Neurodevelopmental gene PAX6 ... is known to help control the development of the iris in an embryo... Previous research has also shown that a mutation of PAX6 is linked to impulsiveness and poor social skills.
Thus inspecting a person's iris may give you clues about their personality.
Close-up pictures were taken of the study participants' irises, and they also filled out a questionnaire about their personalities. The researchers looked at crypts (pits) and contraction furrows (lines curving around the outer edge of the iris), which are formed when pupils dilate.
It was found that those with more crypts were likely to be tender, warm and trusting, while those with more furrows were more likely to be neurotic, impulsive and give in to cravings.
I just went to the staff loos and peered at my eyes in the mirror. If crypts are dark areas between the lines that radiate outwards from the pupil and furrows are concentric circles I have the former rather than the latter. I'm not convinced by this research.
ETA Read the actual research paper here.