Over recent years much interest has been directed toward understanding the process by which refractive errors develop, how this is controlled and the effect of refractive errors on subsequent visual status. There are obvious difficulties in studying such mechanisms in human subjects and for this reason many studies have employed animal models. The present paper compiles the evidence available from human subjects, examining the significance of different aspects of refractive status, normal and abnormal patterns of development and their significance in the development of normal binocular function.