What causes someone to be nearsighted?

MINNEAPOLIS — Nearly 42% of Americans are now nearsighted — up from 25% 50 years ago. And half the world could be squinting by mid-century. 

So what causes myopia? Good Question.

At the Children's Museum of Minnesota, few screens are in sight. It's a welcome tech break in a society glued to their screens.

Research shows screen time is having a real-world impact.

"We're seeing a lot more nearsightedness than we did 20, 30 years ago," said Dr. Andrew Ritter.

Ritter is an optometrist at M Health Fairview.

"I've seen [myopia] in very, very young kids but we tend to see it in school-aged years," Ritter said.

Myopia is actually a change in the eye.

"Physically, a myopic eye is a longer eye," Ritter said. "Far away we can think of two parallel light beams coming in. In a perfect scenario, it focuses right on the retina and it's nice and clear. In nearsighted individuals, it would focus more inside the eye."

Myopia can be caused by genetics, but studies show it can also develop from prolonged close-up activities, screentime and spending too much time indoors.

"Focusing up close, looking at this near, your eyes are working hard and putting strain on them, and by doing that we're seeing an increase in nearsightedness," Ritter said.

Ritter shared his recommendations for kids' screen time.

"I tend to refer to the American Academy of Pediatrics. So under 2, basically FaceTime with Grandma and not much else," he said. "After that, be consistent and try to get as much outdoor time as you can, especially in the summer."

There are ways to prevent and possibly slow the progression of myopia.

"If they're reading in the dark, try to get them a better light so they're not so strained there. Then, just taking breaks occasionally. We call it the 20-20-20 rule. Every 20 minutes, look 20 feet away for 20 seconds," Ritter said.

Ritter also recommends parents bring their children in for an eye checkup if they have concerns.