Roger Dobson, writing in the British Medical Journal, says that uncorrected and undercorrected refractive error is estimated to cost the world economy up to $428bn (£308bn; 333bn) in lost productivity (Bulletin of the World Health Organisation 2009, doi:10.2471/BLT.08.055673).
It "has a potentially greater impact on the global economy than all other preventable vision disorders," say the authors.
The authors, who used national population, epidemiological, and economic data, say that the size of this correctable burden has been overlooked because epidemiological studies have tended to focus on best corrected sight rather than presenting sight.
"Refractive error is correctable with eyeglasses, contact lenses, or laser surgery. In the absence of correction, distance vision impairment may limit function," they say.
In the study, visual impairment resulting from undercorrected refractive error was defined as a visual acuity worse than 6/18 in the better eye that could be improved to 6/18 or better.
An estimated 158.1 million people had visual impairment from undercorrected refractive error based on the 2007 global population. Of these, 8.7 million were blind. The Western Pacific World Health Organization region, including China and Vietnam, had the greatest caseload, with 62.0 million cases. The South East Asia region, including Bangladesh, India, and Nepal, had 48.7 million cases.
The highest prevalence was in the Western Pacific (3.98%) and South East Asia (3.23%). The lowest was in Africa (0.82-0.86%).
After adjustment for rate of participation of labour force and rate of employment for each country the total global loss in productivity associated with undercorrected refractive error was $268.8bn.
Almost half of the potential productivity loss was in the Western Pacific ($111.2bn). The Africa and the Eastern Mediterranean regions had fewer cases (6.7 and 3.4 million) and an estimated loss in productivity of only $3.5bn each.
