Monocular congenital cataracts are usually associated with a poor visual outcome. Factors which continue to limit the visual rehabilitation of these eyes after cataract removal include the less than ideal optical correction of the induced aphakia and amblyopia. This research project is a controlled study using a non-human primate model to evaluate the efficacy and safety of treating infants that have monocular congenital cataracts with intraocular lenses (IOLs). Its major objectives are to assess the effect of this treatment modality on: (1) visual acuity and contrast sensitivity using operant testing; (2) ocular growth; (3) long-term ocular complications evaluated clinically and histopathologically; and (4) neuroanatomical changes in the geniculostriate system using cytochrome oxidase histochemistry and parvalbumin and GABA immunoreactivity. These effects are being assessed in groups of monkeys who are monocularly pseudophakic: 2 groups with monofocal IOLs, 2 groups with multifocal IOLs, and 1 group of monkeys treated with a new paradigm (i.e., a higher powered multifocal IOL with no additional optical correction of the pseudophakic eye or occlusion therapy of the fellow eye). One of the two monofocal IOL groups and one of the two multifocal IOL groups also receive occlusion therapy of the fellow eye. Correlations between clinical, behavioral and neuroanatomical outcomes will be assessed and compared across the treatment groups.