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.
Highlights
The vestibulo-ocular reflex (VOR) has an important function in stabilizing gaze, i.e., keeping the visual target on the fovea during movements of the head to maintain visual acuity [1]
The total unilateral vestibular loss was confirmed by bi-thermal caloric tests, video head-impulse test of all six semi-circular canals and cervical vestibular evoked myogenic potentials
We considered the homogeneity of the group of importance in order to elucidate whether active and passive head impulses differ, both in ocular responses as well as in dynamic visual acuity
Summary
The vestibulo-ocular reflex (VOR) has an important function in stabilizing gaze, i.e., keeping the visual target on the fovea during movements of the head to maintain visual acuity [1]. After a chronic unilateral vestibular loss (uVL), the reflex is impaired and can clinically be tested with the head-impulse test (HIT) This bedside test is quick and easy to perform and consists of a quick low amplitude rotation of the patient’s head, stimulating the semi-circular canals in the plane of the movement. Due to central vestibular compensation the corrective eyesaccade does not always follow after the head movement but can start while the head is still moving. Such a saccade is impossible to detect by the observer [3] but can be recorded with search coils or video-oculography [1, 4]. 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 not being proportionate to symptoms and distresses of the patients
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
