THERE is in the retina, the film of the eye, a spot which is the area of maximum sensitiveness. That spot is right at the center. It is a small circular elevation which is known as the "macula lutea" (yellow spot.) In the center of that spot is the "fovea centralis', a depression of darker color. You will remember the cones, nerve endings which have a much different and more complex function of registering than the rods. The cones occupy this spot to the exclusion of the rods, and they are longer here and closer. When rays of light fall on this spot they are contacting the most acutely receptive area of the retina. When rays contact the retina outside this spot, the objects from which those rays are refracted are not so exactly perceived. The farther from this spot the rays are contacted, the more the sharpness of the visual perception decreases. This means that an eye with normal vision sees best at only one small spot. Whatever is outside of that small spot is not seen as exactly, and the farther outside that tiny area any spot is, the poorer the impression is on the retina. This faculty is known as "central fixation."
This habit of the normal eye has several advantages. Durst, it is easier for the eye to focus on and pay attention to a very small area, instead of trying to see equally well a large surface in the same instant. Second, when the eye gives its undivided attention to a point instead of a large area, it sees the point so perfectly that it is ready instantly to leave for another point. Working that way the eye does not tire. When it does not work that way, and neglects to have a point of central fixation, it is called eccentric fixation. In this abnormal condition, the vision is very poor, and no single spot of the retina is uniformly employed to fix with, so that fixation is uncertain and unreliable. The normal area of most sensitiveness is lost, and the power of vision is impaired, sometimes quite seriously.
It is not easy to realize how infinitely quicker than thought the images are transmitted to the brain through the retina and the optic nerve. To see even a small letter, the eye must see all the outlines of the letter, and likewise all the letters in a word, and so every word on a line, as one reads rapidly down the page. The child begins by making the letters each time into a word. The mechanism of sight soon learns to adjust and save effort. There are those who can see and register so fast that they read a whole page, seeing every word, in a period of seconds. Such eyes have perfect central fixation.
The significance of this is that the loss of central fixation, in any degree, means loss of power of sight, and this loss is present in every condition of abnormal vision. This abnormal conduct of the eye is caused by a tension in the visual center in the brain. By relaxing that central tension, the central fixation of the retina is renewed. The relaxation is secured by the attainment of a condition of central fixation of the mind. This is accomplished by realizing the fault in the mechanism, and enlisting the mind in the effort to correct the dysfunction.
If one would impress on the mind the effects of a marked degree of eccentric fixation, it will be worth while to make a specific effort to see every part of an inch square close to the eye. Such an experiment, if one does it carefully, demonstrates how unnatural it is not to confine the focus of the eye to one tiny spot. If carried out earnestly the experiment will cause actual pain. The endeavor to effect a cure of the abnormal condition is to do just the opposite to the above. Ascertain first how fine, or how poor, a definition your eye makes when you test it for central fixation. When the central spot has lost something of its finer sensitiveness, it will be found that one can look at a point and find that he sees another point just as well, or even better, than he sees the point he is trying to confine his focus to. Some other spot on the retina sees better than the normally most sensitive spot. But this always means, not that the other spot has improved power, but that the retina has lost power in all of its surface, and is disturbed in its functioning.
The remedy is to carry out a series of tests, calling upon the central fixation function of the eye to recover its power. One can select two objects, for instance, two red balls or two black balls, or two lighted candles, or two objects, one round and one square, and make exact comparisons. Confining the glance to one, study how clearly, or not, the other object is apparent. Test also with a letter of good size at reading distance, and with a large letter at ten feet. Confine the focus to one side of the letter, and study the appearance of the other side. One will probably be surprised to find, when looking at the top of the big C on the Snellen Test Card at ten feet, that the bottom is actually clearer than the top of the letter.
It can happen that one will look at the top of a capital L on the page, and find that the bottom is certainly clearer, and reverse so as to look at the bottom of the C and find the top clearer.
If one will keep the mind attentive, and continue the practice as a game, it will gradually develop that the point focused at will displace the other point more and more until the conditions are reversed, and the eye is working normally. This may occur in a few minutes, or it may require considerable attention. The result depends entirely on the conduct of the mind. Central fixation of the mind means an attention which is so close and exclusive that no other thought is allowed to distract. Emerson understood such a conduct clearly when he said: "The hero is the man who is immovably centered." He meant that the man's mind was so impressed with the conception he had of the endeavor he was about to make, that not even the most intimate emotions of his heart could find a place beside that consciousness. With the proper degree of purpose, and an alert attention to the demonstration, one develops an auto suggestion in the mind, the mechanism involved in the function of central fixation is stimulated back to its normal conduct, and the vision is improved.
Eccentric fixation is a symptom caused by strain. It is only a symptom. Whatever procedure relieves the strain will correct the fault. Naturally the most direct method is to work with the function concerned. Having first demonstrated that one can look a certain distance away from a spot and see it better than when the attention is focused on it, one can gradually reduce that distance, until finally the eye will see the spot best when looking right at it. Beginning with the different sides of a large letter, the practice should be directed at a smaller letter, and finally a period can be selected, and it can be demonstrated that whichever side of the period is focused on, the opposite side will be less clear. When that is accomplished it always can be demonstrated that the vision has improved. Such an improvement may be only temporary at first; but with interest and patience, it will be found that an improvement in the function of central fixation is a most necessary and a most satisfactory procedure in the recovery of good normal vision. Above all, the faculty of central fixation protects the eye from abnormal fatigue, and from other sensations which develop when the eye is in use, even when there is sufficient power to work successfully without the use of glasses. Central fixation is fundamental and the most important quality of vision. When the eye has perfect central fixation, it has perfect sight.