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.<br />