Strabismus is a major cause of visual disability in the young, affecting 3 to 4 percent of children within the first six years of life. The developmental consequences of strabismus may be mitigated by surgical intervention during the sensitive period for the development of binocular vision. Functional binocular vision is, however, extremely vulnerable to abnormal early visual experience and, rather than normal binocular vision, the majority of children treated for strabismus develop a form of abnormal sensory binocular vision (the monofixation syndrome) that is characterized by foveal suppression and reduced stereoacuity. Although the clinical characteristics of the monofixation syndrome are well- known, little is known about many fundamental properties of binocular vision following surgical eye alignment in infants. The broad objective of the proposed research is to investigate the alterations of motor and sensory fusion caused by a period of strabismus during infancy. A macaque monkey model, which demonstrates many of the abnormalities of binocular vision usually associated with the monofixation syndrome, has been developed and will be used for a series of psychophysical investigations of functional binocular vision. Specifically, investigations will be conducted to obtain quantitative descriptions of fine and coarse control of disparity vergence, the area and depth of suppression during binocular vision, and stereoscopic depth perception with local and global stereopsis. The results of these investigations should lead to an understanding of the mechanisms underlying the imprecision of disparity vergence, the phenomenon of clinical suppression and the reduced stereoacuity of patients with the monofixation syndrome. A better understanding of the mechanisms that fail to fully recover when interocular alignment is re-established during infancy should, in turn, suggest treatments to enhance the post- surgical recovery of binocular vision in strabismic children.
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