Slit-lamp studies of the rhesus monkey eye: III. The zones of discontinuity.

The rhesus monkey lens exhibits two zones of discontinuity, one anteriorly and one posteriorly. They are first discernible by slit-lamp photography as performed in this study at around age 7 years in iridectomized eyes, and become more distinct with increasing age. Their thickness and distance from each other along the polar axis are independent of lens age, but their distance from the lens surface increases with increasing age. Upon accommodation, the distance between the two zones increases while all other distances along the polar axis remain unchanged, indicating that, as in the human, overall alterations in rhesus lenticular shape and thickness with accommodation primarily reflect changes in the shape of the central region. The curvature of each zone becomes sharper in a linear fashion with accommodation, with the slope of the relationship being similar to those for lens surfaces.