Phase difference of vestibulo-ocular reflex in head autorotation test.

In the head autorotation test (HART) gain is commonly used to determine the vestibulo-ocular reflex (VOR). The purpose of this work was to evaluate the relevance of phase (the phase difference between the eye and corresponding head movement) in describing the VOR. The phase was determined in 5 frequency bands in both degrees and milliseconds (ms) in 4 groups: 30 healthy adults, 15 elderly subjects, 37 vestibular schwannoma (VS) patients, and 35 Meniere's disease (MD) patients. In healthy adults and in MD patients the phase was close to nil in the frequency bands of 3 and 4 Hz. In elderly subjects phase lead was between 5.0 and 15.5 ms in each frequency band. Patients with VS showed a phase lag of -4.2 to -7.6 ms. The mean phase of the elderly in the frequency band of 3 Hz differed statistically significantly from that of MD and VS patients, and in the frequency band of 4 Hz from that of healthy adults and VS patients. In summary, the elderly had phase lead and VS patients showed increased phase lag in the frequency bands higher than 2 Hz. The phase is useful parameter together with gain in evaluating VOR and it seems to change in aged subjects and in patients with permanent vestibular lesion.