You may have come across, even on the internet, some image of humans and other animals with eyes of each color. The process, caused by a lack or excess of melanin, is called heterochromia.


As we mentioned in the previous topic, one of the causes may be the lack or even the excess of melanin, but there are still other causes for heterochromia, such as genetics, disease or some injury during fetal development.

It may also happen because of congenital problems, such as Waardenburg Syndrome and Horner Syndrome. The first is a genetic condition that causes hearing loss, as well as a change in the color of hair, skin and eyes. The second covers a group of damage to the innervation of the sympathetic nervous system with one eye, caused both at birth and inside the uterus. This causes the affected side to have a smaller pupil than the other side, in addition to a lighter iris.

The acquired heterochromia can be caused by diseases and conditions such as iritis, trauma, bleeding, glaucoma, presence of a foreign body in the eyes, malignant melanoma in the iris and more.

Photo: Reproduction


In addition to being a curious fact, heterochromia has three different types: central, sectorial and complete. In these cases, there are three predominant pigments in the iris: blue, brown and yellow which, depending on the quantity, will determine the final color of the eye.

Central heterochromia

Central heterochromia occurs when the iris has two or more circles of color in its composition, for example, when the person has blue eyes, but with an external golden arc or close to the pupil. People who have this type of heterochromia are called “cat eyes” by some.

Sectoral heterochromia

Sectoral heterochromia occurs when the same iris has two different colors, with a dominant color and a touch of a certain second color.

Complete heterochromia

Finally, complete heterochromia is when the two eyes have different colors, such as a green and a brown eye, for example. This, perhaps, is the most impressive of the three types, as it causes more strangeness and admiration.


Although fascinating, heterochromia is relatively rare. As a comparison, we can cite a survey conducted in the United States, where it was estimated that about 11 people in a sample of 1000 people are affected.

This can happen through inheritance from parents, arising from a combination of several genetic and acquired factors, not necessarily symbolizing a sign of genetic weakness.

Leave a Comment