TIME Research

Here’s What Happens To Your Eyes When You Look at Multiple Screens

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Illustration by Sydney Rae Hass for TIME

If you don’t spend a few hours of your day staring at a screen, then statistically, you’re a digital freak. Nearly 90% of Americans use their devices for at least two hours a day.

And a growing number of us—70%—are glued to multiple screens at once. All that eyeballing comes at a cost, according to a new survey by the Vision Council.

The survey polled more than 10,000 adults and found that 65% of Americans experience digital eye strain—physical discomfort, like getting dry, irritated eyes, blurred vision, headaches and neck or back pain—after staring at a screen for hours.

But people who used just one device fared better than those using multiple screens: only 53% of them had symptoms of digital eye strain, compared to 75% of digital multitaskers.

Eye strain is a problem especially for people in their twenties, who have the highest rates of digital eye strain symptoms—73%—of any age group.

“What we’re finding is that Millennials especially are very comfortable working on multiple screens and multiple devices,” says Justin Bazan, an optometrist and medical adviser to The Vision Council. If you use your smartphone as an alarm clock, for example, “you have a digital device the second your eyes are open”—far before you even flip open a laptop screen.

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Several factors contribute to digital eye strain, including how close you are to your screen. People typically hold small devices 8-12 inches away from their faces, a closeness that decreases blinking rates, the report says. “Blinking is crucial to keeping the ocular surface well protected from environmental assaults and our eyes from drying out,” Bazan says. “They’ll become dry and irritated, and vision will become blurry as well.” That’s where the urge to rub your eyes at the end of a long workday comes from.

Blue light, the high-energy visible light emitted by your digital devices, is another contributor. “That light is so close to ultraviolet, which has been known to cause damage on the cells of the eyes for years now,” Bazan says. “Preliminary research is showing that blue light, similar to UV light, can cause damage to the cells inside of our eye, and retinal cells produce vision.” Bright overhead lights can cause glare and increase the amount of blue light penetrating your eye, he adds.

Avoiding blue light with a digital device that isn’t backlit, like the original Kindle, will help. But that still won’t solve the problem of digital eye strain, Bazan says. Reading a non-digital book—that’s ink on paper, if you need a reminder—provides our eyes with a pretty precise point of focus, he says. “When we look at ink on paper, our eyes know at what distance the ink and paper is and we can lock the focus on.” Pixels on a screen, on the other hand, are hard points of focus and compete for our eyeballs, he says. “Since a pixel is a hard target, we see that our focusing system is always in a state of trying to find exactly where the pixel is. That constant focusing causes strain.”

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But even if you can’t print out every page you read, or if your workspace is flanked by flashing screens, there are still way you can protect your eyes, according to The Vision Council. Practice the 20-20-20 rule: for every 20 minutes with your screen, give your eyes a 20 second break and look 20 feet away, which will relax the focusing muscles. Consider wearing yellow-tinged specialized computer eyewear, which takes strain off of eyes by focusing on the computer, reducing glare and filtering blue light. And if you’re a real stickler for eye safety in the workplace, give your screen a friendly high five: that’s the distance you should keep to protect your eyes.

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