Nasal versus temporal illumination of the human retina: effects on core body temperature, melatonin, and circadian phase

Abstract The mammalian retina contains both visual and circadian photo-receptors. In humans, nocturnal stimulation of the latter receptors leads to melatonin suppression, which might cause reduced nighttime sleepiness. Melatonin suppression is maximal when the nasal part of the retina is illumi-nated. Whether circadian phase shifting in humans is due to the same photoreceptors is not known. The authors explore whether phase shifts and melatonin suppression depend on the same retinal area. Twelve healthy subjects participated in a within-subjects design and received all of 3 light conditions—1) 10 lux of dim light on the whole retina, 2) 100 lux of ocular light on the nasal part of the retina, and 3) 100 lux of ocular light on the temporal part of the retina—on separate nights in random order. In all 3 conditions, pupils were dilated before and during light exposure. The protocol consisted of an adaptation night fol-lowed by a 23-h period of sustained wakefulness, during which a 4-h light pulse was presented at a time when maximal phase delays were expected. Nasal illu-mination resulted in an immediate suppression of melatonin but had no effect o