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Eye color

 
Genetics Encyclopedia: Eye Color
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When someone asks, "What color are your eyes?" he should really be asking "What color are your irises?" because it is the iris that contains the pigment that determines the color of your eyes. Despite the fascination eye color holds for us, the genes responsible for it in humans are not well-known and are more complex than most people think.

Iris Structure

The iris is the most visible portion of the uveal tract, which is the middle compartment of the eye. The iris is made up of blood vessels and connective tissue, in addition to melanocytes and other pigmented cells that are responsible for its distinctive color.

The iris contains muscles that control its movement and allow for changes in the size of the pupil, controlling the amount of light that enters the eye and that ultimately reaches the retina. Though its function is easily observed and obvious to any who look at it under varying lighting conditions, it is the appearance of the iris—specifically, its color—that is most striking and apparent. The structure itself takes its name from Iris, the Greek goddess of the rainbow and messenger of the gods.

The iris consists of two layers of different embryological origin. The anterior border of the iris consists of the stroma, a loose and interrupted layer of connective tissue. It is composed of melanocytes and nonpigmented cells, as well as other types of cells and tissues. Melanocytes contain melanin, a brown or black pigment. The overall structure of the stroma is similar in irises of all colors. The iris pigment epithelium forms the densely pigmented posterior layer of the iris. It consists of two layers of tightly fused, pigmented cells.

Differences in iris color depends on the amount of pigmentation in the deep stroma, especially the anterior border layer, and on the density of the stroma, both of which influence how much light, and what wavelengths, are absorbed and reflected. As with other objects, the color we see is the result of reflected light. The stroma of brown irises is densely pigmented with melanin and absorbs much of the light that enters it. In many human populations, brown is the only eye color. Blue irises have lightly pigmented stroma, and light of longer wavelengths (red to yellow) readily penetrates the iris and is absorbed, while some light of shorter wavelength (blue) is reflected back and scattered by the iris stroma; hence the blue color.

The inability to make melanin, as in albinism, leaves the iris without any pigment. The iris appears pink from the color of the blood flowing through it. Albinism is a recessive condition, requiring two defective alleles for melanin production, one inherited from each parent. Albinism also prevents pigment production in the hair and skin.

Genetics of Eye Color

Differences in iris color have been attributed to such causes as the temperature of the brain and eyes. Some people have stressed differences between dark-eyed and light-eyed populations and have suggested that eye color is related to general traits such as temperament or intellect. But, toward the middle of the nineteenth century, it had become clear that iris color was due to iris pigment, that this pigment developed soon after birth, and that the final quantity and distribution of the pigment was a hereditary trait.

Originally, iris color was thought to be a simple trait—one governed by a single gene with multiple forms, or alleles, corresponding to each color. In this scheme, blue was thought to be recessive, requiring two copies of the blue allele in order to be displayed. Therefore, two blue-eyed parents could have only blue-eyed children, since each parent had only blue alleles. However, repeated observation of brown-eyed offspring from two blue-eyed parents showed this view to be wrong. Iris color is likely to be a polygenic trait—one governed by at least two genes and possibly more.

Brown versus blue eye color is believed to be controlled by two genes on chromosome 15, called BEY1 and BEY2. Green versus blue eye color is believed to be controlled by a gene on chromosome 15, called GEY. In this system, blue is believed to be recessive to both brown and green. The protein products of these genes are unknown, however, as is the number of alleles possible for each. Furthermore, these three do not fully explain inheritance of all eye colors. More genes, which likely modify the action of these three, are probably involved.

Traditionally, iris color was felt to be stable throughout adulthood. However, iris color may change in response to disease. For example, there is a gradual unilateral (one-sided) loss of pigmentation in Horner's syndrome and in Fuchs' heterochromic iridocyclitis. There is also evidence for pigment loss in the iris as a result of aging, and changes in iris color may also occur spontaneously in normal people after adolescence. In addition, some commonly used drugs such as latanoprost (which lowers intraocular pressure) have caused hyperpigmentation in some irises.

