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Classification and external resources
A white cat with one blue and one yellow eye
A domesticated cat with full heterochromia
ICD-10 H21.24
ICD-9 364.53
Complete heterochromia in human eyes: one brown and one hazel

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 (a pigment). It may be inherited, due to genetic mosaicism, or due to disease or injury.[1]

Eye color, specifically the color of the irises, is determined primarily by the concentration and distribution of melanin.[2][3][4] The affected eye may be hyperpigmented (hyperchromic) or hypopigmented (hypochromic).[5] In humans, usually, an excess of melanin indicates hyperplasia of the iris tissues, whereas a lack of melanin indicates hypoplasia.

Heterochromia of the eye (heterochromia iridis or heterochromia iridum) 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.

Partial or sectoral heterochromia is much less common than complete heterochromia and is typically found in autosomally inherited disorders such as Hirschsprung's disease and Waardenburg syndrome.


Heterochromia in animals

Although infrequently seen in humans, complete heterochromia is more frequently observed in other species, where it almost always involves one blue eye. The blue eye occurs within a white spot, where melanin is absent from the skin and hair (see Leucism). These species include the cat, particularly breeds such as Turkish Van, Turkish Angora, and (rarely) Japanese Bobtail. These so-called odd-eyed cats are white, or mostly white, with one normal eye (copper, orange, yellow, green), and one blue eye. Among dogs, complete heterochromia is seen often in the Siberian Husky and/or the Australian Shepherd. Horses with complete heterochromia have one brown and one white, gray, or blue eye - complete heterochromia is more common in horses with pinto coloring. Complete heterochromia occurs also in cattle and even water buffalo.[6] It can also be seen in ferrets with Waardenburg Syndrome, although it can be very hard to tell at times as the eye color is often a midnight blue.

Sectoral hypochromia in a blue merle Border Collie

Sectoral heterochromia, usually sectoral hypochromia, is often seen in dogs, specifically in breeds with merle coats. These breeds include Australian Shepherd and Border Collie.

Classification based on etiology

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.[7]

Congenital heterochromia: inherited in autosomal dominant fashion (from men or women)

Congenital heterochromia

Heterochromia that is congenital is usually inherited as an autosomal dominant trait.

Abnormal iris darker

Abnormal iris lighter

  • Simple heterochromia – a rare condition characterized by the absence of other ocular or systemic problems. The lighter eye is typically regarded as the affected eye as it usually shows iris hypoplasia. It may affect an iris completely or only partially.
  • Congenital Horner's syndrome[10] – sometimes inherited, although usually acquired
  • Waardenburg's syndrome[10] – a syndrome in which heterochromia presents as a bilateral iris hypochromia in some cases. A Japanese review of 11 albino children with the disorder found that all had sectoral/partial heterochromia.[11]
  • Piebaldism – similar to Waardenburg's syndrome, a rare disorder of melanocyte development characterized by a white forelock and multiple symmetrical hypopigmented or depigmented macules.
  • Hirschsprung's disease – a bowel disorder associated with heterochromia in the form of a sector hypochromia. The affected sectors have been shown to have reduced numbers of melanocytes and decreased stromal pigmentation.[12]
  • Incontinentia pigmenti[5]
  • Parry-Romberg syndrome[5]

Acquired heterochromia

Heterochromia that is acquired is usually due to injury, inflammation, the use of certain eyedrops, or tumors.

Abnormal iris darker

  • Deposition of material
    • Siderosis – iron deposition within ocular tissues due to a penetrating injury and a retained iron-containing, intraocular foreign body.
    • Hemosiderosis – long standing hyphema (blood in the anterior chamber) following blunt trauma to the eye may lead to iron deposition from blood products
  • Use of certain eyedrops – prostaglandin analogues (latanoprost, isopropyl unoprostone, travoprost, and bimatoprost) are used topically to lower intraocular pressure in glaucoma patients. A concentric heterochromia has developed in some patients applying these drugs. The stroma around the iris sphincter muscle becomes darker than the peripheral stroma. A stimulation of melanin synthesis within iris melanocytes has been postulated.
  • Neoplasm – Nevi and melanomatous tumors.
  • Iridocorneal endothelium syndrome[5]
  • Iris ectropion syndrome[5]

Abnormal iris lighter

  • Fuchs' heterochromic iridocyclitis – a condition characterized by a low grade, asymptomatic uveitis in which the iris in the affected eye becomes hypochromic and has a washed-out, somewhat moth eaten appearance. The heterochromia can be very subtle, especially in patients with lighter colored irides. It is often most easily seen in daylight. The prevalence of heterochromia associated with Fuch's has been estimated in various studies[13][14][15] with results suggesting that there is more difficulty recognizing iris color changes in dark-eyed individuals.[15][16]
  • Acquired Horner's syndrome – usually acquired, as in neuroblastoma,[17] although sometimes inherited.
  • NeoplasmMelanomas can also be very lightly pigmented, and a lighter colored iris may be a rare manifestation of metastatic disease to the eye.

Heterochromia has also been observed in those with Duane syndrome.[18][19]

Central heterochromia

Example of Central Heterochromia showing a gold to blue iris.

Whereas heterochromia (also known as a heterochromia iridis or heterochromia iridum) is an eye condition in which one iris is a different color from the other (complete heterochromia), central heterochromia is an eye condition in which there are two different colors in the same iris. Central heterochromia is where the central (pupillary) zone of the iris is a different color than the mid-peripheral (ciliary) zone.

