Comparison of myopic progression in Finnish and Singaporean children

Purpose To compare 3-year myopic progression between Finnish and Singaporean children. Methods Myopic progression was compared between 9-year-old (mean age 9.7 +/- 0.4 years,n = 92) and 11-year-old (mean age 11.7 +/- 0.4 years,n = 144) Finnish (Finnish RCT) children and Singaporean children matched by age and refraction (SCORMMatched,n = 403) and 7- to 8-year-old Singaporean children matched only by refraction (SCORM Young,n = 186). Spherical equivalent (SE) was between -0.50 and -3.00 D. Refraction with cycloplegia was controlled annually for 3 years. Information on parental myopia, mother's education, time spent on near-work and outdoor time was gathered by parental questionnaire. Results Three-year myopic progression was -2.08 +/- 0.96 D and -1.30 +/- 0.69 D in the Finnish RCT and Singaporean SCORM Matched 9-year-olds, respectively, and -1.34 +/- 0.78 D, and -0.52 +/- 0.44 D in the 11-year-olds, respectively (p < 0.001 between all groups). Myopic progression was fastest (-2.69 +/- 0.89 D) in the SCORM 7-year-olds and similar between the SCORM Matched 9-year-olds and Finnish RCT 11-year-olds (p = 0.55). The Finnish RCT and SCORM Matched children showed significant differences in both daily near-work time (1.8 +/- 1.0 versus 3.4 +/- 1.9 hours per day, p < 0.001) and outdoor time (2.6 +/- 0.9 versus 0.5 +/- 0.4 hours per day, p < 0.001). These differences did not, however, explain the differences in myopic progression between the groups. More time spent outdoors was associated with less myopic progression in the Finnish RCT (r = 0.17, p = 0.009) group only. In the whole materials, greater myopic progression was associated with younger age at baseline (p < 0.001), younger age was associated with mother's higher education (p < 0.001), and mothers higher education was associated with myopia in both parents (p < 0.001). Conclusion Age at baseline was the most significant factor associated with myopic progression. However, at the same age and with the same initial refraction, the Finnish and Singaporean children showed different myopic progression. This result remains unexplained. Thus, age of myopia onset should be considered when comparing myopic progression between different samples and conducting treatment trials. Parental myopia may be a weak indicator of heredity of myopia.