Bibliography

American Academy of Ophthalmology. Fundamentals and Principles of Ophthalmology: Basic and Clinical Science Course. San Francisco: American Academy of Ophthalmology, 1995.

Imesch, Pascal D., et al. "The Color of the Human Eye: A Review of MorphologicCorrelates and of Some Conditions That Affect Iridial Pigmentation." Survey of Ophthalmology 41, supplement 2 (1997): s117-s123.

McKusick, Victor A. Mendelian Inheritance in Man: A Catalog of Human Genes and Genetic Disorders, 12th ed. Baltimore: Johns Hopkins University Press, 1998.

Internet Resource

Online Mendelian Inheritance in Man. Johns Hopkins University and National Center for Biotechnology Information. http://www.ncbi.nlm.nih.gov/Omim.

—Eric A. Postel

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Wikipedia: Eye color
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Eye color is a polygenic phenotypic character and is determined by the amount and type of pigments in the eye's iris.[1][2]

Humans and other animals have many phenotypic variations in eye color, as blue, brown, green and others. These variations constitute phenotypic traits.[3]

The genetics of eye color are complicated and eye color is determined by multiple genes. Some of the eye color genes include EYCL1 (a green/blue eye color gene located on chromosome 19), EYCL2 (a brown eye color gene) and EYCL3 (a brown/blue eye color gene located on chromosome 15). The once-held view that blue eye color is a simple recessive trait has been shown to be wrong. The genetics of eye color are so complex that almost any parent-child combination of eye colors can occur.[4][5]

In human eyes, these variations in color are attributed to varying ratios of eumelanin produced by melanocytes in the iris.[2] The brightly colored eyes of many bird species are largely determined by other pigments, such as pteridines, purines, and carotenoids.[6]

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.[7] In eyes of all colors, the iris pigment epithelium contains the black pigment, eumelanin.[2][7] Color variations among different irises are typically attributed to the melanin content within the iris stroma.[7] The density of cells within the stroma affects how much light is absorbed by the underlying pigment epithelium.[7] OCA2 gene polymorphism, close to proximal 5′ regulatory region, explains most human eye-color variation.[8]

Contents

Genetic determination of eye color

See also: Human genetic variation, Race and genetics, and Human genetic clustering

Eye colours can range from the most common colour, brown, to the least common, green. Rare genetic mutations can even lead to unusual eye colours: black, red, or the appearance of violet. Eye colour is an inherited trait influenced by more than one gene.[9][10] These genes are being sought using associations to small changes in the genes themselves and in neighboring genes. These changes are known as single nucleotide polymorphisms or SNPs. The actual number of genes that contribute to eye color is currently unknown, but there are a few likely candidates. A study in Rotterdam (2009) found that it was possible to predict the color of eyes with more than 90% accuracy for brown and blue, using just six SNPs (from six genes). [11]

The gene OCA2 (OMIM: 203200), when in a variant form the gene causes the pink eye color and hypopigmentation common in human albinism. (The name of the gene is derived from the disorder it causes, oculocutaneous albinism type II.) Different SNPs within OCA2 are strongly associated with blue and green eyes as well as variations in freckling, mole counts, hair and skin tone. The polymorphisms may be in an OCA2 regulatory sequence, where they may influence the expression of the gene product, which in turn affects pigmentation.[8] A specific mutation within the HERC2 gene, a gene that regulates OCA2 expression, is partly responsible for blue eyes.[12] Other genes implicated in eye color variation are: SLC24A4 [13] and TYR.[13]

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 [of the Herc2 gene] 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

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.[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]

As the 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.[16]

Eye color exists on a continuum from the darkest shades of brown to the lightest shades of blue.[9] 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.[17] There are 3 true colors in the eyes that determine the outward appearance; brown, yellow, and blue. How much of each color one has 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 blue and some yellow, making them appear green. Brown eyes appear brown because most of the eye contains the brown color. The above is true only for Homo sapiens; iris color varies greatly in the rest of the animal world. For example, instead of blue in humans, autosomal recessive color in the skink Corucia zebrata is black, whereas the autosomal dominant color is yellow-green.[18]

Changes in eye color throughout life

In European populations, children are most commonly born with unpigmented (blue) eyes. As the child develops, melanocytes, cells found within the iris of human eyes (as well as skin and hair follicles) slowly begin to produce melanin. Because melanocyte cells continually produce pigment, eye color, in theory, can be changed.

