The visual cycle of the cone photoreceptors of the retina

Nutr Rev. 2004 Jul;62(7 Pt 1):283-6. doi: 10.1111/j.1753-4887.2004.tb00053.x.


The photoreceptors of the eye's retina consist of rods and cones; rods serve vision in dim light, whereas cones serve high-resolution color vision in daylight. The first event in vision is the light-initiated isomerization of 11-cis-retinal, which is attached to rod or cone opsin, to all-trans-retinal. The regeneration of 11-cis-retinal comprises the well-known visual cycle in rods. By using cone-dominant retinas from chickens and ground squirrels, a visual cycle has been discovered in cones that differs radically from that in rods, mainly in the mechanism of isomerization of all-trans-retinol to 11-cis-retinol, and the latter's oxidation to 11-cis-retinal.

Publication types

  • Review

MeSH terms

  • Animals
  • Chickens
  • Humans
  • Retina
  • Retinal Cone Photoreceptor Cells / cytology
  • Retinal Cone Photoreceptor Cells / metabolism*
  • Retinal Pigments / chemistry
  • Retinal Pigments / metabolism*
  • Retinal Rod Photoreceptor Cells / cytology
  • Retinal Rod Photoreceptor Cells / metabolism*
  • Retinaldehyde / chemistry
  • Rod Opsins
  • Sciuridae
  • Stereoisomerism
  • Vision, Ocular / physiology*
  • Vitamin A / chemistry


  • Retinal Pigments
  • Rod Opsins
  • Vitamin A
  • Retinaldehyde