7. Project Summary Soon after birth, most infants develop the optimal refractive error (i.e., “clinical” emmetropia) in both eyes that is then maintained throughout childhood and into early adult life. However, for reasons not currently understood, a significant and rapidly increasing proportion of the population develop myopia or nearsightedness. Because of structural changes that take place as the eye becomes myopic, myopia, even low degrees of myopia, pose a significant risk for multiple blinding conditions. As a consequence, myopia is now one of the leading causes of permanent visual impairment in the world. The long-term goal of our research program is to provide a better understanding of the etiology of common forms of myopia (e.g., juvenile onset myopia) and ultimately to develop effective treatment strategies the reduce the burden of myopia. The specific aims of our proposed research are to determine how visual experience affects refractive development, to characterize the operational properties of the vision-dependent mechanisms that regulate eye growth, and to explore new pharmaceutical approaches to eliminate myopia. 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 biometric measurement techniques will be used to determine: 1) the effects of low ambient light levels on emmetropization and vision-dependent changes in eye growth, 2) the influence of the spectral composition of ambient lighting on axial growth and refractive development, and 3) whether adenosine receptor antagonists can retard the development of myopia. The proposed experiments focus on fundamental issues concerning the manner in which visual experience influences refractive development and are an important step in determining how and to what extent visual experience contributes to the genesis of common human refractive errors. More importantly, the results of these studies will potentially provide the scientific foundation for qualitatively new treatment and management strategies for the most common forms of myopia.