Abstract: Objective To investigate the prevalence of myopia and to analyze associated factors in primary and secondary school students in Huaihua City, Hunan Province. Design Cross-sectional survey. Participants 2103 students from Grade 3 to 12 in Hecheng district of Huaihua City. Methods Stratified cluster random sampling approach was conducted to selected 2103 students from September to December in 2014. The students underwent vision examination, non-cylcoplegic auto-refractometry and questionnaires. The difinition of myopia is SE≤-0.50 D in the worse eye. Logistic regression analysis was used for 33 possible risk factors associated with myopia. Main Outcome Measures Prevalence of myopia. Results Out of 2103 eligible students, 2064 (98.1%) students (mean age: 12.5±2.8 years; range: 7~18 years) participated. The overall prevalence of myopia was 46.3% (95% Confidence Interval (CI): 44.1%~48.5%). The prevalence of myopia in primary schools, junior high schools and senior high schools were 22.1% (95% CI: 19.3%~24.9%), 53.8% (95% CI: 50.0%~57.6%), 74.4% (95% CI: 70.8%~78.1%), respectively. There was a statistical significant difference of prevalence of myopia among different grade (χ2=425.626，P=0.000). The prevalence of myopia showed an increasing trend with raising grade, and it increased at age 9 significantly. The prevalence of myopia in girls (50.4%, 95% CI: 47.2%~53.6%) was higher than boys (42.8%, 95% CI: 39.9%-45.7%) (χ2=12.043，P=0.001). There was no statistical significant difference of prevalence of myopia between rural primary schools and urban primary school (χ2=0.140，P=0.708). 69.2% (660/954) students with myopia wore glasses daily. In multivariate logistic regression analysis, a higher prevalence of myopia was associated with parental myopia, longer time spent for near work, shorter near work distance, less sleep time, dim lighting. While comfortable height of desk, outdoor activities, scarcely watching TV or playing computer, without unhealthy habits of using eyes were associated with less myopia. Conclusions There is a higher prevalence of myopia in primary and middle schools of Huaihua city. Prevention of myopia in rural primary schools is urgent. The crucial period of eye protection is before 9 years old. (Ophthalmol CHN, 2016, 25: 241-246)

Key words: myopia/prevalence, myopia/risk factors