The trend of myopia rate in 61 350 children and adolescents: a cross‐sectional research in Ningbo, Zhejiang

Editor, U ncorrected refractive error is the leading cause of global vision impairment (Bourne et al. 2013), with myopia being the most frequently seen refractive error, especially in east and southeast Asian countries (Morgan et al. 2012). It is reported that the prevalence of myopia is estimated to reach 49.8% worldwide by 2050 (Holden et al. 2016). It had been shown in previous studies that changes to refractive error continued from childhood into adulthood. Thus, understanding the trend of myopia rate in children and adolescents is important to be able to provide the eye care needs and perhaps control the diseases secondary to severe myopia. Our study performed a populationbased and cross-sectional investigation to survey the prevalence of myopia in Ningbo, Zhejiang. A total of 61 350 children and adolescents were recruited in our study, including 31 730 males and 29 620 females. Each enrolled subject underwent uncorrected distance visual acuity (UDVA) assessment using a standard logarithmic visual acuity E chart and non-cycloplegic autorefraction examination. Myopia was defined as UDVA < 5.0 and spherical equivalent (SE) < 0.50D. In this study, the myopia rates of kindergarten, primary school, middle school and high school were 9.45% (277/2930), 48.01% (11 775/24 525), 76.50% (13 453/17 586) and 79.15% (12 908/16 309), respectively. In general, maleshad lowermyopia rate than females (primary school: 46.10% versus 50.18%, middle school: 73.19% versus 80.29% and high school: 77.44% versus 80.68%) except kindergarten (9.90% versus 8.95%). In the Fig. 1A, we can observe the increasing trend of myopia rate changed along with the age growth. It is indicated that the fastest growing stage of myopia was 6 years old to 11 years old, which is the stage of children entering primaryschoolandstarting the low-grade studying. We can also notice there is a little drop of myopia rate from 15 years old to 16 years old, which is the stage of adolescents moving from middle school to high school. Figure 1B presents the age-related and eyeball-specific refractive change. It is showed that children aged 5– 6 years still had hyperopic reserve. SE is steady declined with age growing in both eyeballs, and intriguingly right eyeballs had poorer eyesight compared with left eyeballs in each age group. Myopia is a multifactorial process involved with age, gender, ethnicity, living area and many other factors (Rudnicka et al. 2016). Our findings summarized the prevalence of myopia in different age group in Ningbo, which are in accordance with those of Dong et al. (2017) who reported the prevalence of myopia and increase trend in children and adolescents aged 7–18 years in Han ethnic group in China, 2005–2014. Their study also revealed that the detection rate of myopia was high in children and adolescents in China and the age of myopia prevalence peak has become earlier gradually. Our study had several limitations. Firstly, our study is a cross-sectional study and it can only report the current prevalence status. Secondly, ocular axial length was not routinely measured. Thirdly, our study is a population-based myopia screening programme fundamentally and it is lack of other related factors such as health-risk behaviours and environmental factors. So larger cohort studies containing more relevant factors are needed to study the trend of myopia in the children and adolescents.