Amblyopia and strabismus in Iranian schoolchildren, Mashhad

To determine the prevalence of amblyopia and strabismus among the population of schoolchildren Mashhad, Iran.

In a cross-sectional study with cluster sampling, 2510 schoolchildren were selected from schools of district 1 in Mashhad. Uncorrected visual acuity (UCVA) and best corrected visual acuity (BCVA) were recorded for each participant. Amblyopia was distinguished as a reduction of BCVA to 20/30 or less in one eye or 2-line interocular optotype acuity differences in the absence of pathological causes.

Of the 2510 selected schoolchildren, 2150 participated (response rate, 85.6%). The mean (± standard deviation) age of the participants was 13.2 ± 3.2 (range, 6-21) years. The prevalence of amblyopia was 1.9% (95% CI: 0.94-2.90); 2.1% (95% CI: 0.10-3.16) in girls and 1.7% (95% CI: 0.30-3.12) in boys (P = 0.6). Among myopic, hyperopic, and astigmatic students, 3.7%, 27.8%, and 6.5% had amblyopia, respectively (P<0.001). The causes of amblyopia were anisometropia in 65.9%, strabismus in 24.4%, and isoametropia in 9.8%. The prevalence of strabismus was 3.1% (95% CI, 1.3% to 4.3%); 4.2% (95% CI, 3.05 to 5.7%) in girls, and 2.0% (1.3% to 2.9%) in boys (P = 0.0011). Strabismus was significantly more prevalent among hyperopic students (7.9%) compared with myopic ones (3.7%).

Results of the present study indicate that the prevalence rate of amblyopia was in the mid-range of other studies, and the prevalence of strabismus was relatively high. Since refractive errors, especially hyperopia, are responsible for some cases of strabismus.