Abstract
Visually enhanced vestibulo-ocular reflex (VVOR) is a well-known bedside clinical test to evaluate visuo-vestibular interaction, with clinical applications in patients with neurological and vestibular dysfunctions. Owing to recently developed diagnostic technologies, the possibility to perform an easy and objective measurement of the VVOR has increased, but there is a lack of computational methods designed to obtain an objective VVOR measurement. To develop a method for the assessment of the VVOR to obtain a gain value that compares head and eye velocities and to test this method in patients and healthy subjects. Two computational methods were developed to measure the VVOR test responses: the first method was based on the area under curve of head and eye velocity plots and the second method was based on the slope of the linear regression obtained for head and eye velocity data. VVOR gain and vestibulo-ocular reflex (VOR) gain were analyzed with the data obtained from 35 subjects divided into four groups: healthy (N = 10), unilateral vestibular with vestibular neurectomy (N = 8), bilateral vestibulopathy (N = 12), and cerebellar ataxia, neuropathy, and vestibular areflexia syndrome (CANVAS) (N = 5). Intra-class correlation index for the two developed VVOR analysis methods was 0.99. Statistical differences were obtained by analysis of variance statistical method, comparing the healthy group (VVOR mean gain of 1 ± 0) with all other groups. The CANVAS group exhibited (VVOR mean gain of 0.4 ± 0.1) differences when compared to all other groups. VVOR mean gain for the vestibular bilateral group was 0.8 ± 0.1. VVOR mean gain in the unilateral group was 0.6 ± 0.1, with a Pearson's correlation of 0.52 obtained when VVOR gain was compared to the VOR gain of the operated side. Two computational methods to measure the gain of VVOR were successfully developed. The VVOR gain values appear to objectively characterize the VVOR alteration observed in CANVAS patients, and also distinguish between healthy subjects and patients with some vestibular disorders.
Highlights
In the experimental paradigm where a subject oscillates the head while viewing a static target in a stationary scene, a combination of the vestibulo–ocular reflex (VOR), smooth pursuit (SP), fixation, and the optokinetic reflex (OKN) produces almost perfectly compensatory eye movements to keep the visual target centered and clear [1]
visually enhanced VOR (VVOR) gain and vestibulo–ocular reflex (VOR) gain were analyzed with the data obtained from 35 subjects divided into four groups: healthy (N = 10), unilateral vestibular with vestibular neurectomy (N = 8), bilateral vestibulopathy (N = 12), and cerebellar ataxia, neuropathy, and vestibular areflexia syndrome (CANVAS) (N = 5)
The key factors for developing an automated methodology for VVOR gain measurement were analyzing head and eye movements as a virtually periodic signal and removing the fast phases of nystagmus elicited during testing
Summary
In the experimental paradigm where a subject oscillates the head while viewing a static target in a stationary scene, a combination of the vestibulo–ocular reflex (VOR), smooth pursuit (SP), fixation, and the optokinetic reflex (OKN) produces almost perfectly compensatory eye movements to keep the visual target centered and clear [1]. In the case of an abnormally high VOR gain, backup saccades will move the eye in the direction of head rotation [4]. Bedside testing has offered insights for the evaluation of mixed damage, as seen in cerebellar ataxia, neuropathy, and vestibular areflexia syndrome (CANVAS). In this case, the abnormal VVOR, when performed by an experienced examiner, reflects a deficit of the VOR, OKN, and SP [1, 6, 7]. Enhanced vestibulo–ocular reflex (VVOR) is a well-known bedside clinical test to evaluate visuo–vestibular interaction, with clinical applications in patients with neurological and vestibular dysfunctions. Owing to recently developed diagnostic technologies, the possibility to perform an easy and objective measurement of the VVOR has increased, but there is a lack of computational methods designed to obtain an objective VVOR measurement
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