Application of the Video Head Impulse Test to Detect Vertical Semicircular Canal Dysfunction

Objective The video head impulse test (vHIT) is a useful clinical tool to detect semicircular canal dysfunction. However, so far, vHIT has been limited to measurement of the function of the horizontal semicircular canals. The goal of this study was to determine if vHIT can detect vertical semicircular canal dysfunction. Study Design Horizontal and vertical eye movements were recorded in response to abrupt, passive, unpredictable head turns (head impulses) in the planes of the vertical semicircular canals by high-speed video (250-Hz sampling rate) together with measures of the head movement. Head impulses were delivered diagonally in the plane of the vertical semicircular canals, whereas gaze was directed along the same plane. Patients with known vestibular loss as shown by previous scleral search coil recording were tested to identify if the vHIT testing could detect the loss. Results The results of patients with unilateral, bilateral, and individual semicircular canal dysfunction were compared with the results of a healthy control subject. The patient with bilateral vestibular loss had no compensatory slow eye movements in any direction. The patient with unilateral vestibular loss showed reduced response for head impulses activating the canals in their affected right ear (right anterior, right posterior, and right horizontal head impulses). The patient with isolated canal loss showed reduced response for head impulses activating the affected right posterior canal. Conclusion vHIT detects peripheral deficits of both vertical and horizontal semicircular canal function and is a new tool for measuring dysfunction of individual semicircular canals in vestibular patients.