We've all heard the complaint or something like it: "I've been staring at the screen all day. My eyes hurt." But is it really the screen's fault? (And if so, is there any long- or short-term damage?) Would our eyes be any better off perusing printed pages all day?
Yes, you can blame the screen but not for everything. Some of the same eye-care advice you'll hear for computer screens apply to paper-bookworms, too.
Screen-induced eye strain has an official name: computer vision syndrome. The term describes a host of bothersome symptoms, including eye fatigue, burning and itchy eyes, blurred vision, and sensitivity to bright light. People who spend two or more continuous hours at a computer every day are at greatest risk for developing the syndrome, according to the American Optometric Association.
For most people, symptom treatment is enough -- managing their reading position, taking rest breaks or using eye drops to relieve dry eyes. That said, dry and irritated eyes are associated with disorders of the cornea, the transparent layer at the front of the eye. See a doctor if you're putting drops in your eyes five or six times a day and still feel like they're dry, says James Salz, a University of Southern California eye doctor and spokesman for the American Academy of Ophthalmology. Still, he adds, "there's no evidence that there's any long-term damage from reading on a screen."
What is it about computers that irritates our eyes? The problem boils down to a couple of key factors:
■ Blinking. Study after study has found that when reading on screens people tend to stare more than they do when reading on a printed page. More staring means less blinking, which means your eyes get less refreshment from tears. "When you blink, you spread a layer of tears over the eye," says Mark Rosenfield, a professor at the State University of New York College of Optometry. With less blinking, eyes get dry and sore.
Another difference between the printed page and the computer screen is where the words are positioned relative to the eyes. People generally look down while reading a book or newspaper, but staring at screen usually means staring straight ahead. When you look down, more of your eye is covered by the eyelid, but when you look straight ahead more of your eye is exposed to the drying effect of air. Coupled with reduced blinking, this leads to dry eyes.
■ Distance. Not surprisingly, people reading on their smartphones tend to hold the device much closer to their eyes than they would a book. In a 2011 study, Mr. Rosenfield found that the 219 participants held their phones 14 inches from their eyes to read text messages and 12½ inches for a webpage. Typically, people read printed text from a distance of 15¾ inches.
The result is that "your eye has to work much harder to focus at close distances," Mr. Rosenfield says. The eyes turn in more (not quite cross-eyed) ,and that takes effort. Over time, that can lead to fatigue.
Other considerations are resolution, brightness and glare, says Alan Hedge, a professor of ergonomics at Cornell University. "The resolution of print on paper is higher than any screen out there." Brightness should be adjusted for comfort, either on your screen or the lamp by your reading chair. As for glare, it is easier to read a book or an e-ink on an e-reader in the sunshine. But if you're reading late at night in bed, you might prefer the backlit screen of a tablet.
The good thing about electronic reading is that you can change so many things to make the experience more comfortable, such as increasing the size of the text and fiddling with the brightness, which can also help you keep the words at a distance. Dr. Salz says 18 inches is ideal.
Common sense goes a long way too, Dr. Salz says. "As soon as you feel fatigue, look away."
Indeed, workplace advice for people who read on computers for a large part of their days comes in the 20-20-20 rule: Every 20 minutes, look 20 feet away for 20 seconds.