Researchers assess effect of vision impairment and ability to drive

May 4, 2009

Recent research on hemianopia shows that many individuals with this form of visual field loss can safely drive, a finding that has policy and scientific implications. Researchers at the University of Alabama, Birmingham, recruited 30 older drivers with hemianopia or quadrantanopia and an equal number with normal visual fields for an on-road driving performance study. During the test, each driver was accompanied by two masked evaluators, sitting in the back seat, and a certified driving rehabilitation specialist in the front seat, who had her own set of controls for the vehicle. The on-road test was recorded on a four-channel video system.

Fort Lauderdale, FL-Recent research on hemianopia shows that many individuals with this form of visual field loss can safely drive, a finding that has policy and scientific implications. Researchers at the University of Alabama, Birmingham, recruited 30 older drivers with hemianopia or quadrantanopia and an equal number with normal visual fields for an on-road driving performance study. During the test, each driver was accompanied by two masked evaluators, sitting in the back seat, and a certified driving rehabilitation specialist in the front seat, who had her own set of controls for the vehicle. The on-road test was recorded on a four-channel video system.

Assessment showed that two-thirds of the individuals with hemianopia received ratings that were equivalent to those of the control group, said Cynthia Owsley, PhD, MSPH, a professor of ophthalmology and Nathan E. Miles Chair of Ophthalmology at the University of Alabama, Birmingham. She is also director of the clinical research unit and vice chair for clinical research.

Hemianopia is typically caused by cerebrovascular accidents or stroke, tumors, or brain injury. Many states in the United States as well as governmental agencies elsewhere with jurisdiction over driving prohibit individuals with hemianopia from getting behind the wheel. There is little evidence to support this policy, however, Dr. Owsley added.

Particularly in developed countries such as the United States, driving is an extremely important part of daily activities, and being unable to drive contributes to social isolation, depression, lower utilization of health-care resources, and an increased likelihood of long-term care placement, said Dr. Owsley. She spoke during an afternoon symposium on the impact of vision loss on the individual.

The driving test consisted of a 45-minute route covering about 14 miles in Birmingham. The driving rehabilitation specialist evaluated each driver on the basis of several skills, each rated on a scale of 1 to 5 in which 1 indicated performance so unsafe that the drive had to be terminated and 5 indicated no obvious driving errors.

Most of the drivers with normal visual fields received scores of 4 or 5. In the hemianopia group (excluding those with quadrantanopia), some individuals received 1s or 2s, but a large number had 4s or 5s. Lane position problems were the most frequent problem among the drivers with hemianopia.

“In summary, although on average those with hemianopia had lower ratings, we found that two thirds received ratings indicating that they were flawless or had very minor errors,” Dr. Owsley said. She added that the ratings of the evaluators in the back seat were in good agreement with those of the rehabilitation specialist.

The findings lead to new questions and challenges.

“The policy implication of our study calls into question the common practice of categorically denying persons with hemianopia a driver’s license without giving them an opportunity for an on-road evaluation by someone with specific training, such as a driving rehabilitation specialist,” Dr. Owsley said.

The scientific implication is the opportunity to investigate what differentiates individuals with hemianopia who display safe driving skills from those who do not.

“If we knew what those characteristics were, either clinical characteristics or visual-functional characteristics, this could guide the design of driving rehabilitation strategies for drivers who are having problems on the road who also happen to have significant visual field loss, either from hemianopia or other causes,” Dr. Owsley concluded.