2020 Volume 79 Issue 1 Pages 4-11
Head impulse test (HIT), first described in 1988 and conducted at the bedside, is a safe and quick way of assessing semicircular canal function in patients with peripheral vestibular loss. This test is practical even in sick patients and needs no equipment. The clinician identifies overt (=visible) catch-up saccades back to the target after passive head rotation as a clinical sign of canal paresis. However, it is known that some patients with absence of vestibular function do not make overt saccades, but instead make covert catch-up saccades during the passive unpredictable head turn, which are extremely difficult for the clinician to detect by the naked eye.
In 2009, a new lightweight, nonslip, high-speed video-oculography system (vHIT; video head impulse test) that measures the eye velocity during head rotations was 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.
To understand the principle of HIT/vHIT, it is very important to understand the physiology of eye movements, especially the VOR and saccades. In this article, the characteristics of HIT/vHIT are discussed, while explaining the physiology of eye movements.
