Young and old Americans average 7 hours and 3 minutes a day looking at Internet-connected screens. And even kids ages 8 to 12 log around five and a half hours every day accessing entertainment on screened devices.

Most people are blind to the fact that youngsters are doing more than damaging their muscles, blunting cognitive growth, and fueling their chances of developing depression and anxiety by being glued to digital screens.

They're also risking premature and severe nearsightedness (myopia), making the outside world a big blur to them.

A review in JAMA Open Network looked at 45 studies of more than 335,000 kids ages 5 to 13 and found that every hour a day spent staring at a screen was associated with a 21% increased risk of developing nearsightedness. If kids spend four hours or more, maximum damage is done.

Why does that matter?

Children with myopia are at risk of earlier development of cataracts, are more likely to experience retinal detachment, and are three times more likely to develop glaucoma.

Fortunately, banning phones in school and limiting time on screens for anything but homework can help reduce the risks.

Another study that shows that multifocal contact lenses slow the progression of kids' myopia. Ask your eye doctor about that option too.

For activities that can get everyone off screens, check out the full-body workout for your kids and you in our book "YOU Raising Your Child."