Eye color 759008 226167893 2008-07-17T03:25:11Z 201.240.241.92 /* Blue */ '''Eye color''' is a [[polygenic]] trait and is determined by the amount and type of [[pigment]]s in the [[eye]]'s [[Iris (anatomy)|iris]].<ref name="Wielgus">Wielgus AR, Sarna T. "Melanin in human irides of different color and age of donors." ''Pigment Cell Res.'' 2005 Dec;18(6):454-64. PMID 16280011.</ref><ref name="Prota">Prota G, Hu DN, Vincensi MR, McCormick SA, Napolitano A. "Characterization of melanins in human irides and cultured uveal melanocytes from eyes of different colors." ''Exp Eye Res.'' 1998 Sep;67(3):293-9. PMID 9778410.</ref> Humans and animals have many [[phenotypic]] variations in eye color.<ref name="Morris">Morris, PJ. [http://www.athro.com/evo/gen/eyecols.html "Phenotypes and Genotypes for human eye colors."] Athro Limited website. Retrieved May 10, 2006.</ref> In humans, these variations in color are attributed to varying ratios of [[eumelanin]] produced by [[melanocytes]] in the iris.<ref name="Prota"/> The brightly colored eyes of many bird species are largely determined by other pigments, such as [[pteridine]]s, [[purine]]s, and [[carotenoid]]s.<ref name="Oliphant 1">Oliphant LW. "Pteridines and purines as major pigments of the avian iris." ''Pigment Cell Res.'' 1987;1(2):129-31. PMID 3507666.</ref> Three main elements within the iris contribute to its color: the melanin content of the iris pigment [[epithelium]], the melanin content within the [[iris stroma]], and the cellular density of the iris stroma.<ref name="Wang">Huiqiong Wang, Stephen Lin, Xiaopei Liu, Sing Bing Kang. [http://research.microsoft.com/~stevelin/iris.pdf "Separating Reflections in Human Iris Images for Illumination Estimation."] Proc. IEEE International Conference on Computer Vision, 2005.</ref> In eyes of all colors, the iris pigment epithelium contains the black pigment, eumelanin.<ref name="Prota"/><ref name="Wang"/> Color variations among different irises are typically attributed to the melanin content within the iris stroma.<ref name="Wang"/> The density of cells within the stroma affects how much light is absorbed by the underlying pigment epithelium.<ref name="Wang"/> ==Determination of eye color== Eye colors can range from most common, brown, to least common, green. Rare genetic mutations can even lead to unusual eye colors like black, red, and violet. Eye color is an inherited trait influenced by more than one [[gene]].<ref name="Sturm">Sturm RA, Frudakis TN. [http://www.biosci.ohio-state.edu/~pfuerst/courses/eeobmg640/reading1eyecolor.pdf"Eye color: portals into pigmentation genes and ancestry."] ''Trends Genet.'' 2004 Aug;20(8):327-32. PMID: 15262401.</ref><ref name="Grant">Grant MD, Lauderdale DS. "Cohort effects in a genetically determined trait: eye color among US whites." ''Ann Hum Biol.'' 2002 Nov-Dec;29(6):657-66. PMID 12573082.</ref> Two major genes and multiple minor genes account for the tremendous variation of human eye color.<ref>[http://www.wonderquest.com/eye-color.htm Eye color mocks easy rules]</ref> In humans, three genes associated with eye color are currently known: ''EYCL1'', ''EYCL2'', and ''EYCL3''.<ref>Rebbeck TR, Kanetsky PA, Walker AH, Holmes R, Halpern AC, Schuchter LM, Elder DE, Guerry D. [http://cebp.aacrjournals.org/cgi/reprint/11/8/782.pdf "P gene as an inherited biomarker of human eye color."] ''Cancer Epidemiol Biomarkers Prev.'' 2002 Aug;11(8):782-4. PMID 12163334.</ref><ref>[http://www.athro.com/evo/gen/inherit1.html "Eye color is more complex than two genes."] Athro, Limited. Retrieved September 1, 2006.</ref> These genes account for three [[phenotypic]] eye colors (brown, green, and blue) in humans.<ref name="Morris"/> Eye color usually stabilizes when an infant is around 6 months old.<ref>[http://chemistry.about.com/cs/howthingswork/f/eyecolor.htm Why Babies Are Born with Blue Eyes]</ref> In 2006, the molecular basis of the ''EYCL3'' locus was resolved.