Association of Age at Myopia Onset With Risk of High Myopia in Adulthood in a 12-Year Follow-up of a Chinese Cohort

IMPORTANCE Early-onsetmyopia is well known to progress to highmyopia in adulthood. However, no accurate estimation of how a specific age atmyopia onset is associated with the probability of developing highmyopia in adulthood is available, and a very-long-term follow-up study with data from annual visits is needed. OBJECTIVE To estimate the risk of developing highmyopia in adulthood associated with a specific age atmyopia onset from a data set with a 12-year annual follow-up. DESIGN, SETTING, AND PARTICIPANTS This ongoing, population-based prospective cohort study of twins was conducted in Guangzhou, China, on July 11, 2006. Data from baseline to August 31, 2018, were analyzed. The first-born twins completed follow-up until 17 years or older, and the 443 participants (after exclusions) who developedmyopia were included in the analysis. Data were analyzed from September 1, 2018, to January 20, 2020. MAIN OUTCOMES AND MEASURES Age atmyopia onsetwas determined by prospective annual cycloplegic refractions (365 participants [82.4%]) or with a questionnaire. Refraction in adulthood was defined as the cycloplegic refraction measured at the last follow-up visit. RESULTS Among the 443 eligible participants (247 [55.8%] female; mean [SD] age atmyopia onset, 11.7 [2.0] years), 54 (12.2%) developed highmyopia (spherical equivalent, -6.00 diopters or worse determined by cycloplegic refractions) in adulthood. Among participants with age atmyopia onset of 7 or 8 years, 14 of 26 (53.9%; 95%CI, 33.4%-73.4%) developed highmyopia in adulthood; among those with onset at 9 years of age, 12 of 37 (32.4%; 95%CI, 18.0%-49.8%); among those with onset at 10 years of age, 14 of 72 (19.4%; 95%CI, 11.1%-30.5%); among those with onset at 11 years of age, 11 of 78 (14.1%; 95%CI, 7.3%-23.8%); and among those with onset at 12 years or older, 3 of 230 (1.3%; 95%CI, 0.2%-3.8%). Results of multivariate logistic regression analysis suggested that the risk of developing highmyopia in adulthood decreased significantly with delay in the age atmyopia onset (odds ratio, 0.44; 95%CI, 0.36-0.55; P < .001), from greater than 50% for 7 or 8 years of age to approximately 30% for 9 years of age and 20% for 10 years of age. CONCLUSIONS AND RELEVANCE These findings suggest that the risk of highmyopia is relatively high in children withmyopia onset during the early school ages. Each year of delay in the age at onset substantially reduces the chance of developing highmyopia in adulthood, highlighting the importance of identifying effective prevention strategies under investigation, such as increasing outdoor time.