The critical period of myopia, insight from the myopic shift in school age children after COVID-19 home confinement

Purpose : Time spent in outdoor activities is decreased due to home confinement for the Covid-19 epidemic. Concerns have been raised about whether it may have worsened the burden of myopia due to substantially decreased time spent outdoors and increased screen time at home. The purpose of this study is to investigate the refractive change and prevalence of myopia for school-aged children during the Covid-19 home confinement. Methods : In this school-based cross-sectional study in 10 elementary schools in Feicheng, China, and a total of 123,535 children aged 6 to 13 years were screened during 6 consecutive years (2015-2020). The Non-cycloplegic photorefraction was examined by Spot photoscreener. The Spherical Equivalent Refraction (SER) was recorded for each child and the prevalence of myopia for each age group in each year was calculated. The mean SER and prevalence of myopia were compared between the year of 2020 (after home confinement) and the previous 5 years for each age group. Results : A total of 194,904 test results (389,808 eyes) from 123,535 children were included in the analysis. A substantial myopic shift (around-0.3D) was found in the 2020 schoolbased photoscreenings when compared with previous years (2015-2019) for younger school-aged children aged 6 (-0.32D), 7 (-0.28D), and 8 years (-0.29D). The prevalence of myopia in the 2020 photoscreenings was much higher than the highest prevalence of myopia within years of 2015-2019 for children at age of 6 (21.5% vs 5.7%), 7 (26.2% vs 16.2%), and 8 (37.2% vs 27.7%). The differences in SER and prevalence of myopia between 2020 and previous years were minimal in children aged 9-13 years. Conclusions : Covid-19 home confinement was associated with a significant myopic shift for younger children (aged 6-8 years) according to the 2020 school-based photoscreenings. Younger children's refractive status may be more sensitive to environmental changes than older ages, given they are in a critical period for the development of myopia.