The first ever large-scale study in the United States into a degenerative eye disease has estimated that millions of people have a severe form of near-sightedness.
A majority of those could be facing long-term problems — including permanent loss of vision. High myopia could affect nearly 10 million Americans, and scientists say women are at greatest risk.
The new study, led by the American Academy of Ophthalmology, estimates that around 9.6 million adults in the United States are highly myopic. Around 820,000 of those have a degenerative form of the disease called progressive high myopia (PHM). More than 41,000, the researchers say, are suffering from a further complication known as myopic choroidal neovascularization (or mCNV), which could cause long-term vision loss.
Progressive high myopia, also called pathologic myopia, is a form of the disease in which the retina — the light-receiving surface at the back of the eye — can deteriorate and waste away. People with high myopia and the degenerative form, PHM, are at higher risk of mCNV. People with the latter condition experience a growth of new, unstable blood vessels beneath the retina which, if untreated, can cause potentially permanent vision loss.
Myopia has become increasingly common in recent years. In the United States, the number of nearsighted people has risen from about 25% in the early 1970s to 40% by the turn of millennium. Although nearsightedness often can be corrected with eyewear or surgery, more severe forms of near-sightedness cause the eye to continue elongating and this stretching can result in serious complications.
The study, which was conducted jointly by investigators from the American Academy of Ophthalmology (AAO), Genentech, the National Institutes of Health and UC Davis, is published online in the AAO journal Ophthalmology.
To calculate the prevalence of high myopia, the team combined data from 8,865 participants in the National Health and Nutrition Examination Survey (NHANES) from 2005 through 2008 with population information from the 2014 U.S. Census Bureau to estimate the number of people affected. Women appear to be at greatest risk with the rate of progressive high myopia at 0.42% in women compared to 0.25% in men. Around 527,000 women have the condition compared to 292,000 men. Similarly, for mCNV, the rate for women is double that of men.
"Prior to this study, we really had no idea how many people had myopic choroidal neovascularization, which can be devastating," says lead author Dr. Jeffrey Willis. "I think the findings emphasize the growing issue of nearsightedness and the burden it creates in terms of medical complications that cannot be fixed with just glasses or contacts."
The continuing rise of cases of myopia means researchers are hoping to better understand the causes and predict possible treatments of mCNV. The researchers conclude that, although high myopia and progressive high myopia are relatively large problem among adults in the United States, mCNV seems as yet to be a rare disease.