There isn't a name for it and few eye doctors test for it. But many people are having trouble seeing in the middle distance that demands so much of our focus.

Some 80 percent of us use computers, staring intently on screens set well between typical distance and reading range, often for many hours each day. Add in laptops, pagers, e-readers, smartphones, personal-digital assistants and hand-held video games, each with its own optimum distance and tiny flickering screen, and the demands on human eyes today would baffle even Benjamin Franklin, inventor of the bifocal in the late 18th century.

"The information age has taken a toll on our eyesight," says Jeffrey Anshel, an optometrist in Carlsbad, Calif., and president of Corporate Vision Consulting, which advises employers on vision issues.

More people are showing up at eye appointments complaining of headaches, fatigue, blurred vision and neck pain—all symptoms of computer-vision syndrome (CVS), which affects some 90 percent of the people who spent three hours or more at day at a computer, according to the National Institute of Occupational Safety and Healthy.

But vision prescriptions mainly focus on myopia (nearsightedness) or presbyopia (the difficulty focusing on near objects that comes with age). Since there are no set standards for measuring mid-range vision, ophthalmologists and optometrists typically just cut any reading prescription they give patients in half for computer distance. With people sitting anywhere from 18 to 40 inches from their screens, that can be wildly off.

For many people who already wear glasses, their current prescriptions aren't quite cutting it. People who wear bifocals, for example, often try to bring the computer screen into focus by tilting their head back, jutting out their chins and peering through the bottom of the lens.

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