Prevalence of myopia among primary school students in mainland China: A Meta-analysis

Methodological quality of the review: Low confidence

Author: Xi-Qing Xu, Shun-Ping Li1, Yan-Jiao Xu, Jie Wei

Region: Mainland China

Sector: Myopia

Subsector: Prevalence of myopia

Equity focus: No

Study population: School children

Type of programme: School based

Review type: Other review

Quantitative synthesis method: Meta-analyses

Qualitative synthesis method: Not applicable

Background: Myopia is the leading cause of visual impairment among refractive errors, and its prevalence has been increasing globally. It has been reported that myopia rates in East Asia, particularly among the Japanese and Chinese populations, are much higher than in European populations. Myopia has become a growing public health issue, with high prevalence rates in mainland China, particularly in children.

Objectives: The objective of this study was to summarise the prevalence of myopia among primary school students in mainland China and to inform broader initiatives.

Main findings: Thirty-seven eligible studies published between 1980 and 2013 were selected, with a total of 245,248 individuals. The pooled prevalence of myopia among the included individuals was 26.5% (95% CI: 21.8%-31.7%). The pooled prevalence was 32.2% (15.4%-53.3%) in western China, 12.8% (9.4%-17. 3%) in central China and 28.5% (22.4%-35.5%) in eastern China, respectively. The prevalence of myopia increased with age (from 8.4% at 6-8y to 57.4% at 12-14y). Sensitivity analyses were performed by excluding studies one by one to estimate the pooled prevalence of myopia among primary school students in mainland China. The pooled prevalence showed similar results, with no statistically significant differences. The included studies are roughly funnel-shaped distribution, suggesting that publication bias can be ignored.

Authors note, based on findings, that the prevalence of myopia among primary school students in mainland China was much higher than that of western countries or regions. The prevalence of myopia increased with age among primary school students. This study should be valuable for myopia prevention and treatment in mainland China.

Methodology: Inclusion criteria consisted of: 1) population-based studies; 2) focusing on primary school students aged between 6 and 14 years; 3) studying prevalence of myopia; 4) conducted in mainland China; 5) clear diagnostic criteria for myopia; 6) original research; 7) a sample size of more than 500. The Wanfang, Chinese National Knowledge Infrastructure (CNKI) and PubMed databases were searched for relevant articles published between 1 January 1980 and 31 December 2013. Combinations of keywords and medical subject headings, including: myopia OR shortsightedness OR nearsightedness OR visual impairment OR refractive errors, student OR students, prevalence OR incidence and China, were used to search for potentially relevant studies. English and Chinese language restrictions were applied. No attempts were made to retrieve unpublished studies. Data from eligible studies was extracted independently by two reviewers. The following information was extracted from each study: first author and year of publication; study site and period; sample size; myopia criteria; and prevalence of myopia. Disagreements between the two reviewers during data extraction were reconciled by a third investigator. Meta-analyses were conducted using Meta-Analyst software (version 3. 13, National Center for Research Resources, Agency for Healthcare Research and Quality, Tufts Medical Center, Boston, MA, USA) to calculate the pooled prevalence of myopia among primary school students from all of the eligible studies. A summary of prevalence estimates was obtained using fixed-effects meta-analysis or random-effects meta-analysis, which was determined by I².

Applicability/external validity: Despite the statistical power which was greatly improved, the authors acknowledge some limitations which need to be considered when interpreting the results. Subgroup analysis by gender was not performed because of insufficient information among the included studies. Although strict inclusion and exclusion criteria were used to identify studies in the literature, measurement errors were inevitable among included and excluded studies, which could affect the pooled prevalence. There were great disparities in research resources among eastern, central and western China, so the investigation bias may affect the meta-analysis results.

Geographic focus: The study was conducted only on studies published in China mainland.

Summary of quality assessment:

Low confidence was attributed in the conclusions about the effects of this study, as important limitations were identified. Literature searches were not comprehensive enough to ensure that all relevant studies were identified; methods used to screen and extract data were potentially biased and no methods were used to assess the quality of included studies.