Impulsive testing of semicircular-canal function using video-oculography.

The head impulse test (HIT) is a safe, quick way of assessing horizontal semicircular-canal function in patients with peripheral vestibular loss. At the bedside, the clinician identifies "overt" catch-up saccades back to the target after brisk passive head rotation as an indirect sign of canal paresis. However, saccades during head rotation ("covert" saccades) may not be detectable by the naked eye, and so lead to incorrect diagnosis. Up to now, the scleral search coil technique has been the standard for HIT measurement, but that technique is not practical for routine diagnostic use. A new lightweight, nonslip, high-speed video-oculography system (vHIT) that measures eye velocity during horizontal head impulses has been developed. This system is easy to use in a clinical setting, provides an objective measure of the vestibulo-ocular reflex (VOR), and detects both overt and covert catch-up saccades in patients with vestibular loss.