Cataracts, blurred vision 'severely' affect driving

April 18, 2012

Results of motor vehicles agency-administered vision tests do not necessarily reflect fitness to drive, according to a study published in Investigative Ophthalmology & Visual Science.

Rockville, MD-Results of motor vehicles agency-administered vision tests do not necessarily reflect fitness to drive, according to a study published in Investigative Ophthalmology & Visual Science (IOVS).

The researchers found that cataracts and blurred vision, even if moderate, severely reduce the frequency and distance at which drivers recognize pedestrians at night, even in drivers who passed the vision test required to obtain a license to drive.

“Optical blur and cataracts are very common, and lots of people with these conditions continue to drive,” said author Joanne M. Wood, BSc, PhD, of the School of Optometry and Vision Science and Institute of Health and Biomedical Innovation at Queensland University of Technology in Australia. “The aim of our study was to understand [better] how these visual conditions affect the ability to recognize and respond to roadside pedestrians at nighttime, and we also wanted to see if certain types of pedestrian clothing could improve the ability of a driver to recognize pedestrians at night, even when the driver had some level of visual loss.”

The study included 28 young adult licensed drivers who satisfied the minimum Australian driver’s licensing criterion of 20/40 or better vision. They drove at night on a closed road wearing lenses that simulated refractive blur and cataracts.

The pedestrians wore one of three different type of clothing: all black; all black with a reflective vest; and all black with reflectors on their wrists, elbows, ankles, knees, shoulders, and waist, to create a perception of human movement, known as biomotion. Sixteen of the 28 drivers were asked to detect the pedestrian against simulated headlight glare.

Findings demonstrated that cataracts are significantly more disruptive than blurred vision. Drivers with simulated cataracts recognized pedestrians 29.9% of the time, whereas those with simulated blurred vision recognized the presence of a pedestrian 52.1% of the time.

The research team also found that it was easier for drivers to spot pedestrians wearing the reflective strips to create the biomotion condition (82.3% of the time) than those wearing all black (13.5% of the time). Whether or not glare was present, none of the drivers with simulated cataracts recognized the pedestrians wearing all black.

Also, drivers with normal vision recognized pedestrians from farther away than those with impaired vision. The results suggest that to maximize drivers’ ability to see pedestrians from a safe distance, they should wear their optimum optical corrective lenses, according to researchers.

Also, they said, cataract surgery should be performed early enough to avoid potentially dangerous driving conditions.

“Future studies should further explore the impact of uncorrected refractive error, cataracts, and other forms of visual impairment on driving performance and safety as well as determine the value of some relatively new ways to measure visual abilities, such as straylight testing and contrast sensitivity,” said Dr. Wood. “It is possible that measuring only visual acuity does not provide us with the best way to determine who is safe to drive.”

IOVS is a peer-reviewed journal published by the Association for Research and Vision in Ophthalmology.

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