The hidden burden of eye-care needs: how visual acuity definitions change estimates of need in 12 RAAB surveys across six countries

Purpose: Rapid Assessment of Avoidable Blindness (RAAB) surveys are widely used to estimate the prevalence and causes of blindness and vision impairment among adults aged 50 years and older. We examined how far estimates of eye-care need depend on whether presenting or pinhole acuity, and unilateral or bilateral impairment, is used. Methods: We analysed 12 RAAB surveys undertaken between 2018 and 2023 in India, Nepal, Pakistan, Kenya, Tanzania and Uganda. Three person-level measures were compared: presenting visual acuity (PVA) in at least one eye, PVA in the better-seeing eye, and pinhole acuity in the better-seeing eye. Estimates were adjusted for the two-stage cluster design and age-standardised to the WHO world standard population. Results: Of 48,185 participants examined (response rate 94.3%), vision impairment based on pinhole acuity in the better eye (9-19%) was substantially lower than on PVA in the better eye (18-37%) or in at least one eye (33-51%). Increasing age (adjusted odds ratio [AOR] per year 1.106; 95% confidence interval [CI] 1.103-1.109), female sex (AOR 1.13; CI 1.08-1.19) and South Asian survey location (AOR 3.04; CI 2.78-3.33) were independently associated with impairment. Age-standardisation widened the difference between survey locations (prevalence ratio 1.50 crude, 1.66 standardised). Conclusions: Substantial vision impairment persists in the surveyed districts of both regions. The large gap between presenting and pinhole acuity indicates a considerable addressable burden, and restricting estimates to bilateral impairment in the better-seeing eye omits a further substantial share of need. The higher prevalence in the South Asian locations most plausibly reflects survey site selection and uncorrected refractive error rather than a regional epidemiological difference.