Eye color is determined primarily by the concentration and distribution of melanin pigment within the iris tissues; anything affecting those factors may result in a difference of color being observed.[2]

The human iris can be seen in a number of various colors. There are three true colors in the eyes that determine the outward appearance; brown, yellow, and grey. How much of each color an individual has determines the appearance of his or her eye color.[20]

Eyes displaying central heterochromia are often referred to as "cat eyes" because of the appearance of a multi-colored iris. Central heterochromia appears to be prevalent in irises containing low amounts of melanin.[21] Central heterochromia does not label an eye as hazel. This is because the outer ring of an eye affected by central heterochromia is that iris's true color.


See also


  1. ^ 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". Surv Ophthalmol. 41 (Suppl 2): S117–23. doi:10.1016/S0039-6257(97)80018-5. PMID 9154287. 
  2. ^ a b Wielgus AR, Sarna T (December 2005). "Melanin in human irides of different color and age of donors". Pigment Cell Res. 18 (6): 454–64. doi:10.1111/j.1600-0749.2005.00268.x. PMID 16280011. 
  3. ^ Prota G, Hu DN, Vincensi MR, McCormick SA, Napolitano A (September 1998). "Characterization of melanins in human irides and cultured uveal melanocytes from eyes of different colors". Exp Eye Res. 67 (3): 293–9. doi:10.1006/exer.1998.0518. PMID 9778410. 
  4. ^ "All About Eye Color" from Larry Bickford
  5. ^ a b c d e f g h i Loewenstein, John; Scott Lee (2004). Ophthalmology: Just the Facts. New York: McGraw-Hill. ISBN 0-07-140332-9. 
  6. ^ Misk NA, Semieka MA, Fathy A (1998). "Heterochromia iridis in water buffaloes (Bubalus bubalis)". Vet Ophthalmol. 1 (4): 195–201. doi:10.1046/j.1463-5224.1998.00036.x. PMID 11397231. 
  7. ^ Swann P. "Heterochromia." Optometry Today. January 29, 1999. Retrieved November 1, 2006.
  8. ^ van Emelen C, Goethals M, Dralands L, Casteels I (Jan-Feb 2000). "Treatment of glaucoma in children with Sturge-Weber syndrome". J Pediatr Ophthalmol Strabismus. 37 (1): 29–34. PMID 10714693. 
  9. ^ "Sturge-Weber syndrome: Definition and Much More from".<!. Retrieved 2009-11-19. 
  10. ^ a b Wallis DH, Granet DB, Levi L (June 2003). "When the darker eye has the smaller pupil". J Aapos. 7 (3): 215–6. doi:10.1016/S1091-8531(02)42020-4. PMID 12825064. 
  11. ^ Ohno N, Kiyosawa M, Mori H, Wang WF, Takase H, Mochizuki M (Jan-Feb 2003). "Clinical findings in Japanese patients with Waardenburg syndrome type 2". Jpn J Ophthalmol. 47 (1): 77–84. doi:10.1016/S0021-5155(02)00629-9. PMID 12586183. 
  12. ^ Brazel SM, Sullivan TJ, Thorner PS, Clarke MP, Hunter WS, Morin JD (February 1992). "Iris sector heterochromia as a marker for neural crest disease". Arch Ophthalmol. 110 (2): 233–5. PMID 1736874. 
  13. ^ Yang P, Fang W, Jin H, Li B, Chen X, Kijlstra A (March 2006). "Clinical features of Chinese patients with Fuchs' syndrome". Ophthalmology. 113 (3): 473–80. doi:10.1016/j.ophtha.2005.10.028. PMID 16458965. 
  14. ^ Arellanes-Garcia L, del Carmen Preciado-Delgadillo M, Recillas-Gispert C (June 2002). "Fuchs' heterochromic iridocyclitis: clinical manifestations in dark-eyed Mexican patients". Ocul Immunol Inflamm. 10 (2): 125–31. doi:10.1076/ocii. PMID 12778348. 
  15. ^ a b Tabbut BR, Tessler HH, Williams D (December 1988). "Fuchs' heterochromic iridocyclitis in blacks". Arch Ophthalmol. 106 (12): 1688–90. PMID 3196209. 
  16. ^ Bloch-Michel E (1983). "Fuchs heterochromic cyclitis: current concepts" (in French). J Fr Ophtalmol. 6 (10): 853–8. PMID 6368659. 
  17. ^ Mehta K, Haller JO, Legasto AC (2003). "Imaging neuroblastoma in children". Crit Rev Comput Tomogr. 44 (1): 47–61. doi:10.1080/10408370390808469. PMID 12627783. 
  18. ^ Khan AO, Aldamesh M (June 2006). "Bilateral Duane syndrome and bilateral aniridia". J Aapos. 10 (3): 273–4. doi:10.1016/j.jaapos.2006.02.002. PMID 16814183. 
  19. ^ Shauly Y, Weissman A, Meyer E (May-Jun 1993). "Ocular and systemic characteristics of Duane syndrome". J Pediatr Ophthalmol Strabismus. 30 (3): 178–83. PMID 8350229. 
  20. ^ Seddon JM, Sahagian CR, Glynn RJ, Sperduto RD, Gragoudas ES (August 1990). "Evaluation of an iris color classification system". Invest Ophthalmol Vis Sci. 31 (8): 1592–8. PMID 2201662. 
  21. ^ "Key Ocular Signs for Screening". Retrieved 2009-11-19. 

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