A study from the University of Alabama showed that instituting a law requiring drivers who are 80 years old or older to have their eyes checked reduced fatalities among these drivers.

“Vision rescreening laws appear to be effective, but why they’re effective remains an unanswered question,” Dr. Gerald McGwin, Jr. of the University of Alabama at Birmingham, the lead researcher on the study, said.

Starting with January 2004, Florida began requiring people 80 or older who wanted to renew their license to either undergo a vision screening test or provide proof from a doctor or optometrist that they passed a vision screening test in the past year.

Dr. McGwin and his team wanted to see the results of such a law and compared fatality rates for all Florida drivers, as well as motorists 80 or older, between 2001 and 2003 and 2004 and 2006. They found that the fatality rate among all drivers increased by six percent, while fatality rates among older drivers decreased by 17 percent, a decrease that may have something to do with elderly drivers seeking vision care.

“Perhaps the most apparent reason is that the screening law removed visually impaired drivers from the road. However, in reality, the situation is significantly more complex,” Dr. McGwin said.

In fact, the study was the first to show a link between vision tests and lower death rates for older drivers. The researchers said two things may have affected the drop in death rates. First, some older drivers may have decided to stop driving rather than take the test. Second, most who didn’t pass the first time got treatment, such as new glasses or cataract surgery, and then passed the test.

The study, titled The Impact of a Vision Screening Law on Older Driver Fatality Rates, , is published in the November 11 issue of the Archives of Ophthalmology.