What Is Heterochromia?
Heterochromia is when you have 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 U.S.
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. Whilegenetics does play a role, eye color isn't the work of a single gene. Instead, several genes playa role in determining your eye color. It's the result of the amount and distribution ofmelanin (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 this doesn’t mean darker colors always win out because different genes factor in.
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 way light scatters when it hits the eye.
People born withalbinism 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 withblue eyes, which 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 yourpupils 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 duringpuberty orpregnancy, or as you reach your later years.
Heterochromia Symptoms
Your iris gets its color from a pigment called melanin. It's what makes your eyes blue, green, brown, or hazel. Less melanin leads to a lighter eye color. More melanin makes darker eyes. There are no other symptoms of heterochromia.
Types of Heterochromia
There are several types of heterochromia:
Complete heterochromia (heterochromia iridis)
This type means one of your irises is a different color than the other. For example, you may have one blue eye and one brown eye.
Segmental heterochromia(heterochromia iridium)
This is when different parts of one of your irises have different colors.
Central heterochromia
This type is when the outer ring of your iris is a different color from the rest.
Central heterochromia vs. hazel eyes. When you have central heterochromia, you have one distinct color around your pupil and a different color at the outer edge of your iris. But when you have hazel eyes, you have a mixture of different colors throughout the entire surface of your iris.
Acquired heterochromia
This is when you develop differently colored eyes, or eyes of different colors, after infancy.
Heterochromia hair
This is a rare condition in which you grow hair in two different distinct colors.
Causes and Risk Factors for Heterochromia
When you’re born with different-colored eyes, it’s called congenital heterochromia. Conditions that can cause this include:
- Benign heterochromia
- Piebaldism
- Hirschsprung disease
- Bloch-Sulzberger syndrome
- Von Recklinghausen disease
- Bourneville disease
- Waardenburg syndrome
- Sturge-Weber syndrome
- Parry-Romberg syndrome
- Horner’s syndrome
Causes of acquired heterochromia
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 the pressure in your eye. It may cause vision loss, but early detection and treatment can help prevent that.
- Swelling. It may be caused by iritis or uveitis.
- Certain medicines, including glaucoma drugs such as 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.
There are also other causes of acquired heterochromia. Some of those are:
- AcquiredHomer's syndrome
- Glaucoma and some of the meds commonly used to treat it
- Latisse, a repurposed glaucoma medication now used cosmetically to thicken eyelashes
- Pigment dispersion syndrome
- Ocular melanosis
- Posner-Schlossman syndrome
- Iris ectropion syndrome
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.
Heterochromia Diagnosis
Talk to your doctor if you notice a change in the color of one or both eyes.
They'll 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.
Heterochromia Treatment
If a health condition is causing your heterochromia, your doctor may treat it. Otherwise, you won’t need treatment.
Takeaways
- Heterochromia is when you have differently colored eyes or eyes that have more than one color.
- Heterochromia affects only 1% of people in the world.
- Several genes contribute to determiningyour eye color.
- There are different types of heterochromia.
- Unless it's caused by certain medical conditions, heterochromia is not a health issue and requires no treatment.
Heterochromia FAQs
What are the two rarest eye colors?
Green eyes are the rarest, found in only 2% of people in the world. The second rarest eye color is hazel, seen in 5% of people worldwide.
Is heterochromia good or bad?
It's neither good nor bad and doesn't affect your health. But it may be caused by a health condition, so let your doctor know so they can check you.
How rare is heterochromia in humans?
It's extremely rare in humans, affecting only 1% of people in the world. It's more common in some animals.
