Abstract: We identified three randomized controlled trials (855 children enrolled) in this review. These trials were all conducted in the UK with follow-up periods ranging from one to 3.5 years. We judged the included studies to be at high risk of bias, due to use of quasi-random methods for assigning children to treatment, no masking of outcomes assessors, and high proportions of drop-outs. None of the three trials accounted for missing data and analyses were limited to the available-case data (674 (79%) of 855 children enrolled for the primary outcome). These factors impair our ability to assess the effectiveness of treatment. Analyses incorporating the three trials we identified in this review (674 children) suggested the effect of spectacle correction initiated prior to the age of one year in hyperopic children between three and four years of age is uncertain with respect to preventing strabismus (risk ratio (RR) 0.71; 95% confidence interval (CI) 0.44 to 1.15; very low quality evidence). Based on a meta-analysis of three trials (664 children), the risk of having visual acuity worse than 20/30 at three years of age was also uncertain for children with spectacles compared with those without spectacle correction irrespective of compliance (RR 0.87; 95% CI 0.60 to 1.26; very low quality evidence). Emmetropization was reported in two trials: one trial suggested that spectacles impede emmetropization, and the second trial reported no difference in the rate of refractive error change. Although children who were allocated to the spectacle group were less likely to develop strabismus and less likely to have visual acuity worse than 20/30 children allocated to no spectacles, these effects may have been chance findings, or due to bias. Due to the high risk of bias and poor reporting of included trials, the true effect of spectacle correction for hyperopia on strabismus is still uncertain.

Plain-language summary: We identified results from three randomized controlled trials (RCTs; clinical studies where people are randomly put into one of two or more treatment groups) to determine whether glasses were successful in reducing the occurrence of strabismus in far-sighted infants. The trials enrolled infants ages 12 months or younger and measured outcomes between the ages of three and four years. The three trials enrolled 855 infants and included about 79% of the infants in the final analyses of different outcomes. These trials were all conducted in the UK with follow-up periods ranging from one to 3.5 years. The evidence is current up to April 2014. Combining the results of the three trials, we found the risk of strabismus with wearing glasses is uncertain. We identified several potential biases in the way these three trials were conducted. Given the high risk of bias and amount of missing data, it is possible the observed decrease in risk of developing strabismus may be an overestimate of the true effect. The evidence does not currently support the conclusion that glasses prevent strabismus in far-sighted children. More research is required to answer the question. In addition, the prescription of glasses, particularly glasses that correct all of the prescription (full correction), may prevent eyes from developing naturally and normalizing to clear visual acuity. Emmetropization (normalization of vision which usually occurs during the natural growth process) was reported in two trials: one trial suggested that spectacles impede emmetropization, and the second trial reported no difference in the rate of refractive error change. The overall quality of the evidence was very low, particularly due to improper trial design, incomplete outcome data, and the lack of power to provide an accurate estimate of the overall treatment effect of spectacle correction for preventing strabismus.