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The vertical linear vestibulo-ocular reflex in patients with a hyperactive response during horizontal angular acceleration.
OBJECTIVE: In clinical routine, some patients show a bilateral hyperactive response of the angular vestibulo-ocular reflex (AVOR). The aim of this prospective study was to determine whether these patients also show hyperactivity of the linear VOR (LVOR).
MATERIAL AND METHODS: In 10 patients with a hyperactive AVOR (total amplitude of post-rotatory nystagmus > 400 degrees per 30 s) and 10 healthy subjects the AVOR (stopped after 180 s of rotation at 90 degrees/s) and vertical LVOR (amplitude 5 cm, frequency 1.2 Hz) were tested with eyes open in the dark. During vertical linear acceleration, each subject was instructed to look at an earth-fixed target and they performed vertical smooth pursuit as stationary observers.
RESULTS: The mean eye velocity of the AVOR was significantly higher in the patients than the healthy subjects (19 vs 5 degrees/s; p = 0.00016). During vertical linear acceleration in darkness (49 vs 23 degrees/s; p = 0.004) and combined maculo-visual stimulation (88 vs 52 degrees/s; p = 0.007) the patients showed a significantly higher mean vertical eye velocity. When vertical smooth pursuit was performed, no significant differences were registered. All 20 subjects showed a significant (p = 0.01) positive Spearmnan correlation (rs = 0.79) between the eye velocities of AVOR and LVOR.
CONCLUSION: Patients with a hyperactive AVOR also showed hyperactivity of the LVOR. Because two different sensory end organs and neuronal pathways are involved in these responses, a central rather than a peripheral vestibular lesion must be held responsible.
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