The objective of this research is to learn more about the mechanisms underlying both normal eye movement control and human oculomotor disorders. The research strategy is to make quantitative measurements of oculomotor function in both humans and monkeys and to use systems approaches to interpret findings. The latest techniques for measuring and analyzing eye motion around all three axes and imaging the eye muscles will be used. The focus is on mechanisms that maintain oculomotor accuracy with emphasis on binocularity and the problem of acquired paralytic strabismus. The study of adaptive mechanisms will be emphasized - specifically the capability to maintain eye alignment around all axes (horizontal, vertical, torsion) of eye rotation during steady fixation and during eye movements. The superior oblique eye muscle palsy model will be used 1) to understand better the mechanical properties of orbital structures and the central innervation necessary to move the eyes rapidly and hold them steady during fixation and 2) to investigate adaptation to vertical and torsional misalignment. The role of ocular proprioception and the patterns of monocular versus binocular visual inputs in the immediate and long-term adaptive control of these mechanisms will be explored in detail since preliminary findings have shown surprising and counterintuitive changes in eye alignment related to patching after onset of a paralytic strabismus. The effects of surgical correction of experimentally-induced trochlear nerve palsies will also be studied and compared with results of corrective surgery in humans with acquired superior oblique palsy. Parallel and complementary human and monkey experiments are proposed. These results will provide new information about adaptive control of eye alignment relative to strabismus and have the potential to alter clinical practice related to strabismus treatment. The findings will be particularly relevant to the important clinical ophthalmologic problem of long-term increases in ocular misalignment with the increasingly bothersome double vision that so commonly plagues patients with strabismus, and the all too frequent need for multiple surgical procedures for strabismus.