The prevalence of strabismus in 7-year-old schoolchildren in Iran

To determine the prevalence of tropia and phoria in Iran and their association with some related factors.

In a cross-sectional population-based study, multistage randomized cluster sampling was used to select participants from among grade 1 students in the primary schools of 7 cities of Iran. After obtaining their parents' approval, the students underwent the measurement of uncorrected and corrected visual acuity, cycloplegic refraction, and cover test. Distant and near cover test were performed at 6 m and 40 cm, respectively, with the best corrected visual acuity. Tropia and phoria were measured separately.

Of 4157 selected students, 3675 participated in the study. The prevalence of strabismus was 1.68% (95% CI 1.13-2.23). The prevalence of strabismus was 2.17% (95% CI 1.06-3.29) in boys and 1.27% (95% CI 0.57-1.96) in girls (p = 0.216). Moreover, 1.27% (95% CI 0.82-1.72) of the children had exotropia and 0.44% (95% CI 0.22-0.65) had esotropia. The prevalence of constant and intermittent strabismus was 0.73% (95% CI 0.26-1.19) and 0.96% (95% CI 0.55-1.36), respectively. Phoria was detected in 32.98% (95% CI 24.25-41.71) of the children in this study. The prevalence of residual amblyopia was 23.77% (95% CI 9.45-38.08) in strabismic and 1.43% (95% CI 0.09-1.96) in non-strabismic children (p < 0.001). The odds of strabismus were significantly higher in hyperopic and astigmatic children.

This study showed the prevalence of tropia and phoria across Iran. Exotropia was the most common type of tropia in Iran and intermittent strabismus was the most common type of strabismus. Due to prevalent amblyopia in strabismus, attention should be directed toward careful screening and treatment.