<ref name=BBC>Paul Rincon, [http://news.bbc.co.uk/1/hi/sci/tech/6195091.stm Genetics of eye color unlocked], ''BBC News'', 20 December, 2006. </ref> In a study of 3839 people, researchers reported that 74% of total variation in eye color was explained by a number of [[single nucleotide polymorphism]]s (SNPs) near the ''[[OCA2]]'' gene ({{OMIM3|203200}}). ''OCA2'' was previously known because, when mutated, the gene can result in a type of [[albinism]]. The recent study showed that different SNPs strongly associate with blue and green eyes as well as variations in [[freckling]], [[Mole (skin marking)|mole]] counts, [[hair color|hair]] and [[Human skin color|skin tone]]. The authors speculate that the SNPs may be in an ''OCA2'' [[regulatory sequence]] and thus influence the expression of the gene product, which in turn affects pigmentation.<ref name=OCA2>Duffy DL, Montgomery GW, Chen W, Zhao ZZ, Le L, James MR, Hayward NK, Martin NG, and Sturm, RA [http://www.journals.uchicago.edu/AJHG/journal/issues/v80n2/44159/brief/44159.abstract.html "A Three–Single-Nucleotide Polymorphism Haplotype in Intron 1 of OCA2 Explains Most Human Eye-color Variation"] ''Am. J. Hum. Genet.'' 2002 80:000, 2007.</ref> A 2008 study demonstrated that a specific mutation within the HERC2 gene that regulates OCA2 expression is responsible for blue eyes<ref>[http://www.springerlink.com/content/2045q6234h66p744/fulltext.html 10.1007/s00439-007-0460-x<!--Bot generated title -->]</ref> (see below). Blue eyes with a brown spot, Green eyes and Gray eyes are caused by an entirely different part of the genome. As Eiberg said: ''"The SNP rs12913832 is found to be associated with the brown and blue eye color, but this single DNA variation cannot explain all the brown eye color variation from dark brown over hazel to blue eyes with brown spots".'' ==Classification of colors== [[Image:Blue-greyEyes.png|thumb|right|The perception of color depends upon various factors. These are the same eyes; however, depending on the light and surrounding hues, the eye color can appear quite different.]] 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.<ref name="German">German EJ, Hurst MA, Wood D, Gilchrist J. "A novel system for the objective classification of iris color and its correlation with response to 1% tropicamide." ''Ophthalmic Physiol Opt.'' 1998 Mar;18(2):103-10. PMID 9692029.</ref> Various classification systems have ranged from a basic "light" or "dark" description to detailed gradings employing photographic standards for comparison.<ref name="German"/> Others have attempted to set objective standards of color comparison.<ref name="Fan">Fan S, Dyer CR, Hubbard L. [http://www.cs.wisc.edu/~shaohua/research/iris/IrisColor_files/IrisTr1495.pdf Quantification and Correction of Iris Color."] Technical report 1495, University of Wisconsin-Madison, Dec, 2003.</ref> As the [[color vision|perception of color]] is dependent on viewing conditions (e. g. the amount and type of illumination, as well as the hue of the surrounding environment), so is the perception of eye color.<ref>[http://www.edromanguitars.com/tech/color.htm Color Perception]</ref><!--a better citation or link may be available for this assertion--> Eye color exists on a continuum from the darkest shades of brown to the lightest shades of blue.<ref name="Sturm"/> 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 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 blue. How much of each color you have determines the appearance of the eye color. The color of the eyes in turn depends on how much of these colors are present. For example, green eyes have yellow and some blue, making them appear green. Brown eyes appear brown because most of the eye contains the brown color. 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.<ref>Jones, S.L., Schnirel, B.L., ''Subspecies comparison of the Genus: Corucia'', Leeway Corucia Research Center - LCRC, Polyphemos, {2006} Volume 4, Issue 1. pp. 1-25.</ref> ===Amber=== [[Image:Amber Eyes.jpg|thumb|175px|right|Human amber eyes displaying the yellow pigments.]] Amber 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).