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In anatomy, heterochromia (ancient Greek: ἕτερος, ''héteros'', different + χρώμα, ''chróma'', color) is a difference in coloration, usually of the iris 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 caused by genetic mosaicism, chimerism, disease, or injury. Heterochromia of the eye (''heterochromia iridis'' or ''heterochromia iridum''; the common incorrect form "heterochromia iridium" is not correct Latin) is of three kinds. 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 and finally in "central heterochromia" there are spikes of different colours radiating from the pupil. Eye color, specifically the color of the irises, is determined primarily by the concentration and distribution of melanin.〔("All About Eye Color" ) from Larry Bickford〕 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 indicates hypoplasia. ==Classification== 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.〔Swann P. ("Heterochromia." ) ''Optometry Today.'' January 29, 1999. Retrieved November 1, 2006.〕 Most cases of heterochromia are hereditary, caused by a disease or syndrome, or due to an injury. Sometimes one eye may change color following certain diseases or injuries. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Heterochromia iridum」の詳細全文を読む スポンサード リンク
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