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A. Albu, A. R. Bowers, P. M. Bronstad, R. B. Goldstein, E. Peli; Driving With Central Field Loss: Pedestrian Detection in a Simulator. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3625.
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Although age-related macular degeneration (AMD) causes both a reduction in visual acuity (VA) and central visual field loss (CFL), the CFL is rarely considered in driver licensing. Yet a driver with CFL may miss potentially hazardous objects in their path. We therefore investigated the impact of CFL on pedestrian detection in a driving simulator. We tested the hypothesis that scotomas lateral to fixation would impact detection of pedestrians to a greater extent than scotomas above fixation.
To date, 7 subjects with AMD (74-87yrs; VA 20/60 to 20/200) and 3 age-similar subjects with normal vision (NV) have participated. They drove for about 60 minutes in a high-fidelity simulator in two sessions, one week apart. Pedestrian targets (n = 72 per session) were presented in a variety of situations. Subjects pressed the horn to indicate detection. Pedestrians appeared on the left or right of the roadway at a small (4°) or large (14°) eccentricity, then maintained that eccentricity (as if on a collision course) by walking or running towards the subject’s vehicle.
AMD subjects detected > 90% of all pedestrians. However, their reaction times were significantly longer than for the NV subjects (medians = 3.07s and 1.10s, respectively, p< .001). For AMD subjects with a scotoma to the right of fixation (n = 5), reaction times to pedestrians at the small right eccentricity (median = 4.62s) were significantly longer than at the small left eccentricity (median = 1.83s, p < .001), the large right (median = 2.30s, p < .001) and the large left eccentricity (median = 2.07s, p < .001). For the one AMD subject with a scotoma above fixation, reaction times to pedestrians at the small right eccentricity were not significantly longer than at the small left eccentricity (p = .06).
Although CFL had a modest impact on detection rates, reactions times of CFL drivers were much longer than those of NV drivers and in many cases exceeded the recommended 2.5s perception-brake response time. Preliminary analyses indicate that scotoma location is an important consideration: a scotoma to the right of fixation resulted in delayed detection of pedestrians on the near right (about to step off the curb). In addition to measuring VA, the size and location of central scotomas should be assessed when evaluating CFL patients for driving.
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