Presbyopia, the age-related loss of the ability to accommodate, is the most common ocular affliction, affecting every human over the age of 45 years. Its pathophysiology is poorly understood. In the rhesus monkey, the only known animal model for the human condition, the ciliary muscle loses its configuration response to cholinomimetic drugs or central stimulation with age. Although some evidence suggests that this loss of mobility may be due to restriction by a progressively inelastic posterior attachment, it is not clear that the muscle's contractile machinery continues to function normally, nor what roles the lens, lens capsule and zonule might play. This project will determine, by digital image analysis of Scheimpflug, goniographic and infrared photorefractive video recordings in living surgically aniridic rhesus monkeys encompassing the entire species lifespan: ( 1 ) the real-time dynamics of ciliary muscle, lenticular and zonular movement in response to midbrain stimulation; (2) the effect of extra- and intra-capsular lens extraction, posterior capsulotomy and complete posterior capsulectomy following extracapsular lens extraction, and anterior and posterior regional zonulolysis on these real-time dynamics; (3) correlations of these interactions with age; (4) the role of choroidal/ciliary muscle elasticity in the development of presbyopia (by severing or scarifying the posterior attachment of the ciliary muscle). These studies will generate new information about the pathophysiology of presbyopia.