Pupillary response induced by acupuncture stimulation – an experimental study

Objectives To investigate whether acupuncture stimulation affects autonomic nerve function by measuring pupil diameters with electronic pupillography. Methods Two studies were conducted (Experiment 1 and 2) in the Tsukuba University of Technology, Tsukuba, Japan. Experiment 1 examined the responses before, during and after acupuncture. Experiment 2 compared acupuncture and a no acupuncture control in a two period, repeated measurement crossover design. Twelve healthy male university students were recruited for Experiment 1 and nine healthy male university students for Experiment 2. The intervention was superficial acupuncture at the acupuncture point TE5. Following the insertion, gentle repetitive tapping stimulation was applied during the subject’s exhalation phase in a sitting position for 90 seconds. The main outcome measures in Experiment 1 were pupil diameter, heart rate, pulse wave and blood pressure. In both experiments, pupil diameter was measured for three minutes before acupuncture stimulation, during stimulation and for three minutes after stimulation. Results In Experiment 1, a decrease in pupil diameter was observed after acupuncture stimulation (P=0.018) and a decrease in heart rate was observed during the stimulation (P=0.049). Moreover, a significant decrease of pulse wave amplitude was observed during and after acupuncture stimulation. In Experiment 2, a decrease in pupil diameter occurred after acupuncture stimulation (P=0.007), whereas no change occurred under the no acupuncture control. Conclusions It is thought that the pupillary constriction observed after gentle, superficial acupuncture stimulation may be attributed to an increase of parasympathetic nerve function. Further study is necessary in order to further clarify the duration of the observed response and to elucidate the mechanisms behind it.