Changes (lightening or darkening) of eye colors during puberty, early childhood, pregnancy, and sometimes after serious trauma (like heterochromia), do represent cause for plausible argument to state that some eyes can or do change, based on chemical reactions and hormonal changes within the body. Most eye changes happen when the infant is around one year old, although it can happen up to 3 years of age.[19]

Studies on Caucasian twins, both fraternal and identical, have shown that eye color over time can be subject to change, and major demelanization of the iris may also be genetically determined. Most eye color changes have been observed or reported in the Caucasian population with hazel eyes.[20]

Eye color chart (Martin-Schultz scale)

Carleton Coon created this chart by the Martin-Schultz scale often used in physical anthropology.

  1. Light eyes

    Eyes light and light mixed are 16-12 in Martin scale.

    Light
    Grey, blue, green.
    Light-mixed
    1. Very light-mixed (blue with grey or green or green with grey)
    2. Light-mixed (light or very light-mixed with small admixture of brown pigment)
  2. Mixed eyes
    Mixed
    12-6 in Martin scale. Mixture of light eyes (blue, grey or green) with brown pigment when light and brown pigment are the same level.
  3. Dark eyes
    Dark-mixed
    6-4 in Martin scale. Brown with small admixture of light pigment.
    Dark
    4-1 in Martin scale. Brown (light brown and dark brown) and very dark brown (almost black).


Amber

Human amber eyes displaying the yellow pigments.
Amber iris

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).[21][22] Amber eyes should not be confused with hazel eyes; although hazel eyes may contain specks of amber or gold, they usually tend to comprise 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 pteridines.[23] 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.[24] In humans, yellowish specks or patches are thought to be due to the pigment lipofuscin, also known as lipochrome.[25]

Blue

A blue iris

In 2008, new research revealed that people with blue eyes have a single, common ancestor. Scientists tracked down a genetic mutation that leads to blue eyes. The mutation occurred between 6,000 and 10,000 years ago; researchers state that before then, blue eyes did not exist. "Originally, we all had brown eyes," said Hans Eiberg from the Department of Cellular and Molecular Medicine at the University of Copenhagen.[26][27][28] The mutation affected the OCA2 gene, which is involved in the production of melanin, the pigment that gives color to our hair, eyes and skin. Eiberg stated, "A genetic mutation affecting the OCA2 gene in our chromosomes resulted in the creation of a 'switch,' which literally 'turned off' the ability to produce brown eyes:

The genetic switch is located in the gene adjacent to OCA2 and rather than completely turning off the gene, the switch limits its action, which reduces the production of melanin in the iris. In effect, the turned-down switch diluted brown eyes to blue. If the OCA2 gene had been completely shut down, our hair, eyes and skin would be melanin-less, a condition known as albinism.[27]

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.[7] The type of melanin present is eumelanin.[29] The inheritance pattern followed by blue eyes is considered similar to that of a recessive trait (in general, eye color inheritance is considered a polygenic trait, meaning that it is controlled by the interactions of several genes, not just one).[10] 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.[26] The authors concluded that the mutation may have arisen in a single individual in the Near East or around the Black Sea region 6,000-10,000 years ago during the Neolithic revolution.[27][28]