<ref>[http://www.hhmi.org/cgi-bin/askascientist/highlight.pl?kw=&file=answers%2Fgenetics%2Fans_044.html Howard Hughes Medical Institute: Ask A Scientist]</ref><ref>[http://www.eyecarecontacts.com/eyecolor.html Eye Color<!-- Bot generated title -->]</ref> They are nicknamed "Wolf eyes" due to the high rate of the amber eye color in wolves. Amber eyes should not be confused with hazel eyes; although hazel eyes may contain specks of amber or gold, they usually tend to comprise of many other colors, including green, brown and orange. Also, hazel eyes may appear to shift in color and consist of flecks and ripples; while amber eyes are of a solid gold hue. The eyes of some pigeons contain yellow fluorescing pigments known as [[pteridine]]s.<ref>Oliphant LW. "Observations on the pigmentation of the pidgeon iris." ''Pigment Cell Res.'' 1987;1(3):202-8. PMID 3508278.</ref> The bright yellow eyes of the [[Great Horned Owl]] are thought to be due to the presence of the pteridine pigment [[xanthopterin]] within certain [[chromatophore]]s (called ''xanthophores'') located in the iris stroma.<ref>Oliphant LW. "Crystalline pteridines in the stromal pigment cells of the iris of the great horned owl." ''Cell Tissue Res.'' 1981;217(2):387-95. PMID 7237534.</ref> In humans, yellowish specks or patches are thought to be due to the pigment [[lipofuscin]], also known as ''lipochrome''.<ref name="Lefohn"/> {{-}} ===Blue=== [[Image:Blueye.JPG|thumb|100px|left|A blue eye]] 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]].<ref name="Wang"/> The type of melanin present is eumelanin.<ref name="Menon"/> The inheritance pattern followed by blue eyes is considered similar to that of a [[recessive]] trait, however it is a polygenic trait (meaning that it is controlled by the interactions of several genes, not just one).<ref name="Grant"/> Eiberg and colleagues showed in a study published in ''Human Genetics'' that a mutation in the 86th [[intron]] of the HERC2 gene, which is hypothesized to interact with the OCA2 gene [[promoter]], reduced expression of OCA2 with subsequent reduction in melanin production.<ref name="blue mutation">Eiberg H, Troelsen J, Nielsen M, Mikkelsen A, Mengel-From J, Kjaer KW, Hansen L. "[http://www.springerlink.com/content/2045q6234h66p744/fulltext.html Blue eye color in human beings may be caused by a perfectly associated founder mutation in a regulatory element located within the HERC2 gene inhibiting OCA2 expression]" ''Human Genetics'' 2008 Jan 3. PMID 18172690</ref> The authors concluded that the mutation may have arisen in a single individual around the [[Black Sea]] region 6,000-10,000 years ago, perhaps suggesting that all people with true blue eyes are more closely related. However, blue eyes with brown spots around the pupil are not related to this mutation.<ref name="blue mutation" /> Blue eyes are most common in [[Poland]]<ref>[http://carnby.altervista.org/troe/12-09.htm]</ref>, [[Ireland]]<ref>[http://carnby.altervista.org/troe/10-02.htm]</ref>, [[Germany]]<ref>[http://carnby.altervista.org/troe/12-05.htm]</ref> , [[Netherlands]]<ref>[http://carnby.altervista.org/troe/12-04.htm]</ref>, [[Iceland]]<ref>[http://carnby.altervista.org/troe/09-05.htm]</ref> , [[Austria]]<ref>[http://carnby.altervista.org/troe/12-06.htm]</ref>, [[Sweden]]<ref>[http://carnby.altervista.org/troe/09-06.htm]</ref>, [[Norway]]<ref>[http://carnby.altervista.org/troe/09-04.htm]</ref>, [[Denmark]]<ref>[http://carnby.altervista.org/troe/09-07.htm]</ref>, [[Finland]]<ref>[http://carnby.altervista.org/troe/09-11.htm]</ref>, [[France]]<ref>[http://carnby.altervista.org/troe/09-16.htm]</ref> [[Estonia]]<ref>[http://carnby.altervista.org/troe/09-10.htm]</ref>, and the [[United Kingdom]]<ref>[http://carnby.altervista.org/troe/10-03.htm]</ref><ref>[http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WPG-4CBW58K2&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=e178ee28135d39d955ba1c6436b3d082] Rafnsson V, Hrafnkelsson J, Tulinius H, Sigurgeirsson B, Olafsson JH. "Risk factors for malignant melanoma in an Icelandic population sample." ''Prev Med.'' 2004 Aug;39(2):247-52. PMID 15226032</ref> They are also present in Southern Europe, [[Spain]], north of [[Italy]] and the Balkans [http://cogweb.ucla.edu/ep/Frost_06.html] <ref>http://carnby.altervista.org/troe/08-05.htm</ref> , the [[Middle East]] (especially in [[Israel]] and [[Lebanon]]) and are also found in [[Afghanistan]]. 