Causes of vision loss worldwide, 1990-2010: a systematic analysis

Methodological quality of the review: Low confidence

Author: Bourne RR, Stevens GA, White RA, Smith JL, Flaxman SR, Price H, Jonas JB, Keeffe J, Leasher J, Naidoo K, Pesudovs K, Resnikoff S, Taylor HR, Vision Loss Expert Group.

Region: Worldwide

Sector: Blindness and vision impairment

Sub-sector: cataract, refractive error, macular degeneration, diabetic retinopathy and trachoma.

Equity focus: None specified

Review type: Other review

Quantitative synthesis method: Meta-regression

Qualitative synthesis methods: Not applicable

Background

Data on causes of vision impairment and blindness are important for development of public health policies, but comprehensive analysis of change in prevalence over time is lacking.

Research objectives

To estimate the main causes of blindness and vision impairment worldwide and by geographical region, including analysis of trends over time.

Main findings

The authors identified at least two studies for 18 out of the 21 Global Burden of Disease (GBD) study regions including Asia, Europe, Latin America, West Africa, Australasia and North America. No studies with cause-specific data were identified for central Africa or eastern Europe and one study was identified for central Europe. No studies were identified for 126 of the 191 countries.

In 2010, 65% (95% uncertainty interval [UI] 61–68) of 32·4 million blind people and 76% (73–79) of 191 million people with MSVI worldwide had a preventable or treatable cause, compared with 68% (95% UI 65–70) of 31·8 million and 80% (78–83) of 172 million in 1990. Leading causes worldwide in 1990 and 2010 for blindness were cataract (39% and 33%, respectively), uncorrected refractive error (20% and 21%), and macular degeneration (5% and 7%), and for MSVI were uncorrected refractive error (51% and 53%), cataract (26% and 18%), and macular degeneration (2% and 3%). Causes of blindness varied substantially by region. Worldwide and in all regions more women than men were blind or had MSVI due to cataract and macular degeneration.

The authors noted that these temporal changes in cause-specific prevalence of blindness and vision impairment are important for the setting of priorities, development of policies and for planning. Additionally, they also noted that the data reported provide a resource for advocacy efforts to mobilize resources for eye-care services from governments, donors and civil society.

Methodology

The authors included studies that met the following criteria: reported prevalence of blindness and/or VI must be measured from random sample cross-sectional surveys of representative populations of any age of a country or area of a country; definitions of VI or blindness must be clearly stated; best corrected and/or presenting visual acuity must be stated; and the procedures used for measurement of visual acuity must be clearly stated.

Authors conducted a search on the following databases: Medline, Embase and WHOLIS (1980-2012). Search terms included concepts to describe ‘blindness’, ‘VI’, ‘population’, ‘eye’, ‘survey’ and a list of conditions affecting the eye. The search strategy was also combined with search terms to retrieve country-specific records. Additionally, authors also contacted experts/authors for additional data sources.

In the methodology publication referred to in the paper, authors stated that consensus panels judged each paper against the inclusion/exclusion criteria, although methods used to extract data of included studies were not reported.

Data extraction involved the preservation of the smallest bracket of age categorization as possible from the published material to provide a database of age- and sex-specific prevalence and/or incidence of the vision loss categories, overall and by underlying cause. This database also specified the start and end dates of the study, geographical location and the methods used to assess visual acuity. The authors did not report using methods to quality assess each study included in the review.

The authors conducted a systematic analysis of data on the causes of blindness and moderate and severe vision impairment by estimating the proportions of overall vision impairment attributable to cataract, glaucoma, macular degeneration, trachoma, and uncorrected refractive error by age, geographical location and year.

Applicability/external validity

The authors note that worldwide and in all regions more women than men were blind or had MSVI due to cataract and macular degeneration.

Geographic focus

The authors included data from all income settings. Breakdown of the worldwide averages showed large differences in the cause of blindness between regions. In 2010, the proportion of blindness caused by cataracts ranged less than 15%, with the lowest values seen in high-income countries, to more than 40% in South and South-East Asia and Oceania. The proportion of blindness caused by macular degeneration was higher in regions with older populations, such as high-income regions and southern Latin America, and central and eastern Europe, where more than 15% of blindness was caused by macular degeneration, whereas the proportion was much lower in regions such as South Asia (2·6%, 95% UI 1·7–4·2; table 2). The proportion of blindness caused by glaucoma varied notably, with the lowest values being seen in South Asia (4·7%, 3·3–7·5), East and West sub-Saharan Africa (4·0%, 3·1–5·4 and 4·4%, 3·4–5·9, respectively), and Oceania (4·2%, 2·5–7·2), and the highest value being seen in tropical Latin America (15·5%, 9·6–21·9). The authors estimated that there was no trachoma-related blindness in 13 of 21 world regions, but that 3·6% (3·2–4·6) of blindness in West sub-Saharan Africa and 8·1% (6·8–9·5) in East sub-Saharan Africa was caused by trachoma-related corneal scars in 2010.

As with blindness, moderate and severe vision impairment was smallest in the high-income countries and largest in south and south East Asia. In comparison, MSVI caused by macular degeneration was small. Uncorrected refractive error caused a larger proportion of MSVI in South Asia than in other regions.

Quality assessment

There is low confidence in the conclusions about the effects of this study. Although the authors conducted a thorough search of the literature, it is not clear if language bias was avoided. Additionally, the authors did not report assessing the quality and risk of bias of each included study, and did not report the methods used to extract data of studies included in the review. Therefore we cannot determine the validity of included studies and overall findings of the review.