Central heterochromia, where a ring of one color surrounds the pupil while the rest of the iris is a different color, has no precise global prevalence figure. No large-scale study has measured central heterochromia specifically. What we do know is that heterochromia of all types is genuinely rare, with the best available research placing the overall prevalence at roughly 0.063% of the population, or about 1 in every 1,600 people. Central heterochromia is considered more common than complete heterochromia (where each eye is a totally different color) but rarer than most people assume from social media, where striking eye photos get outsized attention.
What the Research Actually Shows
The most rigorous attempt to measure heterochromia prevalence came from a researcher named Stelzer, who personally examined over 25,000 people in Vienna in the late 1960s and found a prevalence of 0.063%. Decades later, a 2022 study using high-resolution yearbook portraits of 11,111 young adults confirmed that number almost exactly, finding 7 cases for an observed prevalence of 0.063%. The 95% confidence interval from that study ranged from about 0.028% to 0.133%, meaning the true rate likely falls somewhere between 1 in 750 and 1 in 3,600 people.
The catch is that both studies measured heterochromia broadly, without breaking results down by type. Central heterochromia, sectoral heterochromia (a wedge of different color in one iris), and complete heterochromia were grouped together or not all captured equally well. So there is no peer-reviewed number for central heterochromia alone. Claims you may see online citing figures like “less than 1%” or specific percentages for central heterochromia are not backed by published population data.
Why Central Heterochromia Happens
Eye color is determined by the amount and distribution of melanin, the same pigment that colors skin and hair, within the iris. In central heterochromia, the inner ring of the iris near the pupil contains a different concentration of melanin than the outer portion. This creates two distinct color zones in the same eye, most commonly a gold or amber ring around the pupil with blue, green, or gray filling the rest of the iris.
The genetics behind this are complex. Up to 150 genes play a role in determining eye color, with two genes on chromosome 15 (OCA2 and HERC2) having the strongest influence. Harmless, isolated genetic mutations that affect how the body makes, transports, or stores melanin are a common cause. Some people inherit these mutations as a dominant trait, meaning only one parent needs to carry the gene for it to appear. Others develop central heterochromia from spontaneous mutations with no family history at all.
Is It More Common in Certain Populations?
There’s no published evidence that central heterochromia is significantly more common in one ethnic group over another. Eye color distribution does vary by race, with lighter iris colors far more prevalent among people of European descent. Because central heterochromia is easier to notice in lighter eyes (a gold ring against a blue or green iris is more visible than against a dark brown one), it may appear more common in lighter-eyed populations. But that likely reflects visibility rather than true prevalence. The condition can occur in eyes of any base color.
When It Signals Something Else
The vast majority of people with central heterochromia have had it since birth or early childhood, and it is completely harmless. It doesn’t affect vision and doesn’t require treatment. Iris color can shift during the first two years of life as melanin production ramps up, so the two-tone pattern sometimes becomes more or less pronounced over time before stabilizing.
In rare cases, heterochromia can be a feature of certain congenital conditions, including Waardenburg syndrome (which also involves hearing loss and changes in skin or hair pigment), Horner syndrome, Sturge-Weber syndrome, and neurofibromatosis type 1. These conditions come with other noticeable symptoms beyond eye color, so heterochromia alone is not a reason for concern.
Heterochromia that develops later in life, rather than being present from birth, is a different situation. Acquired changes in iris color can result from eye injury, inflammation, certain glaucoma medications that increase pigment in the iris, or rarely, conditions like ocular melanosis. If you notice a new change in the color of one or both irises as an adult, that’s worth having an eye doctor evaluate, since it may point to an underlying cause that needs attention.
Central vs. Complete vs. Sectoral
Heterochromia comes in three forms, and they differ in both appearance and rarity. Complete heterochromia, where the two eyes are entirely different colors, is the rarest and most visually obvious type. Sectoral heterochromia creates a patch or wedge of a different color within one iris, like a slice of brown in an otherwise blue eye. Central heterochromia produces concentric rings of color radiating out from the pupil.
Central heterochromia is generally considered the most common of the three types, though “most common” is relative when all forms of heterochromia combined affect fewer than 1 in 1,000 people. It’s also the most subtle. Many people with mild central heterochromia don’t realize they have it until someone points it out or they look closely in a mirror under bright light. This subtlety is part of why it’s so difficult to study at a population level: it can be easy to miss in casual observation or standard photographs.