Background: Dissociated vertical divergence (DVD) has been attributed to a human dorsal light reflex that emerges when single binocular vision is precluded in infancy. If this is the case, then DVD should be associated with a subjective sensation of tilt. Methods: Prospective examination of 9 patients with DVD and 9 control subjects to determine whether monocular occlusion and alternate occlusion induces a subjective sensation of visual tilt or body tilt. Results: Alternate occlusion disclosed a tilt in the subjective visual vertical in 8 of the 9 patients with DVD and in none of 9 control subjects. On occlusion of the fixating eye, a vertical pencil positioned in the sagittal plane was perceived as instantaneously tilted, with its upper pole tipped toward the side of the covered eye. This visual tilt was quickly followed by a perceived rotation back to vertical, which coincided with the dorsally directed drift of the covered eye. Conclusion: In patients with DVD, monocular occlusion is associated with a subjective visual tilt that is annulled by a cyclovertical divergence movement of the eyes. This observation supports the notion that DVD is a human dorsal light reflex, which functions to restore vertical visual orientation when unequal binocular visual input evokes a subjective sensation of visual tilt.
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