Presbyopia occurs with age, as the eye's lens loses its elasticity and ability to focus on close objects, according to background information in the article. "Although known physiology and population demographics suggest that presbyopia is common or nearly universal in people older than 65 years, direct estimates of prevalence are rare," the authors write. "The total number of people with presbyopia is primarily of interest as a precursor to the figures of greatest public health interest: the number of people with impaired vision due to uncorrected or undercorrected presbyopia and the effect on their lives."

Brien A. Holden, Ph.D., D.Sc., of the University of New South Wales, Sydney, Australia, and colleagues analyzed multiple surveys to estimate the global prevalence of presbyopia, along with the rate at which the condition is corrected and the vision impairment caused when it is not. They then used the International Data Base of the U.S. Census Bureau to extrapolate estimates for the future.

Using projections from these surveys, the researchers estimate that 1.04 billion people globally had presbyopia in 2005, 517 million of whom had no eyeglasses or inadequate eyeglasses or spectacles. Most (386 million, or 94 percent) of the individuals whose daily tasks were impaired by uncorrected presbyopia lived in the developing world.

These estimates are based on the best available information, the authors note. "More epidemiological research in presbyopia is needed to decrease the assumptions and generalizations required for a better global estimate," the authors write. "As more data become available, an increasingly accurate picture of the burden of presbyopia will emerge."

The researchers predict that the worldwide prevalence of presbyopia will increase to 1.4 billion by 2020 and 1.8 billion by 2050. "Without intervention to make spectacles more accessible, the global number of individuals who will have a disability associated with uncorrected presbyopia is predicted to grow to 563 million people by 2020," the authors conclude. "If the goal of Vision 2020 to eliminate unnecessary blindness and impaired vision, in this case due to uncorrected refractive error, is to be achieved, planning will have to include the provision of human resources, affordable spectacles and systems of delivery for these half-billion people in need."

This work was supported by a public health grant from the Institute for Eye Research.

Note: If no author is given, the source is cited instead.

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