Functional Head Impulse Testing Might Be Useful for Assessing Vestibular Compensation After Unilateral Vestibular Loss

Abstract

Background: Loss of the vestibulo-ocular reflex (VOR) affects visual acuity during head movements. Previous studies have shown that compensatory eye-saccades improve visual acuity and that the timing of the saccade is important. Most of the tests involved in testing VOR are made with passive head movement, that do not necessarily reflect the activities of daily living and thus not being proportionate to symptoms and distresses of the patients.Objective: To examine differences between active (self-generated) or passive (imposed by the examiner) head rotations while trying to maintain visual focus on a target.Method: Nine subjects with unilateral total vestibular loss were recruited (4 men and 5 women, mean age 47) and tested with video Head Impulse Test (vHIT) and Head Impulse Testing Device-Functional Test (HITD-FT) during passive and active movements while looking at a target. VOR gain, latencies of covert saccades, frequency of covert saccades and visual acuity were measured and analyzed.Results: Active head-impulses toward the lesioned side resulted in better visual acuity (p = 0.002) compared to conventional passive head-impulses and generated eye-saccades with significantly shorter latencies (p = 0.004). Active movements to the lesioned side generated dynamic visual acuities that were as good as when testing the intact side.Conclusion: Actively generated head impulses resulted in normal dynamic visual acuity, even when performed toward the side of total vestibular loss. This might be attributed to the appearance of short-latency covert saccades. The results show a strong relationship between self-generated movements, latencies of covert saccades and outcome in HITD-FT, i.e., a better dynamic visual function with less retinal slip which is the main function of the VOR. The method of active HITD-FT might be valuable in assessing vestibular compensation and monitoring ongoing vestibular rehabilitation.

Improvement After Vestibular Rehabilitation Not Explained by Improved Passive VOR Gain

“…not). Prior studies have shown that the frequency and velocity of CS do change over time with VPT (13,14,(40)(41)(42). Together, these data suggest that the current standard of care prescribing gaze stability exercises for VPT (sinusoidal head rotation) may not be restoring slow phase (i.e., vestibular) eye velocity during passive head rotation, but instead lead to an altered CS velocity putatively to improve gaze stability.…”

Head impulse compensatory saccades: Visual dependence is most evident in bilateral vestibular loss

“…After VOR loss short latency compensatory saccades can improve visual acuity [79][80][81][82], so the VOR and saccades provide complimentary and differential roles in gaze by generating compensatory velocity and position changes respectively [7,53]. The neuro-physiology of saccade modification after loss of the VOR could be explained by saccade motor learning paradigms, in man [83,84] and monkey [85,86], by which saccade characteristics are modulated over time by visual error feedback loops through the super colliculus and cerebellum [87][88][89][90][91][92].…”

Co-morbidities to Vestibular Impairments—Some Concomitant Disorders in Young and Older Adults

“…Baseline information about age, gender, illnesses, and medication was self-reported. Vestibular function was assessed by a specialist in neuro-otology (author MM) with the headshake test, Dix-Hallpike test ( 28 ), and head impulse test ( 29 , 30 ). The Timed up and Go test (TUG), Timed up and Go test with a cognitive task (TUGcog), and Timed Up and Go test with a manual task (TUGman) ( 31 ) were used for measuring balance.…”

“…The test was repeated randomly to each side. The test was considered pathologic if the tested person was not able to keep their eyes focused on the target, but responded with a corrective or compensatory saccade ( 29 , 30 ).…”