Soon after birth, most infants develop near emmetropic refractive errors that are then maintained in both eyes throughout childhood and into early adult life. However, for reasons not currently understood, a significant and possibly increasing proportion of the population develop abnormal refractive errors (currently about 30% of young adults in the USA have significant refractive errors). Refractive errors are a significant public health concern because in addition to the high costs and the complications associated with traditional optical and surgical correction strategies, refractive errors can lead to permanent sensory disorders and ocular abnormalities causing blindness. The long-term goal of our research program is to provide a better understanding of the etiology of human refractive errors. The specific aims of our proposed research are to determine how visual experience affects refractive development and to characterize the operational properties of the vision-dependent mechanisms that regulate eye growth. Since many of the required experiments can not be conducted in humans, but our purpose is to generate knowledge that can be applied to human development, these experiments will be conducted using rhesus monkeys. Controlled rearing strategies and optical and ultrasonographic measurement techniques will be used to determine: 1) the relative contributions of the central and peripheral retina to emmetropization and vision-dependent changes in eye growth. 2) the impact of peripheral refractive errors on emmetropization, and 3) the spatial integration characteristics of the vision-dependent mechanisms that regulate eye growth. These experiments focus on fundamental issues concerning the role of visual experience that have largely been ignored'in previous studies in humans. Overall the proposed studies are an important step in determining how and to what extent visual experience contributes to the genesis of common human refractive errors. The results of these studies will potentially provide the foundation for new treatment and management strategies for human refractive errors.