The subjective visual vertical as a clinical parameter of vestibular function in peripheral vestibular diseases.

The subjective visual vertical, SV, was measured in the upright and side positions in 25 normal subjects and in 73 patients with various peripheral vestibular disorders. Significant deviations of SV (toward the affected ear) were found in 100% of the patients with vestibular nerve section and with Ramsay Hunt syndrome, in 89% of the patients with vestibular neuritis, and in 0% of the patients with benign paroxysmal positional vertigo. The deviation of SV gradually disappeared within a few weeks of the onset of the disease in all patients except in those with total VIIth nerve resection. SV is a parameter of tonic afferent differences between the two labyrinths similar to vestibular spontaneous nystagmus but is mediated by other parts of the inner ear (probably the otolith organs) and thus provides additional information on the labyrinthine function. SV measured in 90 degrees side positions, however, did not reveal asymmetric vestibular sensitivity, which is in contrast to SV tested during eccentric rotation in patients after vestibular neurectomy.