An article in December's Archives of Ophthalmology reports that 1.04 billion people in the world had presbyopia in 2005, and the conditions of 410 million were so bad they prevented them from performing tasks requiring near vision. Of the latter, 94 percent lived in undeveloped countries.

The researchers, Brien Holden and his colleagues at the University of New South Wales in Australia, found that 517 million of the world's presbyopes have no glasses or inadequate glasses. They predict that by 2020 there will be 1.4 billion presbyopes worldwide, and 1.8 billion by 2050.

The authors of the report looked at numerous surveys to estimate their figures, and combined them with data from the International Data Base of the Census Bureau of the U.K. to project the future figures.