High prevalence of myopia and low hyperopia reserve in 4411 Chinese primary school students and associated risk factors

PURPOSE: To investigate the prevalence of myopia in Chinese primary school students and their ocular biometrics including axial length (AL), corneal radius of curvature (CRC) and spherical equivalent refraction (SER). To analyze their association with potential myopia risk factors, such as body mass index (BMI), cram school, time of outdoor activity and electronic screen use. METHODS: In this cross-sectional study of 4500 primary school students from 5 schools, participants underwent refraction using non-cycloplegic autorefractor and visual acuity testing. A follow-up study in the same schools was conducted in 2022. Myopia was defined as SER ≤ -0.50 diopter (D) and uncorrected visual acuity (UCVA) < 0.00 logMAR (6/6). Logistic regression models were used to determine factors associated with myopia. RESULTS: After excluding 389 participants, the overall prevalence of myopia was 33.6%. The prevalence of high myopia was 0.6%. The prevalence of myopia in girls was significantly higher than that in boys (37.6% vs. 30.0%, p < 0.001). The height, weight and BMI were significantly associated with AL (r = 0.471, r = 0.440, r = 0.276, p < 0.001, respectively). AL/CRC ratio was more highly correlated with SER than AL alone. Regression analysis showed that AL/CRC and hyperopia reserve were associated with myopia onset in the subsequent year (F = 201.557, p < 0.001; F = 68.934, p < 0.001). The cut point of hyperopia reserve for myopia in the subsequent year for grade 1 students was + 0.31D. Age (p < 0.001), parental myopia (p = 0.001) and lack of outdoor activity between classes (p = 0.049) were independently associated with higher prevalence rates of myopia. CONCLUSION: The prevalence of myopia among Chinese schoolchildren is alarming high. Consistent with previous cross-sectional data, AL/CRC and hyperopia reserve could function as myopia detection indicators. The hyperopia reserve among children aged between 6 ~ 7 years was low. Healthcare providers need to raise parents’ awareness of the importance of regular eye examination and proper optical correction. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12886-022-02436-5.