Mats Larsson, a psychology graduate student at Örebro University in Sweden has linked iris patterns to personality traits.

He found that a low frequency of crypts was significantly associated with tender-mindedness, warmth, trust, and positive emotions, whereas more distinct and extended furrows were associated with impulsiveness.

t earlier studies have tenuously linked darker eyes to higher scores on extroversion, neuroticism, and sociability, although the effects seem to fade after early childhood. And, he adds, brain and eye development are closely linked in utero, so the appearance of distinctive eye traits might well be related to patterns of brain differences.

Left: A smoothly textured iris with no crypts (gaps) between the fibers. Center: A loosely textured iris with a

Larsson points to a gene called PAX6, which controls iris tissue growth.