Eligibility for driving is most commonly restricted by visual requirement of static (high contrast) visual acuity of 6/12 or better. The aims of this study were to evaluate the effect of progressive visual acuity degradation on different components of driving performance as measured on a closed road driving track, and to determine whether all drivers satisfying the 6/12 minimum visual acuity standard are necessarily equivalent with respect to their driving performance. Twenty four young, visually normal adults acted as subjects for the study. Driving performance was measured using the closed road methods described previously by Wood and Troutbeck (1994a, b). Subjects were tested under each of five binocular visual acuity levels produced by having them wear modified swimming goggles and lenses, while in addition, lens blur was used to produce four of the visual acuity levels (6/6, 6/12, 6/30 and 6/60). Frosted lenses were used to produce the fifth visual acuity level (6/12g) which simulated the effects of glare associated with mild cataracts while allowing visual acuity to remain at a level of 6/12. The results demonstrated that degradation of acuity resulted in significant reductions in the recognition of signs and hazards, as well as significant increase in the time taken to complete the course (p less than 0.05). Gap judgement and manoeuvring ability were, however, relatively unaffected by the level of visual acuity. Interestingly, the 6/12g condition produced selective and significant deficits in detection/recognition of road signs and road hazards that were not predictable from the modest loss in high contrast static acuity associated with this viewing condition. These results indicate that high contrast visual acuity, as employed by driver licensing authorities, is a poor predictor of driving performance when acuity losses resulting from causes other than refractive blue (e.g. cataracts) are considered. (A)
Samenvatting