Effect of school entrance age on myopia among primary schoolchildren using mixed-effect model: The Shantou Myopia...

To investigate the association between children's school entrance age and refractive status and prevalence of myopia in southern China.

Population-based Cross-sectional study was conducted from September 2020 to June 2021 in Shantou, southern China, enrolling primary schoolchildren in the city. The school entrance age was calculated as the months from the birth date to the entrance date, divided by 12. Non-cycloplegic refraction and uncorrected visual acuity test were conducted. Myopia was defined as spherical equivalent refraction (SER) < -0.50D with an uncorrected distant visual acuity < Snellen 20/20. We explored the association between the SER and the school entrance age, with the clustering effect within schools adjusted by the linear mixed-model.

We enrolled 410,080 primary schoolchildren, with a mean age of 9.8 ± 1.6 years. The overall prevalence of myopia was 42.04 %. The mean SER of myopic children was - 2.15 ± 1.70 D. The mixed-effects model revealed a significant correlation between the school entrance age and the SER and the prevalence of myopia. One year later for school entrance age would independently result in a less myopic SER of 0.352 D, and significantly decrease the prevalence of myopia. Children born before September 1st had significantly more myopic SER than those born after September 1st.

Early school entrance, rather than age or prolonged exposure to schooling, was an independent risk factor for myopia. It is important to put forward some scientific and effective measures, preventing children from early exposure to task-heavy school life and near work.