Heterochromia is a condition where a person’s eyes are different colors, or where one eye contains more than one color. It affects roughly 0.06% of the population, making it genuinely rare. Most people with heterochromia are born with it and experience no vision problems at all, but in some cases a change in eye color later in life can signal an underlying health issue worth investigating.
How Eye Color Works
Your iris gets its color from melanin, the same pigment that determines skin and hair color. What varies from person to person isn’t the number of pigment-producing cells in the iris, but how much melanin those cells contain. More melanin produces brown eyes, less produces blue or green. These cells typically reach their genetically determined melanin levels in early childhood, which is why many babies are born with lighter eyes that darken over the first year or two of life. Once that process stabilizes, iris color usually stays constant for the rest of your life.
Heterochromia happens when this pigment distribution is uneven, either between the two eyes or within a single iris. The result is a visible color difference that can be dramatic (one brown eye and one blue) or subtle (a wedge of hazel in an otherwise green eye).
Three Types of Heterochromia
Complete heterochromia is what most people picture: each eye is a distinctly different color. One might be brown while the other is blue or green.
Sectoral heterochromia means part of one iris is a different color from the rest. It often looks like a wedge or pie-slice of a second color within the same eye.
Central heterochromia is the most common form. The inner ring of the iris, closest to the pupil, is a different color from the outer ring. You might notice a gold or amber ring around the pupil in an otherwise blue eye, for example. Many people with central heterochromia don’t even realize they have it until someone points it out.
Congenital Causes
Most heterochromia is congenital, meaning it’s present from birth. In the majority of these cases, the color difference is simply a harmless quirk of how melanin distributed itself during development. There’s no single “heterochromia gene.” Eye color is influenced by multiple genes, and the interplay between them can occasionally produce asymmetric pigmentation without any health consequence.
Less commonly, congenital heterochromia appears as part of a broader genetic syndrome. Waardenburg syndrome, which also involves hearing loss and changes in skin or hair pigmentation, is one of the most well-known examples. Sturge-Weber syndrome, characterized by a port-wine birthmark on the face and potential neurological effects, can also feature heterochromia. Parry-Romberg syndrome, which causes progressive shrinking of tissue on one side of the face, is another rare association. In these cases, heterochromia is one piece of a larger clinical picture, not the condition itself.
When Eye Color Changes Later in Life
Acquired heterochromia, a color change that develops after infancy, deserves more attention than the congenital kind. The causes range from mild to serious.
Physical trauma to the eye can damage pigment cells and lighten or darken the iris. Chronic inflammation inside the eye, particularly a condition called Fuchs uveitis syndrome, gradually changes iris color over time. Fuchs uveitis syndrome is a slow-burning inflammation that often goes unnoticed for years. Its real concern isn’t the color change itself but the complications it causes: cataracts develop in 23% to 91% of patients, and secondary glaucoma (a pressure buildup that can permanently damage vision) occurs in 15% to 59%.
Certain medications can also shift iris color. Eye drops containing prostaglandin analogs, commonly prescribed for glaucoma, can gradually darken the treated eye. The same active ingredient used in some eyelash-growth cosmetics can produce the same effect. Horner syndrome, caused by disruption of nerve signals on one side of the face, can make the affected eye lighter while also causing a drooping eyelid, a smaller pupil, and decreased sweating on that side of the face.
The most concerning cause of acquired heterochromia is melanoma of the iris. This is rare, but a growing dark spot on the colored part of the eye is a key warning sign. Other symptoms that suggest something more serious include flashes of light, new floaters, blurry vision in one eye, a change in pupil shape, or loss of side vision.
When Evaluation Matters
If you’ve had two different-colored eyes since childhood and have no vision problems, it’s overwhelmingly likely to be benign. A routine eye exam can confirm this, but there’s usually no cause for concern.
The situation is different if your eye color changes as an adult, or if a child develops heterochromia after infancy. New color asymmetry warrants an eye exam to rule out inflammation, pressure changes, or growths. This is especially true if the color change comes with any vision symptoms like blurriness, pain, light sensitivity, or floaters.
Treatment and Cosmetic Options
Congenital heterochromia doesn’t require treatment. It’s a physical trait, not a disease. Some people consider it a striking feature; others prefer a uniform appearance. Colored contact lenses are the simplest cosmetic option for anyone who wants their eyes to match, though these should be properly fitted by an eye care professional even when worn for appearance alone.
When heterochromia is acquired, treatment targets the underlying cause rather than the color difference itself. Fuchs uveitis syndrome, for instance, is managed by addressing the cataracts and glaucoma it creates. Cataract surgery in these patients has an 85% success rate for restoring good vision. Glaucoma may require ongoing pressure-lowering drops or, in more resistant cases, surgery. If a medication is causing the color shift, switching to an alternative may prevent further change, though existing darkening is often permanent.