Prevalence and Causes of Blindness and Visual Impairment Among Nigerian Children: A Systematic Review

Author: Eze UA, Obasuyi OC, Salihu DV, Bature M, Yeye-Agba OO, Kanmodi KK. 

Geographical coverage: Nigeria

Sector: Burden of Disease

Sub-sector: Prevalence

Equity focus: Not reported

Study population: Paediatric patients with blindness and visual impairment

Review type: Effectiveness review

Quantitative synthesis method: Narrative synthesis

Qualitative synthesis method: Not applicable

Background: Globally, over 2.2 billion people live with near or distant visual impairment, primarily due to refractive errors and cataracts. More than 80% of these cases occur in low- and middle-income countries. These cases heavily impact socio-economic development, with global productivity losses of around USD 411 billion. Among children, visual impairment is especially devastating as it affects psychosocial and intellectual development. An estimated 450 million children globally have some form of visual impairment, with 90 million classified as blind. In Africa, the prevalence of blindness reaches approximately 1.9%. Nigeria, a home to over 110 million children under 18, lacks nationally representative data, despite being significantly affected. Therefore, aggregating existing evidence is essential to inform effective health policy and intervention.

Objective: To determine the prevalence and causes of blindness and visual impairment among children in Nigeria by interrogating the evidence in the last 20 years.

Main findings: The review included 17 studies, comprising 15,810 participants. All included studies were conducted in Nigeria, and cross-sectional by design, with a sample size per study ranging from 40 to 5,723. Methodological quality of the included studies was rated as moderate to good. The overall mean (range) prevalence of blindness was 0.3% (0.2–0.4%) while that of mild, moderate, and severe visual impairments was 3.9% (0.2–15.9), 2.9% (0.1–10), and 0.2% (0.1–0.5), respectively.

The causes of blindness were cataracts, optic atrophy, cornea scars and cornea-related pathologies, and trauma; while, the causes of mild to severe visual impairment were refractive errors, cataracts (congenital or acquired), corneal opacities (congenital, presumed vitamin A deficiency, infectious or traumatic), glaucoma, and amblyopia.

Methodology:  The searches were conducted in The African Journal Online (AJOL), Bielefeld University Search Engine (BASE), PubMed, and the ProQuest online library databases to identify relevant studies published in English. The review included all primary cross-sectional studies reporting the prevalence and causes of visual impairment in Nigerian children under 18 years between 2003 and 2022.

Two reviewers independently screened the articles, extracted the relevant data and critically appraised the quality of the included studies using the appraisal tool for cross-sectional studies (AXIS). Disagreements between the reviewers were resolved through discussion or by contacting a third reviewer. Meta-analysis was not possible due to heterogeneity. Instead, descriptive statistics (mean and range) were used to estimate the prevalence from the nine included community-based studies. Community-based studies were used to estimate the prevalence because they give a better representation of the general population, and clinic-based studies provided more detailed causes of blindness and visual impairment.

Applicability/external validity: The review noted heterogeneity in the methods of the included studies, which precluded meta-analysis. Nevertheless, the findings offer valuable and verifiable insights into the subject within the Nigerian context.

Geographic focus: The review focused on Nigeria.

Summary of quality assessment: Overall, there is medium confidence in the review’s conclusions. The searches were conducted in multiple databases. Inclusion and exclusion criteria were clearly defined. Study quality was assessed using valid and reliable tool, and findings of the assessment were provided. Two reviewers independently screened the studies and extracted relevant data. A list of included studies was provided. Characteristics of the included studies were presented. The findings were synthesised narratively using descriptive statistics. However, a list of excluded studies was not provided. The review did not report checking reference lists or contacting the authors/experts. English language limits were applied. Grey literature was not searched. The risk of bias was assessed, but the findings were not reported by the risk of bias status.