The risk of motor vehicle collisions is a cause for concern in patients with impaired central and peripheral vision. This study reported on the road driving skills on a 10-km route in Halifax, Canada, of 20 patients with mild to moderate glaucoma and 20 matched controls. The authors concluded that slight or moderate visual field loss in glaucoma patients may impair their ability to detect peripheral obstacles or hazards while driving. This is an interesting study and, if the conclusions are validated by a study with a larger sample size, may have significant implications regarding the advice glaucoma experts give patients.
Study subjects were given a driving test conducted by one professional driving instructor, who was masked to the subjects' ocular status and level of vision. During the test, participants drove the same midsize automatic transmission car, which had a dual brake control system, allowing for the instructor, who was seated in the front passenger seat, to apply the brake. An occupational therapist, also masked to the subjects' visual status, sat in a back seat during each test and assessed each subject.
Statistical analysis of the results indicated that patients with glaucoma were six times more likely to experience one or more at-fault critical interventions by the instructor than the control group after adjusting for a number of variables. The leading cause of an intervention, during which the instructor averted a potentially unsafe situation by applying the dual brake or taking over steering control, was failure to see and yield to a pedestrian. However, the time taken to complete the course, score awarded out of 55 points judging total satisfactory performance and demonstration of specific driving maneuvers and skills, and overall driving performance on a 10-point scale were similar in the two groups of subjects.
Vision measure variables that correlated with scores on the 55-point total satisfactory driving skills measure included contrast sensitivity in the better eye and results of the Useful Field of View test, which assesses cognitive and visual function and has been shown to be predictive of at-fault motor vehicle collisions. The overall driving performance rating of the subjects with glaucoma strongly correlated with mean deviation of the worse eye on the Humphrey visual field test and contrast sensitivity of the better eye. Some of the study's limitations discussed by the authors included the small sample size and uncertainty regarding whether a driving instructor's intervention was truly predictive of real-world collisions.
Dr. Edward is a consultant to Alcon Laboratories, Inc., and Allergan, Inc. He receives lecture fees from Alcon Laboratories and Allergan and grant support from Alcon Laboratories and Pfizer Ophthalmics.