Washington: An estimated 9.6 million adults in the US are highly myopic, or severely nearsighted, a new large-scale study has claimed.
Of those, nearly 820,000 have a degenerative form of the disease and more than 41,000 suffer a complication called myopic choroidal neovascularisation that could cause long-term vision loss, with women at higher risk, researchers said.
This is the first large-scale study ever done to calculate the real-world prevalence of myopic choroidal neovascularisation in the US, they said.
Myopia has become increasingly common over the past several decades. In the US, the number of nearsighted people rose from about 25 per cent in the early 1970s to 40 per cent around the turn of millennium.
While nearsightedness often can be corrected with eyewear or surgery, severe nearsightedness in which the eye continues to elongate can result in complications as the eye stretches.
Progressive high myopia, also called pathologic myopia, is a degenerative form of the disease. It can cause atrophy of the retina that lines the back of the eye. People with high myopia and the degenerative form are at higher risk of myopic choroidal neovascularisation.
This condition is characterised by the growth of new, unstable blood vessels beneath the retina. If untreated, it can cause vision loss that may then become permanent.
The study conducted by researchers from the American Academy of Ophthalmology, Genentech, the National Institutes of Health and University of California, Davis found that nearly 4 per cent of adults in the US have high myopia. That is equivalent to 9.6 million people.
The prevalence of progressive high myopia is 0.33 per cent. That is equivalent to 817,829 adults.
The prevalence of myopic choroidal neovascularisation is 0.017 per cent. While the disease appears rare, it affects 41,111 people in the US.
Women appear to be at greater risk for complications of high myopia, researchers said.
The prevalence rate for progressive high myopia was 0.42 per cent in women compared to 0.25 per cent in men. An estimated 527,000 women have the condition compared to 292,000 men. Similarly, for myopic choroidal neovascularisation, the prevalence rate for women is double that of men.
"Prior to this study, we really had no idea how many people had myopic choroidal neovascularisation, which can be devastating," said lead author Jeffrey Willis, a retina fellow at the UC Davis Eye Centre.
"I think the findings emphasise the growing issue of nearsightedness and the burden it creates in terms of medical complications that cannot be fixed with just glasses or contacts," said Willis.
The findings were published in the journal Ophthalmology.