Light, dark, and melatonin: emerging evidence for the importance of melatonin in ocular physiology

Eye (Lond). 2007 Jul;21(7):901-8. doi: 10.1038/sj.eye.6702597. Epub 2006 Sep 22.


Melatonin is a hormone, which is mainly produced by the pineal gland, a vestigial eye. Rather than the rods and cones, it is a newly discovered subgroup of photosensitive retinal ganglion cells, which is responsible for mediating the light-dark cycles, thus regulating melatonin's secretion. One of the correlates of the circadian rhythm of melatonin release is the habitual sleep pattern. Patients with circadian rhythm sleep disorders, including some blind patients with no light-induced suppression of melatonin, benefit from melatonin treatment. Melatonin is synthesized in the retina, lens, ciliary body as well as other parts of the body. In this review, we discuss the physiological roles of melatonin in the eye, as well as the potential therapeutic avenues currently under study.

Publication types

  • Review

MeSH terms

  • Animals
  • Circadian Rhythm / physiology
  • Humans
  • Light
  • Melatonin / physiology*
  • Melatonin / therapeutic use
  • Ocular Physiological Phenomena*
  • Pineal Gland / metabolism
  • Retinal Ganglion Cells / physiology
  • Sleep Disorders, Circadian Rhythm / physiopathology


  • Melatonin