Driving performance of drivers with impaired central visual field acuity.

This study investigated the performance of drivers with impairment to their central field of vision but with normal peripheral vision, due to retinoschisis, in a safety critical driving tasks. The performance of five male drivers with impaired vision (VA 0.2), aged between 40 and 50 years, all with more than 250,000 km life-time driving experience and a good safety record, and five normal vision controls, matched by gender, age, driving experience and safety record, were tested in 40 km/h city traffic and in a motorway car following situation. All participants displayed appropriate driving ability in city traffic and all were able to detect and respond adequately to a conflicting 'stunt pedestrian' and 'stunt cyclist' situation. There were no apparent differences between the drivers with impaired vision and those with normal vision. In the car following situation, the participants drove at 80 km/h, 50 m behind a lead car, on a 30 km section of motorway in normal traffic. During each trial, the lead car started to decelerate at an average of 0.53 m/s2 while the participant either looked at the car in front (control) or performed a memory and addition task (non-visual attention) while looking at the car in front. The participants were required to press the brake pedal when they noticed a decrease in headway. The participant's brake reaction time to the onset of the lead car's brake lights was also tested. The drivers with impaired vision were significantly slower, by 0.2 s, in detecting the onset of brake lights than the normal vision drivers. Their headway closure detection was 0.7 s slower than normal vision drivers, but this difference was not statistically significant in this small data. In spite of some impairment in car following (central vision task), the results together with the clean record of these drivers with retinoschisis support the idea that visual acuity of 0.5 (the European Union norm) is not a necessary prerequisite for safe driving.