Amblyopia, strabismus, and associated deficits in binocular function affect 6.7% of American children (according to the Rand Health Insurance Experiment, 1985). During the previous grant period, efficacy and effectiveness of early treatment protocols were evaluated using FPL, OPL, and VEP protocols. Continued enrollment and follow-up in this project will permit a finer grain of analysis and allow us to obtain stable long-term sensory and motor outcome data. Although early treatment often results in good acuity outcomes, stereoacuity outcomes are routinely poor. Only rare patients achieve normal stereoacuity and <50% achieve any stereopsis. Two new treatment protocols designed to enhance binocular outcomes in patients with infantile esotropia or congenital unilateral cataract will be evaluated in the upcoming grant period: a combined surgery/Oculinum treatment for strabismus and a graduated occlusion therapy program following very early surgery for congenital unilateral cataract. The interdependence of eye alignment, stereopsis, and motion processing during visual development will be studied in normal infants, infants at high risk for strabismus, and pediatric patients with early onset binocular imbalance. Using a within-subjects design, these studies will yield quantitative growth curves for each aspect of binocular development and will evaluate whether deficits in motion processing and/or stereopsis precede the onset of strabismus. Current models of strabismic and anisometropic amblyopia will be evaluated in a group of amblyopes with prospectively documented clinical and visual development histories. Data from patients matched for onset age and/or depth of amblyopia will be used to define the roles of etiology and onset age in the constellation of deficits observed. Three laboratory tests of binocular function will be adapted for clinical use: random-dot stereotests for infants and preschool children and a video-based Hirschberg test. Valid and reliable tests of binocular sensory and motor status for infants and preschool children will make a significant contribution to clinical research methodology and patient care. These studies will help to define the necessary and sufficient conditions for the development of stereopsis. On the basic science side, these studies will improve our understanding of critical factors in the development of single binocular vision. On the clinical side, improved binocular outcome will improved stability of alignment; i.e., lower incidence of re-operation in infantile esotropia and lower incidence of strabismus in infants treated for congenital unilateral cataract.