Use Your Own Eyes

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



CHAPTER V


ACCOMMODATION


When the word "accommodation" is used by an eye specialist, he means by it the changes which take place in the eye when it is focusing. That is, the eye is accommodating itself to the distance of the object at which it is looking. Just what muscular changes occur in the eye during the act of accommodation has been a subject of most fascinating interest for centuries.


There have been different theories as to how this is accomplished. Some supposed a change in the position of the lens. Another theory was that the eyeball was lengthened. That would amount to the same thing; it would change the relative position of the lens. Such a change would increase the distance between the lens and the most sensitive part of the retina, at the rear of the eyeball. A change in the horizontal length of the eyeball can be accomplished only by the external muscles of the eye.


We must remember that rays of light, while passing through the front of the eye, are so refracted as to present the image of an object upside down on the retina. This is because the rays reflected from the top of the object are directed downward, so as to contact the floor of the retina; and rays reflected from the bottom of the object are directed upward and contact the upper surface of the retina.


In some way, before the "new form of energy" so called in the text books, registers in the cells of the visual center, that inverted image is minverted.


Dr. Helmholtz, who died in 1894, was the authority for the present prevailing belief that accommodation is accomplished by an increase in the convexity of the anterior surface of the lens. He said, however, that his guess was only a theory, and his findings not satisfactory. He simply ignored the transverse muscles, saying that besides the lens, he did not "see" anything else which could accomplish ac, commodation. That certainly was a great man's lapse.


For a century those external muscles had been discussed, and some leaders of thought had believed they did accomplish accommodation. It had been fully proved, too, for many years, that an eye could, and many eyes did, accommodate after the lens was removed. Dr. Helmholtz offered no reply to those records.


The discoveries of. Dr. Bates. explain why eyes can accommodate when the lens of the eye has been removed. They do not conflict with what is known of the structure and functions of the tendon and the tiny ciliary muscles that sustain or modify the convexity of the lens. His discoveries explain many apparent discrepancies in the theories which are held, or discussed, by eye specialists. They show why and how it is possible to prevent and to cure the various abnormal function conditions which are such a distressing problem to the men whose work it is to care for and to help the increasing number of cases of defective vision.


It is established that the normal eye at rest is adjusted only for rays coming from a distance, not for rays reflected from objects nearby. Rays from nearby objects will come to a focus behind the retina. But the myopic eye, that is the nearsighted eye, does constantly focus the rays reflected from near objects. It is accepted that the myopic eye is always longer horizontally than the normal eye at rest, when it is not focused-that is, accommodated-for nearby objects.


Dr. Bates discovered and proved how this change is accomplished. But he too had a lapse. Perhaps he was "made mad" by the Gods, bitter finally from the contumely heaped on him by the specialists, he wrote that "the lens has no part in accommodation". But that is not true.


The eyeball, in changing the distance between the lens and the near end of the retina, changes its shape. Its walls are curved. When the rear end recedes from the lens, the curvature of the walls changes as the ball is made longer horizontally. The lens is placed a short distance back from the inner side of the front end. Its substance is not an unchanging solid. Its capsule, the flexible envelope which holds the contents in shape, is fastened to the curved inner sides of the eyeball by the tendon which controls its shape. Any change in the shape of those walls could modify the convexity of the anterior surface of the lens. This relationship makes it necessary for the exact shape of the lens to perfectly conform to any change made in the curvature of the anterior of the eyeball. This is necessary because the outer covering there, the cornea, is also a refracting medium, and the lens must conform to any changes that may occur in the refraction which takes place in the cornea. It is necessary also for the convexity of the lens to conform perfectly to whatever changes occur in the relationship with the retina consequent upon the changes in the shape of the eyeball.


At that moment the lens must not become less convex. Perhaps, it is kept from so changing; or even it may be made a trifle more convex. This could be done by the ciliary muscle. Dr. Bates ignored that muscle, even as Dr. Helmholtz ignored the comparatively big oblique muscles.


If that theory is correct, it will harmonize the findings of Dr. Helmholtz and Dr. Bates. I have not found it written before. But that is my guess.


It is apparent that the same impulse or nerve control which issues from the visual center in the brain harmonizes the cooperation of the external muscles and the ciliary muscle of the lens.


The highest standard text book writes specifically that the theory of Dr. Helmholtz does not accord with some accepted findings. The explanation offered here would agree with what he offered, and with the discovery of Dr. Bates. The lens serves as an auxiliary adjustment, secondary and compensatory to whatever changes are produced by the action of the two external oblique muscles of the eye.


This is not a text book. This chapter gives a sufficient description of the factor of accommodation, based on factual records in standard text books. You have also the statement f of Dr. Helmholtz, and that of Dr. Bates. I believe you will see the reasonableness of my explanation, which apparently harmonizes the two conflicting claims.


It will probably help you to succeed if you get a clear understanding of the mechanism, and realize that there was no real conflict; because they both were right in their positive claims, and wrong only in their denials, one against the other.


That however, is not of fundamental import to you. The lens is a factor in accommodation, and the oblique muscles are also a factor. The records in the standard books suppo that statement.


What you should emphasize, and impress on your mind, is that the same central control activates both muscles, and when the functioning is normal, the mental conception is correct.


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