A recent study of some 20,000 children in rural China found that 24% of primary school students suffered from reduced uncorrected vision in either eye and 16% in both eyes.
One may therefore ask: could provision of free eyewear promote development? Economists Paul Glewwe, Albert Park and Meng Zhao think so. In a recent paper (attached below) they describe how offering poor children glasses at no cost led to vastly improved educational outcomes.
The increase of the scores of children given a free pair of glasses was equivalent to the increase associated with 0.9 years of extra schooling.
In other words, offering poor students free eyeglasses and making sure that they accept the offer had close to the same positive impact on the students' test scores as putting them through a whole additional year of school.
Source: The Economist