Prevalence of blindness and its major causes in sub-Saharan Africa in 2020: A systematic review and meta-analysis

Author: Xulu-Kasaba, Z. N., & Kalinda, C.

Geographical coverage: Sub-Saharan Africa

Sector: Burden of Disease

Sub-sector: Prevalence

Equity focus: Not reported

Study population: Patients with blindness

Review type: Effectiveness review

Quantitative synthesis method: Meta-analysis

Qualitative synthesis method: Not applicable

Background: The World Health Organisation (WHO) defines blindness as severe visual acuity loss or a significantly restricted visual field, affecting an estimated 36 million people worldwide and remaining a major global health concern. Of these, 75% suffer from preventable or avoidable conditions. Despite initiatives like VISION 2020 and the Global Action Plan, visual impairment persists, especially in low- and middle-income countries (LMICs) where 90% of the blind population resides. Sub-Saharan Africa (SSA) is among the poorest and fastest-growing regions that face increased risks of blindness due to poverty and resource limitations. Moreover, the increasing population in SSA is expected to further escalate the burden. While many primary studies have emerged since the WHO’s call for regional data, identifying the underlying causes of blindness remains essential for developing effective prevention and management strategies.

Objectives: To ascertain the prevalence of blindness and its major causes in SSA and to accurately measure their distribution and extent through meta-analysis.

Main findings: In total, 77 studies from 26 countries, comprising 191,173 participants, were included in this meta-analysis. Of these, one study was conducted in Central Africa, 28 in East Africa, 16 in Southern Africa, and 32 in West Africa.

The pooled prevalence estimate (PPE) of blindness in SSA was 10% (95% CI: 8% to 11%), with West Africa having the highest prevalence (14%, 95% CI: 11% to 18%), followed by East Africa (8%, 95% CI: 6% to 11%). Southern Africa had a lower prevalence (5%, 95% CI: 3% to 7%); limited data from Central Africa hindered a reliable estimate for that region. The study identified cataracts as the leading cause of blindness in sub-Saharan Africa, accounting for 46% (95% CI: 40% to 52%) of cases, followed by glaucoma (14%, 95% CI: 11% to 18%) and diabetic retinopathy (14%, 95% CI: 11% to 17%). Other less significant causes were uncorrected refractive error (URE), macular degeneration, onchocerciasis, and corneal conditions.

The findings revealed a high prevalence of blindness among individuals aged 50 and older, with a PPE of 45% (95% CI: 40% to 50%). Notably, gender disparities were evident in this age group: blindness prevalence was significantly higher in females (50%, 95% CI: 43% to 58%) than in males (39%, 95% CI: 33% to 45%). Regional differences were also observed, with East Africa reporting the highest prevalence rates for both females (52%) and males (34%) in this age category.

Methodology:

Searches were conducted in PubMed, Google Scholar, and EBSCOhost databases to identify published and unpublished studies reporting on the prevalence and causes of visual impairment and blindness in SSA. Studies published in English between 1 January 2010 and 30 June 2020 were included. In addition, a manual search was conducted to identify additional relevant articles.

The identified studies were screened for eligibility. Relevant data were extracted in a standardised data collection form. The methodological quality of the included studies was assessed using the 2018 revised Mixed Methods Appraisal Tool (MMAT). The findings were synthesised using a random-effects meta-analysis. Heterogeneity was assessed using the Cochran’s Q test and I² statistic, and publication bias was assessed with a funnel plot. Subgroup analyses by geographic region were conducted to explore the potential sources of heterogeneity.

Applicability/external validity: The review did not explicitly discuss the applicability or external validity of its findings. However, it acknowledged several limitations that could affect the generalisability of the results, including the exclusion of non-English studies, high variability among the included studies, and an underrepresentation of Central Africa due to insufficient data. Additionally, most studies focused on individuals aged 50 and above, potentially skewing prevalence rates and limiting generalisability to younger age groups. The review emphasised the need to conduct more studies in Central Africa.

Geographic focus: The review was focused on sub-Saharan Africa. The included studies were conducted in Central, East, Southern, and West Africa.

Summary of quality assessment: Overall, confidence in this review’s conclusions is low. The inclusion and exclusion criteria were clearly defined, and a comprehensive search strategy was implemented to identify relevant published and unpublished studies. The findings were synthesised using a random-effects meta-analysis. Heterogeneity was assessed using the Cochran’s Q test and I² statistic, and publication bias was evaluated with a funnel plot. Subgroup analyses by geographic region were conducted to explore sources of heterogeneity. However, the review restricted its search to English-language publications only. Additionally, it did not report how many reviewers independently screened articles or extracted data, nor did it provide a list of excluded studies.