More than 40% of the U.S. is nearsighted—they can see up close better than they can see far away. And especially for kids, nearsightedness is on the rise. 

May Isbell, an optometrist with the Cedars-Sinai Medical Group, diagnoses, manages and treats eye conditions and prescribes glasses and contacts to correct vision. 

Isbell says the main eyesight-damaging culprit is the increased time children spend staring up close at cellphones and other screens.

Untreated nearsightedness—the technical name is myopia— can put people at risk for early cataracts, macular degeneration, glaucoma and even blindness. 

To protect eyesight, Isbell encourages parents, and all patients, to take note of studies showing that kids who spend more time outdoors and get more exercise have healthier eyes and better vision.

Despite the perils of modern technology, along with aging's inevitable toll on vision, there are ways to save your vision from getting worse: Limiting screen time, wearing sunglasses outdoors, not smoking and getting regular eye exams can all help prevent eyesight from worsening. 

But what about the other ways you've heard can wreck or protect your eyes? 

Here, Isbell confirms and debunks popular claims about eyesight. 

Read: The Nature Prescription

Maybe

"The idea that blue light from screens damages your eyes comes and goes, and we're not entirely sure," Isbell says. "We don't have strong evidence that it's the blue light emitted from the screens we're using that causes the damage rather than just the continued uses of screens themselves."

Half true

"Vitamin A and vitamin B12 are both necessary for keeping eyes healthy. Carrots are rich in Vitamin A," Isbell says. "While you can't improve your vision by eating carrots, they do contain nutrients helpful for the health of the eye."

Read: Q & A: Vitamins and Supplements

Myth

"Reading in the dark causes eye strain, which makes your eyes tired—but it won't permanently damage your vision," she says. "Try to avoid it so you don't get uncomfortable and fatigued."

Myth

"Wearing an old prescription does not hurt your eyes, it just causes you to strain and can cause headaches," Isbell says. "Keep your prescription current so your vision is always the best it can be."