Having two different colored eyes is called heterochromia. The full medical term is heterochromia iridis (or iridium), referring specifically to the iris, the colored part of your eye. It affects roughly 1% of the world’s population, and in most cases it’s completely harmless.
Three Types of Heterochromia
Not all heterochromia looks the same. The condition comes in three distinct patterns, and each one has its own name.
- Complete heterochromia: Each eye is a completely different color. One might be brown while the other is blue or green. This is the most recognizable form and what most people picture when they think of two different colored eyes.
- Sectoral (partial) heterochromia: One iris contains two distinct colors, like a wedge of brown in an otherwise blue eye. Think of it as a patch or slice of a second color within the same eye.
- Central heterochromia: The area around the pupil is a different color from the outer ring of the iris. You might see a gold or amber ring near the pupil with a blue or green outer edge. This is the most common form and often goes unnoticed.
Why It Happens: Melanin, Not Melanocyte Count
Eye color comes down to a pigment called melanin in the iris. More melanin produces darker eyes (brown), while less melanin results in lighter eyes (blue, green, hazel). Heterochromia occurs when melanin is distributed unevenly between or within the irises.
What’s interesting is that the actual number of pigment-producing cells in the iris doesn’t vary much between eye colors. Research from the University of Wisconsin found that melanocyte density (the number of pigment cells per square millimeter) is essentially the same regardless of whether an iris is light or dark. About 66% of the iris stroma is made up of melanocytes in everyone. The difference is in how much melanin those cells produce and how it’s packaged, not in how many cells are present. In heterochromia, this production simply differs from one eye to the other, or from one section of the iris to another.
Born With It vs. Developing It Later
Heterochromia falls into two broad categories based on when it appears.
Congenital Heterochromia
Most people with heterochromia have had it since birth or early infancy. Babies are often born with lighter eyes that darken over time as melanin production ramps up, and permanent eye color can take up to three years to fully settle. Congenital heterochromia typically becomes apparent during this window. In the vast majority of cases, it’s a harmless genetic quirk with no effect on vision or eye health.
Rarely, heterochromia present from birth can be associated with certain genetic conditions. Waardenburg syndrome, which also affects hearing and hair pigmentation, is one example. Horner syndrome, which involves nerve damage affecting one side of the face, is another. These conditions come with additional, noticeable symptoms beyond just eye color, so heterochromia alone is almost never a cause for concern in children.
Acquired Heterochromia
When eye color changes later in life, the cause is usually something acting on the iris rather than genetics. Eye injuries, chronic inflammation inside the eye, glaucoma, and certain eye drops used to treat glaucoma can all alter iris pigmentation over time. Some of these changes are gradual enough that you might not notice them right away.
One specific condition worth knowing about is Fuchs uveitis syndrome, a type of low-grade, chronic inflammation inside one eye. It causes the affected iris to slowly lose pigment, creating a color difference between the two eyes. It’s typically painless and progresses quietly, but if misdiagnosed it can lead to cataracts or increased eye pressure. The hallmarks include one-sided involvement, mild inflammation, and gradual lightening of the iris without the sharp pain or redness that usually signals eye trouble.
When a Color Change Deserves Attention
If you’ve had two different colored eyes for as long as you can remember, there’s very likely nothing wrong. But a new change in eye color during adulthood is a different story. As one Cleveland Clinic ophthalmologist put it, a color change in an adult “can absolutely signify something nefarious going on.”
A few scenarios call for a prompt eye exam: you notice one eye looks noticeably different than it used to, you see bleeding in the eye after an impact, or you develop a gray or white ring around the iris before age 40 or in only one eye. Any of these warrant a visit to an optometrist or ophthalmologist, who can do a thorough exam to determine whether the change is cosmetic or a sign of an underlying condition. The exam itself is straightforward and painless, and in many cases the answer is reassuring.
Living With Heterochromia
Heterochromia doesn’t require treatment on its own. It doesn’t affect how well you see, and it carries no inherent health risk. Many people consider it a distinctive feature. Celebrities like Mila Kunis, Kate Bosworth, and David Bowie (whose mismatched eyes actually resulted from a childhood injury rather than true heterochromia) have made it culturally recognizable.
If you’re self-conscious about it, colored contact lenses can create a uniform appearance. But most people with heterochromia never need or seek any intervention at all. It’s simply one of those quirks of human biology, a visible reminder that the way your body distributes pigment doesn’t always follow a perfectly symmetrical plan.