Strange vision: ganglion cells as circadian photoreceptors

Trends Neurosci. 2003 Jun;26(6):314-20. doi: 10.1016/S0166-2236(03)00130-9.


A novel photoreceptor of the mammalian retina has recently been discovered and characterized. The novel cells differ radically from the classical rod and cone photoreceptors. They use a unique photopigment, most probably melanopsin. They have lower sensitivity and spatiotemporal resolution than rods or cones and they seem specialized to encode ambient light intensity. Most surprisingly, they are ganglion cells and, thus, communicate directly with the brain. These intrinsically photosensitive retinal ganglion cells (ipRGCs) help to synchronize circadian rhythms with the solar day. They also contribute to the pupillary light reflex and other behavioral and physiological responses to environmental illumination.

Publication types

  • Research Support, U.S. Gov't, P.H.S.
  • Review

MeSH terms

  • Animals
  • Circadian Rhythm / physiology
  • Light Signal Transduction / physiology*
  • Mice
  • Photic Stimulation
  • Photoreceptor Cells*
  • Rats
  • Retina / cytology
  • Retina / physiology
  • Retinal Ganglion Cells / physiology*
  • Retinal Pigments / metabolism
  • Rod Opsins / metabolism
  • Synaptic Transmission / physiology


  • Retinal Pigments
  • Rod Opsins
  • melanopsin