Mechanical performance of the lens capsule in accommodation

The human lens consists of a relatively stiff capsule surrounding a soft lens substance. It is generally understood that an intralenticular pressure exists within the lens. A simple mechanical model, in which the capsule is represented as a fluid‐filled membrane, suggests that any intralenticular pressure will cause bi‐axial tensile stresses to occur in the capsule near the optical axis. In the equatorial region, however, the circumferential stresses in the capsule are found to be compressive. This indicates that wrinkles may occur in this region. Images of isolated human lenses (e.g. Rosen et al. 2006) typically indicate a smooth outline when viewed in the sagittal plane (suggesting that meridional stresses are tensile at all locations). When viewed in the frontal plane, however, wrinkles are typically visible around the equator. These observations are consistent with the simple capsule model. To investigate the influence that capsule wrinkling might have on the accommodation mechanism, a finite element analysis is conducted, of a 29‐year lens, in which equatorial wrinkles are included in the model. The results indicate that equatorial wrinkles have a modest, but significant, influence on the accommodation amplitude.