What Is Heterochromia?
Heterochromia is when a person has differently colored eyes or eyes that have more than one color.
Most of the time, it doesn't cause any problems. It's often just a quirk caused by genes passed down from your parents or by something that happened when your eyes were forming. In rare cases, it can be a symptom of a medical condition.
Heterochromia is common in some animals but rare in humans. It affects fewer than 200,000 people in the United States.
How Your Eye Color Is Determined
In the past, some believed you could predict the eye color of children by looking at the eye colors of their parents and grandparents. Based on the belief that brown eyes are a dominant trait and blue eyes are recessive, they thought you could get a good idea of what color the child’s eyes would be.
But today we know eye color isn’t that easy to guess. While genetics does play a role, eye color isn't the work of a single gene. Instead, several genes contribute to determining your eye color. It's the result of the amount and distribution of melanin (a natural pigment) in your irises.
Brown eyes have more melanin than blue eyes do, and there are various shades in between. Darker eyes tend to be more dominant, but as different genes factor in, this doesn’t mean darker colors always win out.
So while two brown-eyed parents are more likely to have a child with brown eyes, the result isn’t a guarantee. Nor will children of one brown-eyed and one blue-eyed parent for sure have brown eyes.
About half of all people in the U.S. have brown eyes. Brown eyes are also more prevalent in areas of the world with warmer climates. People with blue eyes have no melanin in the stroma, the front layer of the iris. The lack of pigment in the eyes causes light to scatter when it hits them, making the irises appear blue.
Green eyes are the rarest. Only about 2% of people in the world have green eyes. The color comes from both melanin and the effect of light scattering when it hits the eye.
People born with albinism often have little to no melanin in their bodies. They typically have light blue eyes. In rare cases, they may have clear irises, which can make their eyes look pink or red.
Can Your Eye Color Change?
Your eye color can change in infancy. Many babies are born with blue eyes that eventually become a different color as melanin develops in the stroma. Their eye color usually becomes permanent around their first birthday.
But it’s rare for eyes to change color after that. They may appear to change when your pupils dilate or shrink, but this occurs because the pigments in the irises come together or spread apart. In some cases, eye color can darken slightly during puberty or pregnancy, or as you reach your later years.
Symptoms and Types of Heterochromia
Your iris gets its color from a pigment called melanin. It's what makes them blue, green, brown, or hazel. Less melanin leads to lighter eye color. More melanin makes darker eyes.
There are three types of heterochromia:
- Complete heterochromia (heterochromia iridis) means one iris is a different color than the other. For example, you may have one blue eye and one brown eye.
- Segmental heterochromia (heterochromia iridium) means different parts of one iris are different colors.
- Central heterochromia is when the outer ring of your iris is a different color from the rest.
Causes and Risk Factors of Heterochromia
When you’re born with different-colored eyes, it’s called congenital heterochromia. Conditions that can cause this include:
- Benign heterochromia
- Hirschsprung disease
- Bloch-Sulzberger syndrome
- Von Recklinghausen disease
- Bourneville disease
- Waardenburg syndrome
- Sturge-Weber syndrome
- Parry-Romberg syndrome
- Horner’s syndrome
If your eye color changes after you're an infant, it's called acquired heterochromia. Possible causes include:
- Eye injury. More than 80% of eye injuries happen during projects around the house, sports, or other recreation.
- Glaucoma. This eye disease affects more than 3 million Americans. Fluid buildup raises pressure in your eye. It may cause vision loss, but early detection and treatment can help prevent that.
- Swelling caused by iritis or uveitis.
- Certain medicines, including glaucoma drugs like bimatoprost (Latisse, Lumigan) and latanoprost (Xalatan).
- Neuroblastoma. This is a cancer of the nerve cells that usually affects children under 10. When tumors press on nerves in the chest or neck, kids may have a drooping eyelid and a small pupil. They can also get heterochromia. See a doctor right away if your child's eye color changes.
- Eye cancer. Melanoma can affect your eye in rare cases. It happens in the melanin. One sign of eye melanoma is a dark spot on the iris. Blurry vision or sudden vision loss are also common.
Heterochromia in Infants
If you have a baby with different-colored eyes, talk to your pediatrician. Your child may also need to see an eye surgery specialist called an ophthalmologist. It’s likely that your baby is still developing, and their eye color may be changing naturally.
Talk to your doctor if you notice a change in the color of one or both eyes.
Your doctor will look closely at your eyes as part of a full eye exam. They’ll ask how long you’ve had heterochromia and whether you have any other symptoms. They might order blood or genetic tests to look for the cause.
If a health condition is causing your heterochromia, your doctor may treat it. Otherwise, you won’t need treatment.