Distribution of iris color and its association with ocular diseases in a rural population of Iran

To determine the distribution of iris color and its relationship with some ocular diseases in a rural population of Iran.

Two rural areas of the north and southwest of Iran were selected by a cross-sectional study using multi-stage cluster sampling. After selecting samples, the participants had an eye examination including measuring visual acuity, refraction, and Pentacam imaging. Then an eye examination for individuals was performed by slit-lamp.

Out of 3851 invited people, 3314 participated in this study (participation rate, 86.05%). Dark brown [41.28%, confidence interval (CI) 95% ¼ 31.88e50.68] and blue (0.99%, CI 95% ¼ 0.57e1.41) were the most and the least type of iris colors among participants of this study. Compared to others, people with a dark iris have the biggest anterior chamber depth (ACD), angle and volume while central corneal thickness (CCT), keratometry and pupil were highest among people with a dark brown iris (P < 0.002). Considering the dark brown group as a base group, the chances of being afflicted to cataract among people with dark, light brown, green, and blue irises are 1.89 (CI 95% ¼ 1.25e2.86), 1.53 (CI 95% ¼ 1.17e2.01), 4.60 (CI 95% ¼ 2.17e9.71), and 12.17 (CI 95% ¼ 5.05e29.31), respectively. The chance of being afflicted to myopia among people with green irises and to hyperopia among people with blue irises were high (1.60, CI 95% ¼ 1.08e2.36 and 3.20, CI 95% ¼ 1.03e9.97, respectively).

Dark brown was the most prevalent iris color in rural areas of Iran. The index of cornea among people with dark and dark brown iris color is higher than other people, and people with light iris color are at a higher risk of developing eye disease such as cataract, corneal opacity, and refractive error. To determine this relationship and its usage for therapeutic and public health purposes, further studies are recommended.