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University of Iowa News Release

April 14, 2003

UI Researchers Investigate Vision Impairment And Driving

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 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 when you 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 is generally not a good way to predict who is likely to be an unsafe driver, says Matthew Rizzo, M.D., UI 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," Rizzo said. "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," Rizzo added.

The "useful-field-of-view" test 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 being 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.

Research at the UI focuses on understanding how people with attention impairments and visual attention impairments fail on tests that stress these abilities. The UI researchers use a variety of attention-related tests and tests that investigate a person's ability to perceive and understand motion cues.

By using tools such as a driving simulator the researchers also can safely test people with a "useful field of view" impairment to determine likelihood of crashing. An instrumented vehicle is another research tool 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 on the roads around Iowa City.

In an article published in the April issue of Archives of Ophthalmology Rizzo and co-author Ida Kellison, UI research assistant, discuss the various physiological, neurological and psychological factors that affect visual impairment and the role they play in driver safety as well as current policies and interventions designed to ensure safety for all road users.

Common causes of vision impairment include eye diseases, such as glaucoma and age-related macular degeneration (AMD), or neurological disease, such as stroke or Alzheimer's disease. Depression, fatigue and medications also can impair vision. 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 impairments increase driving risk.

Research on vision and driving also helps test and improve emerging safety interventions such as in-vehicle warning devices and optical and electronic visual aids for visually impaired drivers.

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

Although standard vision tests are not good at predicting which drivers may be at risk for crashes, Rizzo suggests that they are still a reasonable way to screen people and identify potential problems.

"When there is doubt about a driver's vision, that person should be tested in detail because you don't want to unfairly take away someone's driving privileges," Rizzo said. "A combination of visual acuity and visual-attention scores, the useful-field-of-view test and other information on cognitive and visual abilities, together with a person's recent driving history, can provide a good picture of whether a person is a safe driver or not."

University of Iowa Health Care describes the partnership between the UI Roy J. and Lucille A. Carver College of Medicine and UI Hospitals and Clinics and the patient care, medical education and research programs and services they provide. Visit UI Health Care online at

STORY SOURCE: University of Iowa Health Science Relations, 5141 Westlawn, Iowa City, Iowa 52242-1178

MEDIA CONTACT: Jennifer Brown, (319) 335-9917

PHOTOS/GRAPHICS: A photo of Rizzo is available at