Heterochromia Iridis describes a condition in which there are different colors within the iris of an individual’s eye. This is caused by an excess or lack of production of pigmentation in the iris, which is called hyperplasia and hypoplasia, respectively. There are three main types of heterochromia, in which the pigmentation abnormality appears in different regions of the iris. There is central heterochromia, in which there is a ring of color surrounding the pupil that is a different color than the rest of the iris.
Partial heterochromia is when part of one iris is different than the rest.
Complete heterochromia is when each iris of an individual is a different color.
There are several causes of heterochromia including congenital, meaning that the person was born with this coloration or it developed shortly after birth. This form of heterochromia is usually not associated with any disease or visual impairments, and is simply a result of genetics.
In some cases, heterochromia can be a symptom of another disease. One such disease is Waardenburg Syndrome. Infants born with this genetic disorder have symptoms including patches of discoloration in the skin and hair as well as the eyes. Another inheritable disease that can result in heterochromia is Incontinentia Pigmenti. This disease involves progressive skin lesions, in addition to retinal abnormalities, central nervous system changes, and more. In this case, the heterochromia is not what causes the retinal abnormality, but is rather a simple symptom of an underlying genetic problem.
Other forms of heterochromia can stem from trauma later in life, including injury due to a physical contact, bleeding in the eye, or other late onset diseases like glaucoma and diabetes mellitus. Glaucoma is characterized by damage to the optic nerve, often due to excess fluid in the eye. Diabetes mellitus can result in retinopathy, due to swelling and leaking of blood vessels. This sort of damage can effect the melanin production in the iris, resulting in heterochromia.
Animals can have heterochromia too, including common pets such as cats and dogs, and even horses. The causes of these discolorations are similar to ours, but in some breeds it is more common due to genetics.
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