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Heterochromia iridum

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For the tightly packed form of DNA, see Heterochromatin.
Heterochromia iridum
SpecialtyOphthalmology Edit this on Wikidata
Complete heterochromia in human eyes: one brown and one hazel

In anatomy, heterochromia refers to a difference in coloration, usually of the irides 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 due to genetic mosaicism, or due to disease or injury.[1]

Eye color, specifically the color of the irides, 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 indictes hypoplasia.

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

Sectoral heterochromia: a blue iris with a brown section.

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. Famous comedian Dan Aykroyd has heterochromia, as do singer/songwriter Carly Simon, actresses Kate Bosworth, Elizabeth Berkley, Mila Kunis, Jane Seymour, actor Christopher Walken, American mixed martial artist Jens Pulver, and Major League Baseball pitcher Max Scherzer. Musician David Bowie is often thought to have heterochromia, but this is not the case as Bowie's eyes are both blue (his left pupil is permanently dilated due to a childhood injury).

Heterochromia in animals

Main article: Odd-eyed cat
Complete heterochromia in a cat: one blue and one green eye

Although 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. These species include the cat, particularly breeds such as Japanese Bobtail, Turkish Van, and Turkish Angora. 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. Horses with complete heterochromia have one brown and one white, gray, or blue eye. Complete heterochromia occurs also in cattle and even water buffalo.[6]

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
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.
  • Neoplasm — Melanomas 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

A grey-blue iris with a greenish-yellow ring showing Central Heterochromia
File:EyewithCH.jpg
A grey iris featuring Central Heterochromia

Whereas Heterochromia (also known as a heterochromia iridis or heterochromia iridium) is an eye condition in which one iris is a different colour from the other (complete heterochromia), Central Heterochromia (also known as Sectoral Heterochromia) is an eye condition in which there are two different colours in the same iris. Central Heterochromia is where the central (pupillary) zone of the iris is a different colour than the mid-peripheral (ciliary) zone, and may be linked to above average toxic burden in the body.[20] Though not studied widely, Central Heterochromia is the rarest form of Heterochromia.[citation needed]

Eye colour 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 colour being observed.[21]

The human iris can be seen in a number of various colours. There are three true colors in the eyes that determine the outward appearance; brown, yellow, and grey. How much of each colour an individual has determines the appearance of his or her eye colour.[22]

Eyes displaying Central Heterochromia are often referred to as "cat eyes" because of the appearance of a multi-coloured iris. Central Heterochromia appears to be prevalent in irides containing low amounts of melanin[20][23].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' true colour.[23]

See also

References

  1. ^ Imesch PD, Wallow IH, Albert DM. "The color of the human eye: a review of morphologic correlates and of some conditions that affect iridial pigmentation." Surv Ophthalmol. 1997 Feb;41 Suppl 2:S117-23. PMID 9154287.
  2. ^ Wielgus AR, Sarna T. "Melanin in human irides of different color and age of donors." Pigment Cell Res. 2005 Dec;18(6):454-64. PMID 16280011.
  3. ^ Prota G, Hu DN, Vincensi MR, McCormick SA, Napolitano A. "Characterization of melanins in human irides and cultured uveal melanocytes from eyes of different colors." Exp Eye Res. 1998 Sep;67(3):293-9. 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. "Heterochromia iridis in water buffaloes (Bubalus bubalis)." Vet Ophthalmol. 1998;1(4):195-201. PMID 11397231.
  7. ^ Swann P. "Heterochromia." Optometry Today. January 29, 1999. Accessed November 1, 2006.
  8. ^ van Emelen C, Goethals M, Dralands L, Casteels I. "Treatment of glaucoma in children with Sturge-Weber syndrome." J Pediatr Ophthalmol Strabismus. 2000 Jan-Feb;37(1):29-34. PMID 10714693.
  9. ^ [1]
  10. ^ a b Wallis DH, Granet DB, Levi L. "When the darker eye has the smaller pupil." J AAPOS. 2003 Jun;7(3):215-6. PMID 12825064.
  11. ^ Ohno N, Kiyosawa M, Mori H, Wang WF, Takase H, Mochizuki M. "Clinical findings in Japanese patients with Waardenburg syndrome type 2." Jpn J Ophthalmol. 2003 Jan-Feb;47(1):77-84. PMID: 12586183.
  12. ^ Brazel SM, Sullivan TJ, Thorner PS, Clarke MP, Hunter WS, Morin JD. "Iris sector heterochromia as a marker for neural crest disease." Arch Ophthalmol. 1992 Feb;110(2):233-5. PMID 1736874
  13. ^ Yang P, Fang W, Jin H, Li B, Chen X, Kijlstra A. "Clinical features of Chinese patients with Fuchs' syndrome." Ophthalmology. 2006 Mar;113(3):473-80. Epub 2006 Feb 3. PMID 16458965.
  14. ^ Arellanes-Garcia L, del Carmen Preciado-Delgadillo M, Recillas-Gispert C. "Fuchs' heterochromic iridocyclitis: clinical manifestations in dark-eyed Mexican patients." Ocul Immunol Inflamm. 2002 Jun;10(2):125-31. PMID 12778348.
  15. ^ a b Tabbut BR, Tessler HH, Williams D. "Fuchs' heterochromic iridocyclitis in blacks." Arch Ophthalmol. 1988 Dec;106(12):1688-90. PMID 3196209.
  16. ^ Bloch-Michel E. "[Fuchs heterochromic cyclitis: current concepts.]" J Fr Ophtalmol. 1983;6(10):853-8. PMID 6368659.
  17. ^ Mehta K, Haller JO, Legasto AC. "Imaging neuroblastoma in children." Crit Rev Comput Tomogr. 2003;44(1):47-61. PMID 12627783.
  18. ^ Khan AO, Aldamesh M. "Bilateral Duane syndrome and bilateral aniridia." J AAPOS. 2006 Jun;10(3):273-4. PMID 16814183.
  19. ^ Shauly Y, Weissman A, Meyer E. "Ocular and systemic characteristics of Duane syndrome." J Pediatr Ophthalmol Strabismus. 1993 May-Jun;30(3):178-83. PMID 8350229.
  20. ^ a b Key Ocular Signs for Screening
  21. ^ Wielgus AR, Sarna T. "Melanin in human irides of different colour and age of donors." Pigment Cell Res. 2005 Dec;18(6):454-64
  22. ^ Seddon JM, Sahagian CR, Glynn RJ, Sperduto RD, Gragoudas ES. "Evaluation of an iris colour classification system." The Eye Disorders Case-Control Study Group. Invest Ophthalmol Vis Sci. 1990 Aug;31(8):1592-8. PMID: 2201662
  23. ^ a b Iris Color & Iris Pigmentation
  24. ^ [2]
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