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Eye color




Determination of eye color



Classification of colors


Iris color can provide a large amount of information about an individual, and a classification of various colors may be useful in documenting pathological changes or determining how a person may respond to various ocular pharmaceuticals.[14] Various classification systems have ranged from a basic "light" or "dark" description to detailed gradings employing photographic standards for comparison.[14] Others have attempted to set objective standards of color comparison.[15]


Eye color exists on a continuum from the darkest shades of brown to the lightest shades of blue.[6] Seeing the need for a standardized classification system that was simple, yet detailed enough for research purposes, Seddon et. al developed a graded one based on the predominant iris color (brown, light brown, green, gray, and blue) and the amount of brown or yellow pigment present. There are 3 true colors in the eyes that determine the outward appearance; brown, yellow, and gray. How much of each color you have determines the appearance of the eye color. The color the eyes in turn depends on how much of these colors are present. For example, green eyes have yellow and some brown, making them appear green. Blue eyes have a little yellow and little to no brown, making them appear blue. Gray eyes appear gray because they have a little yellow and no brown in them. Brown eyes appear brown because most of the eye contains the brown color. Brown is the most common, blue is second, and green is rarest.[17] The above is true for the species Homo sapiens. The iris color can vary in the animal world. Instead of blue in humans, autosomal recessive color in the species Corucia zebrata is black. whereas, the autosomal dominant color is yellow - green {52} ( Subspecies comparison of the Genus: Corucia - Leeway Corucia Research Center - LCRC, Polyphemos, {2006} Volume 4, Issue 1. pp. 1-25.).


In humans, brown eyes contain large amounts of melanin (eumelanin) within the iris stroma which serves to absorb light, particularly at the shorter wavelengths.[5][18] Very dark brown irises may appear to be black.[19][20]


Brown is predominant[21] and, in many populations, it is (with few exceptions) one of the only iris colors present.[22] It is least common in the countries around the Baltic Sea.

Those of mixed European and non-European ancestry generally have dark eyes, but with more variability in eye color within their families than those from more homogenous origins.[23] Inhabitants indigenous to Africa, Asia and the Americas generally have brown eyes. Brown eyes are equally found in Europe and Oceania, though within some European populations they are not predominant to the same extent.





There is some difficulty in defining the eye color "hazel" as it is sometimes considered to be synonymous with light-brown and other times with dark green.[32][19][25][27][30][33] They have been described as dark green or yellowish brown,[34] or as a lighter shade of brown.[35] Hazel eyes have also been described as being equivalent to a dark green or amber color eyes/light brown.[36] In North America, "hazel" is often used to describe eyes that appear to change color, ranging from light brown to green and even gray, depending on current lighting in the environment. They are nicknamed "cat eyes."



Amber colored eyes are of a solid color and have a strong yellowish/golden and russet/coppery tint. This might be due to the deposition of the yellow pigment called "lipochrome" in the iris (which is also found in green and violet eyes).[37][38][citation needed] They, like hazel eyes, are also nicknamed "cat eyes".


The yellow eyes of some pigeons contain yellow fluorescing pigments known as pteridines.[39] The bright yellow eyes of the Great Horned Owl are thought to be due to the presence of the pteridine pigment xanthopterin within certain chromatophores (called xanthophores) located in the iris stroma.[40] In humans, yellow specks or patches are thought to be due to the pigment lipofuscin, also known as lipochrome.[24]



Green eyes are the product of moderate amounts of melanin. They are most often found among people of North and Eastern European descent, and to a slightly lesser extent, in Southern Europe, and parts of Central and South Asia.[1][2][3][4]. Green eyes are the rarest eye color; only 1-2% of human population possesses this trait. In Iceland 88% of the population have green or blue eyes. Other ethnically nordic countries like Sweden, Denmark, Germany, Austria, Norway, and the Netherlands [5] have a high percentage of green eyes.



Blue eyes contain low amounts of melanin within the iris stroma; longer wavelengths of light tend to be absorbed by the underlying iris pigment epithelium and shorter wavelengths are reflected and undergo Rayleigh scattering.[5] The type of melanin present is eumelanin.[18] The inheritance pattern followed by blue eyes is considered similar to that of a recessive trait.[7]

Blue eyes are relatively common throughout Europe and other areas with populations of European descent, such as the Americas and Oceania. While most common among people of Finno-Ugric descent, there are also rare populations in West Asia, Central and South Asia with fairly uncommon natural occurrences of blue eyes.