Blue eyes are most common in Northern Europe and Central Europe and to a lesser degree in Southern Europe, North America and southern Central Asia; Afghanistan is a notable example.[30] They're also found in parts of North Africa,[31] West Asia, and South Asia[32], in particular the northern areas of India and Pakistan. It can rarely occur as far south as Sri Lanka. Moreover, blue/green/gray eyes can be found within the population of East Asia, especially among Chinese, even Han Chinese,[1] due to the constantly wars and raids between Chinese Empire and Indo-European nomadiac tribes from Eurasia Steppe, such as Göktürks. Those confilcts could result in tens of thousands people, mainly women and children, being captured and brought back to victor's society.[33] Due to unknown reasons, there is little scientific studies of light-color eyed Han Chinese.

A 2002 study found the prevalence of blue eye color among Caucasians in the United States to be 33.8 percent for those born from 1936 through 1951 compared with 57.4 percent for those born from 1899 through 1905.[10] Blue eyes have become increasingly rare among American children with only 1 out of every 6 – 16.6 percent which is 49.8 million out of 300 million (22.4% of white Americans) of the total United States population having blue eyes.[34][35] The plunge in the past few decades has taken place at a remarkable rate. A century ago, 80 percent of people married within their ethnic group. Blue eyes were routinely passed down, especially among people of Western and Northern European ancestry.[34][35][36] In the 1930s, eugenicists[citation needed] used the disappearance of blue eyes as a rallying cry to support immigration restrictions. They went so far as to map the parts of the country with the highest and lowest percentage of blue-eyed people.[citation needed]

The outer surface of the iris of a blue eyed person is actually clear, lacking the outer layer of pigmentation that is found in brown eyes. Their color is caused by the inner layer of pigmentation and the semi-opaque fibrous tissues which lay between the two layers.[37]

Brown

"Brown eyes" redirects here. For other uses, see Brown eyes (disambiguation).
Brown iris
Light brown iris

Brown eyes are dominant in humans[38] and, in many parts of the world it is nearly the only iris color present.[39] It is less common in countries around the Baltic Sea and in Scandinavia. Dark pigment of brown eyes are most common in East Asia , Africa and the Americas. In humans brown eyes contain large amounts of melanin within the iris stroma, which serves to absorb light at both shorter and longer wavelengths. Brown eyes are the most common eye color, with over half of the world's population having them.

Gray

A steel blue-gray iris
Gray iris under magnification, exhibiting small amounts of yellow.

Gray eyes have less melanin than blue eyes,[citation needed] even though they are considered a darker shade of blue (like blue-green). Gray eyes are most common in European Russia, Finland and the Baltic States[citation needed]. It can also be found to a lesser extent in parts of India[32]. Under magnification, gray eyes exhibit small amounts of yellow and brown color in the iris. Ultimately there are at least two things that could determine gray eye color. The first is the amount of melanin made and the second is the density of the proteins in the stroma. [40]

A gray iris may indicate the presence of a uveitis. However, other visual signs make a uveitis obvious. Gray iris color, as well as blue, are at increased risk of uveal melanoma. [41]

Visually, gray eyes often tend to appear to change between the shades of blue, green and gray; this is because gray eyes are extremely light, as mentioned before. The color change for gray eyes is usually influenced by the lighting and the colors in the surroundings (such as clothes, makeup, etc.).

Green

A green iris
Olive green eyes

Green eyes are the product of low to moderate amounts of melanin and probably represent the interaction of multiple variants within the OCA2 and in other genes. Green eyes are most common in Northern and Central Europe.[42][43] They can also be found in parts of South Asia[32], West Asia, and North Africa. In Iceland, 89% of women and 87% of men have either blue or green eye color.[44]A study of Icelander and Dutch adults found green eyes to be much more prevalent in women than in men. Among European Americans, green eyes are most common among those of Celtic and Germanic ancestry, about 16%.[45]

Hazel

This iris shows a mixture of brown, green and amber colors.

