Table 4. Review of Population-based Studies of Association between Refractive error and Strabismus.

	Population	Association between refractive error and strabismus
SMS (Australia), Robaei (2006) [14]	1740 6-year-old school children examined between 2003–4; 26 (1.5%) with esotropia, 14 (0.8%) with exotropia	Myopia, hyperopia (> = 3 D), astigmatism (> = 1 D) and anisometropia (> = 1 D) were associated with strabismus in general (p <0.05). A separate analysis of esotropia and exotropia were not reported.
MEPEDS & BPEDS(USA) Cotter (2011) [13]	9970 children of African-American, Hispanic and non-Hispanic white children aged 6–72 months; 102 (1.0%) with esotropia and 102 (1.0%) with exotropia	For ET, hyperopia 2–<3 D, 3–<4 D, 4–<5 D and > = 5 D compared to 0-<1 D: OR 6.38, 23.06, 59.81 and 122.24, respectively (95% CI 2.56–15.93, 9.56–55.61, 23.61–151.52, and 49.86–299.7, respectively); SE anisometropia > = 1 D compared to <0.5 D: OR 2.03 (95% CI 1.01–3.73). For XT, astigmatism 1.5-<2.5 D and > = 2.5 D compared to <0.5 D: OR 2.49 and 5.88, respectively (95% CI 1.3–4.79 and 2.76–12.54, respectively); J0 anisometropia 0.25-<0.5 D and > = 0.5 D compared to <0.25 D: OR 2.01 and 2.63, respectively (95%CI 1.25–3.22 and 1.26–5.49, respectively).
STARS (singapore) Chia(2013)[1]	2992 Chinese children aged 6–72 months; 3 (0.1%) with esotropia and 20 (0.7%) with exotropia	Astigmatism > = 1 D compared to <1 D: OR 4.02 (95% CI 1.79–9.03); Anisometropia > = 1 D compared to <1 D: OR 7.16 (95% CI 2.08–24.67). A separate analysis of esotropia and exotropia were not reported.
This study (China)	5831 Chinese children aged 3–6 years; 45 (0.8%) with esotropia and 270 (4.6%) with exotropia	For ET, hyperopia 2–<3 D, 3–<4 D, 4–<5 D and > = 5 D compared to 0-<1 D: OR 9.3, 9.28, 14.57 and 180.82,respectively (95% CI 2.63–32.96, 1.48–58.13, 2.32–91.65, and 36.37–898.89, respectively); SE anisometropia 0.5-<1 D and > = 1 D compared to <0.5 D: OR 3.15 and 7.41, respectively (95% CI 1.07–9.29 and 2.5–21.93, respectively). For XT, myopia-1-<0 D and <-1 D compared to SE 0-<1 D: OR 40.54 and 18.93, respectively (95%CI 13.16–124.86 and 5.25–68.22, respectively); hyperopia 1-<2 D, 2–<3 D, 3–<4 D and 4–<5 D compared to 0-<1 D: OR 67.78, 23.13, 25.57 and 8.36, respectively (95% CI 40.8–112.6, 12.7–42.13, 9.97–65.59 and 1.71–40.97, respectively); astigmatism 0.5-<1.0 D and <0 D compared to 0–0.5 D: OR 3.56 and 1.9, respectively (95% CI 1.51–8.4 and 1.9–1.17, respectively).

MEPEDS, Multi-ethnic Pediatric Eye Disease Study; BPEDS, Baltimore Pediatric Eye Disease Study; SMS, Sydney Myopia Study; STARS, Strabismus, Amblyopia and Refractive Error in Singaporean Preschoolers Study

D = diopters; J0 = power in the vertical or horizontal meridian; SE = spherical equivalent; ET = esotropia; XT = exotropia