Methodological quality of the review: Low confidence
Author: Munoz B, West SK.
Region: North, Central and South America including the Caribbean.
Sector: Blindness and Visual impairment
Sub-sector: Americas and Caribbean
Equity focus: None specified
Review type: Effectiveness review
Quantitative synthesis method: Narrative analysis
Qualitative synthesis methods: Not applicable
North, Central and South America including the Caribbean are marked by extreme diversity and include high- and low-income countries as well as varying diversity within country populations including disparities in income, health, race and education. As a result, it is inevitable that there exists a large variation in blindness and visual impairment rates in the region. Authors note that it is very surprising how little is known about the magnitude of blindness and impairment rates in the region, despite the backdrop of diversity.
To summarize available data on the prevalence and causes of visual impairment and blindness in the Americas and the Caribbean.
Although analysis of the prevalence and causes of blindness and visual impairment in the adult population is reported, the total number of studies included in the review is not clear. Studies designs included in the review varied between simple random samples, community-based rural, stratified random samples, multistage random samples and community-based studies. All studies were conducted in North, Central and South America, including the Caribbean. The review also included data from blind registers from schools for the blind. It should be noted that estimates of the magnitude of prevalence of childhood blindness was based on data from blind registers in Europe and few available population-based surveys from Asia and Africa.
From data available, and using mortality in children under the age of five as an indicator, the overall prevalence of childhood blindness (in the under age 15 group) was 0.45/1000 with 67% living in countries with mortality of children under five above 30/1000 live births. Corneal opacities were common in countries where the under-five death rate are above 30/1000 live births including Bolivia, Dominican Republic and Peru. Retinopathy of prematurity (ROP) was an important cause in countries with intermediate death rates, where survival rates have improved, but neonatal care is still problematic.
Authors noted that there are no appropriate models (unlike childhood blindness, where a model was used) that can accurately estimate rates of adult blindness and visual impairment. For adults, overall blindness rates were not estimated because of the social, economic and ethnic diversity in the region. In the USA, it is noted that prevalence of blindness depends on ethnic grouping, location and year the survey was conducted. In Central and South America, studies indicated that there was a higher prevalence of blindness than the prevalence reported among Hispanics in North America.
Causes of blindness varied according to country, but for adults, cataract and glaucoma were leading causes in the African-American and Hispanic population and age-related macular degeneration in the white population. Uncorrected refractive error is an important cause of visual loss in all ages. Onchocerciasis continues to affect the very poor in Brazil, Colombia, Ecuador, Guatemala, Mexico and Venezuela.
Authors searched MEDLINE and LILACS, although it is not clear from the review the period of the search or more generally details of the search strategy. References of the included articles were also searched for relevant articles, which were also reviewed. It is not clear if two reviewers independently conducted study selection and data extraction of included studies.
Due to a lack of data around the prevalence of blindness amongst children, authors adopted a model proposed by Foster et al to estimate the magnitude of blindness in children using the mortality of children under five years old as an indicator. The review also included data from blind registers from schools for the blind in order to establish the causes of childhood blindness.
The authors did not fully discuss how far the results can be generalized but did note that the Americas cover an extremely diverse set of nations. Results of the review include information applicable to low-, middle- and high-income countries. However, it is noted that study designs used in the review have limited extent to which results could be made applicable to other contexts. The analysis into the prevalence and causes of blindness and visual impairment use country-specific population surveys; causes of childhood blindness are reported from specific schools for the blind.
This systematic review was awarded low confidence in the conclusions about the effects as some major limitations were identified. In the literature search, although covering relevant databases, language bias was not avoided and authors of included articles and/or experts were not contacted for additional articles. The search was not sufficiently comprehensive that we can be confident that relevant literature was not omitted. In addition, it was unclear if appropriate methods were used to select studies and extract data of included studies.
The likelihood of bias within included studies was not fully addressed in the review, which may impact on the quality and validity of the study. Nevertheless, authors did acknowledge that the use of blind registers and data from schools for the blind to evaluate causes of blindness in children is subject to selection and survival bias.