On the nature of myopia and the mechanism of accommodation.

An experiment in which pressure was applied to the globe of the eye by artificially-induced contraction of the superior oblique muscles produced two effects: 1) Dual vision, consisting of two separate, superimposed, retinal images, one blurred and one clear; and 2) A 5 diopter increase in myopia. It was concluded that the pressure, transmitted through the sclera to the vitreous, forced the vitreous against the back of the lens, flattening the periphery but not the axial (central) region, resulting in a high degree of negative spherical aberration, combined with accommodation. This suggests that accommodation can be actuated by contraction of the extraocular muscles. When the pressure was released, it took several years for the dual image to subside. This suggests that when the lens is released after a long period of accommodation, the return to the unaccommodated state is extremely slow, and that a significant factor in the etiology of myopia is repeated long periods of accommodation in which periods of rest are insufficient to allow the lens to return completely to the unaccommodated state.