Pigmented rings on the iris

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.

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.

It has been estimated that the structure and patterning of iris development can be inherited up to 70-95%, so genetics is a major contributor to the expression of its associated traits. Through a GWAS study of 2600 individuals of European ancestry, the role of a marker close to the SLC24A4 gene has been identified, which has been associated with the development of a ring of pigmentation in the iris, surrounding the pupil, which depends on the amount of melanin surrounding the pupil, being the ring uniform or uneven.

The results of the study further reported that melanin pigment rings surrounding the pupil were smaller in males than in females, while females had a greater number of crypts, oval shapes formed in the iris as a function of eye development.

Number of observed variants

13.5 million variants

Number of variants analyzed in the study

1 variant

Bibliography

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.

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