The global prevalence of amblyopia in children: a systematic review and meta-analysis

Author: Fu Z, Hong H, Su Z, Lou B, Pan CW, Liu H.

Geographical coverage: Worldwide

Sector: Burden of disease

Sub-sector: Epidemiology

Equity focus: Children

Study population: Children

Review type: Other review

Quantitative synthesis method: Meta-analysis

Qualitative synthesis method: Not applicable

Background: Amblyopia is a common vision disorder among children and is defined as decreased vision due to abnormal development of the visual cortex in infancy or childhood. Epidemiological data about the prevalence of amblyopia around the world varies widely among regions and time periods.

Objectives: To determine the global prevalence of amblyopia in children.

Main findings:

In summary, this review found that the overall worldwide pooled prevalence of amblyopia was 1.36% (95%CI: 1.27-1.46%).

The meta-analysis conducted by the authors encompassed 97 studies. It involved a comprehensive sample of 4,645,274 children, out of which 7,706 were identified as patients with amblyopia.

The authors reported that the global pooled prevalence of amblyopia was 1.36% (95%CI: 1.27-1.46%). The study revealed a higher prevalence of amblyopia in males (1.40%, 95%CI: 1.10-1.70%) compared to females (1.24%, 95%CI: 0.94-1.54%) with an odds ratio of 0.885 (95%CI: 0.795-0.985, p = 0.025). The authors found no significant correlations between the prevalence of amblyopia and factors such as geographical area, year of publication, age, sample size, or whether the study was conducted in a developed or developing country (all p >0.05). However, Begg’s test (p = 0.065) and Egger’s test (p <0.001) indicated a significant publication bias in the reported prevalence of amblyopia.

Pertaining to findings relevant to policy, the authors highlight that amblyopia poses a substantial global vision challenge. They underscore the importance of public health approaches such as early detection, intervention, and management.

Methodology:

Review authors included studies meeting the following eligibility criteria: (1) the type of study had to be a prevalence study; (2) the population had to be children or juveniles, given that amblyopia is a condition that occurs in childhood. Studies were included as long as the authors considered their study population to be underage, acknowledging that the definition of children or juveniles varies among countries; (3) the outcome had to be the prevalence of amblyopia; and (4) the full text had to be published in English. Special groups, such as hospitalised patients or patients with specific ocular or systemic diseases, were not included.

Three electronic databases were searched by the authors including PubMed, EMBASE and the Cochrane Library, from inception up to 5 November 2021.

Potentially relevant publications were screened and evaluated by two reviewers in a double-blind manner. Two researchers independently extracted the data using a structured data collection form. The cross-sectional studies were evaluated using the Healthcare Research and Quality (AHRQ) tool. The cohort studies were evaluated according to the Newcastle-Ottawa scale (NOS).

The analyses were conducted using Stata, combining prevalence with a 95% confidence interval for statistical analysis. Prevalence estimates underwent the Freeman-Tukey transformation and were back-transformed post-quantitative data synthesis. Cochran’s Q-test and the I² index were used to calculate statistical heterogeneity among studies. High heterogeneity was indicated by an I² >50% and Q-test p <0.10, leading to the use of the random-effects model; otherwise, the fixed-effects model was applied. In the random-effects model, the tau square (Tau2) was calculated, with p-values = 0.05 deemed statistically significant. Funnel plots, Egger’s test, and Begg’s test were used to assess potential publication bias. Univariable meta-regression models examined the impact of age, sample size, publication year, region (developed or developing), and geographical location on amblyopia prevalence. Subgroup comparisons were made using odds ratios (ORs) and a 95% confidence interval.

Applicability/external validity: Authors note that their findings are supported by previous meta-analyses, which produced similar results. However, some of the identified limitations may limit the applicability of their results, for example, diverging definitions of children.

Geographic focus: Included studies in the review were carried out in various high-income and low-to-middle-income countries, such as China, Turkey, India, and Pakistan.

Summary of quality assessment:

There are a number of limitations in the approaches used to identify, include and critically appraise studies. The search was limited to published material produced in English and there is no evidence of the references sections of included items being reviewed. While the analysis of the data used a reasonable approach, no attempts were made to separate out higher and lower quality studies, to see if and how this affected the overall results reported. In addition, the authors note a high degree of heterogeneity between included studies and a need to treat some subgroup estimates with caution, because of the small numbers of studies involved in some instances. For these reasons, we attributed a low confidence in the findings of this review.