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A. R. Bowers, A. J. Mandel, R. B. Goldstein, E. Peli; Driving with Hemianopia: Head Scanning and Detection Performance in a Simulator. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4105.
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Drivers with hemianopia may have difficulty detecting objects on the side of the vision loss, which could adversely affect both the safety of the driver and other road users. We conducted a simulator-based evaluation to investigate how well drivers with hemianopia compensated for their vision loss when performing a driving-relevant detection task. In addition, we evaluated head-scanning behaviors and examined whether increased head-scanning resulted in better detection at intersections.
Twelve patients with complete homonymous hemianopia but without visual neglect (6 left and 6 right) were compared to 12 age and gender case-matched normally-sighted drivers. Participants drove for about 60 minutes in a high-fidelity simulator on two occasions, one week apart. The primary task was to detect and respond (by a horn press) to the appearance of pedestrian targets in a variety of traffic situations. "Roadway" targets (72 per session) appeared either on the left or right of the road at small (4°) or large (14°) eccentricities and "intersection" targets (5 per session) were placed at or near intersections. Head movements were recorded with an optical tracking system. An algorithm was developed to identify and quantify head scans (movements away from the straight ahead position).
Roadway target detection rates of hemianopic drivers were lower on the blind side (median 44%) than the seeing side (97%; p = 0.002), and were lower at the larger (25%) than the smaller eccentricity on the blind side (65%; p = 0.002). On the seeing side, detection rates were similar to those of normally-sighted drivers (100%). Amongst the hemianopic drivers, detection rates varied widely (19 to 93%); lower roadway detection rates were associated with older age (Spearman rho = -0.67, p = 0.02). Normally-sighted drivers detected 88% of targets on the extreme right and left of intersections, but drivers with right hemianopia detected only 8% of targets on the extreme right (p < 0.001) and drivers with left hemianopia detected only 39% on the extreme left (p < 0.001). Drivers with hemianopia failed to scan to the blind side at 10% of intersections (range 0 to 30%). Higher detection rates at intersections were associated with lower failure-to-scan rates and greater numbers of scans to the blind side (Spearman rho = -0.90 and 0.78, respectively; p < 0.001).
These results provide evidence of widely varying levels of compensation and detection abilities amongst drivers with hemianopia and suggest that increased head-scanning results in better detection performance at intersections.
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