To determine the prevalence of strabismus and amblyopia, and the distribution of the near point of convergence (NPC) in a population of 4 to 6 year olds

In this cross-sectional study, preschoolers in Mashhad were sampled using a random multi-stage cluster sampling approach. Examinations were done after obtaining parental consent. All participants had measurements of uncorrected visual acuity, corrected visual acuity, and non-cycloplegic refraction, and they had near and far cover tests to determine tropia and phoria

Of the 3765 selected children, 3701 participated in the study. The prevalence of tropia was 1.21% [95% confidence interval (CI): 0.86-1.57]. Near and near/far tropia was observed in 0.83% (95% CI: 0.53-1.12) and 0.39% (95% CI: 0.18-0.59), respectively. Tropia was significantly more prevalent in boys (p=0.005). The most common type of tropia was esotropia, 0.22% (95% CI: 0.07-0.37). Among participants, 63.92% (95% CI: 62.36 -65.48) had phoria; prevalence of far, near and near/far phoria was 0.22% (95% CI: 0.07 -0.37), 60.47% (95% CI: 58.88 -62.07), and 3.22% (95% CI: 2.65-3.8), respectively. Mean NPC was 5.1cm (95% CI: 5.05-5.14). NPC increased by 0.08cm per month of age (p=0.033) and was 0.10cm higher in boys compared to girls (p=0.027). Based on NPC, 61.58% (95% CI: 59.99-63.17) were symptomatic. The prevalence of amblyopia was 0.41% (95% CI: 0.20 -0.61). The type of amblyopia was anisometropic, strabismic, and isoametropic in 75%, 11.1%, and 8.5%, respectively

The prevalence of amblyopia in this study population was not high; however, the prevalence of tropia was average compared to previous studies in Iran. Describing NPC in a 4- to 6-year-old Iranian population for the first time, we found that NPC increased with age in this sample