Principle and practical aspects of recording video head impulse test system

Abstract

　The head impulse test (HIT), which was first introduced by Halmagyi and Curthoys in 1988, is a clinical test to assess the vestibular function by brisk, passive rotation of the head in the plane of the parallel semicircular canal pairs. In healthy subjects, the vestibulo-ocular reflex (VOR) stabilizes the gaze in space by inducing equal eye rotation in the opposite direction to compensate for the head rotations. On the other hand, in patients with vestibular dysfunction, the eyes move with the head because of insufficient VOR leading to catch-up saccade movements in order to re-fixate on the target. It had been difficult to quantify HIT since a scleral search coil system, which is an expensive, complicated and semi-invasive technique, was necessary to record the HIT. However, a simple video recording method of HIT (vHIT), was introduced by McDougall et al. in 2009, and is now used by many clinics around the world. In this article, I describe 1) the physiological basis of HIT, 2) the method of recording vHIT, 3) the usefulness of vHIT in clinical practice, and 3) the pitfalls in recording and interpreting vHIT.