Accommodation dynamics in aging rhesus monkeys

Accommodation, the mechanism by which the eye focuses on near objects, is l ost with increasing age in humans and monkeys. This pathophysiology, called presbyopia, is poorly understood. We studied aging-related changes in the dynamics of accommodation in rhesus monkeys aged 4-24 yr after total iridec tomy and midbrain implantation of an electrode to permit visualization and stimulation, respectively, of the eye's accommodative apparatus. Real-time video techniques were used to capture and quantify images of the ciliary bo dy and lens. During accommodation in youth, ciliary body movement was bipha sic, lens movement was monophasic, and both slowed as the structures approa ched their new steady-state positions. Disaccommodation occurred more rapid ly for both ciliary body and lens, but with longer latent period, and slowe d near the end point. With increasing age, the amplitude of lens and ciliar y body movement during accommodation declined, as did their velocities. The latent period of lens and ciliary body movements increased, and ciliary bo dy movement became monophasic. The latent period of lens and ciliary body m ovement during disaccommodation was not significantly correlated with age, but their velocity declined significantly. The age-dependent decline in amp litude and velocity of ciliary body movements during accommodation suggests that ciliary body dysfunction plays a role in presbyopia. The age changes in lens movement could be a consequence of increasing inelasticity or harde ning of the lens, or of age changes in ciliary body motility.