To determine the prevalence of astigmatism and its determinants in schoolchildren aged 6-12 years.

This cross-sectional study was conducted on urban and rural schoolchildren in Shahroud, north of Iran, in 2015. The examinations were performed after randomly selecting the participants and obtaining informed consent from their parents. First, uncorrected visual acuity was measured; then, refraction was done with an autorefractometer. Manifest refraction was performed with retinoscopy followed by subjective and cycloplegic refraction. The prevalence of astigmatism was reported based on a cylinder power worse than -0.50, -1.00, and -2.00 diopter (D).

Of 6624 selected children, 5620 participated in the study. After applying the inclusion criteria, the data of 5537 children were analyzed. The prevalence of astigmatism worse than 0.50 D in at least one eye was 16.7% (95%CI: 15.6-17.7). The prevalence of astigmatism was 16.6% (95%CI: 15.2-18.0) in boys and 16.8% (95%CI: 15.2-18.3) in girls (p=0.891). The prevalence of astigmatism decreased from 21.5% in 6-year-old children to 13.7% in 10-year-olds, and then again increased to 18.2% in children aged 12 years. Moreover, 17.2% (95%CI: 16.0-18.3) of urban and 12.1% (95%CI: 10.0-14.1) of rural children had astigmatism (P<0.001). The prevalence of with-the-rule, against-the-rule, and oblique astigmatism was 14.2%, 2.1%, and 0.33%, respectively. The prevalence of astigmatism worse than -2.00 D was 2.5% (95%CI: 2.1-2.9). The mean cylinder power was -1.31, -0.47, and -0.44 D in children with spherical myopia, emmetropia, and hyperopia, respectively (p<0.001). With-the-rule astigmatism increased with an increase in spherical refractive error.

This is one of the few studies to evaluate the prevalence of astigmatism in the age group of 6-12 years. The prevalence of astigmatism in this study was not high in comparison with previous studies; however, its prevalence was markedly higher in urban children.