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Strabismus. 2016 Sep;24(3):113-9. doi: 10.1080/09273972.2016.1205103. Epub 2016 Aug 2.

Strabismus and Near Point of Convergence and Amblyopia in 4-6 Year-Old Children.

Author information

a Department of Optometry, School of Paramedical Sciences , Mashhad University of Medical Sciences , Mashhad , Iran.
b Noor Research Center for Ophthalmic Epidemiology , Noor Eye Hospital , Tehran , Iran.
c Noor Ophthalmology Research Center , Noor Eye Hospital , Tehran , Iran.
d Refractive Errors Research Center, School of Paramedical Sciences , Mashhad University of Medical Sciences , Mashhad , Iran.
e Department of Medical Surgical Nursing, School of Nursing and Midwifery , Shahid Beheshti University of Medical Sciences , Tehran , Iran.



To determine the prevalence of strabismus and amblyopia, and the distribution of the near point of convergence (NPC), in a population of children aged 4 to 6 years.


In this cross-sectional study, preschoolers in Mashhad were sampled using a random multistage 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 5.1 cm (95% CI: 5.05-5.14). NPC increased by 0.08 cm per month of age (P=0.033) and was 0.10 cm 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.


Amblyopia; near point of convergence; preschool children; strabismus

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