Eye movements induced by lateral tilt and testing of otolithic function.

In the last few years, we have studied ocular reflexes caused by tilting stimulations in test subjects placed in an upright sitting position on a chair apparatus which tilts continuously. In healthy persons, a weak nystagmus can be observed, and involves a nystagmus of minor amplitude and showing a small number of beats. The actual incidence of nystagmus in the younger group was minimal, but it tended to increase with age. This occurrence is considered to be due to age-related degeneration of the otolithic organ. Patients with vertigo and/or dizziness clearly develop nystagmus. These responses are classified as follows: type I is of fixed direction; type II is of changed direction; and type III is a combination of the first and second types. Among the peripheral vestibular disorders, particularly involving those patients with benign paroxysmal positional vertigo, a nystagmus of changed direction was found. This type was rarely seen in patients with other vestibular disorders, but was a common occurrence in healthy individuals who readily experienced motion sickness. These observations have led us to conclude that patients with benign paroxysmal positional vertigo have definite reactions which are similar to those of individuals with motion sickness, and that such depends on the susceptibility of the otolithic organs.