A recent study found an association between iris color and the presence of astigmatism in a school-based sample of Chinese students. After controlling for the effects of gender and spherical power, individuals with darker iris color tended to have a higher likelihood of being astigmatic, and those with the lightest were significantly less likely to be affected.

Researchers collected data from 2,346 grade seven students ages 13 to 14 years from 10 middle schools in Southwestern China. They used both eye examination results and measures of iris color from slit-lamp photographs to develop their grading system. Astigmatism was defined as a cylinder power of more than 0.50D, 0.75D or 1.00D. The overall prevalence of astigmatism for the three different definitions was 30.4% (<−0.5 D), 12.7 % (<−0.75 D) and 5.3% (<−1.0 D), respectively.

Researchers believe that a more objective method for quantifying iris color may help to achieve more precise and reliable measurements. They also suggest assessing the association in other ethnic groups who have larger variations in iris color such as in Caucasians. Examining the longitudinal influences could help establish iris color impact on astigmatism’s development.