Normative vestibulo-ocular reflex data in yaw and pitch axes using the video head-impulse test

The video head-impulse test (vHIT) measures the vestibulo-ocular reflex (VOR) driven by each semicircular canal, following high-acceleration head rotations. The main measurable response is the ratio of eye movement velocity to the angular head velocity, which reflects canal function. Although normative data is available for VOR gain, most studies only report horizontal VOR characteristics, ignoring variations in vertical plane VOR gains. The purpose of this study was to establish normative data for future comparisons of vestibulopathy patients.
Vestibulo-ocular reflex gain and refixation saccades were assessed across 50 healthy individuals between the ages of 20 and 64, without any previous or current vestibular disorders, by applying and measuring horizontal and vertical head impulses.
The mean VOR velocity gain was 0.96 (SD=0.11) and 0.93 (SD=0.17) for the horizontal and vertical canals, respectively. The variation of the gain in right anterior/left posterior and left anterior/right posterior movements appeared to be wider than in the laterals, but the results were not influenced by direction (p>0.05). Refixation saccades occurred in 7.2 percent of all impulse trials, with a majority occurring covertly in lateral canals. Unlike saccades (more often observed in subjects older than 50), the VOR velocity gain varied independently of age.
The findings suggest these gain values can be used to determine VOR deficits in patients. vHIT values are affected by different factors, especially in the vertical plane, so further study is needed to confirm normal ranges of vertical vHIT values.