Hazel eyes are due to a combination of Rayleigh scattering and a moderate amount of melanin in the iris' anterior border layer.[7][25] Hazel eyes often appear to shift in color from a light brown to a dark golden-green. A number of studies using three-point scales have assigned hazel to be the medium-color between the lightest shade of blue and darkest shade of brown. Hazel mostly consists of Brown and Green. The dominant color in the eye can either be green or light brown/gold.[46][47][48][49][50][51][52] This can sometimes produce a multicolored iris, i.e., an eye that is light brown/amber near the pupil and charcoal or dark green on the outer part of the iris (and vice versa) when observed in sunlight. Hazel is commonly found in Europe, the Middle East, Americas, Central Asia, and parts of South Asia.

Definitions of the eye color hazel vary: it is sometimes considered to be synonymous with light-brown or gold, as in the color of a hazelnut shell.[46][48][51][53] In North America, hazel is often used to describe eyes that appear to change color.

Red

The eyes of people with albinism may appear red under certain lighting conditions owing to the extremely low quantities of melanin,[54] allowing the blood vessels to show through.

"Red" albino eyes.

Purple/Violet

Purple or violet eyes are very rare in humans; the appearance of purple or violet eyes are thought to occur from the mixing of red and blue reflections.[55] Elizabeth Taylor is occasionally described as having violet eyes. [56]

Medical implications

Those with lighter iris color have been found to have a higher prevalence of age-related macular degeneration (ARMD) than those with darker iris color;[50] lighter eye color is also associated with an increased risk of ARMD progression.[57] An increased risk of uveal melanoma has been found in those with blue, green or gray iris color.[41][44] Additionally, an August 2000 study suggests that people with dark brown eyes are at increased risk of developing cataracts, and therefore should protect their eyes from direct exposure to sunlight.[58]

Eye color may also be symptomatic of disease. Aside from the iris, yellowing of the whites of the eyes is associated with jaundice and symptomatic of liver disease, including cirrhosis, hepatitis and malaria.

Aside from the above factors, yellowing of the whites of the eyes in people with darker pigmented skin is often due to melonin being present in the whites of the eyes. However, any sudden changes in the color of the whites of the eyes should be addressed by a medical professional.

Anomalous conditions

Aniridia

Main article: Aniridia

Aniridia is a congenital condition characterized by an extremely underdeveloped iris which appears absent on superficial examination.[59]

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.[60] 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.

Heterochromia

An example of complete heterochromia. The subject has one brown and one hazel eye. The subject also appears to have a faint star pattern in the hazel iris.
An example of sectoral heterochromia. The subject has a blue iris with a brown section.
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.[61] This uncommon condition usually results due to uneven melanin content. A number of causes are responsible, including genetics such as chimerism, Horners Syndrome and Waardenburg syndrome. A common cause in females with heterochromia is X-inactivation, which can result in a number of heterochromatic traits, such as calico cats. Trauma and certain medications, such as some prostaglandin analogues can also cause increased or decreased pigmentation in one eye.[62] On occasion, the condition of having two different colored eyes is caused by blood staining the iris after sustaining injury.

