Characteristics of the autonomic response in the visually evoked reflex in humans.

This study aimed (a) to investigate the effect of the visuogenic reflex on the skin microcirculation of the hand and foot, and (b) to compare it to that evoked by thermal stimuli. Fifteen volunteers took part in this study. The laser Doppler technique was used for measuring blood flow (BF). The results showed that a flash of light with a duration of 300 ms caused a significant decrease in BF (mean 38.4 +/- 14.8%) in 10 out of 15 subjects in the hand but not in the foot. The latency was 5.05 +/- 0.7 s and the duration 7.2 +/- 1.8 s. The reaction did not show a significant change when a longer stimulus of 14 s was applied. Repetitive stimuli evoked habituation (p < 0.01). There is significant difference (p < 0.01) between autonomic responses to visuogenic and to calorically evoked reflexes.