Driving with binocular visual field loss? A study on a supervised on-road parcours with simultaneous eye and head tracking

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.

Trial registration: ClinicalTrials.gov NCT01372319 NCT01372332.

Conflict of interest statement

Competing Interests: The authors have the following interests. PFIZER Pharma GmbH, Berlin, Germany, and MSD, SHARP & DOHME GmbH, Haar, Germany provided financial support to this study. There are no patents, products in development or marketed products to declare. This does not alter the authors' adherence to all the PLOS ONE policies on sharing data and materials, as detailed online in the guide for authors.

Figures

Figure 1. (a) A participant, wearing the mobile eye-tracking head unit; (b) First camera recording the road scene during the drive; (c) Second camera recording the driver during the drive; (d) Calibration points; (e) Scene marker used for calibration.

The subject has given written informed consent, as outlined in the PLOS consent form, to publication of their photograph.

Figure 2. Distribution of the five different AOIs over the visual field for the assessment of HGD.

Figure 3. Driving parameters with significant differences between glaucoma control subjects who passed (GCp), glaucoma patients who passed (GPp) and glaucoma patients who failed (GPf) the driving assessment.

Figure 4. Driving parameters with significant differences between HVFDs control subjects who passed (HCp), patients with right-sided HVFDs who passed (HRp), left-sided HVFDs patients who passed (HLp), and HVFDs patients who failed (HPf) the driving assessment.

Figure 5. Left: Comparison of the proportion of glances in percent (PGP) towards the VFD between patients who passed (Pf) and patients who failed (Pf); Middle: Comparison of PGP towards VFD between glaucoma patients who passed (GPp) and glaucoma patients who failed (GPf); Right: Comparison of PGP towards VFD between patients with right-sided HVFDs who passed (HRp), patients with left-sided HVFDs who passed (HLp), and patients with HVFDs who failed (HPf).

Figure 8. Comparison of the horizontal gaze distribution (HGD) towards the central 20° area of the visual field between patients who passed (Pf) and patients who failed (Pf); glaucoma patients who passed (GPp) and glaucoma patients who failed (GPf); and between patients with right-sided HVFDs who passed (HRp), with left-sided HVFDs who passed (HLp), and patients with HVFDs who failed (HPf).

Figure 6. The proportion of glances in percent (PGP) of patients with homonymous visual field defects towards the VFD during the on-road assessment.

For each of the eight road scenes (Table 1), the upper panel shows the PGP of each participant. The lower panel shows the corresponding VFD tested by binocular semi-automated 90° kinetic perimetry. The red line and the shallow red area represent the border and the extent of the HVFD, respectively.

Figure 7. The proportion of glances in percent (PGP) of glaucoma patients towards the VFD during the on-road assessment (Table 2). Else, see Figure 6.

Figure 9. Venn diagram showing the distribution of subjects who failed the driving task among gaze parameters, head and shoulder movements regarding the capacity of these parameters in predicting failure.

Figure 10. Venn diagram showing false-positives (red) and false-negatives (green) regarding failure prediction.