METHODS:Cross-sectional study. A total of 10 153 primary school students from grade 1-6(age 6-13, three classes per grade)were selected from four primary schools in Xindu District of Chengdu for three consecutive years(2018-2020), by using a random stratified cluster sampling method. All students' visual acuity and spherical equivalent refraction(SE)were measured, a further cycloplegia optometry was conducted for those whose visual acuity was less than 5.0. The SE was recorded and the prevalence of myopia was calculated. Chi-square test was used to compare the difference of prevalence of myopia between different years. One-way Anova was used to compare the difference of SE among different years.

RESULTS: There was statistical difference in prevalence of myopia between the three years(2018: 35.98%, 2019: 36.29%, 2020: 42.52%; χ²=39.374, P<0.001). The prevalence of myopia among 6-9 years old students increased significantly in 2020(P<0.01). They were 2.20 times(6 years old), 2.08 times(7 years old), 1.36 times(8 years old)and 1.24 times(9 years old)of the previous year. Students aged 6-9 years showed an obvious myopic shift in SE in 2020(P<0.05). The increases were -0.34±0.76D(6 years old), -0.28±0.84D(7 years old), -0.29±1.41D(8 years old)and -0.18±1.35D(9 years old)than the previous year. The prevalence of myopia and SE remained stable among 10-13 years old students in 2018-2020(P>0.05).

CONCLUSION: After the COVID-19 home isolation period, there was a significant myopic shift among students aged 6-9 years old. We should pay more attention to the window period for myopia prevention and control of 6-9 years old.