Active Head Oscillation Vestibular Testing with a Terrestrial Magnetism Sensor

The purpose of this study was to determine reference intervals of the characteristics of the visual-vestibuloocular reflex in healthy subjects.Head and eye movements during active head oscillation were examined. The head was oscillated in the horizontal (H) and vertical (V) planes, and head movements were recorded with a terrestrial magnetism sensor. Eye movements were recorded by an elec-tronystagmographic technique. The examination was performed under the following 2 conditions: a) visual fixation on an earth-fixed target in the light (test for visual-vestibuloocular reflex, VVOR), and b) image fixation on an earth-fixed target in the dark (test for vestibuloocular reflex, VOR). The data were stored on a floppy disc in a microcomputer. From the stored data, transfer function was calculated with head movements as input and eye movements as output in a specially designed program.Five healthy adults were tested. From the data obtained, the mean and the standard deviation were calculated.Resultsa) VVOR test:(1)The breakpoint frequencies were 3.3±0.5 Hz (H) and 2.2±0.4 Hz (V).(2)The frequency ranges of 180°±10° were 0.2±0.1-0.9±0.2 Hz (H) and 0.2±0.2-0.6±0.6 Hz (V).b) VOR test(1)The gains at 0.1 Hz were-5±2 dB (H) and-3±2 dB (V).(2)The slopes of the gain enhancement were 6±2 dB/dec (H) and 4 ± 4 dB/dec (V).(3)The frequency ranges of 180°±10° were 0.1±0.1-0.8±0.2 Hz (H) and 0.2±0.1-0.6±0.4 Hz (V).The mean±the standard deviation×2 are presented as reference intervals.