Abstract
Post-chiasmal visual pathway lesions and glaucomatous optic neuropathy cause binocular visual field defects (VFDs) that may critically interfere with quality of life and driving licensure. The aims of this study were (i) to assess the on-road driving performance of patients suffering from binocular visual field loss using a dual-brake vehicle, and (ii) to investigate the related compensatory mechanisms. A driving instructor, blinded to the participants' diagnosis, rated the driving performance (passed/failed) of ten patients with homonymous visual field defects (HP), including four patients with right (HR) and six patients with left homonymous visual field defects (HL), ten glaucoma patients (GP), and twenty age and gender-related ophthalmologically healthy control subjects (C) during a 40-minute driving task on a pre-specified public on-road parcours. In order to investigate the subjects' visual exploration ability, eye movements were recorded by means of a mobile eye tracker. Two additional cameras were used to monitor the driving scene and record head and shoulder movements. Thus this study is novel as a quantitative assessment of eye movements and an additional evaluation of head and shoulder was performed. Six out of ten HP and four out of ten GP were rated as fit to drive by the driving instructor, despite their binocular visual field loss. Three out of 20 control subjects failed the on-road assessment. The extent of the visual field defect was of minor importance with regard to the driving performance. The site of the homonymous visual field defect (HVFD) critically interfered with the driving ability: all failed HP subjects suffered from left homonymous visual field loss (HL) due to right hemispheric lesions. Patients who failed the driving assessment had mainly difficulties with lane keeping and gap judgment ability. Patients who passed the test displayed different exploration patterns than those who failed. Patients who passed focused longer on the central area of the visual field than patients who failed the test. In addition, patients who passed the test performed more glances towards the area of their visual field defect. In conclusion, our findings support the hypothesis that the extent of visual field per se cannot predict driving fitness, because some patients with HVFDs and advanced glaucoma can compensate for their deficit by effective visual scanning. Head movements appeared to be superior to eye and shoulder movements in predicting the outcome of the driving test under the present study scenario.
Highlights
Visual field defects usually occur with lesions involving the visual pathway
Glaucoma patients should suffer from open angle glaucoma with advanced binocular visual field loss
There was no significant difference between the subgroups glaucoma control subjects who passed (GCp) - glaucoma patients who passed (GPp) - glaucoma patients who failed the test (GPf) and HVFDs control subjects who passed (HCp) - HRp - HLp - HPf
Summary
Visual field defects usually occur with lesions involving the visual pathway. (Advanced) glaucoma and post-chiasmal cerebral lesions are common disease entities associated with visual field loss in the binocular visual field. Glaucoma is the second leading cause of blindness in the Western world [1]. It is a characteristic optic neuropathy leading to (usually arcuate) visual field defects that follow the course of the affected retinal nerve fibers. In advanced stages of glaucoma the areas of monocular field defects may spatially coincide and result in binocular field loss. Post-chiasmal lesions of the visual pathway cause contralateral homonymous visual field defects (HVFDs), a loss of vision on the same side in both eyes, which respect the vertical midline. The most common causes for such HVFDs are stroke (70%), brain tumor and trauma [2]
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