Objective To analyze the association between sleep chronotypes and myopia among junior high school students in Changning District of Shanghai, and to provide scientific basis for myopia intervention in this population.

Methods This study was conducted as a cross-sectional survey using stratified cluster sampling. Four junior high schools in Changning District were selected as the research sites. Two methods were used to assess chronotypes, including the sleep-wake pattern calculated based on sleep duration and the sleep chronotype evaluated by the Morningness-Eveningness Questionnaire-5 items (MEQ-5). Myopia status of students was determined through distant visual acuity examination combined with non-cycloplegic computerized refraction. The ${\chi }^{\mathrm{2}}$ test or t test was used to compare the distribution differences of sleep chronotypes between the myopic and non-myopic groups. Furthermore, a multivariate logistic regression model was used to analyze the association between sleep chronotypes and myopia. Statistical analyses were performed using SPSS 27.0 software.

Results A total of 801 middle school students participated in this survey, with a screening-based prevalence of myopia of 81.77%. Univariate analyses showed that both the sleep chronotype calculated based on the sleep-wake pattern (χ²=4.54, P=0.033) and the sleep chronotype assessed by the MEQ-5 (χ²=12.75, P=0.013) were statistically associated with myopia. After adjusting for grade, maternal age at birth, parental myopia, frequency of weekend outdoor activities, and sleep duration, multivariate analyses indicated that a higher grade (e.g., grade 9: OR=3.63, 95%CI=1.92‒6.87) and myopia in both parents (OR=2.73, 95%CI=1.23‒6.06) were associated with a higher risk of myopia. In contrast, older maternal age at birth (OR=0.64, 95%CI=0.49‒0.85) and more frequent weekend outdoor activities (e.g., 1‒2 times per week: OR=0.21, 95%CI=0.05‒0.88; ≥5 times per week: OR=0.16, 95%CI=0.04‒0.71) were associated with a lower risk of myopia. The association between MEQ-5 chronotype and myopia was not statistically significant after multivariate adjustment (P=0.124). However, compared with the “absolute evening type”, the odds ratios (ORs) for myopia risk across sleep chronotypes decreased from 3.22 (moderate evening type) to 0.57 (absolute morning type), with fluctuations in between (0.95 for the “intermediate type” and 0.98 for the “moderate morning type”).

Conclusion A sleep chronotype tending toward the “evening type” in junior high school students may be associated with an increased risk of myopia, and this association requires further prospective studies to validate.