Validity and limitation of manual rotational test to detect impaired visual-vestibular interaction due to cerebellar disorders

The aim of this study was to investigate validity and limitation of the novel infrared system to record and analyze horizontal visual-vestibular interaction using whole-body rotation rapidly and conveniently in the routine vestibular clinic. We examined 11 patients with cerebellar dysequilibrium and 25 patients with peripheral dysequilibrium for vestibulo-ocular reflex in darkness (DVOR), visually-enhanced vestibulo-ocular reflex (VEVOR), and fixation suppression of vestibulo-ocular reflex (FSVOR), and compared the results with those of examination for head-fixed smooth pursuit and fixation suppression during caloric stimulation. The manual rotation stimuli were 0.5-0.75 Hz in frequency and 60-90 degrees /s in maximal angular velocity. Gain of vestibulo-ocular reflex in darkness was not significantly correlated with maximal slow phase velocity (MSPV) of caloric-induced nystagmus at that stimulus condition either in patients with peripheral dysequilibrium or in those with cerebellar dysequilibrium. An index for fixation suppression of vestibulo-ocular reflex during rotation stimulus was significantly lower in patients with cerebellar dysequilibrium than in normal control subjects and those with peripheral dysequilibrium. On the other hand, there was no significant difference among the two disease groups and the normal control group in gain of visually-enhanced vestibulo-ocular reflex. In about a half of patients with cerebellar dysequilibrium, measured smooth pursuit gain was lower than estimated smooth pursuit gain calculated based on a simple superposition theory of vestibulo-ocular reflex and smooth pursuit. Testing fixation suppression using the present system is an unusually convenient tool for detection of cerebellar dysequilibrium.