The Helmholtz1 theory of accommodation appeared in 1855, and since that time the refutation or substantiation of this hypothesis has concerned students of ocular physiology. The difficulty of observing the interior of the anterior segment without mutilating the eye has permitted the theory to persist in explanations of this ocular function.
There are two firmly entrenched schools of thought on the mechanism of accommodation: One supports Helmholtz, and the other favors the Tscherning2 theory. The two agree that the fundamentals of accommodation are contraction of the ciliary muscle and increased convexity of the crystalline lens but differ on the method by which the former accomplishes the latter. The followers of Helmholtz believe that contraction of the ciliary muscle reduces zonular tension, permitting the elastic capsule of the lens to shape the lens. In opposition, Tscherning's disciples think the force of the ciliary muscle acting through the zonule and