Effects of parameters of video head impulse testing on visually enhanced vestibulo-ocular reflex and vestibulo-ocular reflex suppression

A New Suppression Index Calculation Using the Visually Enhanced Vestibulo-Ocular Reflex and Vestibulo-Ocular Reflex Suppression Paradigms in the Video Head Impulse Test

The aim of this study is to calculate the gains of the quantified visually enhanced vestibulo-ocular reflex (qVVOR) and the quantified vestibulo-ocular reflex suppression (qVORS), using a specific system to generate a visual suppression index (SI) in healthy subjects obtained through the gains of qVVOR and qVORS, and to determine the normal values of the index, as well as the influence of age and sex variables on the SI.

METHODS

This prospective observational clinical study includes 83 healthy subjects who underwent the head impulse and suppression tests (HIMP and SHIMP, respectively), qVVOR, and qVORS tests, all of the vHIT. The sinusoidal tests (qVVOR and qVORS) were conducted at an intended frequency of 0.75 Hz. The gains of these tests were calculated using a system specifically designed for this purpose. A formula for the SI was established using a ratio of the gains from these tests. Two SI values are presented: unilateral, distinct for each direction of head movement, and bilateral, representing the suppression of both sides simultaneously.

RESULTS

Mean gains for the qVVORs were 0.981 ± 0.070 and 0.978 ± 0.077 for the rightwards and leftwards qVVORs, respectively. The gains for the suppressed tests were 0.334 ± 0.112 and 0.353 ± 0.110 for the rightwards and leftwards qVORSs, respectively. A difference of 0.05 Hz was observed between the expected (0.75 Hz) and the obtained frequency of head movement, which is statistically significant (p < 0.001). The SI was 0.342 ± 0.118 for the right side (right SI) and 0.363 ± 0.117 for the left side (left SI). The bilateral SI had a mean value of 0.295 ± 0.104. No significant differences in the SI were noted according to the subject's age. The SI for women was lower than in the case of males.

CONCLUSIONS

The VVOR/VORS quantification algorithm allows for the reliable calculation of the numerical gain of qVVOR and qVORS with mathematical soundness and consistency of results. Our data support the use of a single or specific measure for direction of head movement; although significant differences exist, these differences are not clinically relevant.

Insights Into Vestibulo-Ocular Reflex Artifacts: A Narrative Review of the Video Head Impulse Test (vHIT)

Video head impulse test (vHIT) artifacts are defined as spurious elements or disturbances in the recorded data that deviate from the true vestibulo-ocular reflex response. These artifacts can arise from various sources, encompassing technological limitations, patient-specific factors, or environmental influences, introducing inaccuracies in vHIT outcomes. The absence of standardized criteria for artifact identification leads to methodological heterogeneity. This narrative review aims to comprehensively examine the challenges posed by artifacts in the vHIT. By surveying existing literature, the review seeks to elucidate the multifaceted nature of artifacts arising from technological, patient-related, evaluator-related, and environmental factors.

A New Method for Gain Calculation in Quantified Visuo-vestibular Interaction Test

OBJECTIVE

To develop a new method to quantify visually-enhanced vestibulo-ocular reflex (VVOR) gain, in patients with vestibular function loss, that is mathematically suitable given the nature of the test, and determine the reliability of the method by comparing results with those of the gold standard, the video head impulse test (vHIT).

MATERIALS AND METHODS

We developed a new method for VVOR gain quantification and conducted a cross-sectional study in patients diagnosed with vestibular function loss and controls, all participants undergoing both a VVOR test and a vHIT. We measured VVOR gain with three different methods: area under the curve (AUC), slope regression, and a Fourier method (VVORAUC , VVORSP , and VVORFR , respectively); and compared these gain values with vHIT gain calculated using the AUC method.

RESULTS

Overall, 111 patients were included: 29 healthy subjects and 82 patients with vestibular function loss. Intraclass correlation coefficients (ICC(1,1)) between gain from the gold standard and each of the VVOR gain methods were: 0.68 (CI: 0.61-0.75) for VVORAUC , 0.66 (CI: 0.58-0.73) for VVORSP and 0.71 (CI: 0.64-0.77) for VVORFR . No interference was found between VVOR gain calculation methods and potentially influential variables considered (p ≥ 0.98).

CONCLUSION

The new method for quantifying VVOR gain showed good concordance with the vHIT method.

LEVEL OF EVIDENCE

2: Individual cross-sectional studies with consistently applied reference standard and blinding (Diagnosis) Laryngoscope, 133:3554-3563, 2023.

Synchronized refixation saccades in enhanced VVOR test. A new application for PR score

OBJECTIVE

Main objectives for this study were to develop a quantification method to obtain a Perez-Rey (PR) score adapted to the VVOR test and to evaluate the correlation of the PR score obtained with quantified VVOR with the PR score of the vHIT test.

METHODS

A new PR score calculation method for quantified VVOR test was developed using the MATLAB computational software based on saccadic response time latency variability between each head oscillation cycle of the VVOR test. Retrospective correlation between PR scores in VVOR and vHIT tests, performed in the same vHIT testing session for patients with vestibular neuritis and vestibular neurectomy, was performed to correlate new PR (VVOR) score with the classic PR (vHIT) score.

RESULTS

Thirty patients were included: 11 post-neurectomy and 19 subacute vestibular neuritis. Pearson's correlation coefficient (R2) for the overall sample was 0.92 (p < 0.001) and 95% confidence interval was 0.85 -0.96. In the linear mixed-effects statistical model developed, only PRVHIT and PRVVOR scores showed statistical association in Wald X2 test (p = 0.008).

CONCLUSION

The new developed PR score for synchronization measurement of saccadic responses in VVOR testing is a valid method that outputs synchronization values and highly correlates with PR score in vHIT test.

Enhanced Eye Velocity With Backup Saccades in vHIT Tests of a Menière Disease Patient: A Case Report

Reduced eye velocity and overt or covert compensatory saccades during horizontal head impulse testing are the signs of reduced vestibular function. However, here we report the unusual case of a patient who had enhanced eye velocity during horizontal head impulses followed by a corrective saccade. We term this saccade a "backup saccade" because it acts to compensate for the gaze position error caused by the enhanced velocity (and enhanced VOR gain) and acts to return gaze directly to the fixation target as shown by eye position records. We distinguish backup saccades from overt or covert compensatory saccades or the anticompensatory quick eye movement (ACQEM) of Heuberger et al. (1) ACQEMs are anticompensatory in that they are in the same direction as head velocity and so, act to take gaze off the target and thus require later compensatory (overt) saccades to return gaze to the target. Neither of these responses were found in this patient. The patient here was diagnosed with unilateral definite Meniere's disease (MD) on the right and had enhanced VOR (gain of 1.17) for rightward head impulses followed by backup saccades. For leftwards head impulses eye velocity and VOR gain were in the normal range (VOR gain of 0.89). As further confirmation, testing with 1.84 Hz horizontal sinusoidal head movements in the visual-vestibular (VVOR) paradigm also showed these backup saccades for rightwards head turns but normal slow phase eye velocity responses without backup saccades for leftwards had turns. This evidence shows that backup saccades can be observed in some MD patients who show enhanced eye velocity responses during vHIT and that these backup saccades act to correct for gaze position error caused by the enhanced eye velocity during the head impulse and so have a compensatory effect on gaze stabilization.