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Kathryn Rose, Amanda French, Paul Mitchell, Ian Morgan; The role of time outdoors on the progression of refractive error in Australian children. Invest. Ophthalmol. Vis. Sci. 2013;54(15):5959.
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© ARVO (1962-2015); The Authors (2016-present)
To establish the effect of time spent outdoors on the development of refractive error in a longitudinal cohort of Australian children.
Sydney Adolescent Vascular Eye Disease Study, a 5 year follow-up of the Sydney Myopia Study (SMS), a population-based randomly selected cluster sample of 4093 children aged 6 and 12 years at baseline, was completed in 2010. A comprehensive ocular examination including cycloplegic autorefraction (cyclopentolate 1%; Canon RK-F1) was performed. Spherical equivalent refraction was calculated for the right eye. Myopia was defined as ≤-0.50, emmetropia as >-0.50- <+0.50, mild hyperopia ≥+0.50 - ≤+2.00 and significant hyperopia >+2.00 dioptres (D). These studies adhered to the tenants of the Declaration of Helsinki.
Of the original SMS sample, 892 (50.5%) and 1211 (51.5%) children were re-examined in the younger (mean age 12.8yrs) and older (mean age 17.2 yrs) cohorts, respectively. Overall 2059 had complete baseline and follow-up refraction. The younger cohort had a mean annual change in refraction of -0.16D and the older cohort -0.15D. If myopic at baseline (aged 6), the mean annual progression was -0.45D, emmetropic -0.26D, mildly hyperopic -0.15D and significantly hyperopic -0.20D. For the older cohort it was; -0.33D, -0.15D, -0.10D and -0.26D, respectively. For the younger cohort, children spending low hours of time outside had a mean annual progression rate of -0.20D (95% confidence interval (CI) -0.228 to -0.181), moderate hours outside, -0.16D (95% CI -0.178 to -0.140) and high hours, -0.13D (95% CI -0.139 to -0.116). In the older cohort, those spending low hours outside progressed annually by -0.17D (95% CI -0.188 to -0.151), moderate hours, -0.14D (95% CI -0.155 to -0.124) and high hours, -0.13D (95% CI -0.152 to -0.117).
The mean annual rate of change in refraction varied by age and baseline refractive category. In general, the rate of change declined with age, with those myopic at age 6 demonstrating the fastest progression. In both cohorts, those significantly hyperopic at baseline also negatively progressed faster than those who were mildly hyperopic. In the younger cohort, less time outdoors significantly increased the annual progression rate, but while a similar trend was seen in the older cohort, it did not reach statistical significance. Time spent outdoors appears to have its greatest impact at a young age.
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