We've been observing these general effects for centuries. In his 1713 magnum opus, De Morbis Artificum Diatriba [Diseases of Workers], Italian physician Bernardino Ramazzini described reading-induced transient myopia long before it had a name:
Those who remain seated and work with their hands are threatened with another misfortune from having to keep the eyes continually fixed on those black letters, for they gradually contract weakness of vision, and when their eyes are not strong to begin with they are afflicted with dimness of sight, suffusions (bloodshot eyes) and other diseases of the eyes.
The advent of computer screens has put a modern twist on these historical ailments. Ophthalmologists have coined the term "computer vision syndrome" to describe an amalgam of symptoms that most often includes eyestrain, headache, dry eyes, and blurry vision, as well the neck and back pain that result from poor posture. Somewhere between 14 percent and 23 percent of computer users in the United States may experience computer vision syndrome, though up to 90 percent complain of its constituent symptoms.
Screens' greatest contribution to visual discomfort may be rooted in how terribly engaging they are. During conversation, we blink about 15 times per minute. Blinking wipes away debris and refreshes the eye's surface with new tears to keep our eyes moist and lubricated for smooth functioning. While reading (either on paper or a screen), our involuntary blink rate slows profoundly, to typically fewer than six blinks each minute, leading to dryness and irritation. Desktop displays can make this even worse: When you're looking up at a monitor (as opposed to down in your hands or your lap), your eyes tend to be open wider, with more surface area exposed to evaporation.
Researchers also blame lighting conditions for much of computer vision syndrome. Computer screens are typically higher-contrast, brighter, and reflect glare more than paper. Self-illumination often results in computer screens shining much brighter than their surroundings. As we shift from the screen to the environment and back again, our pupils contract, dilate, and contract again—a potential source of eyestrain, headaches, and fatigue. The great contrasts that computers can produce in a single window can cause similar problems.
There's plenty we can do. Ophthalmologists now recommend that a screen be less than three times brighter or dimmer than its surroundings, and 5 degrees to 40 degrees below your horizontal line of sight—the sweet spot for optimizing both eye and neck comfort. To stimulate tear production, try daily eyelid massages. If you have some spare change, prescription computer glasses could help. Simple fixes, like converting text to the more legible Arial and Verdana typefaces, may reduce eyestrain. It's also a good idea to follow the 20/20/20 rule—look at something 20 feet away for 20 seconds every 20 minutes of computer use.
As screens come closer to approximating (and in some instances, exceeding) the readability of the printed page, our eyes may strain less to overcome computer-specific annoyances such as glare, high contrast, and the like. The success of the iPad—and any other device that asks us to spend ever-longer stretches glued to a screen—will depend in part on how well it minimizes eyestrain. To this end, Steve Jobs appears to be listening: The iPad and newer laptops automatically adjust their brightness to match ambient lighting. Yet photons are photons and nearwork is nearwork. No matter the medium, staring in front of our noses for hours on end will never feel great. But let's rest somewhat easier knowing it won't blind us.