Objective  To explore the effect of outdoor activity time on myopia among lower-grade primary school students in Guangzhou city and to provide evidences for myopia prevention among children.

  Methods  Using cluster random sampling, we conducted a baseline survey among 3 171 first and second grade students in 12 primary schools in Guangzhou city of Guangdong province during December 2018 – March 2019. Relevant information of the students were collected with ophthalmologic examinations and questionnaires completed by the students′ parents. One year later, the participants were followed up for their visual acuity. The incidence rate of myopia was determined and its relationship with outdoor activity time was analyzed.

  Results  For the 3 171 students at the baseline survey, the prevalence rate of myopia was 6.6% and the mean daily time spent on outdoor activity was 0.84 ± 0.63 hour. For the 1 868 students successfully followed up for one year, the prevalence rate of myopi was 11.4%, and the incidence rate of myopia during the follow-up period was 6.2% for the 1 764 non-myopic students at the baseline survey. The mean daily outdoor activity time (0.70 ± 0.5 hour) of the students with incident myopia was significantly less than that (0.84 ± 0.62 hour) of the students without incident myopia (t = 2.317, P = 0.021). The results of logistic regression analysis indicated that outdoor activity was an independent protective factor for incident myopia (odds ratio = 0.627, 95% confidence interval: 0.421 – 0.934).

  Conclusion  The time spent on outdoor activity is associated with myopia incidence and increasing outdoor activity may help prevent the onset and development of myopia among lower-grade primary students.