Eye color

The irises of human eyes exhibit a wide spectrum of colours

Eye color is a polygenic phenotypic trait determined by two factors: the pigmentation of the eye's iris[1][2] and the frequency-dependence of the scattering of light by the turbid medium in the stroma of the iris.[3]: 9 

In humans, the pigmentation of the iris varies from light brown to black, depending on the concentration of melanin in the iris pigment epithelium (located on the back of the iris), the melanin content within the iris stroma (located at the front of the iris), and the cellular density of the stroma.[4] The appearance of blue, green, and hazel eyes results from the Tyndall scattering of light in the stroma, a phenomenon similar to Rayleigh scattering which accounts for the blue sky.[5] Neither blue nor green pigments are present in the human iris or vitreous humour.[3][6] This is an example of structural color, which depends on the lighting conditions, especially for lighter-colored eyes.

The brightly colored eyes of many bird species result from the presence of other pigments, such as pteridines, purines, and carotenoids.[7] Humans and other animals have many phenotypic variations in eye color.[8]

The genetics and inheritance of eye color in humans is complicated. As of 2010, as many as 16 genes have been associated with eye color inheritance. Some of the eye-color genes include OCA2 and HERC2.[9] The earlier belief that blue eye color is a simple recessive trait has been shown to be incorrect. The genetics of eye color are so complex that almost any parent-child combination of eye colors can occur.[10][11] However, OCA2 gene polymorphism, close to proximal 5' regulatory region, explains most human eye-color variation.[12]

  1. ^ Wielgus AR, Sarna T (2005). "Melanin in human irides of different color and age of donors". Pigment Cell Res. 18 (6): 454–64. doi:10.1111/j.1600-0749.2005.00268.x. PMID 16280011.
  2. ^ Prota G, Hu DN, Vincensi MR, McCormick SA, Napolitano A (1998). "Characterization of melanins in human irides and cultured uveal melanocytes from eyes of different colors". Exp. Eye Res. 67 (3): 293–9. doi:10.1006/exer.1998.0518. PMID 9778410.
  3. ^ a b Fox, Denis Llewellyn (1979). Biochromy: Natural Coloration of Living Things. University of California Press. ISBN 978-0-520-03699-4.
  4. ^ Huiqiong Wang; Lin, S.; Xiaopei Liu; Sing Bing Kang (2005). "Separating reflections in human iris images for illumination estimation". Tenth IEEE International Conference on Computer Vision (ICCV'05) Volume 1. pp. 1691–1698 Vol. 2. CiteSeerX 10.1.1.87.418. doi:10.1109/ICCV.2005.215. ISBN 978-0-7695-2334-7. S2CID 2215768.
  5. ^ Sturm R.A. & Larsson M., Genetics of human iris colour and patterns, Pigment Cell Melanoma Res, 22:544-562, 2009.
  6. ^ Mason, Clyde W. (1924). "Blue Eyes". Journal of Physical Chemistry. 28 (5): 498–501. doi:10.1021/j150239a007.
  7. ^ Oliphant LW (1987). "Pteridines and purines as major pigments of the avian iris". Pigment Cell Res. 1 (2): 129–31. doi:10.1111/j.1600-0749.1987.tb00401.x. PMID 3507666.
  8. ^ Morris, PJ. "Phenotypes and Genotypes for human eye colors." Athro Limited website. Retrieved 10 May 2006.
  9. ^ White, Désirée; Rabago-Smith, Montserrat (14 October 2010). "Genotype–phenotype associations and human eye color". Journal of Human Genetics. 56 (1): 5–7. doi:10.1038/jhg.2010.126. PMID 20944644.
  10. ^ No Single Gene For Eye Color, Researchers Prove. Sciencedaily.com (22 February 2007). Retrieved on 2011-12-23.
  11. ^ "Eye color definition – Medical Dictionary definitions of popular medical terms easily defined on MedTerms". Medterms.com. 29 October 2003. Archived from the original on 5 June 2011. Retrieved 19 October 2011.
  12. ^ Duffy, David L.; Montgomery, Grant W.; Chen, Wei; Zhao, Zhen Zhen; Le, Lien; James, Michael R.; Hayward, Nicholas K.; Martin, Nicholas G.; Sturm, Richard A. (2007). "A three-single-nucleotide polymorphism haplotype in intron 1 of OCA2 explains most human eye-color variation". Am. J. Hum. Genet. 80 (2): 241–52. doi:10.1086/510885. PMC 1785344. PMID 17236130.