Increased retinal image velocity after vestibular lesion.

The vestibulo-ocular reflex stabilizes gaze during head movements by producing compensatory eye movements. Retinal image velocity (RIV) is defined as the difference between the eye and head velocities. The RIV of 20 vestibular schwannoma (VS) patients and 17 healthy controls was measured with a head autorotation test. The head autorotation test had a sensitivity of 80% and a specificity of 88%. The mean RIV (degree/second) +/- 95% confidence intervals of the VS patients in the 5 frequency bands of 1 to 5 Hz was respectively 4.8 (4.2 to 5.5), 11.5 (8.6 to 14.4), 21.7 (15.5 to 27.9), 25.2 (17.1 to 33.4), and 26.1 (13.1 to 39.1). The RIV of the VS patients was asymmetrically larger on the operated side (P<0.05) in the frequency band of 1 Hz. The mean RIV was significantly (P<0.05) larger in the VS patients than in the controls in the frequency bands of 1 to 4 Hz. The vestibulo-ocular reflex is inaccurate after VS surgery; but the inaccuracy may not lead to the occurrence of any symptoms.