Dec. 17, 2009 -- Nearsightedness has been increasing dramatically in the U.S. in recent years, but the reasons are blurry, new research indicates.
In nearsightedness (myopia), light that enters the eye is focused in front of the retina rather than directly on it, so that distant objects appear blurred. Nearsightedness can be corrected with eyeglasses, contact lenses, or surgery. Learn more about LASIK eye surgery for nearsightedness.
Susan Vitale, PhD, MHS, and colleagues at the National Eye Institute compared myopia statistics gathered in government surveys from 1971-1972 and 1999-2004.
Nearsightedness was much more common from 1999 to 2004 than it was 30 years ago, researchers report in the December issue of the Archives of Ophthalmology.
The key finding: Myopia prevalence increased by almost 42% from 1999 to 2004, compared to a 25% increase in the early 1970s.
Myopia prevalence rates rose at a faster rate among men and women, and among whites and African-Americans; myopia rates for African-Americans more than doubled between the two time periods studied.
The study doesn't show why myopia rates are rising.
"The cause of refractive error is not known, but it is likely due to both environmental and genetic factors," the researchers write.
Vitale tells WebMD that scientists don't yet know what's causing more nearsightedness. But she notes that studies from overseas have identified risk factors such as "near work." That includes reading, more time behind computers and TV sets, and playing video games.
Vitale stresses that these possible causes have been reported by scientists in other countries, but so far not by the National Eye Institute.
"This is a big issue and we are devoting millions of dollars to study the problem," she tells WebMD. "We are studying the risk factors, but thankfully, this is a condition we really have good treatments for."
Today, 47 million Americans aged 20 and older are myopic and billions of dollars are spent annually on glasses and contact lenses. A clearer understanding of the factors driving this rise is needed so that appropriate measures can be taken, says the American Academy of Ophthalmology.