Improving economic productivity by correcting presbyopia in India: the PROSPER trial

The presumed causal association between good health and productive work is a cornerstone of global health policy, but until recently only a handful of randomised trials had examined the question of whether health interventions could improve workplace productivity.^1-5 Among these, the majority concerned nutritional interventions,^2-5 and only two had statistically-significant effect sizes, both <15%.^1,4

Presbyopia, the nearly-universal decline in unaided near vision with ageing, affects over 1 billion people globally.⁶ Beginning at around the age of 40 years, presbyopia becomes apparent at the height of the productive working years.⁷ Although presbyopia is safely, effectively and inexpensively treated with glasses, as few as 10% of affected persons in LMICs have the spectacles they need for normal near vision.^8,9

PROSPER (PROductivity Study of Presbyopia Elimination in Rural-dwellers) was the first randomized trial to address whether provision of near-vision spectacles to workers with presbyopia could improve workplace productivity.¹⁰ When spectacles correcting near vision at the usual working distance were provided in random fashion to 751 Indian tea workers aged 40 years and above, mean intervention group productivity (daily tea picked) increased from 25·0 to 34·8 kg/day (9·84 kg/day), which was significantly more than controls (26·0 to 30·6, 4·59 kg/day, P<0·001), a difference of 5·25 kg/day (21·7%, Cohen’s d effect size=1.01, 95%CI 4·50-5·99, P<0·001). The intervention cost was low ($10·20 per person), acceptance was high (nearly 85%), presbyopia was common (>50%) among workers aged ≥40 years, and a significantly greater effect of the intervention was observed among older participants in this age-related condition, enhancing biological plausibility. Nearly 95% of those given spectacles reported that they would buy a new pair if theirs were lost or broken.

Provision of near-vision spectacles to older workers may be a scalable and sustainable strategy for poverty alleviation. Innovative strategies are needed to increase access for underserved communities. Correction of even modest degrees of presbyopia led to significantly improved productivity in this setting. Further trials in other work environments and countries are currently underway.

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