PROductivity Study of Presbyopia Elimination in gaRment workers (PROSPER II): a randomised trial on the productivity impact of providing near glasses to Indian garment factory workers

BACKGROUND: Correction for presbyopia, the world's most common cause of vision impairment, significantly improves productivity in agriculture and crafts. However, effects on productivity in manufacturing remain unstudied. METHODS: PROSPER II was an individually randomised, investigator-masked, controlled trial conducted in Karnataka, India. Eligible garment factory workers aged ≥35 years with presbyopia (better-eye near vision N6.3 or worse (Snellen 6/12), correctable to N4 (Snellen 6/7.5)) and not owning glasses were randomised (1:1) to intervention (immediate delivery of glasses suited to working distance) or control (identical glasses delivered at endline). The primary outcome was work productivity, defined as the hourly number of items completed, normalised to a factory target rate, over 12 weeks. Secondary outcomes included glasses wear adherence, visual function, and ROI. RESULTS: Among 4990 potentially eligible workers, 3648 (73.1%) underwent eye examinations, and 682 (18.7%, mean age 41.0 years, 99.0% female) were enrolled and randomised (intervention: n=344, 50.4%; control: n=338, 49.6%). All participants completed 12-week observation. In panel regression models for the pre-specified primary analysis, intervention group assignment (difference=0.0325, 95% CI 0.006 to 0.060, p=0.017) was significantly associated with greater productivity. Compared with workers in the highest skill grade (A), those in the lowest grade (C) had significantly lower productivity (difference=-0.049, 95% CI -0.087 to -0.011, p=0.011). Glasses increased productivity in the intervention group relative to controls by 5.70% (95% CI 1.04% to 10.4%). CONCLUSIONS: Free near glasses confer a significant productivity benefit in this factory setting, and are substantially less costly than other successful interventions such as management training. TRIAL REGISTRATION NUMBER: NCT04629820.