Purpose: Despite the importance of information on the prevalence of strabismus, which can be effective in planning preventive and curative services, no study has addressed its prevalence comprehensively. In this study, a systematic search was done to estimate the regional and global prevalence of strabismus in different age and sex groups and factors affecting prevalence heterogeneity. Methods: A comprehensive and systematic search was done in different international databases, including Web of Science, Scopus, PubMed, Embase, etc. to find published articles on the total prevalence of strabismus and the prevalence of exotropia and esotropia. A binomial distribution was used to calculate the prevalence and 95% confidence interval (CI). The Cochran's Q-test and I2 were applied to evaluate heterogeneity and a random-effects model was used to assess the pooled prevalence. The Begg's test was administered to investigate publication bias and finally, a meta-regression method was applied to determine the factors affecting the heterogeneity among studies. Results: Of 7980 articles, 56 articles with a total sample size of 229,396 were analyzed. Many of these articles (n = 14) were from the Regional Office for the Americas. The estimated of pooled prevalence (95% CI) of any strabismus, exotropia, and esotropia was 1.93% (1.64-2.21), 1.23% (1.00-1.46), and 0.77% (0.59-0.95), respectively. The heterogeneity in prevalence of strabismus and its subtypes according to I2 was above 95% (p value <.001 for all). Age had a direct effect on heterogeneity in the prevalence of exotropia (b: 3.491; p: 0.002). Moreover, WHO region had a significant direct effect on heterogeneity in the prevalence of strabismus (b: 0.482; p < .001) and esotropia (b: 0.168; p: 0.027), and publication year had a significant direct effect on heterogeneity in the prevalence of exotropia (b: 0.059; p: 0.045). Sample size and publication year did not have any association with strabismus nor with other variables. There was no publication bias according to the Begg's test. Conclusion: The prevalence of strabismus varies widely in the world. As for factors affecting heterogeneity in the prevalence of strabismus, the results showed that age affected heterogeneity in the prevalence of exotropia, WHO region affected heterogeneity in the prevalence of strabismus and esotropia, and publication year affected heterogeneity in the prevalence of exotropia. Information about the global prevalence of strabismus can help health care planners design interventions and prioritize resource allocation.
Keywords: Prevalence; esotropia; exotropia; meta-analysis; strabismus.