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.<ref name="Grant"/> ===Brown=== [[Image:Brown eyes.jpg|thumb|200px|left|brown human iris]]Brown eyes are predominant in humans<ref>Eiberg H, Mohr J. "Assignment of genes coding for brown eye color (BEY2) and brown hair colour (HCL3) on chromosome 15q." ''Eur J Hum Genet.'' 1996;4(4):237-41. PMID 8875191.</ref> and, in many populations, it is (with few exceptions) the only iris color present.<ref>[http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=227220 OMIM - SKIN/HAIR/EYE PIGMENTATION, VARIATION IN, 1; SHEP1<!-- Bot generated title -->]</ref> It is less common in countries around the [[Baltic Sea]], such as Finland and Estonia. In humans, brown eyes contain large amounts of melanin (eumelanin) within the iris stroma, which serves to absorb light, particularly at the shorter wavelengths. Brown is the most common eye color. <ref name="Wang"/><ref name="Menon">Menon IA, Basu PK, Persad S, Avaria M, Felix CC, Kalyanaraman B. "Is there any difference in the photobiological properties of melanins isolated from human blue and brown eyes?" ''Br J Ophthalmol.'' 1987 Jul;71(7):549-52. PMID 2820463.</ref> Very dark brown irises may appear at a glance to be black.<ref name="Hammond">Hammond BR Jr, Fuld K, Snodderly DM. "Iris color and macular pigment optical density." ''Exp Eye Res.'' 1996 Mar;62(3):293-7. PMID 8690039.</ref><ref>Prieto JG. "Eye color in skin cancer." ''Int J Dermatol.'' 1977 Jun;16(5):406-7. PMID 873674.</ref> {{-}} ===Gray=== [[Image:Mybluishgrayeye.JPG|thumb|100px|left|A steel blue-gray eye]] [[Image:greyeyes.jpg|thumb|175px|right|Female gray eyes]] [[Image:Example of grey eyes.jpg|thumb|175px|right|Male gray eyes]] Gray eyes have less melanin than blue eyes, even though they are considered a darker shade of blue (like blue-green). They are most common in European Russia, Finland and the [[Baltic States]]. It is unusually common in the [[Crimean Peninsula]] and in people who are descended from cossacks.{{Fact|date=June 2008}} Under magnification, gray eyes exhibit small amounts of yellow and brown color in the iris. A gray iris may indicate the presence of a [[uveitis]]. However, other visual signs make a uveitis obvious. Visually, gray eyes often tend to appear to change between the shades of blue, green and gray. This is said to be influenced by the lighting and the surroundings (such as clothes, makeup, etc.). The [[Greek mythology|Greek]] [[goddess]] [[Athena]] was renowned for having "[[owl]]-gray" (in [[Greek language|Greek]], ''γλαυκῶπις'' &ndash; ''glaukōpis'') or "sea-gray" eyes.<ref>[http://www.perseus.tufts.edu/cgi-bin/ptext?doc=Perseus:text:1999.01.0137:hymn=28:line=1 The Perseus Digital Library: Homeric Hymns]</ref> {{-}} ===Green=== [[Image:greeneyes.jpg|thumb|175px|left|Green eyes]] Green eyes are the product of moderate amounts of melanin. Only 1-2% of the world population have Green eyes. They are most often found among people of [[Northern Europe|Northern]] origin. Countries with a high percentage of green eyes are [[Iceland]], [[Sweden]], [[Denmark]], [[Finland]], [[Norway]], [[Germany]], [[Ireland]] and the [[Netherlands]]. To a lesser extent, green eyes can also be present in Eastern and Southern Europe, in the [[Middle East]], Northern parts of [[India]], [[Pakistan]], and [[Afghanistan]]. {{-}} ===Hazel=== [[Image:My_Hazel_Eye.JPG‎|thumb|left|100px|This eye shows a mixture of brown, green and amber colors.]] [[Image:Movie Eyes.jpg|thumb|right|100px|Some eye colors are too mixed to identify properly, and are identified as hazel for simplicity's sake.]] Hazel eyes are due to a combination of a [[Rayleigh scattering]] and a moderate amount of melanin in the iris' anterior border layer.