See also

References

  1. ^ Wielgus AR, Sarna T (December 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. ^ a b c Prota G, Hu DN, Vincensi MR, McCormick SA, Napolitano A (September 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. ^ Morris, PJ. "Phenotypes and Genotypes for human eye colors." Athro Limited website. Retrieved May 10, 2006.
  4. ^ http://www.sciencedaily.com/releases/2007/02/070222180729.htm
  5. ^ http://www.medterms.com/script/main/art.asp?articlekey=25003
  6. ^ 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. 
  7. ^ a b c d e f 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. ^ a b Duffy DL, Montgomery GW, Chen W, et al. (February 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. PMID 17236130. 
  9. ^ a b Sturm RA, Frudakis TN (August 2004). "Eye colour: portals into pigmentation genes and ancestry". Trends Genet. 20 (8): 327–32. doi:10.1016/j.tig.2004.06.010. PMID 15262401. http://www.biosci.ohio-state.edu/~pfuerst/courses/eeobmg640/reading1eyecolor.pdf. 
  10. ^ a b c Grant MD, Lauderdale DS (2002). "Cohort effects in a genetically determined trait: eye colour among US whites". Ann. Hum. Biol. 29 (6): 657–66. doi:10.1080/03014460210157394. PMID 12573082. 
  11. ^ "DNA test for eye colour could help fight crime", New Scientist 14 March, 2009. Fan Liu, van Duijn K, Vingerling JR, et al. (10 March 2009). "Eye color and the prediction of complex phenotypes from genotypes". Current Biology 19 (5): R192–R193. doi:10.1016/j.cub.2009.01.027. http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VRT-4VT0BCK-B&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=54b555b22ad247b14c52eefca5927645. 
  12. ^ Kayser M, Liu F, Janssens AC, et al. (February 2008). "Three genome-wide association studies and a linkage analysis identify HERC2 as a human iris color gene". Am. J. Hum. Genet. 82 (2): 411–23. doi:10.1016/j.ajhg.2007.10.003. PMID 18252221. 
  13. ^ a b Sulem P, Gudbjartsson DF, Stacey SN, et al. (December 2007). "Genetic determinants of hair, eye and skin pigmentation in Europeans". Nat. Genet. 39 (12): 1443–52. doi:10.1038/ng.2007.13. PMID 17952075. 
  14. ^ a b German EJ, Hurst MA, Wood D, Gilchrist J (March 1998). "A novel system for the objective classification of iris colour and its correlation with response to 1% tropicamide". Ophthalmic Physiol Opt 18 (2): 103–10. doi:10.1016/S0275-5408(97)00070-7. PMID 9692029. http://www3.interscience.wiley.com/resolve/openurl?genre=article&sid=nlm:pubmed&issn=0275-5408&date=1998&volume=18&issue=2&spage=103. 
  15. ^ Fan S, Dyer CR, Hubbard L. Quantification and Correction of Iris Color." Technical report 1495, University of Wisconsin-Madison, Dec, 2003.
  16. ^ Color Perception
  17. ^ Seddon, J.M.; CR Sahagian, RJ Glynn, RD Sperduto and ES Gragoudas (01 Aug 1990). "Evaluation of an iris color classification system". Investigative Ophthalmology & Visual Science (Association for Research in Vision and Ophthalmology) 31 (8): 1592–8. PMID 2201662. http://www.iovs.org/cgi/content/abstract/31/8/1592. Retrieved 2009-05-04. 
  18. ^ 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.
  19. ^ Aluzri, Shan Z., All About Eyes., retrieved on june, 1, 2009.
  20. ^ Arch Ophthalmol
  21. ^ Howard Hughes Medical Institute: Ask A Scientist
  22. ^ Eye Color
  23. ^ Oliphant LW (1987). "Observations on the pigmentation of the pigeon iris". Pigment Cell Res. 1 (3): 202–8. doi:10.1111/j.1600-0749.1987.tb00414.x. PMID 3508278. 
