Nearsightedness varies a bit by region—high-income countries in North America and Asia see more cases than other countries. Which makes sense, since, as the researchers write, “the projected increases in myopia and high myopia are widely considered to be driven by environmental factors … principally lifestyle changes resulting from a combination of decreased time outdoors and increased near-work activities.” Richer countries are likely to have more people working on and playing with screens.

In the U.S., at least, myopia has been increasing for some time. A few years ago, a JAMA Ophthalmology study found that between the early 1970s and the early 2000s, cases of nearsightedness in the U.S. increased by 66 percent. According to the new Ophthalmology study, worldwide nearsightedness cases are set to rise even more quickly, increasing by an estimated 140 percent between 2010 and 2050.

The study authors note that they made their projections assuming that “these lifestyle changes”—less outdoor time, more screen time—“will continue to spread with increasing urbanization and development.” But they also note that things could well change before 2050—people could, theoretically, have a less screen-based lifestyle by then. They could also, theoretically, invent time travel by 2050, in which case my myopic buddies and I would do well to stick to anything after the 13th century, when glasses were invented.