Evaluation of the vestibulo-ocular reflex using sinusoidal off-vertical axis rotation in patients with canal paresis

The vestibulo-ocular reflex (VOR) was studied to determine the utility of off-vertical axis rotation (OVAR) in evaluating vestibular function in patients with canal paresis (CP). Our goal was to determine whether there is any correlation between caloric responses and sinusoidal rotatory responses.

Subjects were rotated in a sinusoidal pattern with eyes open in complete darkness. Frequencies of 0.4 and 0.8Hz with a maximum angular velocity of 60°/s at either earth-vertical axis rotation (EVAR) or OVAR were used.

Twenty-three control subjects and 21 patients with CP were investigated. Results showed that (1) the VOR gain difference between EVAR and OVAR in the CP patients was not significant at 0.4Hz and at 0.8Hz; (2) the gain during 0.4Hz EVAR was less in the bilateral CP patients compared to controls; and (3) the VOR gain of the affected side at 0.8Hz was significantly less during OVAR than during EVAR.

We concluded that the absence or reduction of caloric responses does not indicate the absence of vestibular function. In addition, separation analysis of the VOR gain of affected and intact sides is useful for evaluating laterality of otolith function in patients with CP.