Nearsightedness could be rising in the US, researchers concluded after comparing eyesight information for more than 4,400 people tested in 1971 and 1972 with data from another set of 8,300 people tested from 1999 to 2004.
The 1971-1972 National Health and Nutrition Examination
Survey provided the earliest nationally representative estimates
for US myopia prevalence; myopia was diagnosed by an algorithm
using either lensometry, pinhole visual acuity, and presenting
visual acuity (for presenting visual acuity 20/40) or retinoscopy
(for presenting visual acuity 20/50).
Using a similar method
for diagnosing myopia, we examined data from the 1999-2004 National
Health and Nutrition Examination Survey to determine whether
myopia prevalence had changed during the 30 years between the
2 surveys, researchers said in their findings published in the Archives of Opthalmology.
When using similar methods for each period,
the prevalence of myopia in the United States appears to be
substantially higher in 1999-2004 than 30 years earlier. Although myopia can be treated relatively easily with corrective
lenses, it engenders substantial expenditures on a population
basis owing to its high prevalence. If 25% of those aged 12
to 54 years had myopia, the associated annual cost would be
more than $2 billion; an increase in prevalence to 37%
would increase the cost to more than $3 billion. The question
of whether myopia prevalence is increasing is therefore important
to health planners and policy makers.
modifiable risk factors for myopia could lead to the development
of cost-effective interventional strategies, the paper said.
Among blacks, the overall myopia rate was lower than in whites but still jumped from 13 to 34 percent over the three-decade span, says study coauthor Susan Vitale, an epidemiologist at the National Eye Institute in Bethesda, Maryland.
The cause of nearsightedness is poorly understood. A previous review had
concluded that increasing levels of education combined with
possible genetic susceptibility were likely to be responsible
for the reported increases in the prevalence of myopia.
There is clear evidence for a high and increasing prevalence of myopia in East Asia, apparently driven by increasing educational pressures and urbanization. Data from the USA, Europe and Australia are consistent with the data from Asia in terms of the role of these risk factors, the 2001 review had found.
"Some people would say near work is a reasonable explanation," Vitale says, particularly with the advent of video games and other electronic devices. Children also spend less time outdoors than they once did, she says.
Jane Gwiazda, a psychologist at the New England College of Optometry in Boston, told Nathan Seppa of the Wired that there was compelling data to link increased myopia risk with a lack of outdoor time.
Nearsighted eyes tend to be elongated. Natural light might also stimulate dopamine production, which is known to inhibit eye growth, she says, and extra vitamin D from the sun might contribute to regulating eye growth.