The iris is the colored part of the eye that surrounds the pupil. As with fingerprints, iris color patterns are very complex and unique to each individual.
Pigmented rings on the iris
The color of the iris is genetically determined and is a consequence of the amount and proportion of melanins. Its main function is to control the amount of light entering the eye through the pupil. A person's iris can tell a lot about him or her. Like the fingerprint, pigmentation patterns are complex and unique. Because of this, in some countries iris recognition is used as a personal identifier.
In addition to the overall iris color, pigment distribution appears to be genetically determined as well. The peripupillary ring or pigment ring is the change in iris color in the area closest to the pupil, usually darker, and is particularly characteristic of green and light eyes. Studies to date have shown that, like eye color, the presence of the pigment ring is genetically determined.
If you want to learn more about how genetics influences who you are, visit the DNA traits test section.
Larsson M, et al. GWAS findings for human iris patterns: associations with variants in genes that influence normal neuronal pattern development. Am J Hum Genet. 2011 Aug 12;89(2):334-43.
Mackey DA, Wilkinson CH, Kearns LS, Hewitt AW. Classification of iris colour: review and refinement of a classification schema. Clin Exp Ophthalmol. 2011 Jul;39(5):462-71.