You roll your head, hoping to loosen the knots in your neck, and shut your eyes. After rubbing them you settle back into staring, hunched inches away from the computer screen. Despite the brief reprise your vision remains cloudy, causing the words on the monitor to blur. At this point, you need to know: With each further click on the keyboard, video watched on YouTube, and e-mail sent—are you damaging your vision?

Ophthalmologists, optometrists and other eye professionals note a seeming link between myopia, also called nearsightedness, and "near work"—visual activities that take place at a distance of about 40 centimeters (16 inches) from the eye—such as reading a book. Staring at a computer screen qualifies as well, though monitors usually are around 50 centimeters (20 inches) away.

But only a small—and mysterious—subset of people see myopic progression from near work, whether they are focusing on a computer or accounting books. "We are not very clever in identifying who [is affected] yet," says James Sheedy, a professor at the Pacific University College of Optometry in Oregon.

The fact that near work doesn't lead to myopia in all of us, however, doesn't mean sitting close to a computer screen causes no problems. Though for most it is not permanently damaging, computer near work leads to an uncomfortable, at times debilitating, list of symptoms collectively known as eyestrain.

Eyestrain, says Mark Bullimore, a professor at The Ohio State University College of Optometry, results from staring at a screen over long periods of time. Such activity causes eye exhaustion: burning, dryness and muscle aches—all unpleasant and potentially incapacitating symptoms while they last.

The simplest way to understand why eyestrain develops—and learn how to prevent it—is by looking at the way our built-in binoculars show us the fine print. When we "see" something, light reflects from an object through the cornea, the transparent, dome-shaped layer covering the eye. The cornea and the crystalline lens (a transparent, round, flexible structure behind the iris) then bend the wavelengths so they hit the rods and cones—photoreceptors on the retina that gather incoming light information. This innermost layer at the back of the eye is responsible for collecting and then moving light information, via the optic nerve, to the brain, which produces an image.

Staring closely at a screen forces our ciliary muscle, which controls the shape of our lens and therefore how well we focus, to remain contracted, without rest. This is demanding—and tiring—for the poor little muscle. Up close focusing also stops us from blinking.

Blinking is essential because it spreads tears over the surface of the eye; if blinking stops, the corneal surface dries out. When this happens, the cornea becomes cloudy, causing "foggy" vision, according to Sheedy. The normal blink rate is around 20 times per minute but using a computer can drop it to as low as seven, though experts believe this has no long-term effect.

Staring at a screen—surrounded by glaring peripheral lights—also causes us to squint, says Dennis Robertson, an ophthalmology professor at the Mayo Medical School in Rochester, Minn.

And though squinting cuts down on glare and prevents exorbitant amounts of light from assaulting your eyeballs (which solves some of the problems created by not blinking), it's exhausting. Freezing the muscles around your eye into a tense, squinched position all day long is just as tiring as it would be to hold a stomach-crunch for nine hours.

These eyestrain symptoms usually only last a few hours, dissipating as we allow ourselves time to blink and focus on things farther away. But once they start, they hamper productivity and, more importantly, make us grumpy. All is not lost, however. We can fix these burning, aching, dried out sensations one ergonomic workstation at a time.

Invest in one of today's nonglare computer screens, and don't be afraid to change your computer's brightness, contrast or text size, all of which will alleviate eye stress. Also, position your screen slightly lower than your eyes; the top of your monitor should be level with your eyebrows. For physiological problems, hit your doctor up for a pair of corrective lenses.

Finally, eliminate any glaring peripheral light. To find out what lights are bothersome, Sheedy recommends performing the hand-as-visor trick: Shield your eyes with your hand, and see if that makes the tension in your face and shoulders dissipate. If it does, manually adjust the lamps you blocked out as bothersome. As for watching TV, experts recommend laughing along with your favorite sitcom from a comfortable distance. (Finally, a reason to be a couch potato.)

But by far the simplest and best expert advice for eliminating eyestrain from any type of medium: take regular breaks. Go on, walk over to the water cooler, even if you aren't thirsty; and by all means, move your easy chair at least two feet from the television. Above all: don't forget to blink.