[Study on relationship between outdoor activities and self-reported myopia among middle school students]

Objective: To examine the relationship between the prevalence of self-reported myopia and outdoor activities among middle school students and to explore the influence factors of the self-reported myopia. Methods: A total of 12 979 participants were recruited from junior and senior middle school students in in Shenzhen, Nanchang, Zhengzhou and Shenyang by random cluster sampling method between December 2015 and March 2016. All participants completed an anonymous questionnaire to collect the information of demographic characteristics, self-reported myopia, outdoor activities, etc. 12 603 out of 12 979 copies of questionnaire were valid. The prevalence of self-reported myopia was compared among middle school students with different characteristics. Logistic regression models were used to analyze the relationship between myopia and outdoor activities. Results: The prevalence of self-reported myopia among middle school students was 69.6% (8 766/12 603); which was separately 52.1% (1 216/2 335) in seventh grader, 61.6% (1 459/2 369) in eighth grader, 69.0%(1 470/2 129) in ninth grader, 80.0% (1 812/2 265) in freshmen, 79.4% (1 622/2 042) in sophomore, and 81.1%(1 187/1 463) in junior. The prevalence of self-reported myopia showed an increasing trend with the increase of grade (χ(2)=639.67, P<0.001). The prevalence of self-reported myopia was separately 63.5%(4 927/7 756) in non-myopic parents group, 78.0%(2 664/3 415)in either myopic parent group, and 82.1%(1 175/1 432) in both myopic parents group(χ(2)=328.28, P<0.001). Outdoor activities were associated with self-reported myopia. Binary logistic regression analysis showed that the risk of self-reported myopia was significantly increased by always staying at home in extracurricular time among the middle school students (OR=1.58, 95%CI: 1.36-1.82). The risk of self-reported myopia were significantly decreased by always physical exercise and recreational activities after school among middle school students: the ORs were separately 0.67 (95%CI: 0.57-0.78) for physical exercise and 0.77 (95%CI: 0.64-0.92) for recreational activities. After stratified analysis by the parents' myopia status, in non-myopic parents group, exercise and recreational activities after school among middle school students decreased the risk of myopia: the ORs were separately 0.68 (95%CI: 0.55-0.82) for physical exercise and 0.76 (95%CI: 0.61-0.95) for recreational activities; in either myopic parent group, OR(95%CI) were separately 0.65 (0.47-0.90) and 0.68 (0.47-0.98). Conclusion: Outdoor activities was negatively associated with self-reported myopia among middle school students. However, the parents' myopia status may affect the protective effect.