In anatomy, heterochromia refers to 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. It may be inherited, or caused by genetic mosaicism, disease, or injury.
Heterochromia of the eye 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.
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 indicates hypoplasia.
Heterochromia iridium can be inherited through autosomal dominant fashion from men or women where the gene is passed on. It can also be caused through injury. It can also be caused by tumours, inflammation through use of eye drops or disease.
Complete heterochromia iridium is more frequently observed in other animal species such as dogs like the siberian husky or cats. Complete heterochromia iridium in other species almost always involves one blue eye. In animals melanin is used to give colour of skin, hair and eyes. In eyes, if there is low melanin pigment to none, they will be blue, if there is a bit of pigment they will be green and if there is a lot of pigment they will be brown. Therefore in animals with complete heterochromia ridium the blue eye is caused by a very little amount of melanin to none.
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