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

Abstract

The normal vestibulo-ocular reflex (VOR) generates almost perfectly compensatory smooth eye movements during a 'head-impulse' rotation. An imperfect VOR gain provokes additional compensatory saccades to re-acquire an earth-fixed target. In the present study, we investigated vestibular and visual contributions on saccade production. Eye position and velocity during horizontal and vertical canal-plane head-impulses were recorded in the light and dark from 16 controls, 22 subjects after complete surgical unilateral vestibular deafferentation (UVD), eight subjects with idiopathic bilateral vestibular loss (BVL), and one subject after complete bilateral vestibular deafferentation (BVD). When impulses were delivered in the horizontal-canal plane, in complete darkness compared with light, first saccade frequency mean(SEM) reduced from 96.6(1.3)-62.3(8.9) % in BVL but only 98.3(0.6)-92.0 (2.3) % in UVD; saccade amplitudes reduced from 7.0(0.5)-3.6(0.4)˚in BVL but were unchanged 6.2(0.3)-5.5(0.6)˚in UVD. In the dark, saccade latencies were prolonged in lesioned ears, from 168(8.4)-240(24.5) ms in BVL and 177(5.2)-196(5.7) ms in UVD; saccades became less clustered. In BVD, saccades were not completely abolished in the dark, but their amplitudes decreased from 7.3-3.0˚and latencies became more variable. For unlesioned ears (controls and unlesioned ears of UVD), saccade frequency also reduced in the dark, but their small amplitudes slightly increased, while latency and clustering remained unchanged. First and second saccade frequencies were 75.3(4.5) % and 20.3(4.1) %; without visual fixation they dropped to 32.2(5.0) % and 3.8(1.2) %. The VOR gain was affected by vision only in unlesioned ears of UVD; gains for the horizontal-plane rose slightly, and the

Video Head Impulse Test in Darkness, Without Visual Fixation: A Study on Healthy Subjects

“…Several studies that performed HIT in darkness have been conducted (Peng et al 2005;Lehnen et al 2013;Van Nechel et al 2019;Pogson et al 2020). However, they focused on 2019), the mean VOR gain was significantly reduced.…”

“…Several studies that performed HIT in darkness have been conducted (Peng et al 2005; Lehnen et al 2013; Van Nechel et al 2019; Pogson et al 2020). However, they focused on compensatory saccades and centered on vestibular deficits, mainly bilateral vestibular deficits.…”

“…Several studies that aimed to eliminate visual fixation for HIT realization have been previously conducted (Peng et al 2005; Lehnen et al 2013; Van Nechel et al 2019; Pogson et al 2020). However, they focused on the compensatory saccades in vestibular deficits, mainly bilateral vestibular deficits, to demonstrate its visual dependence.…”

Vestibular contributions to the Romberg test: Testing semicircular canal and otolith function

“…The basic vHIT measure is VOR gain, that is, eye velocity divided by head velocity. Catch‐up saccades which compensate for impaired VOR gain are a supplementary measure [47].…”

Diagnosing vestibular hypofunction: an update

“…The accuracy of pupil detection can be affected by incorrect camera adjustment, poor calibration, blinking, eyelashes, narrow eyelids, poor illumination, mascara, spontaneous nystagmus, and goggle slippage. These factors can cause recording artifacts that might not be detected by the software and which could negatively influence the reliability of test outcomes [ 21 – 25 ]. Training of examiners is, therefore, imperative, since it significantly reduces artifacts [ 26 ].…”