Being nearsighted is far more common than it once was. The prevalence of myopia, the condition’s medical name, in Americans has soared by 66 percent since the early 1970s, according to a 2009 study by the National Eye Institute; in China and other East Asian countries, as many as 90 percent of recent high school graduates are thought to be nearsighted.

Myopia results when eyeballs are longer than normal, changing the angle at which light enters the eye and therefore the ability to focus on distant objects. The disorder involves a complex interplay of genetics and environment and usually begins before adolescence, when the eye is growing, but it can worsen in early adulthood.

Some experts connect the elevated rates of myopia to the many hours young people stare at computers and other screens. But a recent study published in JAMA Ophthalmology suggests that a greater factor may be a side effect of all that screen-watching — it’s keeping children inside. This new study joins a growing body of research indicating that a lack of direct sunlight may reshape the human eye and impair vision.

Researchers at King’s College London, the London School of Hygiene and Tropical Medicine and other institutions gave vision exams to more than 3,100 older European men and women and interviewed them at length about their education, careers and how often they remembered being outside during various stages of their lives. This biographical information was then cross-referenced with historical data about sunlight, originally compiled for research on skin cancer and other conditions.