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GBD 2019 Blindness and Vision Impairment Collaborators; Vision Loss Expert Group of the Global Burden of Disease Study. Causes of blindness and vision impairment in 2020 and trends over 30 years, and prevalence of avoidable blindness in relation to VISION 2020: the Right to Sight: an analysis for the Global Burden of Disease Study. The Lancet. Global health. 2021;9:e144-e160. PMID 33275949

One-paragraph summary

A systematic review and meta-analysis of population-based eye-disease surveys from January 1980 to October 2018, fitted with hierarchical models to estimate prevalence of moderate-to-severe vision impairment (presenting acuity <6/18 to 3/60) and blindness (<3/60 or field <10°) by cause, age, region and year, focused on adults aged 50 and older because of data sparsity at younger ages. Cataract was the leading global cause of blindness in that age group in 2020 at 15.2 million cases (95% UI 12.7–18.0), ahead of glaucoma (3.6 million, 2.8–4.4), undercorrected refractive error (2.3 million, 1.8–2.8), age-related macular degeneration (1.8 million, 1.3–2.4) and diabetic retinopathy (0.86 million, 0.59–1.23); for MSVI the leading causes were undercorrected refractive error (86.1 million, 74.2–101.0) and cataract (78.8 million, 67.2–91.4). Measured against the World Health Assembly Global Action Plan target of a 25% reduction from 2010 to 2019 in avoidable vision impairment, the target was missed: crude prevalence did not change (−0.2%, 95% UI −1.5 to 1.0), age-standardised avoidable blindness fell 15.4% (−16.8 to −14.3) but avoidable-blindness case counts rose 10.8% (8.9–12.4) and avoidable-MSVI counts rose 31.5% (30.0–33.1).

Key findings

  • Cataract blindness, adults ≥50, 2020: 15.2 million (12.7–18.0) — the largest single cause.
  • Cataract MSVI, adults ≥50, 2020: 78.8 million (67.2–91.4).
  • WHA Global Action Plan 25% reduction target: not met.
  • Age-standardised avoidable blindness −15.4%, while avoidable-blindness counts +10.8% and avoidable-MSVI counts +31.5%.
  • The divergence between rates and counts — driven by population growth and ageing — is the structural fact of the field.

Limitations

  • Restricted to adults ≥50 because paediatric data are too sparse, so childhood cataract is invisible here (Sheeladevi 2016, PMID 27518543).
  • Cause attribution in eyes with multiple pathologies is a modelling decision that varies between surveys and shifts cataract's share.
  • Wide uncertainty intervals reflect genuinely sparse population-based cause data.
  • Uses presenting rather than best-corrected acuity, which raises apparent cataract burden relative to a best-corrected definition (Song 2018, PMID 29977532).
  • Does not distinguish nuclear, cortical and PSC cataract, which have different risk factors and progression.

Why it matters

This analysis is the standard citation for cataract's global rank and for the failure of the VISION 2020/WHA framework to bend the absolute burden. It is also the source of the field's central paradox: prevalence falling while counts rise. Read alongside the cataract-specific all-ages model — 17.0 million blind (39.6% of all blindness) and 83.5 million with MSVI (28.3%), 60% and 59% of them women, with cataract-blind counts up 29.7% and age-standardised prevalence down 27.5% from 1990 to 2020 (Vision Loss Expert Group 2024, PMID 38461217) — it produced the shift from a prevalence-reduction target to the 2030 effective-cataract-surgical-coverage target (Keel 2021, PMID 34237266), whose own trajectory now looks like an 8.4-percentage-point rise against a 30-point goal (McCormick 2026, PMID 41687671).

Cited by wiki pages

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