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

Background: The 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. Objective: This study aimed to investigate the clinical characteristics of patients who showed CS with normal VOR gain in vHIT. Materials and methods: Among 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. Results: The 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). Conclusion: The 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.

Assessment of semicircular canal function in benign paroxysmal positional vertigo using the video head impulse test and caloric test.

Objective: To assess semicircular canal function in benign paroxysmal positional vertigo (BPPV) using the video head impulse test (vHIT) and caloric test. Methods: We retrospectively reviewed 39 patients with idiopathic BPPV who underwent both vHIT and the caloric test. Twenty-one patients had posterior BPPV (p-BPPV) and eighteen had horizontal BPPV (h-BPPV). Vestibulo-ocular reflex (VOR) gain and corrective saccades (CS) were analyzed in vHIT and canal paresis (CP) was calculated in the caloric test. Results: The mean VOR gain of the posterior canal in p-BPPV was 0.75 ± 0.28 on the affected side, which was significantly smaller than that on the contralateral side (0.93 ± 0.24, p = .00738). On the other hand, there were no significant differences in the VOR gain of the horizontal canal in h-BPPV between the affected and the contralateral sides (p = .769). The rates of the presence of CS were not significantly different between the affected canal and the contralateral canal either in p-BPPV (p = .111) or h-BPPV (p = .0599). The mean CP value in h-BPPV patients (43.5 ± 31.3%) was significantly higher than that in p-BPPV patients (22.2 ± 22.9%; p = .0184). Conclusion: The VOR gain of vHIT in the affected canal was significantly smaller than that in the contralateral canal in p-BPPV, but not in h-BPPV. The caloric responses of the affected canal are reduced to a significantly larger extent in h-BPPV compared to p-BPPV. These results suggest that BPPV affects the semicircular canal function differently depending on which semicircular canal is involved.

Quantitative Analysis of Saccade Gain in Video Head Impulse Testing.

OBJECTIVE: To quantitatively analyze corrective saccade (CS) gain and further characterize the specific relationship between vestibulo-ocular reflex (VOR) gain and CS gain in patients with vestibular loss and healthy controls. STUDY DESIGN: Prospective combined with retrospective study. SETTING: Affiliated Sixth People's Hospital, Shanghai Jiao Tong University. SUBJECTS AND METHODS: Forty patients with unilateral vestibular loss and 40 participants with normal vestibular function were subjected to video head impulse testing (vHIT). The analysis of the horizontal semicircular canal VOR and CS gains was based on individual head impulses. RESULTS: The patient group had significantly higher CS gain and lower VOR gain than the control group (P < .001). While there was no significant correlation between VOR and CS gains in the control group after adjusting for age and sex (P = .689), VOR gain negatively correlated with CS gain in the patient group (r = -0.853, P < .001). The specific relationship between VOR and CS gains was characterized as y = -1.17x + 1.12 (x: VOR gain, y: CS gain; r2 = 0.732, P < .001) in the patient group. CONCLUSIONS: In healthy participants, CS was not correlated with VOR gain, suggesting that CS is not due to VOR hypofunction. In patients with unilateral vestibular loss, CS was closely associated with VOR gain and can almost correct gaze position errors required for visual stabilization. CS gain could be an important indicator to diagnose vestibular loss and help physicians identify abnormal vHIT curves caused by artifacts and irregular practices.

Clinical Usefulness of Video Head Impulse Test-Comparison of Bithermal Caloric Test and Bedside Head Impulse Test / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: Video head impulse test system (vHIT) is an easy-to-use test and there are numerous studies showing its efficacy. The aim of the study was to evaluate the clinical usefulness of vHIT as an initial test in determining vestibular hypofunction in patients with dizziness. SUBJECTS AND METHOD: The study recruited 103 outpatients who visited our ear clinic with dizziness. We performed both bedside head impulse test (bHIT), vHIT and bithermal caloric tests for 103 patients. Both bHIT and vHIT were consecutively performed in each subject on the same day by the same examiner. RESULTS: The sensitivity of bHIT and vHIT was determined based on the bithermal caloric test results, which showed that vHIT was more sensitive than bHIT. There was a significant negative correlation between vHIT gain and canal paresis (p < 0.05). Results of some patients indicated dissociation between vHIT and caloric test. CONCLUSION: T here is a significant correlation between the results of vHIT and caloric test. Although vHIT does not replace the caloric test, it would be useful to evaluate the initial vestibular loss in patients with dizziness.

Revisiting corrective saccades: role of visual feedback.

To clarify the role of visual feedback in the generation of corrective movements after inaccurate primary saccades, we used a visually-triggered saccade task in which we varied how long the target was visible. The target was on for only 100ms (OFF100ms), on until the start of the primary saccade (OFFonset) or on for 2s (ON). We found that the tolerance for the post-saccadic error was small (-2%) with a visual signal (ON) but greater (-6%) without visual feedback (OFF100ms). Saccades with an error of -10%, however, were likely to be followed by corrective saccades regardless of whether or not visual feedback was present. Corrective saccades were generally generated earlier when visual error information was available; their latency was related to the size of the error. The LATER (Linear Approach to Threshold with Ergodic Rate) model analysis also showed a comparable small population of short latency corrective saccades irrespective of the target visibility. Finally, we found, in the absence of visual feedback, the accuracy of corrective saccades across subjects was related to the latency of the primary saccade. Our findings provide new insights into the mechanisms underlying the programming of corrective saccades: (1) the preparation of corrective saccades begins along with the preparation of the primary saccades, (2) the accuracy of corrective saccades depends on the reaction time of the primary saccades and (3) if visual feedback is available after the initiation of the primary saccade, the prepared correction can be updated.