Full visual function depends on the coordinated action of vision and eye movements. We must direct our line of sight on an object of interest so that it will be imaged on the fovea of each eye. Furthermore, to achieve maximum visual acuity and depth perception, we must be able to hold our eyes steady on a stationary or moving target. These important capabilities require appropriate postnatal visual and oculomotor experience. The visual and oculomotor systems are immature at birth and sensitive to injury in both monkeys and humans. When synergistic interactions between visual and oculomotor systems are impaired early in life, strabismus (eye misalignment) and loss of visual function (e.g., amblyopia, stereopsis) occur. These disorders, which affect at least 3% of children born in the United States, are permanent and difficult to treat. Human infantile strabismus syndrome is comprised of impaired gaze-holding, eye misalignment and abnormal smooth pursuit and saccadic eye movement coordination. We have developed effective animal models for studying the development of the visual and oculomotor systems by raising infant monkeys (Macaca mulatta) with either surgical or prism induced strabismus. Our non-human primate model of infantile esotropia syndrome allows us to examine neural mechanisms associated with impaired visual-oculomotor function in strabismus. Our studies are directed at understanding the role of cortical-cortical and cortical-brainstem circuits essential for normal visual-oculomotor function and how these circuits are compromised in disease. During the previous finding cycle, we demonstrated that the pretectal nucleus of the optic tract (NOT) was a likely locus for a common gaze-holding disorder (latent nystagmus) associated with infantile esotropia syndrome. Our current studies indicate that alteration in visual and eye movement signals in the medial superior temporal (MST) area may contribute to defective smooth pursuit of strabismic subjects. Our proposed studies address a significant problem in visual-oculomotor development related to strabismus and development of the cortical smooth pursuit system in health and disease. Our studies are hypothesis driven and use behavioral, single unit recording and modeling approaches to examine the potential role of neurons in MST, frontal eye fields (FEF) and their brainstem targets in normal and pathological smooth pursuit eye movements. Completion of our studies will provide important perspectives that could lead to improved diagnosis and treatment options for developmental disorders affecting vision and eye movements in children. In addition, the strabismic monkey provides important opportunities to uncover fundamental neural mechanisms associated with plasticity in the visual-oculomotor systems. PUBLIC HEALTH RELEVANCE Human infantile strabismus syndrome is a common problem affecting at least 3% of children born in the United States. The abnormal gaze-holding, eye misalignment and asymmetric eye movements of infantile strabismus impair vision. We have developed effective animal models (Macaca mulatta) for studying development of visual and oculomotor behavior and the underlying neural mechanisms associated with strabismus. Our research is important for improving understanding of clinically important disorders effecting children and developing new treatment options.