<ref name="Lefohn">Lefohn, A., Budge, B., Shirley, P., Caruso, R., and Reinhard, E. 2003. An Ocularist's Approach to Human Iris Synthesis. IEEE Comput. Graph. Appl. 23, 6 (Nov. 2003), 70-75. DOI= http://dx.doi.org/10.1109/MCG.2003.1242384</ref><ref name="Wang"/> Hazel eyes often appear to shift in color from a light brown to a medium golden-green. A number of studies using three-point scales have assigned "hazel" to be the medium-color between light blue and dark brown.<ref name="Zhu">Zhu G, Evans DM, Duffy DL, Montgomery GW, Medland SE, Gillespie NA, Ewen KR, Jewell M, Liew YW, Hayward NK, Sturm RA, Trent JM, Martin NG. "A genome scan for eye color in 502 twin families: most variation is due to a QTL on chromosome 15q." 1: Twin Res. 2004 Apr;7(2):197-210. PMID 15169604.</ref><ref>Albert DM, Green WR, Zimbric ML, Lo C, Gangnon RE, Hope KL, Gleiser J. [http://www.pubmedcentral.nih.gov/picrender.fcgi?artinstid=1358991&blobtype=pdf "Iris melanocyte numbers in Asian, African American, and Caucasian irides."] ''Trans Am Ophthalmol Soc.'' 2003;101:217-21; discussion 221-2. PMID 14971580.</ref><ref name="Mitchell">Mitchell R, Rochtchina E, Lee A, Wang JJ, Mitchell P; Blue Mountains Eye Study. "Iris color and intraocular pressure: the Blue Mountains Eye Study." ''Am J Ophthalmol.'' 2003 Mar;135(3):384-6. PMID 12614760.</ref><ref>Lindsey JD, Jones HL, Hewitt EG, Angert M, Weinreb RN. "Induction of tyrosinase gene transcription in human iris organ cultures exposed to latanoprost." ''Arch Ophthalmol.'' 2001 Jun;119(6):853-60. PMID 11405836.</ref><ref name="Frank">Frank RN, Puklin JE, Stock C, Canter LA. [http://www.pubmedcentral.gov/articlerender.fcgi?tool=pubmed&pubmedid=11190014 "Race, iris color, and age-related macular degeneration."] ''Trans Am Ophthalmol Soc.'' 2000;98:109-15; discussion 115-7. PMID 11190014.</ref><ref name="Regan">Regan S, Judge HE, Gragoudas ES, Egan KM. "Iris color as a prognostic factor in ocular melanoma." ''Arch Ophthalmol.'' 1999 Jun;117(6):811-4. PMID 10369595.</ref><ref>Hawkins TA, Stewart WC, McMillan TA, Gwynn DR. "Analysis of diode, argon, and Nd: YAG peripheral iridectomy in cadaver eyes." ''Doc Ophthalmol.'' 1994;87(4):367-76. PMID 7851220.</ref> This can sometimes produce a multicolored iris, i.e., an eye that is light brown near the pupil and charcoal or amber/dark green on the outer part of the iris (and vice versa) when observed in sunlight. Hazel is mostly found in some regions of [[Central America]], [[Europe]], the [[Middle East]], parts of [[Central Asia]], parts of North [[India]], Northern [[Pakistan]] and in Afghanistan. Rarely, hazel eyes can be found in people of sub-saharan African and East Asian descent. Definitions of the eye color "hazel" vary: it is sometimes considered to be synonymous with light-brown, gold, or other times with green or dark green.<ref>[http://www.thetech.org/genetics/ask.php?id=126 Understanding Genetics: Human Health and the Genome<!-- Bot generated title -->]</ref><ref name="Hammond"/><ref name="Zhu"/><ref name="Mitchell"/><ref name="Regan"/><ref>Naldi L, Altieri A, Imberti GL, Giordano L, Gallus S, La Vecchia C; Oncology Study Group of the Italian Group for Epidemiologic Research in Dermatology (GISED). "Cutaneous malignant melanoma in women. Phenotypic characteristics, sun exposure, and hormonal factors: a case-control study from Italy." ''Ann Epidemiol.'' 2005 Aug;15(7):545-50. PMID 16029848.</ref><ref>April Holladay. [http://www.usatoday.com/tech/columnist/aprilholladay/2004-10-08-wonderquest_x.htm "Funny — you can't hide those lightening eyes."] USATODAY.com. October 8, 2004. Retrieved September 17, 2006.</ref> <ref>English JS, Swerdlow AJ, MacKie RM, O'Doherty CJ, Hunter JA, Clark J, Hole DJ. [http://www.pubmedcentral.nih.gov/picrender.fcgi?artinstid=1245163&blobtype=pdf "Relation between phenotype and banal melanocytic naevi."] ''Br Med J (Clin Res Ed).'' 