Heterochromia iridum

Not to be confused with Heterochromatin or Dichromatic (disambiguation).
Heterochromia
Complete heterochromia iridum
SpecialtyOphthalmology Edit this on Wikidata
SymptomsDifferent or partially different eye color
DurationLifelong
TreatmentIris implant surgery (controversial for cosmetic purposes)

Heterochromia is a variation in coloration most often used to describe color differences of the iris, but can also be applied to color variation of hair[1] 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.[2] It occurs in humans and certain breeds of domesticated animals.

Heterochromia of the eye is called heterochromia iridum or heterochromia iridis. It can be complete, sectoral, or central. 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.

Though multiple causes have been posited, the scientific consensus is that a lack of genetic diversity is the primary reason behind heterochromia, at least in domestic animals. 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.[3] Though common in some breeds of cats, dogs, cattle and horses due to inbreeding, heterochromia is uncommon in humans, affecting fewer than 200,000 people in the United States, and is not associated with lack of genetic diversity.[4][5]

The affected eye may be hyperpigmented (hyperchromic) or hypopigmented (hypochromic).[3] 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 derived from Ancient Greek: ἕτερος, héteros "different" and χρῶμα, chrôma "color".[6]

  1. ^ Kumar P (2017). "Focal Scalp Hair Heterochromia in an Infant". Sultan Qaboos University Medical Journal. 17 (1): e116–118. doi:10.18295/squmj.2016.17.01.022. PMC 5380409. PMID 28417041.
  2. ^ Imesch PD, Wallow IH, Albert DM (February 1997). "The color of the human eye: a review of morphologic correlates and of some conditions that affect iridial pigmentation throughout life". Survey of Ophthalmology. 41 (Suppl 2): S117–23. doi:10.1016/S0039-6257(97)80018-5. PMID 9154287.
  3. ^ a b Loewenstein, John; Scott Lee (2004). Ophthalmology: Just the Facts. New York: McGraw-Hill. ISBN 0-07-140332-9.
  4. ^ Konovalova EN, Gladyr EA, Kostiunina OV, Zinovieva LK (2017). "Congenital Defects of Beef Cattle and General Principles of their Prevention". Journal of Agriculture and Environment. 2 (3). doi:10.23649/jae.2017.2.3.1.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  5. ^ Ur Rehman H (2008). "Heterochromia". CMAJ. 179 (5): 447–448. doi:10.1503/cmaj.070497. PMC 2518194. PMID 18725617.
  6. ^ "heterochromia iridis - definition of heterochromia iridis in the Medical dictionary - by the Free Online Medical Dictionary, Thesaurus and Encyclopedia". Medical-dictionary.thefreedictionary.com. Retrieved 2014-04-27.