The abundant melatonin levels in children is believed to inhibit sexual development. When puberty arrives, melatonin production is reduced. There is a pathway from the retinas to the hypothalamus called the retinohypothalamic tract. These impulses inhibit the production of melatonin. The pineal gland is therefore a photosensitive organ and an important timekeeper for the human body.
Retinal research done with hamsters demonstrates another center for melatonin production.
Located in the retina, this center implies that the eyes have their own built in circadian timepiece. Biologists found that they could throw the retinal rhythms out of sync with other circadian cycles. They also found that they could set and reset the retinal clock even when the SCN was destroyed. People are taking regular doses of the hormone. There is a question whether or not regular doses of melatonin may damage the eye over time.