Vestibulopathy With Vestibulo Ocular Reflex (VOR) Gain Deficit - Characteristics of Overt and Covert Saccadic Eye Movements Measured by the Video Head Impulse Test (vHIT)

The vestibular system receives and conveys information about head motion in space, and is the main human sensory system dedicated to detecting self-motion.The vestibular system plays a crucial role in static and dynamic balance control, stabilizing the head and trunk, especially on unstable surfaces . In terms of postural control and falls, the literature describes a direct association between VOR deficits, gait instability, and falls.The "gain" of the VOR is defined as the change in the eye angle divided by the change in the head angle during the head turn. Under ideal conditions, the gain of the rotational VOR is 1.0, meaning there is a compensatory eye velocity equal to the head velocity and in the opposite direction. In case of a positive vHIT, the VOR gain is decreased and refixating saccades are observed. The video Head Impulse Test measures eye velocity during head rotation. Instant feedback about every single head impulse allows the examiner to apply a set of standardized graded impulses. The system is easy to use in a clinical setting, provides an objective measure of the VOR, and detects both overt and covert catch-up saccades in patients with vestibular loss. Measurements are quick and noninvasive, and the automated analysis software provides instant results.