The work we describe in this chapter constitutes some first attempts to come to grips with the problem raised by Salapatek and Banks, specifically in the context of the commonest forms of "visual abnormality," refractive errors, amblyopia, and strabismus. To examine the relationship between visual abnormality in infancy and in later childhood for "large enough samples" implies working with groups of hundreds of infants over periods of several years. Consequently, these studies are still in progress and the data presented here are in most cases less than the complete results. However, they go far enough for us to consider how far we can answer any of the questions that arise when we try to specify the relationships between early and later abnormality. As with most research, the outcome is often not so much to answer the questions as to refine them.