Global prevalence and causes of visual impairment and blindness in children: A systematic review and meta analysis

Author: Yekta A, Hooshmand E, Saatchi M, Ostadimoghaddam H, Asharlous A, Taheri A, Khabazkhoob M.

Geographical coverage: Saudi Arabia, Nepal, Nigeria, Sudan, South Africa, China, India, Ethiopia, Atlanta, Israel, Iran, Ireland, Malaysia, Suriname, Africa, Malawi, Oman, Tanzania, Ghana, Vietnam, Beijing, Chile, Brazil, Equatorial Guinea, Northern Ireland, Sydney, South Korea, Western China, Bangladesh, Delhi, Kathmandu, Haryana, Chiang Mai (Thailand), Australia, Turkey, United States and Egypt.

Sector: Burden of Disease

Sub-sector: Prevalence, visual impairment and blindness

Equity focus: Not reported

Study population: Children and adolescents aged 20 years or under with visual impairment or blindness

Review type: Effectiveness review

Quantitative synthesis method: Meta-analysis

Qualitative synthesis method: Not applicable

Background:

Childhood visual impairment (VI) significantly affects psychological, educational, and social development, continuing into adulthood and impacting quality of life. The World Health Organization’s VISION 2020 Initiative aimed to eliminate preventable blindness globally. Early estimates indicated that 19 million children under the age of 15 years were visually impaired, with 1.4 million cases of irreversible blindness, half of which were preventable. Prevalence varies widely: among children under 15, it ranges from 0.2 to 7.8 per 10,000 in low- and middle-income countries, compared to approximately 6 per 10,000 in developed countries. Causes also vary, with retinal disorders, glaucoma, corneal ulcers from vitamin A deficiency, cataract, and neurological issues being common in lower-income regions, while neurological disorders dominate in industrialised nations. Despite extensive data, regional differences in causes and prevalence complicate the formulation of global policy.

Objective:

To investigate the worldwide prevalence and primary causes of visual impairment and blindness in children.

Main findings:

Overall, the review highlights the global prevalence of visual impairment (VI) and blindness in children, revealing significant regional variations and identifying refractive errors as the most common cause of VI. The review included a total of 80 studies, encompassing data from 769,720 individuals across 28 countries. Notably, China leads with nine studies, followed by India with eight, and Iran with six. The studies were conducted across Asia, Africa, Europe, and the Americas, covering themes such as the prevalence of VI and blindness (including differences among age groups), demographic characteristics, and the effectiveness of health interventions.

The findings of the review indicate that the overall prevalence of VI based on uncorrected visual acuity (UCVA) of 20/40 or worse in the better eye is 12.72% (95% CI: 9.26%–16.19%), and 7.26% (95% CI: 4.34%–10.19%) for UCVA of 20/60 or worse. The prevalence of VI based on presenting visual acuity (PVA) of 20/40 or worse is 7.34% (95% CI: 5.53%–9.15%), and 3.82% (95% CI: 2.06%–5.57%) for PVA of 20/60 or worse. The prevalence of VI based on best-corrected visual acuity (BCVA) of 20/40 or worse is 0.77% (95% CI: 0.56%–0.97%), and 1.67% (95% CI: 0.97%–2.37%) for BCVA of 20/60 or worse. The highest rates of VI were observed in the Pacific region and the Americas, with notable variations across regions. Refractive errors were identified as the most common cause of VI, accounting for 77.20% (95% CI: 73.40%–81.00%) of cases.

The review highlights several methodological issues that need to be addressed in future research. These include the need for standardised study designs, larger sample sizes, and more rigorous data collection methods. Future research should also focus on longitudinal studies to better understand the long-term effects of interventions. Additionally, there is a call for more collaborative studies that span multiple countries to provide a more comprehensive understanding of the global impact of health interventions.

In conclusion, while the current evidence base provides valuable insights into the prevalence and causes of VI and blindness in children, there is a clear need for improved methodological approaches and more extensive research to address regional disparities and enhance the overall quality of evidence.

Methodology:

The review authors included all population-based cross-sectional studies on the topic, regardless of publication language or the study population’s gender, region, or race. Studies were selected based on quality; those focusing on schools for the blind were excluded. The primary outcomes were the prevalence of VI and blindness, as well as their causes. Searches were conducted in Scopus, PubMed, and Web of Science up to January 2018. Additionally, the authors scanned the reference lists of the included studies and Google Scholar to identify further relevant publications. Two researchers independently reviewed and selected articles, achieving a kappa agreement index of 80.2%. Discrepancies were resolved through discussion or consultation with a third reviewer.

Two reviewers independently extracted data from the included studies using predefined variables and assessed the quality of these studies using the STROBE checklist. Studies were categorised as low, moderate, or high risk of bias based on their reporting. Heterogeneity was analysed using the I² test, with values above 75% indicating significant heterogeneity.

The study authors calculated the prevalence of VI based on uncorrected visual acuity (UCVA), best-corrected visual acuity (BCVA), and presenting visual acuity (PVA), with all measurements converted to feet for consistency. Blindness was defined according to WHO guidelines. Data analysis was conducted using Stata (version 11), employing a random-effects model with a 95% confidence level. Publication bias was not assessed due to the nature of the prevalence data.

Applicability/external validity:

The review discusses the generalisability of the results by using credible population-based studies to estimate the global prevalence of visual impairment (VI) in children. The inclusion of diverse geographical locations and age groups enhances the external validity of the findings. The review compares prevalence rates across different regions and age groups, providing insights into how the findings may vary depending on context.

Geographic focus:

Included studies were conducted in Saudi Arabia, Nepal, Nigeria, Sudan, South Africa, China, India, Ethiopia, Atlanta, Israel, Iran, Ireland, Malaysia, Suriname, Africa, Malawi, Oman, Tanzania, Ghana, Vietnam, Beijing, Chile, Brazil, Equatorial Guinea, Northern Ireland, Sydney, South Korea, Western China, Bangladesh, Delhi, Kathmandu, Haryana, Chiang Mai (Thailand), Australia, Turkey, United States and Egypt.

Summary of quality assessment:

Overall, there is medium confidence in review’s conclusion, as the authors did not analyse the data from the included studies based on their risk of bias status.