Increased Magnitude of Bilateral Visual Impairment and Reduced Effective Coverage of Eye Service Delivery in Zanzibar, Tanzania: A Longitudinal Population-Based Survey Between 2007 and 2025

Background: Low- and middle-income countries account for 90% of global visual impairment (VI); however, population-based evidence for eye-care planning remains scarce. Repeating Zanzibar’s 2007 survey in 2025 provides vital, updated data to determine long-term changes in blindness prevalence and service coverage, helping local interventions effectively align with ongoing demographic shifts.

Methods: We compared responses to two population-based surveys among adults aged ≥ 50 years using Rapid Assessment of Avoidable Blindness (RAAB) methodology. We assessed the age- and sex-adjusted prevalence, VI causes, coverage and effective coverage of cataract and refractive services, and barriers to cataract surgery.

Findings: Between 2007 and 2025, the prevalence of bilateral blindness and moderate-to-severe VI increased from 21·8% to 30·4%, particularly among women. Although the changes in prevalence were modest, the absolute burden sharply increased, with bilateral blindness more than doubling and moderate-to-severe VI nearly tripling, reflecting population aging and growth. Untreated cataract remained the leading cause of blindness (64·7%), and 87·0% of blindness was preventable/treatable. Cataract surgical coverage increased modestly, whereas effective coverage decreased, indicating a quality gap. Fear of surgery emerged as a key barrier. The unmet-need for refractive services, especially for distance vision, was substantially greater.

Interpretation: Eye-care coverage gains have not kept pace with demographic change. The persistent increase in bilateral VI, reduced effective coverage, and fear-related barriers highlight gaps in eye-care services in Zanzibar. Shifting from volume-based targets toward quality-, equity-, and outcome-focused strategies may help sustainably reduce avoidable vision loss.