Presence of corrective saccades in patients with normal vestibulo-ocular reflex gain in video head impulse test

Abstract

BackgroundThe video head impulse test (vHIT) is a valuable clinical tool that can help identify dysfunction of the semicircular canals. While in cases with semicircular canal dysfunction, both decreased vestibulo-ocular reflex (VOR) gain and corrective saccades (CS) are usually observed, there are cases which show CS despite normal VOR gain in vHIT.ObjectiveThis study aimed to investigate the clinical characteristics of patients who showed CS with normal VOR gain in vHIT.Materials and methodsAmong 390 patients who underwent vHIT, 51 patients (20 males and 31 females, age 31–87 years, average 61.3 years old) who showed CS with normal VOR gain unilaterally during horizontal vHIT were included. All patients had normal vHIT (normal VOR gain and absent CS) on the contralateral side.The VOR gain of vHIT, the maximum slow phase velocity in the caloric test, and the amplitude of cervical and ocular vestibular evoked myogenic potentials (cVEMPs and oVEMPs) were analyzed.ResultsThe VOR gain on the affected side (0.95 ± 0.08) was significantly smaller than that on the contralateral side (1.03 ± 0.13) in horizontal vHIT (p < 0.001). The maximum slow phase velocity in the caloric test on the affected side (17.9 ± 17.8 degrees/s) was significantly smaller than that on the contralateral side (21.3 ± 16.6 degrees/s, p = 0.020). There were no significant differences in the amplitude of cVEMPs or oVEMPs between the affected side and the contralateral side (p = 0.096 for cVEMP; p = 0.770 for oVEMP).ConclusionThe side that showed CS with normal VOR gain in horizontal vHIT showed significantly smaller VOR gain as well as smaller caloric responses compared to the contralateral side. Having CS with normal VOR gain could be a sensitive indicator of mild dysfunction of the semicircular canals.

Vestibular function in cases of posterior semicircular canal canalolithiasis and cupulolithiasis

“…However, other studies have suggested that the presence of free otoliths can affect the results of vHIT ( 4 , 14 , 15 ). In this study, most of the abnormal vHITs of BPPV were normal gain with saccades, which can be considered as a relatively light degree of semicircular canal injury ( 8 , 16 , 17 ). Comparing the proportion of saccades between groups, only the proportion of HC saccades in the pc-ca group was higher than that in the control group, and there was no difference between the healthy side and the affected side within the group, which also suggested that there is a lack of correlation between abnormal vHIT and the responsible semi-regulation of bppv.…”

“…The following conditions are considered abnormal in vHIT: (1) horizontal semicircular gain <0.8, vertical semicircular gain <0.7 ( 6 ), accompanied by CS. (2) normal gain, with CS in more than 50% of trials, i.e., the ratio of CS is over 50% ( 7 , 8 ).…”

Suppression head impulse test in children—experiences in a tertiary paediatric vestibular centre

“…Intuitively, it can be inferred that the amplitude of the compensatory overt saccade (i.e., the saccadic velocity) is proportional to the degree of weakness of the VOR, i.e., more the weakness, more is the amplitude of the saccade ( 4 ). Furthermore, it has emerged that in compensating vestibular weakness, the VOR gain might recover without saccades ( 5 ), but saccades may also persist ( 6 ) due to prolonged central adjustment regulating mechanisms.…”