Citation

Peli E, Bowers AR, Goldstein R, Mandel A, Bronstad M, Albu A. Eye Auto 2009; 2009: 35.

Copyright

(Copyright © 2009, Detroit Institute of Ophthalmology)

DOI

unavailable

PMID

unavailable

Abstract

Visual field loss may be expected to affect a driver‘s ability to detect a potential collision or other driving-relevant objects. Driving with hemianopia (the loss of half the field of vision) is prohibited in half the states and discouraged in others; however, it is permitted in some countries in Europe. Recent studies of on-road driving with hemianopia suggest that many patients with hemianopia may drive safely (with or without field expanders). In these studies, the main reasons for failing seem to be related to vehicle-control (lane position, steering) difficulties rather than detection failures. Central field loss (CFL), associated with age-related macular degeneration (AMD) and many other conditions, is treated in most jurisdictions as merely a loss of visual acuity without direct consideration of the impact of the central scotoma (blind area), or more specifically the position of the scotoma relative to the preferred retinal locus (PRL). We have been studying driving with visual field loss in a simulator where the environment and scenarios are more easily controlled than in an on-road evaluation, and can be equally applied for all subjects. For patients with hemianopia we found a wide variability in the ability to detect pedestrians in hazardous positions, with only 1 out of 12 subjects having detection rates at a (safe) level similar to that of normal controls. Head scanning appeared to be an effective compensation at intersections (more head scanning was associated with better detection); however, there was wide variability in the amount of head scanning, with some subjects failing to scan to the blind side at 30% of intersections. While statistically significant differences in vehicle control (lane position) could be found even between left and right hemianopes, the magnitude of the shifts in lane position were generally small and may represent an increasing of the safety margin on the blind side. The patients with hemianopia also had a slightly more variable lane position and were out of lane more often than normally sighted drivers. For patients with CFL, we found increased reaction times to pedestrians in all locations; however, the greatest increases were at locations on the same side as the scotoma relative to the PRL. These findings indicate that the detection performance of patients with CFL is affected not only by the reduced acuity, but also by the position of the central scotoma; in particular drivers with a scotoma to the right of the gaze point will have very long reaction times for pedestrians about to step off the nearside curb.