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E. Peli, A. R. Bowers, A. J. Mandel, R. B. Goldstein; Effect of Hemianopia on Lateral Lane Position in a Driving Simulator. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4106.
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Hemianopic visual field loss may have adverse effects on vehicle control skills. We conducted a simulator-based evaluation to investigate the effects of hemianopia on lateral lane position and time out-of-lane for specific road segments.
Twelve patients with complete homonymous hemianopia but without visual neglect (6 left LH, and 6 right RH) were compared to 12 age and gender case-matched normally-sighted (NS) drivers. Participants drove for about 60 minutes in a high-fidelity simulator on two occasions, one week apart. Each session included city driving (30mph) and rural driving (60mph) with a variety of traffic situations. The average and standard deviation (variability) of the lateral lane offset (LLO) from the center of the travel lane (3m wide), and percent time out of lane (PTOL) were evaluated for straight road segments (city and rural), right and left curves (city and rural), and right and left turns (city only).
There were significant differences in LLO between RH and NS drivers for city and rural straight segments (p = 0.028) and rural right curves (p = 0.028); their LLO was (on average) 0.2m to the left of NS drivers. By comparison, LLO of LH drivers was similar to that of NS drivers for straights and curves (p = 0.6), but was 0.8m to the right of NS drivers in left turns (p = 0.05). Both RH and LH drivers had more variable LLO than NS drivers (p = 0.02). All drivers (RH, LH, NS) tended to "cut the curve" with the greatest left-LLO in city left curves (LH -0.50m, RH -0.67m, NS -0.63m) and the greatest right-LLO in rural right curves (LH 0.48m, RH 0.22m, NS 0.66m). For city left curves, left-PTOL varied widely within each vision group (from 0 to 73-80%), and there were no between-group differences. However, for rural right curves, right-PTOL was higher for LH than both RH and NS drivers (19, 5, 8% respectively, p = 0.04). Larger LLOs were associated with higher PTOL for both hemianopic and NS drivers (Spearman rho > 0.78 p < 0.003).
Even with a modest sample size, our results provide evidence that drivers with hemianopia adopted a lane position with a bias away from the blind side. These effects varied individually, with segment type, and were more apparent for right than left hemianopes. However, with the exception of rural right curves, hemianopes did not spend a greater percent time out of lane than the NS drivers on the analyzed straight and curved road segments.
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