1987 Jan 17;294(6565):152-4. PMID 3109545.</ref><ref>Hara T. "[Increased iris pigmentation after use of latanoprost in Japanese brown eyes.]" ''Nippon Ganka Gakkai Zasshi.'' 2001 May;105(5):314-21. PMID 11406947.</ref> 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. {{-}} ===Red=== The eyes of an [[albinism|albinistic]] person may appear red under certain lighting conditions due the very low quantities of [[melanin]]. "True" red eyes also exist in albinistic populations, but are very rare. <ref>[http://www.albinism.org/publications/what_is_albinism.html NOAH — What is Albinism?<!-- Bot generated title -->]</ref> The [[red-eye effect]] in flash photographs makes the pupils (rather than the irises) appear red. It is not related to eye color. {{-}} ===Violet=== The appearance of "violet" eyes is thought to occur from the mixing of red and blue reflections.<ref>[http://www.bbc.co.uk/dna/h2g2/A734933 BBC - h2g2 - Determination of Eye Colour<!-- Bot generated title -->]</ref> Some [[Albinism|albinos]] have eyes that appear violet. Violet eyes are either a form of blue eyes or a mutation. <ref>[http://www.albinism.org/publications/what_is_albinism.html NOAH — What is Albinism?<!-- Bot generated title -->]</ref> [[Elizabeth Taylor]] famously has violet eyes.[http://www.imdb.com/name/nm0000072/bio] ==Medical implications== Those with lighter iris color have been found to have a higher prevalence of [[macular degeneration|age-related macular degeneration]] (ARMD) than those with darker iris color;<ref name="Frank"/> lighter eye color is also associated with an increased risk of ARMD progression.<ref name="Nicolas">Nicolas CM, Robman LD, Tikellis G, Dimitrov PN, Dowrick A, Guymer RH, McCarty CA. "Iris colour, ethnic origin and progression of age-related macular degeneration." ''Clin Experiment Ophthalmol.'' 2003 Dec;31(6):465-9. PMID 14641151.</ref> An increased risk of [[uveal melanoma]] has been found in those with blue, green or gray iris color.<ref name="Stang">Stang A, Ahrens W, Anastassiou G, Jockel KH. "Phenotypical characteristics, lifestyle, social class and uveal melanoma." ''Ophthalmic Epidemiol.'' 2003 Dec;10(5):293-302. PMID 14566630.</ref><ref>[http://www.ncbi.nlm.nih.gov/sites/entrez?cmd=Retrieve&db=pubmed&dopt=AbstractPlus&list_uids=15226032]</ref> Eye color can also be symptomatic of disease. In particular, yellowing of the whites of the eyes is associated with [[jaundice]] and symptomatic of liver disease, including [[cirrhosis]], [[hepatitis]] and [[malaria]]. ==Anomalous conditions== ===Aniridia=== {{main|Aniridia}} [[Image:BlackEyesAniridia.jpg|thumb|Aniridia: Eyes wherein the irises are not present; the eyes appear to be two large pupils.]] [[Aniridia]] is a congenital condition characterized by an extremely underdeveloped iris which appears absent on superficial examination.<ref>[http://www.emedicine.com/oph/topic43.htm eMedicine - Aniridia : Article by Daljit Singh<!-- Bot generated title -->]</ref> ===Ocular albinism and eye color=== Normally, there is a thick layer of melanin on the back of the iris. Even people with the lightest blue eyes, with no melanin on the front of the iris at all, have dark brown coloration on the back of it, to prevent light from scattering around inside the eye. In those with milder forms of [[albinism]], the color of the irises is typically blue, but can vary from blue to brown. In severe forms of albinism, there is no pigment on the back of the iris, and light from inside the eye can pass through the iris to the front. In these cases, the only color seen is the red from the hemoglobin of the blood in the capillaries of the iris. Such albinos have pink eyes, as do albino rabbits, mice, or any other animal with total lack of melanin. [[Transillumination]] defects can almost always be observed during an [[eye examination]] due to lack of iridial pigmentation.<ref>[http://www.emedicine.com/OPH/topic260.htm eMedicine - Ocular Manifestations of Albinism : Article by Mohammed O Peracha, MD<!