Is there any difference in human pupillary reaction to acupuncture between light- and dark-adaptive conditions?

OBJECTIVES To determine if acupuncture stimulation elicits a pupillary response under light adaptation and whether there is any difference in the pupillary response between light and dark adaptation environments during acupuncture stimulation. METHODS The participants consisted of 55 healthy individuals who had no known eye diseases or pupil abnormalities. Experiment 1 compared pupillary responses between acupuncture stimulation and no-stimulation groups under light adaptation. Experiment 2 compared pupillary responses to acupuncture between two conditions (dark and light adaptation) with a two-period repeated measurement crossover design. For both experiments the pupil diameter was continuously measured for 3 min before stimulation, during stimulation and for 3 min after stimulation. For all acupuncture stimulation interventions an acupuncture needle was inserted superficially at the TE5 acupuncture point followed by gentle tapping stimulation for 90 s. RESULTS In experiment 1 the pupil diameter was significantly decreased during (p<0.01) and after stimulation (p<0.0001) compared with the pupil diameter before stimulation under light adaptation. No significant difference was noted in the serial changes in pupil diameter in the no-stimulation group. In experiment 2 the pupil diameter was significantly decreased 90 s after stimulation (p<0.05) and 150 s after stimulation (p<0.05) under light adaptation conditions. Furthermore, the pupil diameter was significantly decreased 120 s after stimulation (p<0.05) and 150 s after stimulation (p<0.01) under dark adaptation conditions. No significant difference in the serial changes in pupil diameter was noted between the groups. CONCLUSIONS This study shows that pupil constriction occurs following acupuncture stimulation under light adaptation and this response is no different from that seen under dark adaptation.