Melatonin suppression by light in humans is maximal when the nasal part ofthe retina is illuminated

This study investigated whether sensitivity of the nocturnal melatonin supp ression response to Light depends on the area of the retina exposed. The re ason to suspect uneven spatial sensitivity distribution stems from animal w ork that revealed that retinal ganglion cells projecting to the suprachiasm atic nuclei (SCN) are unequally distributed in several species of mammals. Four distinct areas of the retinas of 8 volunteers were selectively exposed to 500 Iue between 1:30 a.m. and 3:30 a.m. Saliva samples were taken befor e, during, and after light exposure in l-h intervals. A significant differe nce in sensitivity was found between exposure of the lateral and nasal part s of the retinas, showing that melatonin suppression is maximal on exposure of the nasal part of the retina. The results imply that artificial manipul ation of the circadian pacemaker to alleviate jet lag, to improve alertness in shift workers, and possibly to treat patients suffering from seasonal a ffective disorder should encompass light exposure of the nasal retina.