Refractive Errors and Concomitant Strabismus: A Systematic Review and Meta-analysis

This systematic review and meta-analysis is to evaluate the risk of development of concomitant strabismus due to refractive errors. Eligible studies published from 1946 to April 1, 2016 were identified from MEDLINE and EMBASE that evaluated any kinds of refractive errors (myopia, hyperopia, astigmatism and anisometropia) as an independent factor for concomitant exotropia and concomitant esotropia. Totally 5065 published records were retrieved for screening, 157 of them eligible for detailed evaluation. Finally 7 population-based studies involving 23,541 study subjects met our criteria for meta-analysis. The combined OR showed that myopia was a risk factor for exotropia (OR: 5.23, P = 0.0001). We found hyperopia had a dose-related effect for esotropia (OR for a spherical equivalent SE of 2-3 diopters D: 10.16, P = 0.01; OR for an SE of 3-4D: 17.83, P < 0.0001; OR for an SE of 4-5D: 41.01, P < 0.0001; OR for an SE of ≥5D: 162.68, P < 0.0001). Sensitivity analysis indicated our results were robust. Results of this study confirmed myopia as a risk for concomitant exotropia and identified a dose-related effect for hyperopia as a risk of concomitant esotropia.