Heterochromia iridis

Eye color is determined by the concentration and distribution of melanin (a pigment) in the iris. A variety of genetic and acquired (non-genetic) factors influence the final outcome and continued maintenence of the iris color.

Most cases of heterochromia iridis occur sporadically and are not associated with any additional symptoms or health problems. Acquired factors that may lead to heterochromia iridis include:

• Injury or trauma to the eye
• Melanoma of the eye
• Treatment of glaucoma with certain medications such as Latanoprost or Bimatoprost
• Neuroblastoma

Rarely, heterochromia iridis may be part of a congenital (present from birth) syndrome, such as Waardenburg syndrome, Sturge-Weber syndrome, congenital Horner's syndrome, or Parry-Romberg syndrome. Waardenburg syndrome (due to mutations in many different genes) and Sturge-Weber syndrome (due to somatic mutations in the GNAQ gene) have genetic causes. The exact underlying cause of Horner's syndrome and Parry-Rombery syndrome is currently unknown. Later-onset cases of heterochromia iridis may be associated with a syndrome called Fuchs heterochromic iridocyclitis, which also has an unkown cause.

Most cases of heterochromia iridis occur sporadically in people with no family history of heterochromia iridis. However, heterochromia iridis rarely is part of an inherited genetic syndrome. For example, heterochromia iridis is reported in some people with Waardenburg syndrome, which is generally inherited in an autosomal dominant manner.

Rennie IG. Don't it make my blue eyes brown: heterochromia and other abnormalities of the iris. Eye (Lond). 2012 Jan;26(1):29-50.

The American Academy of Ophthalmology offers a summary on heterochromia, which includes a list of possible causes.