THE PHYSIOLOGY of accommodation has invited the interest of the greatest minds in history, including the attentions of none less than Kepler, Descartes, and Young. It was Helmholtz who first outlined a theory that implicated the action of the ciliary body and zonules on crystalline lens shape, and his comprehensive treatise is an enlightening recount of the inventive speculation that preceded his hypothesis.1 In light of the abundant evidence provided by experimental physiology throughout the last century, it is remarkable that fundamental elements of the mechanism of accommodation remain contentious. Nevertheless, using ultrasound biomicroscopy and goniovideography, Glasser and Kaufman2 have provided strong support for the classic Helmholtz theory, namely that upon accommodative effort, contraction of the ciliary muscle releases zonular tension on the equatorial crystalline lens, allowing the lens to assume more spherical geometry.
McLeod SD. The Challenge of Presbyopia. Arch Ophthalmol. 2002;120(11):1572-1574. doi:10.1001/archopht.120.11.1572