Pupil diameter variability in humans

The aim of this study was to investigate the origin of the pupil fluctuations in humans. The authors assess whether and to which extent LF and HF cardiovascular rhythms contribute to spontaneous pupil diameter fluctuations at rest, during sympathetic activation by Head-Up Tilt Test 70/spl deg/ and during a non-invasive modulation of carotid baroreceptors by Neck Suction (NS). The responses of the pupil to the NS was studied at stimulation frequencies of 0.10 and 0.20 Hz. The effect of tilting on PD fluctuations spectra and the physiological background of the pupil control are consistent with the hypothesis that pupil fluctuations reflect a generalized increase of the sympathetic tone. The findings obtained with the NS stimulation suggest that blood pressure fluctuations propagate to the pupil via carotid baroreceptor afferent pathways. However a central contribution can not be excluded.