User Contributed Dictionary

English

Adjective

  1. Having more than one colour
  2. Of light, having more than one wavelength
  3. Of, or relating to heterochromatin

Extensive Definition

In anatomy, heterochromia refers to a difference in coloration, usually of the irises but also of hair or skin. Heterochromia is a result of the relative excess or lack of melanin (a pigment). It may be inherited, or due to genetic mosaicism, or due to disease or injury.
Eye color, specifically the color of the irises, is determined primarily by the concentration and distribution of melanin. The affected eye may be hyperpigmented (hyperchromic) or hypopigmented (hypochromic). In humans, usually, an excess of melanin indicates hyperplasia of the iris tissues, whereas a lack of melanin indictes hypoplasia.
Heterochromia of the eye (heterochromia iridis or heterochromia iridium) is of two kinds. In complete heterochromia, one iris is a different color from the other. In partial heterochromia or sectoral heterochromia, part of one iris is a different color from its remainder.
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. Famous comedian Dan Aykroyd has heterochromia, as do singer/songwriter Carly Simon, actresses Kate Bosworth, Elizabeth Berkley, Mila Kunis, Jane Seymour, actor Christopher Walken, American mixed martial artist Jens Pulver, and Major League Baseball pitcher Max Scherzer. Musician David Bowie is often thought to have heterochromia, but this is not the case as Bowie's eyes are both blue (his left pupil is permanently dilated due to a childhood injury).

Heterochromia in animals

Although seen in humans, complete heterochromia is more frequently observed in other species, where it almost always involves one blue eye. The blue eye occurs within a white spot, where melanin is absent from the skin and hair. These species include the cat, particularly breeds such as Japanese Bobtail, Turkish Van, and Turkish Angora. These so-called odd-eyed cats are white, or mostly white, with one normal eye (copper, orange, yellow, green), and one blue eye. Among dogs, complete heterochromia is seen often in the Siberian Husky. Horses with complete heterochromia have one brown and one white, gray, or blue eye. Complete heterochromia occurs also in cattle and even water buffalo.
Sectoral heterochromia, usually sectoral hypochromia, is often seen in dogs, specifically in breeds with merle coats. These breeds include Australian Shepherd and Border Collie.

Classification based on etiology

Heterochromia is classified primarily by onset: as either genetic or acquired. Although a distinction is frequently made between heterochromia that affects an eye completely or only partially (sectoral heterochromia), it is often classified as either genetic (due to mosaicism or congenital) or acquired, with mention as to whether the affected iris or portion of the iris is darker or lighter.

Congenital heterochromia

Heterochromia that is congenital is usually inherited as an autosomal dominant trait.
Abnormal iris darker
  • Lisch nodules — iris hamartomas seen in neurofibromatosis.
  • Ocular melanosis — a condition characterized by increased pigmentation of the uveal tract, episclera, and anterior chamber angle.
  • Oculodermal melanocytosis (nevus of Ota).
  • Simple heterochromia — a rare condition characterized by the absence of other ocular or systemic problems. The lighter eye is typically regarded as the affected eye as it usually shows iris hypoplasia. It may affect an iris completely or only partially.
  • Congenital Horner's syndrome — sometimes inherited, although usually acquired
  • Waardenburg's syndrome
  • Piebaldism — similar to Waardenburg's syndrome, a rare disorder of melanocyte development characterized by a white forelock and multiple symmetrical hypopigmented or depigmented macules.
  • Hirschsprung's disease — a bowel disorder associated with heterochromia in the form of a sector hypochromia. The affected sectors have been shown to have reduced numbers of melanocytes and decreased stromal pigmentation.
  • Incontinentia pigmenti with results suggesting that there is more difficulty recognizing iris color changes in dark-eyed individuals.
  • Acquired Horner's syndrome — usually acquired, as in neuroblastoma, although sometimes inherited.
  • NeoplasmMelanomas can also be very lightly pigmented, and a lighter colored iris may be a rare manifestation of metastatic disease to the eye.
Heterochromia has also been observed in those with Duane syndrome.
  • Chronic iritis Though not studied widely, Central Heterochromia is the most rare form of Heterochromia.
Eye colour is determined primarily by the concentration and distribution of melanin pigment within the iris tissues, Anything affecting those factors may result in a difference of colour being observed.
The human iris can be seen in a number of various colours. There are three true colors in the eyes that determine the outward appearance; brown, yellow, and grey. How much of each colour an individual has determines the appearance of his or her eye colour.
Eyes displaying Central Heterochromia are often referred to as "cat eyes" because of the appearance of a multi-coloured iris. Central Heterochromia appears to be prevalent in irises containing low amounts of melanin.Central Heterochromia does not label an eye as hazel. This is because the outer ring of an eye affected by Central Heterochromia is that iris' true colour.
The potential to acquire central heterochromia may be inherited genetically, though Central Heterochromia in itself is the condition where drug and toxic settlements in the body make the iris colour appear different from its basic predominant colour. These toxic signs that show in the iris indicate the amounts of the toxins the system has failed to eliminate.

See also

References

External links

heterochromatic in German: Iris-Heterochromie
heterochromatic in Spanish: Heterocromía
heterochromatic in French: Hétérochromie
heterochromatic in Korean: 홍채 이색증
heterochromatic in Italian: Eterocromia
heterochromatic in Hebrew: הטרוכרומיה
heterochromatic in Dutch: Heterochromie
heterochromatic in Japanese: 虹彩異色症
heterochromatic in Norwegian: Heterokromi
heterochromatic in Polish: Różnobarwność tęczówki
heterochromatic in Portuguese: Heterocromia
heterochromatic in Swedish: Heterokromi
heterochromatic in Chinese: 虹膜異色症
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