Eliminating doubts of time outdoors as a significant intervention to reduce the prevalence of myopia

We thank Dr. Li Deng et al. and Dr. Enis Kocak et al. for their comments on our previous study of outdoor time and myopia development. Clearly, as noted in Dr. Li Deng et al.’s paper, we did not measure the academic performance of subjects or near work time in the trial. Though these are important confounders of myopia, their effect may be considerably reduced by randomization in the study. We also agree that the questionnaire measurement of outdoor time outside school hours forms a limitation, as noted by Dr. Enis Kocak et al., and accept that this was the most cost-effective examination for a trial of this size at that time. Moreover, the outdoor activity time between the two groups was not significantly different at baseline. Recent developments in real-time and objective monitoring through the use of mobile devices may be incorporated into future studies to reduce reporting bias.