Received: 25 April 2019
Accepted: 30 March 2020
First Online: 15 April 2020
Ethics approval and consent to participate
: The study was approved by the Sichuan University, West China School of Public Health Institutional Review Board, and was conducted in accordance with the ethical standards of the Declaration of Helsinki. Written informed consent forms were obtained from the children’s parents before the eye examinations and questionnaires.
: Not applicable.
: The authors declare that they have no competing interests.