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New Way Of Prescribing Glasses Reduces Computer Eye Strain

January 5, 1998
Lewis And Clark College
Red, sore eyes. Fatigue. Headaches. Blurred vision. If you work long hours on a computer, you know the symptoms.

PORTLAND, Ore.--Red, sore eyes. Fatigue. Headaches. Blurred vision. If you work long hours on a computer, you know the symptoms.

As far back as 1991, a Harris poll identified eyestrain as the top office-related complaint, affecting 47 percent of all office workers.

"It's scary to think of the long-term effects computers will have on my eyes," says Lewis & Clark College senior Leland Peterson.

Peterson has been known to sit in front of his computer for 16 hours straight. Between his studies and his computer-related campus jobs, he spends at least five hours a day, seven days a week looking at a computer monitor.

"I get a little dazed after a while," he admits. "Images start to melt together."

Emily French '88 uses a personal computer at work and a laptop for notetaking in her law school classes at night. At home, she has two laptop computers and a large PC--all networked.

"We're very 90s," she quips.

She figures she spends a minimum of six hours a day staring at a computer screen. She suffers from blurred vision, sore eyes and even headaches.

Eye-care clinicians are seeing more and more patients like Peterson and French with computer-related problems.

"The numbers are expanding across the spectrum," reports Dr. Cosmo Salibello, a Portland optometrist. "We now see children, 6, 7 or 8 years old who are suffering from visual stress. And we certainly see computer-related symptoms with college students, who spend many hours on the computer doing research and writing papers."

All this is troubling news to students and workers whose futures depend on computers. But a new technology for prescribing glasses offers hope for markedly reducing eyestrain.

Erik Nilsen, assistant professor of psychology at Lewis & Clark, and Lewis & Clark student researchers have conducted three major studies to evaluate the new technology.

Nilsen, a respected researcher on human-computer interaction, explains that an image on a computer screen differs remarkably from a printed image on paper.

A black character printed on white paper has well-defined borders, sharp contrast and constant density. On the other hand, characters on a computer monitor are formed from a series of dots called pixels. A pixel is brighter in the center and dimmer and fuzzier around the edges.

"Our eyes have a very hard time remaining focused on these images," Nilsen explains.

The result is that we must constantly refocus when working at a computer. Salibello describes this constant flexing of the eye muscles as a form of repetitive stress--like carpal-tunnel syndrome.

"Our focusing system is pushed and pulled 15,000 to 20,000 times during each work day," he says.

Most optometrists use the Snellen chart, characters printed on paper, to prescribe glasses. But Salibello and his colleagues have developed a diagnostic tool called the PRIO VDT vision tester to simulate the image on a computer monitor and to duplicate the visual experience of a typical computer user.

Nilsen and Salibello analyzed data collected from 324 patients who spent at least two hours per day working in front of their computer monitor to describe the typical visual stress patient. Then Nilsen conducted a double-blind experiment to compare the effectiveness of glasses prescribed using the PRIO system with glasses prescribed using the Snellen method in reducing visual stress for computer users.

The Lewis & Clark researchers recruited 37 subjects. Each used computers at least two hours daily, wore corrective glasses or contacts, and reported visual stress symptoms. Each subject received two sets of eyeglasses--one prescribed using the vision tester, the other pair prescribed using a standard Snellen chart.

Seventy percent of the subjects preferred the PRIO prescribed glasses. Subjects also reported less eyestrain and fewer headaches when wearing the experimental glasses.

The results weren't due to guessing, according to Nilsen. Only 22 of the subjects correctly identified the PRIO prescribed glasses.

French claims the experimental glasses make a definite difference.

"Five years from now, everyone will have glasses prescribed using this technology. We won't remember when we weren't tested for computer use," she says.

Nilsen presented the results of his research at CHI '95 Conference on Human Factors in Computing Systems. The paper, "Reducing Visual Stress Symptoms of VDT Users with Prescription Eyeglasses," also is available at

Nilsen recently completed a third study. The experimental tasks were similar to those in the previous study, but this time all subjects shared the same job to further control subject variables. All were technical help-line consultants for a local software company.

"We found the same results," Nilsen says. "Seventy percent of the subjects preferred the PRIO glasses."

Nilsen is exploring further studies involving another 1,000 subjects.

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Lewis And Clark College. "New Way Of Prescribing Glasses Reduces Computer Eye Strain." ScienceDaily. ScienceDaily, 5 January 1998. <>.
Lewis And Clark College. (1998, January 5). New Way Of Prescribing Glasses Reduces Computer Eye Strain. ScienceDaily. Retrieved May 22, 2017 from
Lewis And Clark College. "New Way Of Prescribing Glasses Reduces Computer Eye Strain." ScienceDaily. (accessed May 22, 2017).