Abstract
In the head-up position, horizontal head rotation stimulated the horizontal canal which causes the horizontal vestibuloocular reflex (HVOR). In the supine position, vertical rotation stimulates both the canal and the otolith organs, which causes the vertical vestibulo-ocular reflex (VVOR). The dynamic otolith response was then studied by comparing these two types of harmonic rotation in 19 normal adults. Using a static analysis of variance (ANOVA), a significant difference was found to exist between the HVOR and the VVOR (p>0,05). The VVOR indicates a higher gain in the lower frequency such as 0.17Hz, and a higher phase lag in the higher frequencies such as 0.67 and 1.0Hz. The dynamic otolith response is characterized by a so-called low pass filter, which suggests that the otolith organs support visual fixation while the head movements in lower frequencies decrease the canal function. At VVOR no significant difference was seen between the supine and prone positions, and thus the various outputs of the otolith ocular reflex may not affect the in-put phase. Based on the findings of this examination for the patients with 4 acoustic tumors who demonstrated complete canal palsy, a unilateral otolithic lesion does not alway cause decrease in gain of the otolith ocular reflex. In the 6 benign paroxysmal positional vertigo (BPPV) patients, a variable value of the gain was observed which may have been caused by some otolithic lesion.
