Objective: To determine the influencing factors of electronic screen time of urban preschoolers before and after the COVID-19 outbreak, so as to provide a scientific basis for the control of digital screen use and early prevention of myopia among preschoolers. Methods: Using multi stage cluster random sampling method, a cross sectional survey of 8 244 kindergarten students in a district of Shanghai was implemented, through parent questionnaire collecting the time child spent on various electronic screens before and after the COVID-19 outbreak, estimated the weighting screen time, and emphatically analyzed the relationship between family electronic screen supervision behavior and preschoolers weighting screen time. Results: The proportion of daily over use time on average of mobile phones, computers and TV/projection screens among the surveyed preschool children during COVID-19 was 30.52%, 51.40% and 56.82%, respectively. On school days before the epidemic, the proportion was 21.94%, 41.80% and 47.51% respectively. After controlling for primary covariates, parents frequent control of children s electronic screen use, parents guidance for electronic screen use were significantly associated with lower weighted screen refractive time ( OR =0.60-0.77, P < 0.05 ). The use of electronic screen when parents accompanied their children, the use of electronic screen time by parents but not strictly implemented were significantly associated with higher weighted screen refractive time and increased screen refractive time ( OR =1.18-1.80, P <0.05). Conclusion Urban preschoolers electronic screen time was high during and before COVID-19. In the control measures of preschool children s electronic screen time, attention should be paid to the management of electronic screen use within the family and parents role model.

Objective: The current situation and associated factors of primary and middle school students screen time and related eye hygiene in different periods before and after COVID-19 were investigated, so as to provide a scientific basis for taking targeted measures of preventing and controlling myopia among those students. Methods: A total of 11 402 students were selected from 24 primary schools, 18 junior high schools and 16 high schools by multi stage stratified cluster sampling method. And a questionnaire survey was conducted among students and their parents to understand students screen time and screen hygiene behaviors and related factors in different periods before and after the outbreak of COVID-19. Results: The rate of screen overuse was 7.26%, 9.12% and 35.30% during school days, weekends and home study, respectively. The overuse rate of mobile phones and tablets at home increases with the increase of school stage. Totally 16.30% of students use mobile phones for online learning. The screen overuse rate of those who have not been diagnosed with myopia was lower than that of those who have been diagnosed during home study( OR=0.77, P <0.05). The higher the parents educational level was, the lower the screen overuse rate of children during the weekends became( P <0.05). In any period, the high proportion of screens used in homework and poor home screen eye environment increased the risk of screen overuse and poor eye hygiene ( P <0.05). Parental good behavior was conducive to reducing the risk( OR= 0.65-0.97, P <0.05). When the family had regulation on the screen use time, the implementation of laxity would increase the risk of screen overuse ( OR=1.18-2.48, P <0.05). Conclusion The screen overuse rate of urban primary and middle school students during home study is high, and a certain proportion of students still use mobile phones for online learning. The proportion of screens used in homework, home screen eye environment and screen use management are related to screens overuse. More attention should be paid to those with myopia and low educational level of parents.