In addition to irritating our eyes, too much screen time is hurting our wallets, says a report released Tuesday by the American Optometric Association and the Deloitte Economics Institute, a consultancy. 

About 1 in 2 adults are exposed to "excessive" screen time of seven or more hours per day, according to the report, including 70% of office workers and 42% of workers in other fields. Those seven-plus hours of having our faces in screens can lead to eyestrain symptoms like dry eye or headache and things like neck and back pain from poor posture -- and they cost the United States $73 billion a year, the report says.

When too much screen time is "unmanaged," meaning people don't go to the eye doctor, the yearly cost is $151 billion, the report estimates.

Researchers got these numbers by considering people's productivity at work and the cost to the health care system, and by applying a formula that puts a monetary value on a loss of well-being, or healthy years lost. 

The report is based on a sample of 1,000 people ages 18 to 64 across the US, and it comes as we continue our dependence on laptops, phones and other devices for work and everyday life. 

"The amount of stress that we're putting on our visual systems just from staring at a screen -- or different screens -- all day is huge," Dr. Ronald Benner, president of the AOA, told CNET. He added that screen time has health effects beyond just the eyes or body and that it can cause fatigue and can impact how people feel overall. 

"The biggest takeaway on this is, not only is there an economic consequence in terms of work, but there's also a quality of life issue," he said.

Here's what to know about technology's effect on eye health, plus tips to stay healthy when you need your screens for work and school.

What is 'excessive' screen time? 

The AOA-Deloitte report defines this as seven or more hours per day. This is the threshold, according to the report, of where there's an "established link" between increased risk of certain health conditions, like migraines, and screen time.

But there really isn't an official number when it comes to how much screen time is too much for adults. At least, not like we have hard numbers for other areas of wellness, like the seven or more hours of sleep we need each night, or the 150 minutes per week of physical activity. 

There are recommendations on how much time children should spend with screens (and what kind of content they should consume), but there are no such guidelines for adults, who often depend on technology for work and daily life.

Certain apps can help you refrain from staring at your phone, and Apple has recently expanded its wellness efforts into eye health by introducing features meant to better protect your eyes against its screens. But we're mostly left to our own devices... literally.

Read more: The Strange and Unique Way I Cured My Phone Addiction

How screens hurt our eyes (and bodies)

Staring at a screen can cause digital eyestrain or computer vision syndrome, with symptoms like dry eyes, blurred vision, headaches, muscle fatigue, neck pain and more. 

Research has continued to build on the relationship between lots of "near work," like reading or holding an iPad, and increased myopia risk in children whose eyes are still developing. Such a link hasn't yet been established for adults, though more research is needed. 

Your vision is more than just your eyeballs, though. It's an entire system that routes sensory information from the external world to your brain, complete with muscles that flex and focus to bring in that data. And, Benner said, those muscles get tired.

If we get fatigued from sitting in front of a screen the whole work day, "that's muscles," Benner said. "Once those muscles are fatigued, it takes a while for them to relax." That fatigue can bleed into the remainder of the day, and even affect our sleep patterns, potentially dragging down our quality of life.

And our posture, as well, can take a hit from too much time spent peering at a phone, computer, tablet or maybe even a smartwatch (depending on how you tilt your head to look at your wrist). This in turn can damage the health of our neck, spine and musculoskeletal system. 

"Tech neck" is a real thing -- the strain of chronically staring down at a phone or computer can lead to muscle stiffness, pinched nerves, herniated discs and more. 

Read more: Is There a Link Between Dementia and Vision Problems? 

How to stay healthy in front of a screen

The 20-20-20 rule calls for you to look at something 20 feet away for 20 seconds every 20 minutes you're in front of a screen. Unfortunately, that probably isn't enough, either in terms of reducing risk of myopia in people whose eyes are still developing or in helping out folks who want to address excessive screen time.

But it's a good start, according to Benner. 

As a general rule, the more time you're able to give your eyes away from a screen, the more relaxed your visual system should feel. Finding pieces of time in your day when you aren't looking at your phone, tablet or laptop is a great start to improving the health of your visual system. Maybe leave the phone on your desk while you take a walk, for instance, or wait an hour longer after work before you play video games.

More tips for improving your eye health and work environment include the following.

• If you can, reduce the number of devices you're working on. This may not always be possible, depending on your job, but working on multiple screens at once is "much harder" on your visual system and causes more strain, Benner said. 
• Set up your desk, chair and posture for success. According to Penn Medicine, the height of your chair should be adjusted so your knees are at a 90-degree angle with your feet flat on the floor, or resting on a footrest. Your keyboard and mouse should be lower than your elbows and within easy reach, and you should be sitting up straight. In terms of facial distance, the AOA says the screen should be about 20 to 28 inches from your face, and that most people find it more comfortable for their eyes to look downward. 
• Set the mood with good lighting. Try to reduce glare on your screen, moving your device away from overhead lights or a window, if possible. Consider playing with lower lighting in your office, if it eases your symptoms of eye strain. 
• If you notice yourself straining your neck or eyes, pause. It's easy to get so caught up in work that you don't notice your face scooching closer and closer to your screen. But the more aware you become of your posture, the easier it'll be to correct it in the moment, and ultimately form new habits. 
• Go to the eye doctor regularly. People with glasses or contacts are more likely to experience eye, neck or back pain, according to Penn Medicine: it's important to find the right vision adjustment so you don't need to strain to see. But even if you have perfect vision, you should still prioritize an annual exam -- especially if you work daily with technology. Your doctor may recommend specific glasses or a treatment plan to help you work more comfortably and healthily. And if your doctor doesn't ask about your screen time, be sure to bring it up and make it a priority during your appointment. 

Read more: 7 Must-Have Ergonomic Upgrades for Your Home Office