To investigate the effects of aging and visual impairment on driving and visual performance, Australian researchers fielded a sample group of 46 subjects to execute a series of driving performance tests on a closed-road circuit. Subjects included 10 young visually normal drivers (mean age 22.6 years), 18 elderly drivers with no visual impairments (mean age 67.7 years), and 18 elderly drivers with early cataracts (mean age 68.6 years). Researchers gathered data on driving tasks including: peripheral awareness, maneuvering, reversing, reaction times, speed estimation, road position, and time to complete the course. Joanne M. Wood and Rod J. Troutbeck reported the methods and results of this study in their article, "Effect of Age and Visual Impairment on Driving and Vision Performance," presented at the January 1994 Transportation Research Board annual meeting in Washington D.C. Information in this summary is from that report.

The population is aging, and the number of elderly drivers is increasing. Statistics show older drivers have more traffic convictions and accidents per mile than any other age group and are more frequently cited for being at fault in accidents. Studies suggest elderly drivers have slower reaction times and poorer merging behavior than their younger counterparts. Although there is no strong research evidence showing that increased accident rates result from decreased visual acuity, the lens does become yellow and less transparent with age and pupils become smaller and less able to dilate in dim light. The study described by Wood and Troutbeck is one of a series of ongoing studies attempting to determine possible correlation between alleged deterioration in driving performance in elderly drivers and age-related changes in visual function.

Subjects volunteered for this study from an advertisement in a motoring magazine. The sample group participated in assessments of driving and visual performance. Driving performance was tested on a closed circuit course taking about five minutes to execute. Researchers tested and evaluated peripheral awareness, reaction time, speed estimation ability, road position, total time to complete the course, maneuvering skill, and reversing proficiency. In the laboratory, researchers used standard tests of visual function to assess visual acuity, functional visual field (involving central and peripheral search within empty and cluttered fields), letter identification in high- and low-contrast environments, glare sensitivity, and reaction time (more a test of information processing than visual acuity).

Results showed "elderly subjects had poorer driving performance as assessed on a closed-circuit driving course compared with the young subjects, and the elderly subjects with early cataracts had poorer driving performance than those who were visually normal. . ." (pp. 87-88). All subjects had sufficient visual acuity to pass high-contrast vision tests given at driver testing centers and would be eligible to hold a driver's license.

Significant differences in results occurred on several driving and vision performance tests. In driving performance assessments, elderly subjects with early cataracts showed increased total driving times, peripheral reaction times, and maneuvering times when compared with younger drivers. While elderly subjects with cataracts took longer to complete the course and accomplish maneuvering tasks than visually normal older drivers and younger drivers, they did not make significantly more errors during these tasks than other groups. Elderly visually normal drivers did not perform as well on peripheral reaction time tests and had more maneuvering errors and poorer scores on speed estimation than did young drivers. Visual performance assessments showed that older drivers were more sensitive to light scatter than younger drivers and had more problems discerning low-contrast images. Reaction-time tests on the driving course (measured by the time taken to touch the brake when a red light came on either in the driver's central or peripheral viewing area) and in the laboratory showed longer times for older drivers than younger drivers, but results were less significant in the laboratory than on the road. Older subjects also had more difficulty in locating a target within a cluttered array than did younger persons.

Wood and Troutbeck cited an earlier study suggesting that when older drivers were informed about possible hazards due to natural deterioration in visual acuity, they may regulate their own driving practices and reduce risks by avoiding difficult driving situations. Since elderly drivers appear to drive and respond more slowly, results of this study may indicate older drivers should avoid peak-hour traffic that requires a given speed to maintain traffic flow and demands quicker reaction times in response to more complex situations. Results showing older drivers, particularly those with early cataracts, have greater sensitivity to glare and difficulty in detecting low contrast images might suggest they have poorer vision for nighttime driving and are almost blinded by intense sunlight. Older drivers, especially those whom doctors diagnose with early cataracts, might be well advised to avoid night driving or driving in late afternoon when the sun is on the horizon.