Both strabismic and anisometropic amblyopia are characterized by a reduction in visual acuity, however, recent psychophysical investigations of human amblyopes have revealed substantial differences in the visual characteristics of these two types of amblyopia. Although monkeys reared with either artificially-induced anisometropia or strabismus exhibit reduced spatial resolving capacities, it has not been deteremined if the visual characteristics of these amblyopic monkeys are similar to those manifested by humans with these two types of amblyopia. In the proposed study rhesus monkeys will be subjected to three rearing procedures (optically-induced anisometropia, optically-induced strabismus, and surgically-induced exotropia) which have previously been shown to produce a clinically-representative degree of amblyopia. Psychophysical techniques will be used to determine the effects of these rearing procedures on the monkeys' 1) spatiotemporal transfer function, 2) letter acuity as a function of the degree of contour interaction (i.e., "crowding"), and 3) spatial sense for suprathreshold stimuli (vernier acuity and displacement thresholds). These behavioral investigations will determine the adequacy of these animals as models for strabismic and anisometropic amblyopia. Subsequently, occlusion thereapy will be initiated in some experimental monkeys to determine if any of the induced abnormalities can be remediated. Histological and neurophysiological techniques will be used 1) to investigate the effects of the rearing procedure on the response characteristics of neurons in the striate cortex and on neuronal cell size in the lateral geniculate nucleus, 2) to evaluate the effects of occlusion therapy, and 3) to test the hypothesis that different neural loses are associated with strabismic and anisometropic amblyopia. The results of this study will provide a more complete understanding of amblyopia and thus be helpful in the development of successful treatment procedures.