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.