The association between iris color and refractive errors in children.

This study aimed to evaluate the association between iris color and refractive errors in children aged 6-12 years. This cross-sectional study was based on data obtained from the first phase of the Shahroud Schoolchildren Eye Cohort Study. The target population was 6 to12 year-old students living in urban and rural areas. Iris colors were classified by comparing eye colors with close-up images of iris colors. Myopia was defined as a spherical equivalent (SE) ≤ - 0.5 diopter and hyperopia was defined as SE ≥ 2 diopter in cycloplegic refraction. The association of iris color with hyperopia and myopia was investigated by fitting two separate multiple logistic regression models adjusted for place of residence, age, sex, and times for outdoor activity and near work. Among the 5394 participates with the mean age of 9.7 year, the prevalence of myopia and hyperopia was 4.8% and 4.7% respectively. The number and proportion (in parentheses) of amber, light blue, light brown, dark brown, gray, green and hazel iris colors were 19(0.4%), 26(0.5%), 645(12.0%), 4517(83.7%), 4(0.1%), 59(1.1%), and 124(2.3%) respectively. Compared to dark brown, the odds ratios and 95% confidence intervals (in parentheses) of myopia were 4.8(1.2-18.7), 0.8(0.1-5.8), 1.0(0.7-1.5), 0.4(0.1-2.7) and 0.6(0.2-1.8) for amber, light blue, light brown, green and hazel iris colors in multiple logistic regression model. No significant association was observed between iris colors and hyperopia. This study shows that amber iris is significantly associated with higher odds of myopia. These children should be further monitored and examined. More studies with higher sample size in all iris colors are recommended.