Section 2: Vision
2.7 Loss of Vision in One Eye
Research on the monocular driver is limited, with many of the studies conducted before the early 70s (Freytag and Sachs, 1969; Keeney, 1968; Kite and King, 1961; Liesman, 1973). Results of those investigations reveal that, in general, drivers with monocular vision have a greater number of crashes, more hazardous driving patterns, and a greater number of road problems compared to normal sighted drivers. Keeney et al. (1981) reported on the driving performance of 52 monocular drivers enrolled in Kentucky’s Driver Limitation Program from 1976 through 1980. Crash and traffic violations were obtained from state driving records. Results indicated that monocular drivers have almost double the rate of crashes compared to the general motoring public. Monocular drivers also were found to have more reckless driving violations compared to their binocular counter-parts. Side of monocularity was found to be a significant factor. Individuals with right eye blindness had significantly more traffic violations than those with left eye blindness. Interestingly, there were no significant differences between the crash or violation rates of drivers with license restrictions (mandatory left hand outside mirror) compared to those without license restrictions.
The most recent study was conducted by McKnight, Shinar, and Hilburn (1991). McKnight et al. evaluated the visual and driving performance of 40 monocular and 40 binocular tractor-trailer drivers. The monocular drivers exhibited impairments in contrast sensitivity, visual acuity under low illumination and glare, and binocular depth perception. Interestingly, there were no significant differences between the two groups of drivers of measures of visual search, lane keeping, clearance judgment, gap judgment, hazard detection, and information recognition. The authors concluded that despite the reductions in selective visual functions, monocular drivers are not significantly worse than binocular drivers in the safety of most day-to-day driving functions. Measures of crash rates were not included in the study.
Despite the evidence that monocular drivers have greater crash and traffic violation rates than binocular drivers, there are few restrictions placed on this category of drivers (see Table 1).