S01-1 Variations in Light-Induced Suppression of Nocturnal Melatonin with Special Reference to Papillary Light Reflex in Humans

This study was conducted to examine if a significant relationship was observed between nocturnal melatonin suppression and pupil diameter responses to the light because retinal ganglion cells passes the photic signal to suprachiasmatic nucleus and to ciliary ganglion projecting to iris muscles. Pupil diameter was measured in nine young male adults under blue, green and red monochromatic light with 2, 5, 15, 100 and 1000 lx. The variation of pupil diameter was getting greater at lower illuminance level, especially below 5 lx at each monochromatic light stimulus and the reproducibility of the variation among subjects was confirmed by rank correlation significances. Pupil diameter and nocturnal melatonin concentration in twelve young males were measured under green light-emitting diode (LED) with 0, 30 and 600 lx. A linear relationship between a ratio of pupil diameter at each illuminance level to one at darkness condition or retinal illuminance and melatonin suppression could not be observed. However, An individual who shows the greater melatonin suppression has a characteristic papillary response with the larger diameter at each illuminance level, which implied that the melatonin suppression was dependent not only on physical amount of light reaching to retina through iris but also on the sensitivity of individual pupillary response to the light.