Car safety tied to vision testing, clarity.

States that require drivers to pass vision tests to renew a driver's license have a lower incidence of traffic fatalities involving people over age 60 than do states that don't require such testing, a new study shows.

Optometrist Melvin D. Shipp of the University of Alabama at Birmingham assessed the effect of vision policies on the 48 contiguous U. S. states and the District of Columbia. He found that several factors--including high population density and license renewal without a vision test--boosted the probability of fatal traffic crashes involving elderly drivers.

Shipp then isolated the effect of vision tests from other variables. Applying his model to Alabama, one of the 10 states without a mandatory vision test as of 1990, he estimated that instituting such a policy would cut crash fatalities among the elderly from 48 to 43 per 100,000 people. Similar calculations for other states lacking mandatory vision tests yielded, on average, a potential 12 percent rate cut, says Shipp.

Besides Alabama, no vision test is required for license renewal in Connecticut, Kentucky, Mississippi, New Jersey, Oklahoma, Pennsylvania, Tennessee, Vermont, and West Virginia. Some groups representing elderly people oppose vision screening, saying it discriminates against the elderly.

Many older people don't notice poor vision creeping up on them, Shipp says. "There is no pain associated with it, no discomfort," he notes. Thus, many elderly people don't seek help.

Development of a cataract, in which the lens of the eye becomes opaque and produces cloudy vision, is one such slowly advancing condition. Cynthia Owsley, an experimental psychologist and epidemiologist also at Alabama, reports that older drivers who have cataracts removed are significantly less likely to get into an auto accident than are those who aren't treated for the condition.

Between 1994 and 1999, she tracked 288 drivers between 55 and 85 years of age who had cataracts; nearly all had them in both eyes. Of these people, 187 elected to have surgery and 101 didn't. Adjusted for miles driven over a 3-year period, those not getting surgery were twice as likely to be involved in an accident as those who did have the operation, Owsley says)

People with cataracts see an increasingly "washed-out" world, similar to that seen when one turns down a television's contrast, says Owsley. This makes driving more difficult.

While it's not clear why some people don't get surgery, those who don't read much and don't do fine, detailed work that requires good acuity of sight may simply not want to bother, Owsley suggests.