Automated head motion system improves reliability and lessens operator dependence for head impulse testing of vestibular reflexes

Abstract

Deficiency of the eye-stabilizing vestibulo-ocular reflex (VOR) is a defining feature in multiple diseases of the vestibular labyrinth, which comprises the inner ear’s sensors of head rotation, translation and orientation. Diagnosis of these disorders is facilitated by observation and measurement of eye movements during and after head motion. The video head impulse test has recently garnered interest as a clinical diagnostic assessment of vestibular dysfunction. In typical practice, it involves use of video-oculography goggles to measure eye movements while a clinician examiner grasps the subject’s head and manually rotates it left or right at sufficient acceleration to cover ~20 deg over ~150 mS, reaching a peak velocity of >120 deg/S midway through the movement. Manual delivery of head impulses incurs significant trial-by-trial, inter-session and inter-operator variability, which lessens the test’s reliability, efficiency, safety and standardization across testing facilities. We describe application of a novel, compact and portable automated head impulse test (aHIT™) device that delivers highly repeatable head motion stimuli about axes parallel to those of the vestibular labyrinth’s six semicircular canals, with programmable Gaussian and sinusoidal motion profiles at amplitudes, velocities and accelerations sufficient to test VOR function over the spectral range for which the VOR dominates other vision-stabilizing reflexes. We tested the aHIT™ on human subjects and demonstrated its high reproducibility compared to manually delivered head impulses. This device has the potential to be a valuable clinical and research tool for diagnostic evaluation and investigation of the vestibular system.

Continuous vestibular implant stimulation partially restores eye-stabilizing reflexes

“…We measured binocular 3D eye movement responses to prosthetic vestibular stimulation using Labyrinth Devices 3DBinoc video-oculography goggles, which reported 3D angular position for each eye at 100-180 frames/s. We used 3D rotational kinematic transformations to convert data to yaw, LARP, and RALP angular velocity components in semicircular canal coordinates, accounting for canal orientation relative to the HWU sensor and skull using HWU responses to standardized head rotations delivered using a Labyrinth Devices aHIT Automated Head Impulse Test motion system and 3D reconstructions of post-implantation computed tomography scans (44)(45)(46)(47)(48).…”

Quantifying a Learning Curve for Video Head Impulse Test: Pitfalls and Pearls

“…This aHIT device consists of a servomotor assembled with a curved track guided by six bearings, which rotates a mouthpiece. The subject bites onto the mouthpiece covered with a silicon bite splint and as a result the head is moved horizontally in each direction according to predefined head velocity/acceleration profiles (Gaussian, peak angular velocity 150 • /s, peak acceleration 3,000 • /s 2 ) (9).…”

Corrective saccades in acute vestibular neuritis: studying the role of prediction with automated passively induced head impulses

“…Head impulses were performed using an automated device (aHIT™) (25) positioned on a table in front of the seated subject and consisting of a silicone mouthpiece moving on a curved track. Eye and head movements were recorded using an EyeSeeCam TM VOG system with an integrated full inertial measurement unit (IMU) within the VOG infrared camera at a sampling rate of 220Hz.…”

“…The main goal of our study was to determine how the brain estimates head velocity when labyrinthine function is deficient or absent, and in turn, how that information is used to generate corrective saccades. Here, we used an automated high acceleration HIT device (aHIT) (25) to analyze corrective saccades in response to standardized passive head impulses in patients with acute vestibular neuritis. Comparing responses to predictable versus unpredictable head impulses, we measured the latencies of the first corrective saccades and the gaze error at their beginning and end.…”