-- Bot generated title -->]</ref> The ocular albino also lacks normal amounts of melanin in the retina as well, which allows more light than normal to reflect off the retina and out of the eye. Because of this, the pupillary reflex is much brighter in the albino, and this can increase the [[red eye effect]] in photographs. [[Edgar Winter]]'s eyes are an example of this trait. ===Heterochromia=== [[Image:Heterochromia.jpg|thumb|An example of ''heterochromia''. The subject has one brown and one hazel eye.]] {{main|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 [[Biological inheritance|inherited]] or acquired by [[disease]] or [[injury]].<ref name="Imesch">Imesch PD, Wallow IH, Albert DM. "The color of the human eye: a review of morphologic correlates and of some conditions that affect iridial pigmentation." ''Surv Ophthalmol.'' 1997 Feb;41 Suppl 2:S117-23. PMID 9154287.</ref> This uncommon condition usually results due to uneven [[melanin]] content. A number of causes are responsible, including genetics such as [[Chimera (genetics)|chimerism]] and [[Waardenburg syndrome]]. Trauma and certain medications, such as some [[prostaglandin analogue]]s 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. British singer [[David Bowie]] 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. American Actress [[Elizabeth Berkley]] has sectoral heterochromia; her right eye is half green and half brown, and her entire left eye is green. So does actor [[Anthony Head]] - he has a patch of hazel in his left eye where both eyes are blue-green overall. 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 blue eye and one brown-green eye. American Actress [[Demi Moore]] also has heterochromia, by having one green eye, and the other hazel. ===Eye color change=== Often, paler newborns have blue eyes, which change to green, hazel, light brown or dark brown. This is possibly the origin of the idiom "being blue-eyed" (i. e. naïve; gullible). It is thought that exposure to light after birth triggers the production of melanin in the iris of the eye. By three years of age, the eyes produce and store enough melanin to indicate their natural shade. While changes in eye color of infants are more common, even in adults, eye color changes are seen, most often as a result of exposure to the sun. Sunlight triggers melanin production in the eye, as it does to the skin. Eyedrops containing a [[prostaglandin analogue]] (such as [[latanoprost]]) may result in a permanently darkened iris; these eyedrops are commonly used to treat open-angle [[glaucoma]].<ref>{{cite journal |author=Hejkal TW, Camras CB |title=Prostaglandin analogs in the treatment of glaucoma |journal=Seminars in ophthalmology |volume=14 |issue=3 |pages=114–23 |year=1999 |pmid=10790575 |doi=10.153/SOPH01400114 |doi_brokendate=2008-06-21}}</ref> ==Eye color and red-eye effect== The photographic [[red-eye effect]] is more prominent in people with pale (blue or grey) eyes, and a similar effect (possibly the same) is observed in the [[tapetum lucidum|eyeshine]] of blue-eyed cats and dogs. ==References== <div class="references-small" style="-moz-column-count:2; column-count:2;"> <references/> </div> ==See also== *[[Iridology]] *[[Hair color]] *[[Human skin color]] *[[Xanthophore]] *[[List of Mendelian traits in humans]] ==External links== {{commonscat|Eyes}} *[http://www.thetech.org/genetics/ask.php?id=29 Genetics of eye color] *[http://longevity-science.blogspot.com/2007/02/eye-color.html Eye Color and Human Diseases] *[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15262401 Eye colour: portals into pigmentation genes and ancestry] *[http://www.kumc.edu/gec/support/eyecolor.html Various links on human eye color] [[Category:Eye]] [[Category:Facial features]] [[da:Øjenfarve]] [[de:Augenfarbe]] [[es:Color de ojos]] [[fa:رنگ چشم]] [[fr:Couleur des yeux]] [[gd:Dath nan sùilean]] [[it:Colore degli occhi]] [[he:צבע עיניים]] [[ja:虹彩の色]] [[nl:Iris (anatomie)]] [[pl:Kolor oczu]] [[pt:Olho humano]] [[fi:Silmien väri]] [[sv:Ögonfärg]] [[ta:கண் நிறம்]] [[zh:眼睛色彩]]