Heterochromia
| Heterochromia | |
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Complete heterochromia in human eyes: one brown and one green/hazel |
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| Classification and external resources | |
| Specialty | ophthalmology |
| ICD-10 | Q13.2, H20.8, L67.1 |
| ICD-9-CM | 364.53 |
| OMIM | 142500 |
| DiseasesDB | 31289 |
| MedlinePlus | 003319 |
| MeSH | C538115 |
Complete heterochromia in human eyes: one
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) 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 colors radiating from the pupil.
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.
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 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, caused by certain diseases and syndromes. Sometimes one eye may change color following disease or injury.
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