Heterochromia iridis

Heterochromia is a difference in coloration, usually of the iris but also of hair or skin. Heterochromia is determined by the production, delivery, and concentration of melanin (a pigment). It may be inherited, or caused by genetic mosaicism, chimerism, disease, or injury. It occurs in humans and certain breeds of dogs and cats.Actress Alice Eve has complete heterochromia: her left eye is blue and right eye is green.Actor Dominic Sherwood has sectoral heterochromia.Heterochromia in a child.Complete heterochromia in a teenager who also has anisocoria.Example of central heterochromia showing an orange to blue iris.Example of central heterochromia in green eye with speckled brown pigment.A young adult exhibiting sectoral heterochromia in the form of an orange segment in her right, blue eye. The individual's mother exhibited a similar orange section in her left eye, although her iris color was green.A cat with complete heterochromia.This cat's yellow eye has what looks like central heterochromia, as the outside of the eye is yellow, and the iris is green.Complete heterochromia in a Siberian Husky: one eye blue, one eye brown.Sectoral hypochromia in a blue merle Border Collie.Heterochromia in a mutt dog Heterochromia is a difference in coloration, usually of the iris but also of hair or skin. Heterochromia is determined by the production, delivery, and concentration of melanin (a pigment). It may be inherited, or caused by genetic mosaicism, chimerism, disease, or injury. It occurs in humans and certain breeds of dogs and cats. Heterochromia of the eye is called heterochromia iridum or heterochromia iridis. It can be complete or sectoral. In complete heterochromia, one iris is a different color from the other. In sectoral heterochromia, part of one iris is a different color from its remainder. In central heterochromia, there is a ring around the pupil or possibly spikes of different colors radiating from the pupil. Heterochromia of the eye was described by the Ancient Greek philosopher Aristotle, who termed it heteroglaucos. The historian Plutarch describes Alexander the Great as having this condition. Though multiple causes have been posited, the scientific consensus is that a lack of genetic diversity is the primary reason behind heterochromia. This is due to a mutation of the genes that determine melanin distribution at the 8-HTP pathway, which usually only become corrupted due to chromosomal homogeneity. Though common in some breeds of cats, dogs and horses, due to inbreeding, heterochromia is uncommon in humans, affecting fewer than 200,000 people in the United States of America, and is not associated with lack of genetic diversity. 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, an increase of melanin production in the eyes indicates hyperplasia of the iris tissues, whereas a lack of melanin indicates hypoplasia. The term is from Ancient Greek: ἕτερος, héteros meaning different and χρώμα, chróma meaning color. 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. Most cases of heterochromia are hereditary, and are entirely benign and unconnected to any pathology, however, some are associated with certain diseases and syndromes. Sometimes one eye may change color following disease or injury. In sectoral heterochromia, sometimes referred to as partial heterochromia, areas of the same iris contains two completely different colors.It is unknown how rare sectoral heterochromia is in humans. Acquired heterochromia is usually due to injury, inflammation, the use of certain eyedrops that damages the iris, or tumors.