A model for accommodation in the young human eye: The effects of lens elastic anisotropy on the mechanism

An explanation of the mechanism of visual accommodation depends heavily on understanding the mechanical properties of the lens, as well as the way in which its shape is altered in small accommodative changes. An initial attempt to relate these properties to a mechanism has already been performed (Koretz and Handelman, 1982) for the young (age 11 yr) human lens, using certain simplifying assumptions (spherical curvature on the anterior lens surface and elastic isotropy). However, since it has been shown that the lens behaves as an anisotropic body, the previous treatment has been extended to include the variation of lens elastic properties in the polar and radial directions. With this modified representation, it is found that only one combination of elastic constants is consistent with the generally accepted qualitative theory of accommodation and with clinical data on the accommodative range of the emmetropic age 11 human eye. For this unique solution of the equations, however, the general mechanism already suggested by us, which includes support by the vitreous and alteration of the magnitude and angle of application of zonular force with accommodation, remains little changed.