Prevalence, incidence, and risk factors for myopia among urban and rural children in southern China: protocol for a school-based cohort study.

introductionMyopia is the common cause of reduced uncorrected visual acuity among school-age children. It is more prevalent in urban than in rural areas. Although many myopia studies have focused on the effect of urbanisation, it remains unclear how visual experience in urban regions could affect childhood myopia. This study aims to investigate the incidence and prevalence of myopia among school-age children in urban and rural settings, thereby identifying the environmental factors that affect the onset and progression of myopia. METHODS AND ANALYSIS: A school-based cohort study will be conducted. We will enroll all first-grade students from an urban (10 primary schools) and a rural (10 primary schools) regions of Zhaoqing city, China. Over 3-year follow-up period, students will receive detailed eye examinations annually and complete questionnaires about living habits and environment. In a 5% random subsample of the cohort, physical activity, light intensity and eye-tracking data will be obtained using wearable devices, and high-resolution macular images will be obtained by optical coherence tomography (OCT). The primary outcome is incident myopia, defined as myopia (spherical equivalent refractive of at least -0.5D) detected during follow-up among those without myopia at baseline. ETHICS AND DISSEMINATION: Ethics approval was obtained from the ethics committee of the Zhongshan Ophthalmic Center (number: 2019KYPJ171). Study findings will be published in a peer-reviewed journal. TRIAL REGISTRATION NUMBER: NCT04219228.