Refractive error correction and harvest worker productivity in the Guatemalan coffee sector: A quasi-experimental analysis

Uncorrected refractive error - a condition affecting nearly 1 billion people globally - is a potentially significant constraint to economic productivity. Despite its prevalence, limited research has explored productivity impacts from refractive error correction in low-and middle-income countries where 90% of avoidable sight loss occurs. This study estimates the effect of refractive error correction on productivity by providing glasses to 332 seasonal harvesters across 12 Guatemalan coffee operations during the 2023–2024 season. Daily harvest weights were recorded and compared to a non-intervention group without visual impairment. We used an ANCOVA model as the primary specification with alternative difference-in-differences specifications as robustness checks. A financial benefit-cost analysis assessed whether returns exceeded costs for workers and farm owners. Results show a significant average daily harvest increase of 12.2 lbs (95% CI 3.5–20.8, p = 0.004), corresponding with a 7.9% relative productivity gain (95% CI 1.0%–14.8%, p = 0.02). Providing glasses costs $29.4 per worker, yielding returns of $10.9 to $1 to harvesters if they make this investment directly and $2.6 to $1 to the farm owners if they provide the glasses. Findings indicate substantial productivity gains and financial incentives for vision correction. This simple, cost-effective intervention has the potential to benefit millions in agriculture.