Relative roles of luminance and fixation in inducing dissociated vertical divergence.

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We evaluated the roles of luminance and fixation in the pathophysiology of dissociated vertical divergence (DVD). Vertical eye position was measured in 6 subjects with DVD (ages 11-47 years, 5 females) and 6 controls (ages 16-40 years, 5 females) using video-oculography (VOG) under conditions of change in fixation and luminance. Subjects with DVD showed the following VOG responses. When fixation was precluded with a translucent filter and bright light was shone into one eye to produce a marked binocular luminance disparity, we found some subjects had a small induced vertical divergence causing the illuminated eye to be lower than the nonilluminated eye (mean -1.6° ± 1.5°, P = 0.06 compared to no vertical divergence using the signed rank test). When fixation was precluded with a translucent filter, while alternate occlusion produced a mild binocular luminance disparity, we found a smaller vertical divergence of the eyes that was not statistically significant (1.2° ± 2.1°, P = 0.3). When alternate occlusion produced reversal of monocular fixation in the dark (with essentially no change in peripheral luminance disparity), there was a significant vertical divergence movement causing the covered eye to be relatively higher than the uncovered eye (7.2° ± 3.1°, P = 0.03). The amplitude of this vertical divergence was similar to that measured under conditions of alternate occlusion in a lighted room (where there also was a significant average relative upward movement of the covered eye of 8.1° ± 2.9°, P = 0.03). Control subjects showed no vertical divergence under any testing conditions. Dissociated vertical divergence is mediated primarily by changes in fixation and only to a minor degree by binocular luminance disparity.