Blue eyes are mostly common throughout northern Europe, especially in Sweden, Iceland, Norway, Denmark, Germany, Finland, the Netherlands, Estonia, and Austria. One survey estimated that nearly 90% of Icelanders have blue or green eyes,[41] while another reported 50-80%, in contrast to 20%-49% of Spaniards and Italians of the north.[42] A 2002 study found the prevalence of blue eye color among whites in the United States to be 33.8% for those born between 1936 and 1951 compared to 57.4% for those born between 1899 and 1905.[7]




Gray eyes are a variant of blue eyes and are sometimes very hard to tell apart, but are most common in Finland and the Baltic States. Usually, gray eyes are considered a darker shade of blue (like blue-green), where in fact they are lighter. Under magnification, gray eyes exhibit small amounts of yellow and brown color in the iris.






The appearance of violet eyes is thought to occur from the mixing of red and blue reflections.[44] Some albinos have eyes that appear violet., though many people with violet eyes are not albino.[45]


'Red' eyes are also found in an extremely small (<0.001%) percentage of the world's population. This is believed to be a result of either large quantities of the normally scarce red areas in the eye, or a small leakage of blood into the iris; however the number of people on record as having red eyes apart from albinos, is believed not to exceed 20 (Recording of this condition started in 1964). This should be noted as being very different from the 'red-eye' condition found in photography.

Anomalous conditions




Ocular albinism and eye color




Main article: Heterochromia

Heterochromia (also known as a heterochromia iridis or heterochromia iridium) is an ocular condition in which one iris is a different color from the other iris (complete heterochromia), or where the part of one iris is a different color from the remainder (partial heterochromia or sectoral heterochromia). It is a result of the relative excess or lack of pigment within an iris or part of an iris, which may be inherited or acquired by disease or injury.[48] This uncommon condition usually results due to uneven melanin content. A number of causes are responsible, including genetics such as chimerism and Waardenburg syndrome. Trauma and certain medications, such as latanoprost can also cause increased or decreased pigmentation in one eye. On occasion the condition of having two different colored eyes is caused by blood staining the iris after sustaining injury. David Bowie (Jones) is a famous person often wrongly attributed with heterochromia. His apparent condition is due to a teenage injury. (One eye appears darker because the pupil is permanently dilated.) American actress Kate Bosworth has sectoral heterochromia, resulting in a hazel section at the bottom of her right blue eye, while the left is completely blue. The lead vocalist of American band Rise Against, Tim McIlrath, has heterochromia; his left eye is blue while his right is brown. American actress Mila Kunis also has heterochromia, resulting in one green eye and one brown eye.

Eye color change

Often, paler newborns have blue eyes, which change to green, hazel, light brown or dark brown, as they grow older. This is probably the origin of the idiom "being blue-eyed" (= naïve; gullible).



Medical implications


Eye color can also be symptomatic of disease. In particular, yellow eyes are associated with jaundice and symptomatic of liver disease, including cirrhosis, hepatitis and malaria.


  3. ^ a b Morris, PJ. "Phenotypes and Genotypes for human eye colors." Athro Limited website. Retrieved May 10, 2006.
  5. ^ a b c d e f g Huiqiong Wang, Stephen Lin, Xiaopei Liu, Sing Bing Kang. "Separating Reflections in Human Iris Images for Illumination Estimation." Proc. IEEE International Conference on Computer Vision, 2005.
  8. ^ Eye color mocks easy rules
  10. ^ "Eye color is more complex than two genes." Athro, Limited. Retrieved September 1, 2006.
  11. ^
  12. ^ Paul Rincon, Genetics of eye color unlocked, BBC News, 20 December, 2006.
  16. ^
  17. ^ Seddon JM, Sahagian CR, Glynn RJ, Sperduto RD, Gragoudas ES. "Evaluation of an iris color classification system." The Eye Disorders Case-Control Study Group. Invest Ophthalmol Vis Sci. 1990 Aug;31(8):1592-8. PMID: 2201662.
  22. ^
  23. ^ Frudakis T, Thomas M, Gaskin Z, Venkateswarlu K, Chandra KS, Ginjupalli S, Gunturi S, Natrajan S, Ponnuswamy VK, Ponnuswamy KN. Sequences associated with human iris pigmentation." Genetics. 2003 Dec;165(4):2071-83. PMID 14704187.
  32. ^
  37. ^ Howard Hughes Medical Institute: Ask A Scientist
  38. ^
  39. ^ Oliphant LW. "Observations on the pigmentation of the pigeon iris." Pigment Cell Res. 1987;1(3):202-8. PMID 3508278.
  42. ^
  43. ^ The Perseus Digital Library: Homeric Hymns
  44. ^
  45. ^
  46. ^
  47. ^
  49. ^ Hejkal TW, Camras CB (1999). "Prostaglandin analogs in the treatment of glaucoma". Seminars in ophthalmology 14 (3): 114-23. doi:10.153/SOPH01400114. PMID 10790575.
  • 52. Jones, S.L., Schnirel, B.L., " Subspecies Comparison of the Genus: Corucia" Polyphemos, (2006). pp 1-25.

See also

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Eye_color". A list of authors is available in Wikipedia.