Abstract
The contributions of semicircle-canal versus otolith-organ signals to the vestibulo-ocular reflex (VOR) were investigated by providing canal-only (earth vertical axis rotation: EVAR) and canal plus otolith 30-degree nose-down conditions (off-vertical axis rotation: OVAR). Horizontal and vertical eye movements were recorded in eight healthy adults, ranging in age from 28 to 40 (mean 29.5), using an infrared video recording system. Stimuli were carried out, sinusoidally, at 0.2 Hz, 0.4 Hz and 0.8 Hz in frequency and 60/s in maximum angular head velocity in both EVAR and OVER. VOR gain at 0.2 Hz showed 0.84±0.31 (mean ±S.D.) in EVAR and 0.77±0.21 in OVAR, percent gain change of which resulted in -2.6±31.5%. VOR gain at 0.4 Hz was 0.71±0.16 in EVAR and 0.61 ±0.15 in OVAR, and percent gain change was -11.5±52.1%. All subjects showed VOR gain reduction in OVAR at 0.8 Hz (0.73±0.1 in EVAR and 0.55±0.11 in OVAR). Percent gain change was -23.5±12.5%. There was a significant difference of VOR gain between EVAR and OVAR only at 0.8Hz (p<0.05). Furthermore, VOR phase lead was recognized in all subjects only at 0.8 Hz, which showed a significant difference between EVAR (-64.2±18.2 deg.) and OVAR (-99.0±22.8) (p<0.05).
VOR gain reduction and phase lead in OVAR at 0.8 Hz brought about otolith, which was principally the utricle. There has not been the suitable examination to evaluate the otolith function for patients with dizziness because assessment of the otolith function by constant rotation in an off-vertical condition, which has been used so far, gave patients various symptom caused by vestibulo-spinal reflex. It was concluded that the stimulation of 0.8 Hz and 60/s in maximum angular head velocity in sinusoidal OVAR may evaluate the otolith function without discomfort for patients.
