Complete heterochromia is definitely rare — fewer than 200,000 Americans have the condition, according to the National Institutes of Health. That’s only about six out of every 10,000 people.
It’s currently unknown how rare central heterochromia is, but we do know that it isn’t quite as rare as complete heterochromia.
Much of this comes down to the fact that central heterochromia is hard to document, and, unless it’s acquired later in life (causing a change in eye color), it doesn’t necessarily need to be documented. There are fewer questions about it because, unlike complete and sectoral heterochromia, it doesn’t seem out of the ordinary.
Having central heterochromia can actually be confused with having hazel eyes, though there are a few differences. The colors in hazel eyes can appear to change in different lighting, and they tend to blend together more as they radiate away from the pupil. With central heterochromia, each ring of color is distinct within the iris.
Source:
https://www.allaboutvision.com/conditions/rare-heterochromia/