Driving licence eye tests not thorough enough

USA Today (Society for the Advancement of Education), March, 2005

That good vision is necessary for safe driving is just common sense, but scientists in the University of Iowa Roy J. and Lucille A. Carver College of Medicine, Iowa City, are looking beyond the standard vision tests in the hope of developing better tools to detect visually impaired drivers at greatest risk for a crash.

The standard eye exam administered to get a driver's license tests an ability known as visual acuity, which is a measure of the fine detail of your vision. However, visual acuity generally is not a good way to predict who is likely to be an unsafe driver, contends Matthew Rizzo, professor of neurology, engineering and public policy. "There are higher visual and cognitive functions that are much more important than visual acuity in predicting how safe a driver a person is. These functions depend on our ability to perceive motion, our attention abilities, and the speed our brain can process information.

"In fact, the best predictor of crashes to date is a test of speed of visual processing and visual attention, which is called the 'useful-field-of-view' test."

This measures the ability to attend to important objects in a cognitively busy situation. A person with low attention or cognitive impairment or someone already busy with other tasks like conversing on a cell phone has reduced peripheral vision--essentially their vision shrinks to a tunnel. This kind of functional visual field loss is not evident in standard eye tests.

By using tools such as a driving simulator, researchers safely can test people with a useful-field-of-view impairment to determine the likelihood of crashing. An instrumented vehicle is another method that allows scientists to assess the integrity of a driver's useful vision in tasks such as navigation and sign identification. The instrumented vehicle is a real car that uses sensors on the pedals and steering wheel and miniature cameras to record driver behavior while traveling.

Common causes of vision impairment include eye diseases, such as glaucoma and age-related macular degeneration, or neurological diseases, such as stroke or Alzheimer's. Depression, fatigue, and medications can impair vision as well. Numerous aspects of vision can be affected by these conditions, including decreased visual field, impaired depth and motion perception, and increased chance of getting lost. Any of these increase driving risk.

Pedestrians also can take advantage of what science has learned about drivers' visual processing. When out in the dark, reflective tape on joints makes an individual much more visible to drivers than wearing reflective clothing. Motion cues are critical in helping drivers discern and identify objects, and highlighting the joints gives drivers a better impression of a person's biological motion.