and the rear walls than it properly should be. Such an abnormal condition is present when an eye is what is called farsighted. The two so-called oblious muscles serve to compress the eye in the middle. and flatten it there. so that it becomes longer horizontally. In this condition. the distance is longer between the front and rear walls of the eve, called the focal distance. Such a longer focal distance is necessary when the eye is focused on nearby objects.


The inside of the eye is divided into two compartments.


Immediately behind the anterior wall of the eye is a small chamber, filled with a thin fluid, which separates the front of the eye from the lens. The lens is fastened to the inner walls of the eye by a ribbon-like circular band of tendon, attached edgewise. Behind the lens, filling the remainder of the eyeball, is a different liquid which resembles a jellyFt


in consistency. The spherical shape of the eye is sustained t by the pressure outward of the fluids with which it is filled. The crystalline lens consists of an elastic capsule holding in an oval shape its fluid-like contents.


The walls of the eye are opaque, and light can enter only through the transparent lens in the middle of the front wall. The colored circle just inside the front of the, eye is called the iris, and the opening in the center of that circle is called the pupil. This opening constantly varies in diameter. It is furnished with a diaphragm, of which the diaphragm in a camera is something of an imitation., Its function is to control the amount of light which NJ permitted to enter through the lens. In a poor light, it enlarges, and in a strong light it contracts. The outer walls of the eye are composed of a dense, firm tissue, with a lining of opaque pigment, and contain vessels which supply the nutriment required. The inner membrane, lining the eyeball,


is called the retina. Tbis membrane, although it is thinner than the finest paper, consists of ten distinct layers. In its surface are spread out the nerve terminations, which are the microscopic endings of the nerves that receive and carry the impressions made upon the surface of the retina' I" the rays of light. We have some understanding of this when we remember the film in a camera, which also is acted upon, although in a way infinitely simpler, by rays of light.


The terminations of the nerve tendrils in the retina


are of two kinds. They are distinguished as rods and cones, and there is much difference in their exact functions. The most sensitive part of the retina is a small area at the very back of the eye in the center, which is called the macula. Here form and color and very sharp definition are registered. In this area there are no rods, which are nerve endings plainer and less highly specialized than the cones. Beyond this spot cones and rods mingle, but toward the front edges of the retina no cones are found. The rods seem to be more sensitive to the presence of simple light than are the cones.


When light rays contact the surface of the retina a chemical transformation takes place. The force called radiant energy is changed into "another form of energy". This new force is carried by the nerve fibres which terminate in the cones and rods, back through the collection of fibres called the optic nerve. In order that light rays coming into either eye, from right or from left may be registered simultaneously in the visual centers of both sides of the brain, there is a switch in the course of the optic nerves from both eyes. This is the beginning of the mechanism of sight: The comparatively simple reception and absorption and assimilation of those rays of light which are reflected from external objects and come into contact with the retina.


Vision is classified as a psychic function. The eye does not see. It is the brain that sees. The force or energy which courses up through the optic nerves to the vision center in the brain creates a transformation in those brain cells. Just how those impressions are registered so that they become conscious conceptions, has not yet been discovered. The process is a brain function, and part of the mind. Previous similar impressions upon brain cells make it possible for a harmonious cooperation of memories to interpret the newly registered images. This involves memory, imagination, and every element of the intellect.


Does not this brief description impress the tremendous significance of the prevailing custom of neglecting all this marvelous mechanism?


Reminding the reader that this is exactly what is being done by the eye specialists who allege that the different, common types of abnormal vision are not curable, should help the patient realize the factors and their conduct which are involved in the mechanism of vision.


This theory on the part of those specialists is founded on statements formulated by medical men long dead.


Under the present stress of necessity as much has been discovered in the field of medicine as in any other branch of science. The military authorities of the United States have learned that it is possible to cure or to sufficiently improve the defective vision of the men they needed in the service.


Is it not obvious that anyone who continues to maintain that an abnormal fuction in the mechanism of vision is no curable, is ignoring this record of accomplishments.


The import of what I am trying to impress on the patients, in calling attention to this field of thought, is the influence of unconscious inhibitions, in any effort to accept an entirely new conception, the more especially concerning a subject which is unfamiliar.


I am not concerned here with the belief or the practice of a specialist who is prescribing glasses for those who want them. My purpose is to constrain the patient against his own unconscious reluctance. That is, the failure to discard the teaching which has been, may I say incorporated in his mind, during the years, as a part of what I think of as the mechanism of vision.


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