Clinical significance of the subjective vertical in patients with unilateral vestibular disorders.

The subjective vertical was estimated by using a concentrically movable spotlight-line on a specially devised dome-shaped screen and a controller in patients with unilateral vestibular disorders. The test was performed in a dark room to measure the deviation of the subjective vertical from the true vertical to the earth gravity. The result showed characteristic deviation of the subjective vertical to the affected ear side in most subjects. The relationship between the subjective deviation and body sway was investigated to estimate the clinical significance of the subjective vertical. The locus pattern, area, locus length and the trajectory of head movements while measuring the subjective vertical were recorded. The patterns were centripetal or right-left types, the values of the head movement seemed to be proportional to the magnitude of the subjective vertical. The time course of the subjective vertical depended on the stage of the disorder. Some cases with active vestibular disorders showed directional changes of the subjective vertical deviation depending on the extent of the lesion. The most interesting results were obtained in the relationship between the caloric response and the subjective vertical, suggesting the clinical significance of the subjective vertical in vestibular function.