  24. ^ Oliphant LW (1981). "Crystalline pteridines in the stromal pigment cells of the iris of the great horned owl". Cell Tissue Res. 217 (2): 387–95. doi:10.1007/BF00233588. PMID 7237534. 
  25. ^ a b Lefohn A, Budge B, Shirley P, Caruso R, Reinhard E (November 2003). "An Ocularist's Approach to Human Iris Synthesis". IEEE Comput. Graph. Appl. 23 (6): 70–5. doi:10.1109/MCG.2003.1242384. 
  26. ^ a b Eiberg H, Troelsen J, Nielsen M, et al. (March 2008). "Blue eye color in humans may be caused by a perfectly associated founder mutation in a regulatory element located within the HERC2 gene inhibiting OCA2 expression". Hum. Genet. 123 (2): 177–87. doi:10.1007/s00439-007-0460-x. PMID 18172690. http://www.springerlink.com/content/2045q6234h66p744/fulltext.html. 
  27. ^ a b c Bryner, Jeanna (2008-01-31). "Genetic mutation makes those brown eyes blue". MSNBC. http://www.msnbc.msn.com/id/22934464/. Retrieved 2009-10-19. 
  28. ^ a b http://www.telegraph.co.uk/scienceandtechnology/science/sciencenews/3323607/Blue-eyes-result-of-ancient-genetic-mutation.html
  29. ^ Menon IA, Basu PK, Persad S, Avaria M, Felix CC, Kalyanaraman B (July 1987). "Is there any difference in the photobiological properties of melanins isolated from human blue and brown eyes?". Br J Ophthalmol 71 (7): 549–52. doi:10.1136/bjo.71.7.549. PMID 2820463. PMC 1041224. http://bjo.bmj.com/cgi/pmidlookup?view=long&pmid=2820463. 
  30. ^ Pigmentation, the Pilous System, and Morphology of the Soft Parts
  31. ^ q:Berber people
  32. ^ a b c Herbert Risley, William Crooke, The People of India, (1999)
  33. ^ These campaigns are described in detail by Michael Loewe, "The campaigns of Han Wu-ti", in Chinese ways in warfare, ed. Frank A. Kierman, Jr., and John K. Fairbank (Cambridge, Mass., 1974).
  34. ^ a b Don't it make my blue eyes brown
  35. ^ a b "Don't it make my blue eyes brown Americans are seeing a dramatic color change - The Boston Globe | Encyclopedia.com". http://www.encyclopedia.com/doc/1P2-7981364.html. 
  36. ^ Blue eyes are increasingly rare in America
  37. ^ Mason, Clyde (January 1924). Journal of Physical Chemistry 28 (5): 498–501. doi:10.1021/j150239a007. http://pubs.acs.org/doi/abs/10.1021/j150239a007. Retrieved 2009-04-17. "...the various shades [of blue eyes] are due to the dark inner layer of pigment — the uvea — showing through fibrous structures of different densities or degrees of opacity.". 
  38. ^ Eiberg H, Mohr J (1996). "Assignment of genes coding for brown eye colour (BEY2) and brown hair colour (HCL3) on chromosome 15q". Eur. J. Hum. Genet. 4 (4): 237–41. PMID 8875191. 
  39. ^ Online 'Mendelian Inheritance in Man' (OMIM) SKIN/HAIR/EYE PIGMENTATION, VARIATION IN, 1; SHEP1 -227220
  40. ^ Lucy Southworth. "Are gray eyes the same as blue in terms of genetics?". Understanding Genetics: Human Health and the Genome. Stanford School of Medicine. http://www.thetech.org/genetics/ask.php?id=232. 
  41. ^ a b Stang A, Ahrens W, Anastassiou G, Jöckel KH (December 2003). "Phenotypical characteristics, lifestyle, social class and uveal melanoma". Ophthalmic Epidemiol 10 (5): 293–302. doi:10.1076/opep.10.5.293.17319. PMID 14566630. 
  42. ^ Blue Eyes Versus Brown Eyes: A Primer on Eye Color - EyeDoctorGuide.com
  43. ^ Why Do Europeans Have So Many Hair and Eye Colors?
