Fixation-suppression of caloric nystagmus in normal subjects

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Effects of ocular fixation upon caloric nystagmus have been used as a routine test. Percentage reduction in slow-phase velocity of caloric nystagmus induced by ocular fixation, however, varies depending upon the test condition employed.<BR>In the present experiment, we standardized the effects of ocular fixation upon caloric nystagmus in 58 normal individuals. The electronystagmographic test was performed in total darkness. The caloric stimulus was 50m<I>l</I> water, most often 30°C or 44°C, sometimes 20°C, for an irrigation period of 20 sec, with about 7-minute intervals. Subjects were requested to fix their gaze upon a spot on the ceiling about 3m away during the maximum intensity of slow-phase velocity for 10 sec. The amount of reduction of slow-phase velocity induced by ocular fixation was obtained during the first half of the 10-sec period and compared with the control period. The percentage reduction in slow-phase velocity induced by ocular fixation did not depend upon the temperature of the water applied as a caloric stimulus. The mean percentage reduction in slow-phase velocity induced was about 82±12%. On the basis of these results, fixation-suppression of caloric nystagmus was studied in 669 consecutive cases. An analysis of caloric nystagmus with failure of fixation-suppression (FFS) made it possible to classify patterns of FFS into three types. Together with the recent anatomical and physiological data, the underlying neuroanatomical substrates responsible for the FFS was discussed.
日本めまい平衡医学会の論文

Fixation-suppression of caloric nystagmus in normal subjects

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