Hard braking events in bioptic drivers with central vision impairment.

Abstract

Purpose: Some individuals with central vision impairment can obtain or maintain driving privileges using bioptic telescopes. Previous work has often demonstrated an increased collision risk for bioptic drivers, but some on-road studies find similar safety to that of normally sighted drivers. The purpose of this study was to compare exposure-controlled hard braking and speeding events measured with naturalistic recording in visually impaired bioptic drivers and normally sighted control drivers.

Methods: Visual acuity was measured for each eye individually and through the bioptic when indicated. Contrast sensitivity was measured binocularly with the Mars chart. Binocular integrated visual fields were constructed from monocular 24-2C SITA Faster plots. A commercially available GPS recorder was installed into drivers' personal vehicles for at least 6 weeks. Total mileage, instances of hard braking, travel over 65 miles per hour (mph) and posted speed limit violations were counted. Exposure-controlled rates were calculated for each of these safety events. Driver characteristics and hard braking events were compared using median tests, and Spearman correlation was used to assess the relationships among vision measurements and driving safety events.

Results: Twenty licensed bioptic drivers and 20 control drivers were enrolled. Bioptic drivers were significantly more likely to perform hard braking manoeuvres than controls. Among bioptic drivers, hard braking frequency was not predicted by visual acuity, contrast sensitivity or binocular integrated visual field deviation. Bioptic drivers with poorer contrast sensitivity were more likely to travel above 65 mph. Speeding events were not related to hard braking.

Conclusions: Bioptic drivers demonstrated nearly three times as many hard braking events per 1000 miles driven, but vision measurements did not predict hard braking. Bioptic drivers with poorer contrast sensitivity were more likely to drive faster than 65 mph. Further work exploring relationships among vision and driving safety in bioptic drivers is warranted.