Heterochromia is a word that is the combination of two ancient Greek words—hetero and chroma. Hetero means different and chroma means color, so the term is used for things that are of two different colors. Heterochromia of the iris means that the eyes are two different colors.
The iris of the eye is the colored part of the eye that is responsible for controlling the size of the pupil and the amount of light that reaches the retina. The iris is made of two pigmented layers that give eyes their color.
Heterochromia affects humans, dogs, cats, and horses. It is usually caused by a harmless genetic mutation and only rarely does it relate to an underlying illness. It can also happen after an eye injury or from certain types of medications.
Types of Heterochromia
- Complete heterochromia causes each eye to be a completely different color.
- Central heterochromia is when the inner “ring” or the iris, around the pupil, is a different color than the outer edges of the iris. It usually affects both eyes similarly.
- Sectoral heterochromia, also called partial heterochromia, is when there are splashes of secondary colors that vary in size and range from a single thin streak to a larger wedge that can cover half the iris. This type can affect one or both eyes.
In rare instances a sectoral heterochromia can develop into a cancerous melanoma so it’s a good idea to have an eye doctor monitor this type of heterochromia.
In most cases people are born with heterochromia. It can develop later in life, but then it is usually the result of disease, injury, or certain types of medication. For example, some glaucoma eye drops can permanently change eye color.
Heterochromia does not affect the size of your pupils. There is a condition that does affect pupil size and that condition is called anisocoria. In most cases that condition is also benign and not a cause for concern. The late singer-songwriter David Bowie had anisocoria. His one enlarged pupil caused that eye to look darker than the other.