Contact lenses were fitted for 51 aphakic infants. From this group data were obtained that support the hypothesis that much of the visual defect in cases of congenital cataract is due to functional amblyopia, and that it is therefore largely preventable and even treatable. The implications of the results for the management of these patients and for human amblyopia are that early treatment and optical correction are essential, since the effects of deprivation start at about 4 months of age and continue to a cumulative but decreasing degree throughout the first decade of life.