Increasing Time Spent Outdoors Influences On Myopia Onset And Progression Among Primary And Junior High School Students

ObjectiveTo describe vision acuities among primary and junior high school students in Sujiatun, Shenyang, China and investigate risk factors associated with poor vision. To test the effect of increasing time spent outdoors on myopia and ocular biometric parameters. MethodsStudents of two primary(grades 1~5) and two junior high schools(grades 7~8) in both urban and rural locations participated. Two primary schools in urban area which were selected for the comparable academic burden and adjacent location were assigned to intervention arm and control arm randomly, so did the 2 urban junior high schools, 2 rural primary schools and 2 rural junior high schools. A total of 3 051 children were enrolled in this study(1 735 in intervention group and 1 316 in control group). The interventions composed of performing two additional 30 minutes recess program outside the classroom. The control school did not have any interventions. Data were obtained through a detailed questionnaire with parents and children together. Uncorrected vision acuity(UCVA) was measured using a E Standard Logarithm Vision Acuity Chart(GB11533-2011) at baseline, at the 6 month and 1 year interval in both intervention and control schools. A random subsample(n=391) participated in the clinic visits and underwent cycloplegia at the beginning and after 1 year. Differences in the three UCVA results between the two groups were analyzed by multivariate analysis of variance for repeated measures; Logistic regression analyses were used to analyze potential risk factors associated with poor vision. Simple linear and multiple linear regression were performed to analyze the association between the myopic progression, ocular biometric parameters changes and potential risk factors. ResultsA total of 3 521 students had done detailed questionnaire and 3 316 students were included in analysis. 1 654(49.9%) were boys, 1 553(46.8%) were lived in rural areas, and 2 755(83.1%) were Han nationality. The mean age of participants were 10.61±2.59. Logistic regression analyses showed that poor vision in school children in Sujiatun was associated with female gender, higher age, parental myopia, higher family income and longer daily studying duration. Longer time spent outdoors was a protective factor against poor vision.A total of 3 051 students were enrolled in the 1 year intervention study, 1 735 in the intervention group and 1 316 in the control group. There were no significant differences in the two groups in terms of gender, age, nationality, region of habitation, and UCVA at baseline. The UCVA in the intervention was significantly better than the control group after 1 year(4.85±0.24 vs. 4.81±0.27,P<0.001). Multiple linear regression analysis showed that the speed of vision loss was slower in the intervention group. Higher age, parental myopia, and sleeping with light on were risk factors against vision loss.A total of 391 students were enrolled in the subgroup study, 214 in the intervention group and 177 in the control group. There were no significant differences in the two groups in terms of gender, age, nationality, region of habitation, SER and prevalence of myopia at baseline(both P>0.05). At the end of the 1-year follow-up, the incidence of new myopia onset and the mean progression of refractive error in the myopic direction during the study period were both significantly lower in the intervention group than in the control group(3.70% vs. 8.50%, P = 0.048;-0.10±0.65 D/year vs.-0.27±0.52 D/year, P = 0.005). Moreover, changes in axial length and IOP(intraocular pressure) were also significantly lower in the intervention group than in the control group(0.16±0.30 mm/year vs. 0.21±0.21 mm/year, P = 0.034;-0.05±2.78 mm Hg/year vs. 0.67±2.21 mm Hg/year, P = 0.006). Corneal curvature and anterior chamber depth changes had no significant differences between groups. ConclusionIncreasing time spent outdoors by conducting recess program have a significant effect on the control of UCVA loss, and myopia onset and progression among school-aged children in northeast China. Moreover, increasing time spent outdoors also have a significant effect on axial length elongation and elevated IOP.