People who have lost their eyesight because of cataract are more likely to live in poverty than those with normal sight, according to a new study.
The study was conducted in three developing countries-Kenya, the Philippines, and Bangladesh.
According to figures, blindness affects about 45 million people worldwide, and more than a third is caused by cataract.
While cataract can be treated with an inexpensive, simple operation, some evidence suggests that lack of money is a major barrier to uptake of cataract surgery by individuals in poor countries.
In the new study, Hannah Kuper (International Centre for Eye Health, London School of Hygiene and Tropical Medicine) and colleagues identified 596 people aged 50 years or more with severe cataract-induced visual impairment, mainly through a survey of the population in these three countries.
They matched each case to a normally sighted person (a "control") of similar age and sex living nearby. Poverty was measured through monthly per capita expenditure (PCE), as well as self-rated wealth and ownership of assets.
It was found that in all three countries, cases were more likely than controls to be in the lowest quarter (quartile) of the range of PCEs for that country.
In the Philippines, for example, people with cataract-induced visual impairment were three times more likely than controls to have a PCE in the lowest quartile than in the highest quartile.
Also, the risk of cataract-related visual impairment increased as PCE decreased in all three countries. Similarly, severe cataract-induced visual impairment was more common in those who owned fewer assets and those with lower self-rated wealth.
However, there was no consistent association between PCE and the level of cataract-induced visual impairment.
"This study confirms an association between poverty and blindness and highlights the need for increased provision of cataract surgery to poor people, particularly since cataract surgery is a highly cost-effective intervention in these settings," said the authors.
The study is published in the open access international health journal PLoS Medicine.