Predicting components of closed road driving performance from vision tests.

PURPOSE Mild cataracts can interfere with visually dependent everyday activities, although they only minimally affect static visual acuity. This study compared the effects of simulated cataracts with that of optical blur on driving performance and determined the extent to which acuity could account for variations in driving performance either alone or in combination with supplementary vision tests. METHODS Closed road driving performance was measured in 24 young, normally sighted subjects under five binocular acuity levels, four produced by different levels of optical blur (6/4.5, 6/12, 6/30, 6/60) and one by frosted lenses simulating mild cataracts (6/12c). Driving measures included gap perception, total driving time, sign recognition, road hazard avoidance, maneuvering time, and errors. Subjects were also tested with the Pelli-Robson chart, SKILL card, and Berkeley Glare Test under comparable acuity levels. RESULTS Total driving time, sign recognition, and hazard avoidance were linearly related to the acuity degradation produced by blur; performance in the 6/12c condition was similar to that in the 6/60 blur condition. Static acuity predicted 30% to 60% of the variance in these driving measures when the 6/12c condition was excluded from analysis; this proportion was reduced by a factor of two to three when the 6/12c condition was included. However, using any one of the three supplementary tests with visual acuity in a multiple regression analysis recaptured much of the lost variance. CONCLUSIONS Static acuity can only predict variations in closed road driving performance measured under degraded conditions that include simulated mild cataracts when it is combined with supplementary vision tests.