From The Loh Down:
A limbal ring is a dark circle around the iris -- the colored part of the eye. Because limbal rings diminish with age, they're more COMMON in young, healthy people, and more VISIBLE in those with light-colored eyes. University of California, Irvine, psychology graduate student Darren Peshek takes it one step further. He says limbal rings give people an automatic way to judge each other's facial attractiveness.

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