In anatomy,<unk>  refers to a difference in coloration, usually of the irises but also of hair or skin.<unk>  (also known as a<unk>  iridis or<unk>  iridium) is an eye condition in which one iris is a different color from the other (complete<unk> , or where part of one iris is a different color from the remainder (partial<unk>  or sectoral<unk> . It is a result of the relative excess or lack of pigment within an iris or part of an iris, which may be genetically inherited or due to mosaicism,  or acquired by disease or injury.
Eye color, specifically the color of the irises, is determined primarily by the concentration and distribution of melanin pigment within the iris tissues. 
Consequently, anything affecting those factors may result in a difference of color being observed.
The affected eye may be hyperpigmented (hyperchromic) or hypopigmented (hypochromic). 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,<unk>  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 and Turkish Vans; 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 "wall-eyed" horses have one brown and one white or blue eye), and even water buffalo. Partial or sectoral<unk>  is much less common than complete<unk>  and is typically found in autosomally inherited disorders such as Hirschsprung's disease and Waardenburg syndrome. Famous comedian Dan Akroyd has this condition.
Heterochromia
Hypodontia
Iniencephaly
Elfin facies
Micrognathism
Aniridia
Microdontia
Pitted nails