Heterochromia means “different (hetero-) colors (-chromia).” Usually the term is used to describe the condition where a person has different colored eyes — one blue eye and one green eye, for example. The amount of melanin in the iris determines whether we have blue eyes, green eyes, hazel eyes or brown eyes. Blue eyes have the least amount of melanin in the iris; brown eyes have the most. Heterochromia usually is benign. In other words, it is not an eye disease, and it does not affect visual acuity.

Benign heterochromia can give a person a captivating, even exotic, appearance. In fact, a number of celebrities — including Dan Aykroyd, Kate Bosworth, Henry Cavill, Alice Eve, Josh Henderson, Mila Kunis, Jane Seymour and Christopher Walken — have heterochromia.

Heterochromia also occurs in animals. Breeds of dogs that commonly exhibit heterochromia include Siberian husky, Australian shepherd, border collie, collie, Shetland sheepdog, Welsh corgi, Great Dane, dachshund and Chihuahua. Such cat breeds include Turkish Van, Turkish angora, Japanese bobtail and sphynx. Often such “odd-eyed cats” have been bred specifically to have this feature.

Types Of Heterochromia
There are three types of heterochromia, based on where the different colors are located:

1. Complete heterochromia. This is where the iris of one eye is a completely different color than the iris of the other eye.

2. Partial heterochromia (or sectoral heterochromia). This is where only a portion (or sector) of the iris of one eye has a different color than the rest of the iris of that eye. Partial heterochromia can occur in one eye or both eyes.

3. Central heterochromia. In this type of heterochromia, the iris has a different color near the border of the pupil (compared with the color of the rest of the iris), with spikes of the central color radiating from the pupil toward the middle of the iris.

What Causes Heterochromia?
As already mentioned, most cases of heterochromia are benign. An infant can be born with benign heterochromia, or it can become apparent in early childhood as the iris attains its full amount of melanin. These types are called congenital heterochromia. Usually, congenital heterochromia is a genetic trait that is inherited. Benign heterochromia also can occur as the result of a genetic mutation during embryonic development.

Heterochromia that develops later in life is called acquired heterochromia. Causes of acquired heterochromia include eye injuries, uveitis and certain glaucoma medications. Latisse, a repurposed glaucoma medication now used primarily as a cosmetic agent to thicken eyelashes, also can cause the iris to change color.

Occasionally, a difference in pupil sizes can be quite large, such as when it’s due to a nerve palsy or a traumatic eye injury. When the pupil of one eye is widely dilated and the other is normal in size, this can mimic the appearance of heterochromia, with the eye with the dilated pupil looking darker in color than the normal eye.

Have An Eye Exam To Be Safe
Though most cases of heterochromia are congenital and benign, if you or your child has different colored eyes (or different colored segments of one or both eyes), see your eye doctor for a comprehensive eye exam to rule out other causes.