The vergence eye movement system changes the angle between the eyes during shifts in gaze between far and near objects. This system is responsible for the normal alignment of the visual axes during binocular viewing. Although misalignment of the eyes is the most common human oculomotor complaint, the neurophysiology of the vergence system has received little experimental attention. The proposed project is a comprehensive examination of the neural substrates of the vergence system using electrophysiological, lesion, and anatomical techniques. Monkeys will be trained to maintain precise ocular fixation and to make conjugate and vergence eye movements on demand. The position of each eye in the orbit will be measured using the accurate search coil technique. In addition, the accommodative responses of the animal will be recorded in some experiments. The general goal of the study is to determine the flow of information through midbrain and pontine areas which control vergence eye movements. Specifically, signals related to binocular disparity will be sought in the pretectum and superior colliculus, two areas with both visual and oculomotor connections. Other experiments are designed to determine the sites and actions of cross-linkages between vergence and accommodation. These will look for an accommodative signal on vergence burst cells, and will study the effects of tonic accommodation on the vergence system. Other experiments will seek the neural signals of the hypothesized tonic vergence integrator which is thought to be responsible for the phoria and the phenomenon of prism adaptation. Another study will investigate the mechanism of unequal saccades which may mediate changes in the vergence angle. Lesions will be made at possible sites of a vergence integrator. Results of these experiments may have important implications for clinicians in determining brain sites responsible for acquired disorders of vergence. Finally, an intra-axonal horseradish peroxidase (HRP) experiment will investigate the morphology and connections of cells carrying vergence signals. A detailed body of knowledge about the neuronal mechanisms which underlie disjunctive eye movements and the control of binocular alignment might lead to improved clinical management of strabismus and disorders of binocular vision.
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