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.