The main emphasis of this Ph.D.-thesis was put on the use of compensatory vieuwing strategies. It was hypothesized that subjects with visual field defects who use compensatory viewing strategies might reduce the negative impact of their visual field impairment. Compensatory viewing strategies may consist of eccentric viewing in case of central visual field defects and of scanning in case of peripheral visual field defects. It was investigated whether driving performance of subjects who used compensatory viewing strategies was considered to be more safe than that of subjects who did not use compensatory viewing strategies. It was further investigated whether compensatory viewing strategies could be trained and whether improved viewing strategies resulted in improved driving performance. It was concluded that a considerable percentage of drivers with visual field defects is able to drive safely and smoothly. Driving was assessed according to the official standard in the Netherlands to assess practical fitness to drive in drivers who do not quite meet the vision requirements for driving. Of 100 subjects with visual field defects, 44 passed the driving test. Of those who did not meet the vision requirements for driving, still 34% passed. Moreover, of those who (nearly) failed the driving test before training, 42% passed the driving test after training. These numbers illustrate that some drivers were able to drive safely despite their physical impairment. Several variables determined whether subjects passed or failed the driving test. First, it was observed that the proportion of subjects with central visual field defects passing the driving test was smaller (25%) than that of subjects with peripheral visual field defects (45%) or mild visual field defects (64%). This finding suggests that subjects with central visual field defects are at a disadvantage with regard to practical fitness to drive. Second, compensatory viewing efficiency (AFOV) was significantly related to the pass/fail score of the on-road driving test (r=0.52). Subjects who used compensatory viewing strategies were more likely to pass the driving test than subjects who did not do so. Third, as variables related to vision, compensatory viewing efficiency, and visual attention accounted for a relatively small portion of the variance in on-road driving performance, it must be concluded that other variables, such as motivation to drive or travel independently, driving experience, and traffic insight might have been important factors in determining whether subjects passed or failed the driving test. The study of these poorly understood factors remains an important issue to be addressed in the future. (A)
Abstract