Quantification of slow compensatory eye movements in patients with bilateral vestibular loss. A study with a broad frequency-band rotatory test.

Seven patients with bilateral vestibular dysfunction were investigated with a new broad frequency oscillatory test. The vestibular stimulation was of two types: a pseudo-random oscillation in the frequency range 0.5-4 Hz and a sinusoidal frequency sweep from 0.5 to 3.5 Hz. Compensatory eye movements were recorded by EOG. Gain and phase values between eye and head movements were extracted using power spectral analysis technique. Two different visual conditions were used: 1) fixating a stationary target and /) fixating a moving target (visual suppression test). At high frequencies all patients showed a reduced VOR gain compared to normal subjects. At low frequencies gain values were close to normal when using a predictable (sinusoidal) stimulation. With a non-predictable (pseudo-random) stimulation gain values were significantly reduced even at low frequencies. The patients with the most severe loss showed a phase lag at higher frequencies (condition 1). The results in the oscillatory test were compared to subjective symptoms and caloric responses. The new test appears to be better suited to assess the vestibular function in patients with suspected bilateral vestibular loss than the caloric test or other traditional procedures.