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Heterochromia

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An example of heterochromia iridis. The subject has a brown and green eye.
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An example of heterochromia iridis. The subject has a brown and green eye.

In anatomy, heterochromia refers to a difference in coloration, usually of the irises but also of hair or skin.

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 (complete heterochromia), or where 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.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.

Eye color, specifically the color of the irises, is determined primarily by the concentration and distribution of melanin pigment within the iris tissuesWielgus 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.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. [link]. Consequently, anything affecting those factors may result in a difference of color being observed.

An excess of pigmentation is usually associated with hyperplasia of the iris tissues whereas a lack of pigmentation is associated with hypoplasia. Although seen in humans, heterochromia in which one iris differs in color from the other iris is more frequently observed in non-human species such as cats (for example, Japanese Bobtails; white, shorthaired cats can be "odd-eyed" with one copper or orange eye and one blue eye, and the Turkish Angora), dogs (for example, Siberian Huskies as well as Australian Shepherds, Border Collies, and other breeds with merle coats), horses (so-called "walled-eyed" horses have one brown and one white eye), and even water buffalo.Misk NA, Semieka MA, Fathy A. "Heterochromia iridis in water buffaloes (Bubalus bubalis)." Vet Ophthalmol. 1998;1(4):195-201. PMID 11397231. Partial or sectoral heterochromia is much less common than complete heterochromia and is typically found in autosomally inherited disorders such as Hirschsprung's disease and Waardenburg syndrome.

Blue merle Border Collie with blue-and-brown eye.
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Blue merle Border Collie with blue-and-brown eye.

Classification based on etiology

Although a distinction is frequently made between heterochromia that affects an eye completely or only partially, it is often classified as either congenital or acquired with mention as to whether the affected iris or portion of the iris is darker or lighter.

Heterochromia can occur in several species of animals, including cats.
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Heterochromia can occur in several species of animals, including cats.

A Siberian husky with heterochromia.
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A Siberian husky with heterochromia.

Congenital heterochromia

Heterochromia that is congenital is usually inherited as an autosomal dominant trait.

Abnormal iris darker
Abnormal iris lighter
An example of sectoral heterochromia iridis. The subject has a blue iris with a brown section.
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An example of sectoral heterochromia iridis. The subject has a blue iris with a brown section.

Acquired heterochromia

Heterochromia that is acquired is usually due to injury, inflammation, the use of certain eyedrops, or tumors.

Abnormal iris darker
Abnormal iris lighter

Examples

Celebrities

Fictional characters

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References

External links

See also

 


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