THE SUBJECTIVE HORIZONTAL IN ECCENTRIC ROTATION INFLUENCED BY PERIPHERAL VESTIBULAR LESION

Peripheral vestibular equilibrium disorders may originate in various p arts of the labyrinth or the vestibular nerve. Traditionally, the func tion of the lateral semicircular canals has been assessed with caloric irrigation, and sometimes falsely been interpreted as a vestibular ne rve lesion. The vertical semicircular canals are not easily assessed. Caloric testing with the head in different positions is not very helpf ul, but the canals may pairwise be tested using specific rotational te chniques. Often the otolithic organs, capable of detecting linear acce leration forces, are forgotten as a source of vertigo and dizziness. W e have implemented horizontal rotatory testing with the subject seated eccentrically facing the direction of rotation as a means of assessin g otolithic function. The subject experiences a lateral tilt and is in structed in darkness to put a short light bar in the position he think s a water surface would have, which is identical to his perceived tilt . In 39 normal subjects, a theoretical tilt of 24 degrees was estimate d as approximately 19.5 degrees, and the standard deviation was 6 degr ees. A side difference index was proposed to be normal if below 25%. T he preliminary findings in a few patients with known labyrinthine lesi ons are presented. We propose that otolithic as well as lateral semici rcular canal functions are useful to monitor in patients with suspecte d peripheral equilibrium disorders.