The Lens In Myopia

Did everybody get it wrong about the role of the lens in myopia? If you are nearsighted you probably know the reason: your eyeballs are too long. This has been known for more than a hundred years, and no reputable eye researcher would dispute it. However, there is another reason: you probably use your eyes too much for near vision, most commonly reading or computer use. The result is that with prolonged periods of focusing for nearwork the crystalline lens within the eye finds it difficult to re-focus to see well at a distance. It is proposed here that the contribution of the lens in myopia is as much as or more so than the contribution of axial length. A MAJOR CAUSE OF MYOPIA IS THE CRYSTALLINE LENS BEING PERMANENTLY FOCUSED FOR NEAR VIEWING Although this hypothesis will be denounced as preposterous, it is an established fact that nearwork causes myopia. . This phenomenon (accommodative hyteresis or NITM-Nearwork-Induced Transient Myopia) is so well documented that it is beyond dispute. If, after a period of near focus, the gaze is then shifted to a distant object, the result is a temporary myopia (typically 0.25 - 0.30 D), because the eye requires a certain period of time to re-focus for distance viewing. The time required is related to the amount of time spent on the nearwork task: the longer the period of nearwork, the longer the decay time, i.e. the more time is required for the eye to relax its accommodation. Some experiments have shown that with longer nearwork tasks, the eye can take as long as six hours to recover its capacity for distance vision. In these experiments the eye has always recovered its ability to focus for far vision, but these experimental nearwork times have always been relatively brief, usually for a period of minutes, or at most for a few hours; it is not inconceivable that in the real-world situation of long periods of nearwork over months and years a transient myopia could become permanent. The inability of the lens to change its focus is so common as to be almost universal--in anyone in their 40's. s. Although this condition, presbyopia, refers to the inability to focus for near, the principle is the same: the lens is unable to change its shape, and therefore its focusing power, due to the viscosity of the lens substance (there are a few other explanations).

Two other experiments also support the lens hypothesis: The prolonged recovery period from accommodation following an experiment in artificially-induced myopia. The changes in accommodation produced by the application of vibration to the eye. Recovery From Artificially-Induced Myopia An experiment was performed which, accidentally, produced an extreme form of accommodative hysteresis. It showed that recovery from a high degree of accommodation can take years. The experiment involved forcing the oblique muscles to contract to a degree much higher than that which occurs during normal rotational eye movements, such as those involved in reading (described in Myopia, Experiments and Contradictions, on this site). This contraction caused a dramatic 5-diopter increase in myopia. It was initially assumed that the increase was caused by axial elongation, but another phenomenon was observed: an extreme degree of monocular diplopia, presumably caused by spherical aberration. Since spherical aberration always accompanies accommodation, this suggested strongly that compression of the globe not only lengthened the eye, but also caused the lens to accommodate. This correlates well with the fact that spherical aberration increases as the eye accommodates, becoming negative as the accommodation goes beyond some 3 D. Also, it is well-documented that spherical aberration. is more common in high myopia. It was surmised that external pressure on the globe had forced the vitreous forward against the posterior surface of the lens, which in turn flattened its periphery. This change in lens shape is precisely what happens when the lens accommodates under normal conditions. According to Roorda and Glasser, "The increasing negative aberration of the accommodating lens arises from a more pronounced increase in optical power near the central region of the lens compared to the peripheral region. In other words, as the lens accommodates, the central curvature steepens while the peripheral curvature flattens. When the experiment was stopped, it required some two years for the refraction to revert to the pre-experiment state. Vibration and The Eye On the assumption that it might be possible to alter crystalline lens power, a device was constructed for the purpose of applying vibration to the eye. Application was through a

soft rubber tip placed on the upper eyelid and vibrated at a rate of 60 Hz and amplitude of 1 mm. The vibrated eye was abducted as far as possible and the other eye was occluded. The result was that the visual acuity improved significantly. This suggests that the lens had been accommodated, and, and that vibration had "softened" the lens allowing it to revert to a less accommodated state. There are a number of very strong arguments against the lens hypothesis, and these are addressed in Myopia, Experiments and Contradictions, on this site. The argument that this hypothesis can not be true because it would have been discovered by now is weak. In the history of science there are numerous examples of wellestablished long-standing theories that were eventually overturned. See: http://www.amasci.com/freenrg/wbelief1.html To state the hypothesis in the simplest possible terms: A major cause of myopia is that with prolonged nearwork the lens becomes permanently accommodated for near vision.

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The Lens in Myopia Abstract Experiments in Myopia Greatest Blunder in the History of Eye Research?