Global Vision Impairment and Blindness Due to Uncorrected Refractive Error, 1990-2010

Methodological quality of the review: Low confidence

Author: Kovin S. Naidoo, Janet Leasher, Rupert R. Bourne, Seth R. Flaxman, Jost B. Jonas, Jill Keeffe, Hans Limburg, Konrad Pesudovs, Holly Price, Richard A. White, Tien Y. Wong, Hugh R. Taylor and Serge Resnikoff

Region: Worldwide

Sector: Uncorrected refractive error (URE)

Subsector: Global Vision Impairment and Blindness due to URE

Equity focus: No

Study population: Adults

Type of programme: Global prevalence

Review type: Other review

Quantitative synthesis method: Systematic review

Qualitative synthesis method: Not applicable

Background: Refractive error (RE) is one of the most common ocular conditions, and uncorrected refractive error (URE) is a major public health challenge. Worldwide, URE is the leading cause of vision impairment (VI) and the second leading cause of blindness. Vision impairment due to URE has been observed to have extensive social and economic impacts, for example, limiting educational and employment opportunities of economically active people, healthy individuals and communities. We conducted, as part of the Global Burden of Disease, Risk Factors and Injuries Study 2010 (GBD), a systematic review of all available population-based prevalence studies performed worldwide between 1990 and 2010. The results informed a meta-analysis to estimate the number of people affected by blindness and VI globally, regionally and by cause, and yielded estimated temporal trends in prevalence from 1990 to 2010, and investigated regional differences worldwide.

Objectives: The purpose of this systematic review was to estimate worldwide the number of people with moderate and severe visual impairment (MSVI; presenting visual acuity G6/18, Q3/60) or blindness (presenting visual acuity G3/60) due to uncorrected refractive error (URE), to estimate trends in prevalence from 1990 to 2010, and to analyse regional differences.

Main findings: A total of 243 high-quality, population-based studies remained after application of the above rigorous selection criteria and review by an expert panel. URE was the second leading worldwide cause of blindness (after cataract), contributing in 1990 to 19.9% (95% confidence interval [CI]:14.9-24.9%) of all blindness and in 2010 to 20.9% (95% CI: 15.2-25.9%). In 1990 and 2010, the proportion of MSVI due to URE was 51.1% (95% CI: 45.6-56.0%) and 52.9% (95% CI: 47.2-57.3%), respectively, and as such remains the leading cause of all MSVI worldwide. In 2010, URE was the leading cause of MSVI in all regions, with the proportion ranging between 43.2 and 48.1%, except in South Asia. The proportion in South Asia where there is a relatively younger population was 65.4% (95% CI: 62.0-72.0%). South Asia also had a proportion of 36.0% of blindness due to URE, compared to a low of 13.1% in North Africa/Middle East and Eastern sub-Saharan Africa. The prevalence of blindness in all ages due to uncorrected refractive error decreased from 0.2% (0.2%; 95% CI: 0.1-0.2%) in 1990 to 0.1% (0.1%; 95% CI: 0.1-0.1%) in 2010, a 33% reduction. Age-standardised prevalence of refractive error-related blindness worldwide was 0.4% (95% CI: 0.3-0.5%) in adults aged 50+ years in 2010 and a reduction of 33% to 0.6% (95% CI: 0.4-0.7%) for 1990. The age-standardised prevalence of refractive error-related MSVI worldwide decreased to 5.3% (95% CI: 4.6Y6.5%) in 2010 from 6.9% (95% CI: 5.6-8.0%) in 1990.

Authors conclude that in 2010, uncorrected refractive error continues as the leading cause of vision impairment and the second leading cause of blindness worldwide, affecting a total of 108 million people or 1 in 90 people.

Methodology: Inclusion criteria consisted of: 1) the 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. 2) The definitions of VI or blindness must be clearly stated, using thresholds of visual acuity, in the better eye. 3) Best-corrected and/or presenting visual acuity must be stated. 4) The procedures used for measurement of visual acuity must be clearly stated. A systematic review of medical literature from 1 January 1990 to 31 January 2012 identified indexed articles containing data on incidence, prevalence and causes of blindness and VI. Authors identified 14,908 relevant manuscripts using Medline, Embase, and the WHO library information system. Data analysis was carried out in three steps: 1) data identification and access, described previously; 2) estimation of cause fractions for each cause, by severity of VI, sex, age and world region (for each cause, we used the subset of studies for which causal data were available); and 3) application of cause fractions to the prevalence of all-cause presenting VI, which were estimated as described previously. For the statistical analysis, the DisMod-MR model from the GBD study was used to calculate the fraction of VI due to URE and the other causes.

Applicability/external validity: Regarding external validity, the authors reported some limitations which need to be considered: many country-years remained without data or only had sub-national data. Only a few national studies reporting VI for all ages and all causes were available. Few studies from Central Africa were identified.

Geographic focus: Worldwide study

Summary of quality assessment:

Low confidence was attributed to this review’s findings, as important limitations were identified. Although authors conducted thorough searches of the literature, language bias was not avoided. It is not clear whether quality assessment of included studies was conducted and how the risk of bias of each study impacted on the validity of study findings.