Prevalence and time trends of refractive error in Chinese children: A systematic review and meta-analysis

Author: Tang Y, Chen A, Zou M, Liu Z, Young CA, Zheng D, Jin G.

Geographical coverage: China

Sector: Burden of disease

Sub-sector: Epidemiology

Equity focus: Study focuses on children in China.

Study population: Children in China

Review type: Other review

Quantitative synthesis method: Meta-analysis

Qualitative synthesis method: Not applicable

Background: Refractive error (RE) is a major health concern, particularly in East Asia, and is increasing among the young. Although numerous population-based or school-based studies and meta-analyses have been performed to evaluate the prevalence of RE in China, most of them focus on myopia and high myopia, which does not shed light on the magnitude and time trend of total RE, especially hyperopia and astigmatism, among the young Chinese population. There is no study reporting the epidemiologic characteristics of RE in China as a whole.

Objectives: To investigate the prevalence and time trends of refractive error (RE) among Chinese children under 18 years old.

Main findings:

Authors found the pooled prevalence of myopia, high myopia, hyperopia, astigmatism in Chinese children to be 38.0%, 2.8%, 5.2%, 16.5%, respectively. The review also found an increasing trend for prevalence of myopia and hyperopia, while there is a decreasing trend for prevalence of high myopia and astigmatism in Chinese children.

This review encompassed a total of 41 studies for qualitative synthesis, involving 1,051,784 participants. Among these studies, 15 studies were conducted in Northern China including 196,547 subjects (18.7%); 19 studies with 98,885 participants (9.4%) were conducted in Southern China; 6 studies including 89,213 subjects (8.5%) were launched in Hong Kong, Macao and Taiwan (HMT), and one multicentre study included 667,139 individuals (63.4%).

Among the 41 studies involving 1,051,784 subjects, the combined prevalence of myopia, high myopia, hyperopia, and astigmatism in Chinese children was found to be 38.0% (95% CI = 35.1%-41.1%), 2.8% (95% CI = 2.3%- 3.4%), 5.2% (95% CI = 3.1%-8.6%), and 16.5% (95% CI = 12.3%-21.8%), respectively. Children in urban areas were more likely to have refractive errors. The studies found a higher prevalence of myopia and hyperopia in Northern China compared to Southern China, and higher rates of high myopia and astigmatism in Hong Kong, Macau, and Taiwan compared to mainland China. Over time, there was an increasing trend in myopia and hyperopia, and a decreasing trend in high myopia and astigmatism.

According to the result of the Begg’s and Egger’s test, authors found no publication bias detected for the prevalence of myopia, hyperopia and astigmatism (p >0.05). Authors conducted sensitivity analysis and the pooled prevalence of RE did not change significantly compared with the initial results, suggesting good homogeneity of the included studies.

Considering the large magnitude of refractive errors, authors note that more attention should be paid to RE prevention and treatment strategy development in China.

Methodology:

The inclusion criteria were as follows: 1) school-based studies or population-based studies with clearly defined sampling strategies; 2) studies reporting the prevalence of refractive errors in Chinese children younger than 18 years old; 3) studies with a clear definition of refractive errors; and 4) sample size of at least 1,000 subjects. Studies with a sample size less than 1,000 were excluded because age-defined subgroups would be too small for a reliable assessment of the prevalence of refractive errors. The exclusion criteria were as follows: 1) hospital-based or clinical-based surveys; 2) conducted only in a single school; 3) using visual acuity as the measurement for refractive errors; 4) missing or incomplete data; 5) obvious limitations in their statistical analysis or design; and 6) different studies based on the same population without providing additional information. Non-English material was excluded.

To extract articles providing prevalence data of refractive errors in Chinese children, bibliographic databases including PubMed, EMBASE and Web of Science were searched with different combinations of words. The search was conducted by two investigators independently with the final search date of 28 July 2019.

Forty-one articles that met the inclusion criteria were reviewed by two investigators. The extracted data of these articles is listed as follows: 1) characteristics of the study: author, study year, design of study, refraction with or without mydriatics; 2) characteristics of the studied population: sample size, age range, district and region (urban or rural) of the sample, percentage of female subjects; 3) prevalence data: definition and prevalence of refractive errors.

Pooled prevalence of refractive error and its 95% confidence interval (95% CI) was estimated. Subgroup analyses were conducted for potential difference in region and study year. The I² test was performed to estimate the heterogeneity of the included studies (50% presents high degree of heterogeneity). When the I² test suggested a high degree of heterogeneity, a random-effects model was used, otherwise a fixed-effects model was used. To access the publication bias of these studies, Egger’s tests and Begg’s tests were performed and the significance level was set at p.

Applicability/external validity: Authors note that many studies were recent and few had been conducted in rural areas, with different definitions of RE being employed in some instances.

Geographic focus: Although the study focused on children in China, authors sought to compare their prevalence estimates with those obtained from a number of other high, medium and low income countries.

Summary of quality assessment:

There were several limitations in the approaches used to select, include and critically appraise studies. The search was limited to material published in English and there is no evidence of reference sections of relevant studies being checked or experts being consulted. No data is provided on the quality of the included studies. While the data analysis was generally of a high standard, there was no attempt to assess how the risk of bias associated with different studies may have influenced the reported results. For these reasons, we have attributed low confidence in the findings of this review.