The rhesus monkey has evolved as a useful model for the study of amblyopia caused by neonatal lid closure and experimental strabismus and anisometropia. In view of the behavioral and anatomic similarities of the visual system in humans and rhesus monkeys, there is reason to believe that the neurophysiologic and anatomic anomalies identified in animals as part of the "visual deprivation syndrome" occur in humans as well. Animal research has led to better understanding of the basic mechanisms responsible for the development of amblyopia and the manner in which form vision deprivation and abnormal binocular interaction contribute to the various forms of unilateral and bilateral amblyopia. The period of susceptibility to abnormal visual stimulation in humans needs to be better defined, and the clinician must take precautions to avoid uncontrolled occlusion or prolonged unilateral cycloplegia in infants. Even though the factors leading to amblyopia in patients with unilateral or bilateral congenital cataracts are now better understood, the visual results are still disappointing. It is possible that the residual aniseikonia after contact lens correction may be amblyopiogenic in these patients.