A black band around the outer part of the iris. Generally more noticeable on people with lighter eye colors, such rings tend to make a person's gaze much more striking. Those should not, however, be mistaken with the classic black outline that's characteristic to many artists, although limbal rings do tend to give the same emphasis on a real person's eyes.

A good example of this in action is the picture of Sharbat Gula, the 'Afghan Girl', where the girl's striking eyes are due both to her very large limbal rings as well as a very pronounced central heterochromia.