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

background and aim: 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. methods: 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. results: 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. conclusion: 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.