CHICAGO » It used to be that staring at a computer screen all day was bad for your eyes. Now we interrupt that staring to look at our smartphones, smartwatches, tablets and e-readers, all while keeping an eye on the TV. And that, it seems, is especially bad.

Three-quarters of people who use two or more devices simultaneously report symptoms of digital eye strain, compared with just over half of people who use one device at a time, according to a survey of more than 10,000 people that was released Wednesday by The Vision Council, a trade group representing manufacturers and suppliers of the optical industry.

Symptoms include, in order of prevalence, neck/shoulder/back pain, eye strain, headache, blurred vision and dry eyes.

Twentysomethings are the most likely age group to say they suffer symptoms, at 73 percent, and are also the most likely to say they juggle multiple devices and read the news on smartphones, whose small screens require extra eyeball exertion.

“It’s the problem everyone has but no one knows they have,” said Dr. Justin Bazan, a Brooklyn-based optometrist and medical adviser to The Vision Council. “Millennials are experiencing the most symptoms but also have most normalized it.”

While heavy screen time has been a way of life for many years, the proliferation of all sorts of digital gadgets has made it more difficult to escape. Nearly 60 percent of survey respondents said they use digital devices for five or more hours a day.

Sixty-five percent of respondents overall said they experience symptoms of digital eye strain, which typically develop after two or more hours in front of a screen, a share that has remained about steady since the group started issuing its annual survey in 2012. Women, who are more likely to be device multitaskers, are more likely to report symptoms than men.

Digital eye strain, which used to be called computer vision syndrome, is becoming more widely recognized as a diagnosis, said Geoffrey Goodfellow, associate professor at the Illinois College of Optometry and an attending optometrist at the Illinois Eye Institute.

It is, for the most part, a temporary problem. The discomfort typically results from the tiny muscles in the eye working overtime to focus on objects in close proximity and adjust to different lighting levels, Goodfellow said. Failure to blink, which happens when people are concentrating, also dries out and irritates eyes, he said.

Most people recover after taking a break. Even those who are glued to their tablets until bedtime typically feel refreshed by the time they reach for their smartphones in the morning to turn off their alarm and check email, Goodfellow said.

But there are concerns about more permanent effects. Some emerging research has linked cumulative and constant exposure to the high-energy blue light emitted from digital screens with damage to the light receptors at the back of the eye. That could lead to age-related macular degeneration, which is the loss of central vision, Goodfellow said.

Evening exposure to blue light wavelengths, important for color perception and being alert during the day, has also been shown to disrupt the melatonin that regulates circadian rhythms, making it hard to sleep.

Yet a third of Americans who are aware of the potential damage don’t do anything to curb their exposure, according to The Vision Council survey.

“It will be interesting to see, 30 years from now, what is the long-term toll on our eyes from using all of these devices,” Goodfellow said.

Even though it’s not known if there’s lasting physical harm, Vinnie Sikka can attest to the effect on short-term workplace productivity.

Sikka estimates he spends 10 to 14 hours a day in front of a computer screen, much of it scrutinizing PowerPoint or Excel spreadsheets on his laptop. About six hours in, he said, his eyes start to give out. Text blurs. Headaches creep up. Errors go unnoticed.

“You start seeing exclamation points when they’re actually 1s,” said Sikka, who works from his home office in Darien as a freelance procurement consultant and runs a side venture selling custom dress shirts online. Early in his career, he could handle that heavy screen time. But now, at the ripe age of 36, “I tend to jumble things,” he said.

“In equations that I should be able to do in my sleep, I will have a brain freeze and put something that’s not correct at all,” Sikka said.

Sikka tried an anti-glare guard on his screen, but it had little benefit, and he takes breaks from the office every few hours to give his eyes a rest. He has an astigmatism that has worsened over the years. Though it has not been connected to computer use (he gets his eyes checked by his wife, an optometrist and a colleague of Goodfellow’s at the Illinois Eye Institute), underlying conditions can exacerbate eye strain.

There are ways to give your eyeballs a break. Here is some advice from Goodfellow and Bazan.

—A relaxed eye automatically focuses on a distance of about 20 feet or more away. Hence the 20-20-20 rule touted by the American Optometric Association to refresh your eyes: Every 20 minutes, take a 20-second break, and look at something 20 feet away. If that isn’t a practical schedule to keep, take a five-minute break from digital devices every hour.

—Position your computer to be arm’s length away, untilted, at a height that allows you to look down 4 to 5 inches at your work. Magnify the text to a 15- or 16-point font so you’re not tempted to slump forward to make it out. If you can, avoid doing work curled up on a couch for too long, which throws posture, and therefore eyes, out of whack. It’s better for your body to be in a chair with both feet on the floor.

—Match your screen to the brightness of the room, so your pupils don’t have to keep adjusting to varying light levels. If you’re in a dark room, set the screen to a dark setting, and if in a bright room, brighten the monitor. Also, pull the drapes to reduce glare.

—Blinking keeps the eye moist and protects it from irritants, so when 15 to 20 seconds pass between blinks, as happens in front of digital screens, eyes dry out and can burn. Remember to blink a few times every few seconds, or make it a point to blink after reading a paragraph.

—People tend to hold their smartphones 8 to 12 inches from their face, which increases strain as eyes try to focus. A better distance that is also realistic: Make a fist, and put it at your chin, and hold your phone at your elbow. And keep your head up: The continual weight we put on our spines when we stoop our heads to read smartphones, called “text neck,” can lead to early wear and tear, degeneration and surgery, according to research published last year by the chief of spine surgery at the New York Spine Surgery and Rehabilitation Medicine. A 60-degree bend puts about 60 pounds of weight on the cervical spine, his research found.

—Consider investing in computer glasses, which are tinted yellow or have other coatings to filter out high-energy light and are customized to focus on the mid-distance range for viewing digital screens. They come with or without a prescription. Also available is computer software that cuts some of the blue wavelengths on the screen. A free one for Windows is f.lux, which shifts the screen’s brightness from high-energy blue light during the day to a soft yellow when the sun goes down in hopes of preventing sleep disruptions.

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