The Impact of Visual Field Loss on Driving Performance: Evidence From On-Road Driving Assessments

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Abstract
The purpose of this study was to investigate the relationship between visual field loss and driving performance as determined by on-road driving assessments. We reviewed the files of 1350 patients enrolled in a rehabilitation program at the Bloorview MacMillan Rehabilitation Centre, Toronto, Canada. We identified 131 patients with visual field loss who had undergone an on-road driving assessment. These patients had a primary diagnosis of visual impairment or a primary diagnosis of cerebral vascular accident (CVA) with a secondary diagnosis of visual impairment. None of these patients had documentation of neglect, substantial motor or cognitive deficits. We report the data obtained from 13 hemianopics, 7 quadrantanopics, 25 patients with monocular vision, 10 patients with moderate peripheral losses (<135° of horizontal visual field measured at the midline), and 76 patients with mild peripheral losses (between 135° and 186° of horizontal visual field). The on-road assessment consisted of driving in the area surrounding the rehabilitation center, and the outcome was based on performance on a number of tasks commonly encountered in daily driving. For the purposes of this study, the assessment outcomes were classified as safe, unknown, or unsafe. Overall, the extent of visual field loss did not have a significant impact on driving performance (χ2 = 4.37, p = 0.358). However, hemianopia tended to have a worse impact on driving performance than quadrantanopia with a marginally significant result (χ2 = 3.33, p = 0.068). Overall, the location of the visual loss was not significantly related to driving fitness (χ2 = 1.05, p = 0.30). However, localized defects in the left hemifield (χ2 = 9.561, p = 0.002) and diffuse visual loss in the right hemifield (χ2 = 10.395, p = 0.001) seemed to be associated with driving impairments. A large proportion of monocular drivers were safe drivers and the location of their deficit had no significant impact. Although the extent of visual field defects appears to be related to driving performance as determined by an on-road driving assessment, large individual differences were observed. This highlights the need for individualized on-road assessments for patients with visual field defects.