Myopia Development During Transition From Kindergarten to Early Grades in Elementary School: Population-Based Evidence From an Epidemic Area in Taiwan.

Purpose: The purpose of this study was to investigate the incidence of myopia, its association, and refractive progression among kindergarten non-myopic children after entering elementary schools in Yilan, Taiwan.

Methods: A cohort study was conducted on first- and second-grade elementary school students. Ocular examinations and caregiver-administered questionnaires were performed between December 2023 and March 2024, with data linked to kindergarten records from Yilan Myopia Vision Improvement Program (YMVIP). Myopia was defined as spherical equivalent (SE) ≤ -0.5 diopters (D), and premyopia as -0.5 D < SE ≤ 0.75 D.

Results: Of 1754 enrolled students, 1680 (95.73%) underwent ocular examinations, and 1554 (88.55%) were linked to kindergarten data. Among 1428 non-myopic preschoolers, the incidence density of myopia was 8.70% per person-year (95% confidence interval [CI] = 7.60%-9.80%). Children with incident myopia had a more negative baseline SE (0.33 ± 0.50 D vs. 1.02 ± 0.80 D, P < 0.001) and greater annual myopic progression (-0.60 ± 0.42 D/year vs. -0.20 ± 0.34 D/year). A multiple logistic regression model identified risk factors for incident myopia as premyopia in preschool (odds ratio [OR] = 9.641, 95% CI = 5.936-15.660, P < 0.001), having two myopic parents (OR = 1.819, 95% CI = 1.003-3.297, P = 0.049), and older age at the time of the elementary school examination (OR = 1.635, 95% CI = 1.224-2.183, P = 0.001). Spending more than 30 minutes/day outdoors on weekdays in preschool was protective against myopia (OR = 0.528, 95% CI = 0.366-0.762, P = 0.001).

Conclusions: The incidence density of myopia in Yilan County was 8.70% per person-year. Risk factors included premyopia, having myopic parents, and less outdoor time in kindergarten.