Vestibular dysfunction typically disrupts postural stability and gaze stability and underlies patient complaints of vertigo, disequilibrium and oscillopsia. Results from studies on experimental animals and in human beings with unilateral and/or bilateral vestibular deficits suggest that a proper program of exercises enhances compensation. Most studies, however, have focused on the recovery of postural stability and have not addressed the issue of exercise-induced recovery of gaz stability. The few studies that have examined gaze stability in patients with vestibular deficits have shown that the strategy used to compensate for the gaze instability varies from patient to patient. This study will determine the effect of exercises on visual acuity during head movement, as an index of gaze stability, in patients with vestibular deficits. The exercises used in this study will be based on our understanding of vestibular function and adaptation and on the strategies used by patients with bilateral vestibular loss to compensate for the lost vestibular function. We will quantify the effects of exercises on the recovery of visual acuity in patients with unilateral and wit bilateral vestibular loss. The results from the exercised group will be compared with results from a control group to determine the effectiveness of the treatment. The use of a control group will also enable us to determine the time course for the development of the underlying mechanisms for the recovery of gaze stability. The potential underlying mechanisms include VOR, cervico-ocular reflex, central pre-programming, saccadic Iterations, and perceptual learning. We will investigate the role of each of these factors in the recovery of gaze stability in he following manner: VOR will be assessed using the rotary chair test and COR will be assessed using the rotary chair with trunk-on-head rotations. The contribution of central pre-programming will be assessed by comparing dynamic visual acuity during active and passive head rotations. Saccadic alterations will be assessed by comparing saccade amplitud and direction during active and passive high velocity VOR in the dark. The rol of perceptual learning will be assessed by comparing the re- and post-exercise values of dynamic visual acuity measured in a target motion-head still paradigm.
