Amanda Albu

Driving with central field loss I: effect of central scotomas on responses to hazards.

OBJECTIVES To determine how central field loss (CFL) affects reaction time to pedestrians and to test the hypothesis that scotomas lateral to the preferred retinal locus will delay detection of hazards approaching from that side. METHODS Participants with binocular CFL (scotoma diameter, 7°-25°; visual acuity, 0.3-1.0 logMAR) using lateral preferred retinal fixation loci and matched controls with normal vision drove in a simulator for approximately 1½ hours per session for 2 sessions a week apart. Participants responded to frequent virtual pedestrians who appeared on either the left or right sides and approached the participants lane on a collision trajectory that, therefore, caused them to remain in approximately the same area of the visual field. RESULTS The study included 11 individuals with CFL and 11 controls with normal vision. The CFL participants had more detection failures for pedestrians who appeared in areas of visual field loss than did controls in corresponding areas (6.4% vs 0.2%). Furthermore, the CFL participants reacted more slowly to pedestrians in blind than nonscotomatous areas (4.28 vs 2.43 seconds, P < .001) and overall had more late and missed responses than controls (29% vs 3%, P < .001). Scotoma size and contrast sensitivity predicted outcomes in blind and seeing areas, respectively. Visual acuity was not correlated with response measures. CONCLUSIONS In addition to causing visual acuity and contrast sensitivity loss, the central scotoma per se delayed hazard detection even though small eye movements could potentially compensate for the loss. Responses in nonscotomatous areas were also delayed, although to a lesser extent, possibly because of the eccentricity of fixation. Our findings will help practitioners advise patients with CFL about specific difficulties they may face when driving.

Hazard Detection by Drivers with Paracentral Homonymous Field Loss: A Small Case Series.

INTRODUCTION Stroke frequently causes homonymous visual field loss. We previously found in a driving simulator that patients with complete homonymous hemianopia had difficulty detecting potential hazards on the side of the field loss. Here we measured the effects of limited paracentral homonymous field loss on detection performance. METHODS Three patients with paracentral homonymous scotomas, yet meeting vision requirements for driving in the United States, performed a pedestrian detection task while driving in a simulator. Pedestrians appeared in a variety of potentially hazardous situations on both sides of the road. Three age- and gender-matched control participants with normal vision participated for comparison purposes. RESULTS Pedestrians appearing in the scotomatous side of the visual field were less likely to be detected, and when they were, reaction times were longer, frequently too late to respond safely. CONCLUSIONS Although legally permitted to drive in the U.S.A., and possibly in other countries, patients with paracentral homonymous field loss may have impaired hazard detection and may benefit from education about their deficit and a fitness-to-drive evaluation.

Driving with central visual field loss II: how scotomas above or below the preferred retinal locus (PRL) affect hazard detection in a driving simulator

We determined whether binocular central scotomas above or below the preferred retinal locus affect detection of hazards (pedestrians) approaching from the side. Seven participants with central field loss (CFL), and seven age-and sex-matched controls with normal vision (NV), each completed two sessions of 5 test drives (each approximately 10 minutes long) in a driving simulator. Participants pressed the horn when detecting pedestrians that appeared at one of four eccentricities (-14°, -4°, left, 4°, or 14°, right, relative to car heading). Pedestrians walked or ran towards the travel lane on a collision course with the participant’s vehicle, thus remaining in the same area of the visual field, assuming participants steady forward gaze down the travel lane. Detection rates were nearly 100% for all participants. CFL participant reaction times were longer (median 2.27s, 95% CI 2.13 to 2.47) than NVs (median 1.17s, 95%CI 1.10 to 2.13; difference p<0.01), and CFL participants would have been unable to stop for 21% of pedestrians, compared with 3% for NV, p<0.001. Although the scotomas were not expected to obscure pedestrian hazards, gaze tracking revealed that scotomas did sometimes interfere with detection; late reactions usually occurred when pedestrians were entirely or partially obscured by the scotoma (time obscured correlated with reaction times, r = 0.57, p<0.001). We previously showed that scotomas lateral to the preferred retinal locus delay reaction times to a greater extent; however, taken together, the results of our studies suggest that any binocular CFL might negatively impact timely hazard detection while driving and should be a consideration when evaluating vision for driving.

Driving with central field loss III: vehicle control

Visual impairment associated with central field loss may make vehicle control more difficult due to the degraded view of the road. We evaluated how central field loss affects vehicle control in a driving simulator.