Heterochromia: Why Do Some People Have Two Different Colored Eyes?
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.
Other terms to describe different colored eyes are heterochromia iridis and heterochromia iridum. "Iridis" and "iridum" refer to the iris of the eye. The iris is the thin, circular structure that surrounds the pupil and contains the pigment melanin, which gives our eyes their distinctive color.
A dog with different-colored eyes. [Enlarge]
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.
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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.
Something that's often confused with heterochromia is a benign growth called an iris nevus. A pigmented nevus in the iris usually is round in shape and brown in color. Usually, only one iris nevus is present, but it's possible to have more.
Though a person might argue that a brown iris nevus on a blue, green or hazel eye is a type of partial heterochromia, the term heterochromia usually isn't used when the cause of the color variation in the iris is a nevus.
Iris nevi (plural of nevus) typically remain stable in size. If you have an iris nevus, your eye doctor usually will want to see you every six months (for a while, at least) to measure its size and rule out any growth that could indicate malignancy.
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.
Kate Bosworth, Josh Henderson, Elizabeth Berkley, Mila Kunis and Alice Eve all have heterochromia. [Enlarge] (Images: Everett Collection, Helga Esteb, s_bukley, Joe Seer / all at Shutterstock.com)
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.
In some cases, heterochromia is a symptom of another condition that's present at birth or develops shortly thereafter.
One example of a condition that causes heterochromia is Horner's syndrome. This is the combination of a constricted pupil, partial ptosis and loss of the ability to sweat on half of the face, all caused by an interruption of certain nerve impulses to the eye.
Latisse, a repurposed glaucoma medication now used primarily as a cosmetic agent to thicken eyelashes, also can cause the iris to change color.
David Bowie's Eyes: Anisocoria, Not Heterochromia
Sometimes, a condition called anisocoria can make people look like they have two different colored eyes when they do not. Anisocoria is a common condition characterized by unequal pupil sizes. It affects about 20 percent of the population.
David Bowie's anisocoria from a childhood injury made it look like he had different colored eyes. (Image: Everett Collection / Shutterstock.com)
In most cases, anisocoria is present at birth and is perfectly harmless. Also, the difference in pupil sizes usually is small less than a millimeter difference between the right and left eye.
But occasionally, the difference in pupil sizes can be quite large, such as when anisocoria is 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.
This was the case with David Bowie, the late singer, songwriter, actor and record producer. Bowie was born with blue eyes. When he was a teenager, he got in a fistfight with a school pal over a girl they were both enamored of. His friend socked Bowie in his left eye, and the injury left his pupil permanently dilated. The severe anisocoria from the damage made him look as though he had two different colored eyes a blue right eye and a nearly black left eye.
Despite the dust-up and lasting effect of the fight, apparently there were no hard feelings. The boy who landed the punch George Underwood ended up being Bowie's lifelong friend and artistic collaborator.
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.
After your eye doctor confirms your eyes are healthy, enjoy the compliments you are likely to receive about the unique appearance of your two different colored eyes.
[Page updated April 2016]