MECHANISM OF ACCOMMODATION; THEORY OF HELMHOLTZ
Of the facts concerned in the act of accommodation, two have been established beyond any reasonable doubt. One is that the increase in refracting power of the eye required in order to produce accommodation is effected solely by an increased convexity of the lens. The other is that this increased convexity itself is brought about by a contraction of the ciliary muscle.
There is not, however, absolute agreement as to the way in which contraction of the ciliary muscle makes the lens more convex. The prevailing theory, substantiated by many observations and ingenious experiments, is that of Helmholtz. This theory, briefly, is as follows:
The lens, owing to the elasticity of its capsule,1 tends constantly to assume a spherical shape. It is prevented from doing this by the zonula, which is inserted on its two surfaces and runs thence outward and
ALEXANDER DUANE. ACCOMMODATION. Arch Ophthalmol. 1931;5(1):1–14. doi:10.1001/archopht.1931.00820010011001