Ergo Rule Number Two: Head, Neck and Shoulders Straight; Eyes Focused Comfortably

One of the most common mistakes made by computer users is that they haven't positioned their height and proximity sufficiently. The goal: to focus comfortably on the keyboard without having to drop the head down or raise it back.

"Ideally, your chin should be about in the center of the monitor and it should be somewhere between 16 and 18 inches from your eyes," says Scott Bautch, a chiropractor in Wausau, Wisc. "That's where most people's visual acuity is good enough where they don't need to lean forward to look at it."

Leaning forward or backward puts pressure on discs in the neck. These discs, along with those in the lower back, are the most susceptible to injury because they aren't supported by the rib cage, says Bautch.

Finding a good distance from the screen and reducing glare also reduces strain on eye muscles. Ronald Leopold, M.D., medical director at MetLife Disability in Atlanta, says there's no evidence that eyesight gets worse as a result of computer use, but it can contribute to eye muscle fatigue, irritation and dryness.

It's also helpful to position reading material in a holder alongside of the computer screen since the neck and shoulders can become strained if you're repeatedly turning your head more than six degrees in either direction, says Van Fleet.

Another source of strain to neck and shoulders is the telephone. Avoid crunching it between the shoulders and ear because it causes neck strain, which can lead to headaches and soreness. Headsets or speaker phones allow better positioning than handset cradles.