[Retinal and pineal melatonin--from a circadian signal to therapeutic use].

Melatonin, the major product of the pincal gland, is also synthesized in the retina of several vertebrate species. Retinal melatonin levels show a marked daily variation, with high levels at night and low levels during the light period. Melatonin rhythm generating system includes photodetector, circadian clock and melatonin synthesis machinery and they are located in pincal organ and retina.