  44. ^ a b Rafnsson V, Hrafnkelsson J, Tulinius H, Sigurgeirsson B, Olafsson JH (August 2004). "Risk factors for malignant melanoma in an Icelandic population sample". Prev Med 39 (2): 247–52. doi:10.1016/j.ypmed.2004.03.027. PMID 15226032. 
  45. ^ "Gene Expression: NLSY blogging: Eye and hair color of Americans". http://www.gnxp.com/blog/2008/12/nlsy-blogging-eye-and-hair-color-of.php. 
  46. ^ a b Zhu G, Evans DM, Duffy DL, et al. (April 2004). "A genome scan for eye color in 502 twin families: most variation is due to a QTL on chromosome 15q". Twin Res 7 (2): 197–210. doi:10.1375/136905204323016186. PMID 15169604. 
  47. ^ Albert DM, Green WR, Zimbric ML, et al. (2003). "Iris melanocyte numbers in Asian, African American, and Caucasian irides". Trans Am Ophthalmol Soc 101: 217–21; discussion 221–2. PMID 14971580. PMC 1358991. http://www.aosonline.org/xactions/2003/1545-6110_v101_p217.pdf. 
  48. ^ a b Mitchell R, Rochtchina E, Lee A, Wang JJ, Mitchell P (March 2003). "Iris color and intraocular pressure: the Blue Mountains Eye Study". Am. J. Ophthalmol. 135 (3): 384–6. doi:10.1016/S0002-9394(02)01967-0. PMID 12614760. http://linkinghub.elsevier.com/retrieve/pii/S0002939402019670. 
  49. ^ Lindsey JD, Jones HL, Hewitt EG, Angert M, Weinreb RN (June 2001). "Induction of tyrosinase gene transcription in human iris organ cultures exposed to latanoprost". Arch. Ophthalmol. 119 (6): 853–60. PMID 11405836. 
  50. ^ a b Frank RN, Puklin JE, Stock C, Canter LA (2000). "Race, iris color, and age-related macular degeneration". Trans Am Ophthalmol Soc 98: 109–15; discussion 115–7. PMID 11190014. 
  51. ^ a b Regan S, Judge HE, Gragoudas ES, Egan KM (June 1999). "Iris color as a prognostic factor in ocular melanoma". Arch. Ophthalmol. 117 (6): 811–4. PMID 10369595. 
  52. ^ Hawkins TA, Stewart WC, McMillan TA, Gwynn DR (1994). "Analysis of diode, argon, and Nd: YAG peripheral iridectomy in cadaver eyes". Doc Ophthalmol 87 (4): 367–76. doi:10.1007/BF01203345. PMID 7851220. 
  53. ^ Hammond BR, Fuld K, Snodderly DM (March 1996). "Iris color and macular pigment optical density". Exp. Eye Res. 62 (3): 293–7. doi:10.1006/exer.1996.0035. PMID 8690039. http://linkinghub.elsevier.com/retrieve/pii/S0014483596900354. 
  54. ^ NOAH — What is Albinism?
  55. ^ BBC - h2g2 - Determination of Eye Color
  56. ^ http://www.imdb.com/name/nm0000072/bio
  57. ^ Nicolas CM, Robman LD, Tikellis G, et al. (December 2003). "Iris colour, ethnic origin and progression of age-related macular degeneration". Clin. Experiment. Ophthalmol. 31 (6): 465–9. doi:10.1046/j.1442-9071.2003.00711.x. PMID 14641151. http://www3.interscience.wiley.com/resolve/openurl?genre=article&sid=nlm:pubmed&issn=1442-6404&date=2003&volume=31&issue=6&spage=465. 
  58. ^ Cumming RG, Mitchell P, Lim R (August 2000). "Iris color and cataract: The Blue Mountains Eye Study". American journal of ophthalmology 130 (2): 237-238. http://www.ajo.com/article/S0002-9394(00)00479-7/abstract. 
  59. ^ Aniridia at eMedicine
  60. ^ Ocular Manifestations of Albinism at eMedicine
  61. ^ Imesch PD, Wallow IH, Albert DM (February 1997). "The color of the human eye: a review of morphologic correlates and of some conditions that affect iridial pigmentation". Surv Ophthalmol 41 (Suppl 2): S117–23. doi:10.1016/S0039-6257(97)80018-5. PMID 9154287. 
  62. ^ Hejkal TW, Camras CB (1999). "Prostaglandin analogs in the treatment of glaucoma". Seminars in ophthalmology 14 (3): 114–23. doi:10.3109/08820539909061464. PMID 10790575. 

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