Heterochromia: the three types, what causes them, and when to get it checked

Eye color depends on how much melanin sits in the front of the iris. Heterochromia happens when that amount differs between the two eyes or between parts of one iris. Most cases present from birth or early childhood are simply how that person developed: an uneven distribution of pigment, often running in families, with no effect on vision or eye health.

Less often, heterochromia present at birth is part of a wider condition affecting pigment or the nerves to the eye, and a pediatrician or eye doctor can tell these apart on examination. That makes a single check in childhood worthwhile if it has not already happened. For most adults with lifelong heterochromia, that check was done long ago and nothing further is needed.

A new change in eye color in an adult, or a change in one eye only, is a reason to see an eye doctor promptly. Causes can include injury, inflammation inside the eye, some glaucoma eye drops that darken the iris over months, and conditions affecting the nerves that supply the eye. Some of these need treatment, and none can be judged from a photo.

The distinction is time. Heterochromia you have had for as long as anyone remembers, visible in childhood photos, is a stable feature. A difference that has appeared or grown recently is a change, and changes are what an examination is for. An article or a tool can describe what you see; it cannot tell you why it happened.

Complete heterochromia is rare, with commonly cited estimates of well under 1 percent of people. Sectoral and central heterochromia are more common, and central heterochromia in particular is often not recognized as heterochromia at all, because it is simply called hazel. There is no reliable global count of any type, so treat every figure you see as a rough estimate.

Heterochromia is also common in some animals, including dog breeds such as huskies and Australian shepherds, and in white cats, which is where many people first see it. In people it attracts attention because complete heterochromia is visible from across a room, while the sectoral and central types usually only show up close or in good light.

Heterochromia can look dramatic in one photo and invisible in another. Warm light can flatten the difference between a hazel and a brown eye, cool light exaggerates blue against brown, and a sectoral patch can disappear when the pupil is large. Camera white balance and flash affect both eyes, but not always equally, especially if one eye catches more light.

For a clear view, face a window in daylight with no flash and look at each eye separately, checking the ring near the pupil and the outer edge of each. To record the color of each eye, check it with the eye color detector on this site, which reads the iris on your device and corrects for lighting; it describes color and does not diagnose anything.