Look at the chart on the wall, and read me the letters in the first four rows.
This standard, paper-based examination for prescribing eyeglasses may serve most folks just fine, but as information workers spend more time glued to their PC screens, a new method for diagnosis may be in order.
"Eye-strain is the real repetitive stress syndrome of the information age, much more so than typing," said Erik Nilsen, a human-computer interaction expert and assistant professor of psychology at Lewis & Clark College in Portland, Oregon. "Heavy computer users suffer from red, sore eyes, fatigue, headaches, and blurred vision."
In light of this growing problem, scientists at the Lewis & Clark human-computer interaction laboratory are conducting research intended to show how optometrists can more effectively examine the vision of knowledge workers and prescribe corrective lenses that will reduce pains. Part of the problem is that PC video display terminals emit light patterns which the human eye must constantly adjust to, and readjust to, during the business day.
Nilsen and student researchers have during the past three years conducted three major studies to evaluate the impact of PCs on human vision. Another series of research projects is planned for this year. Thus far, researchers have found that images on a computer screen are quite different from a printed image on paper. The black characters printed on white paper have well-defined borders, sharp contrast, and constant density. The so-called Snellen chart - the letter chart common in optometrists' offices - tests eyes using that solution.
"But characters on a computer monitor are formed from a series of dots called pixels. Pixels are brighter in the center and dimmer and fuzzier around the edges," said Nilsen. "As a result, the human eye must refocus 15,000 to 20,000 times during each work day."
The Lewis & Clark researchers employed a medical device made by PRIO Corp.. The diagnostic tool, called the PRIO VDT, simulates the image of a computer monitor and then duplicates the visual experience of a user. Nilsen and his colleagues placed an ad in the local paper and recruited people who wore glasses and worked on PCs. Patients were fitted for glasses using the traditional test as well as the new technology. Subsequent interviews revealed that 70 percent of patients who wore glasses prescribed using the PRIO system preferred the lenses to glasses prescribed using the Snellen method. Subjects also reported less eye-strain and fewer headaches when wearing the experimental glasses, Nilsen said.
The researchers are continuing the studies to determine if the results can be confirmed with larger groups of patients, and if there is a superior eye-testing technology out there for computer users.
But some scientists are skeptical. Dr. Mary Flynn, an assistant professor at the Illinois College of Optometry, the oldest optometry college in the United States, says that a competent eye doctor should "consider all factors," including a patient's computer usage patterns, when prescribing corrective lenses. She does not think that special technology is necessarily needed to prescribe eye glasses.
Those who have taken the tests, though, are enthusiastic. Emily French, a law school student and PC user, thinks the experimental glasses make a visual difference.
"Years from now, everyone will have glasses prescribed using this technology. We won't remember when we weren't tested for computer use," said French.
