In certain jurisdictions, people with homonymous hemianopia (HH) are permitted to drive. Drivers with the condition may be able to compensate for hemifield vision loss by scanning toward the blind side, utilizing eye and head movements, according to research published in JAMA Ophthalmology.
According to the report, “prior research suggests that drivers with HH sometimes fail to scan to the blind side when approaching an intersection or do not scan far enough, resulting in impaired responses to hazards.”
Between October 2018 and May 2019, researchers conducted a cross-sectional, single-visit driving simulator study at a vision rehabilitation research laboratory. They included a volunteer sample of people with HH without visual neglect in the analysis.
Participants finished drives with and without scanning reminder cues (a single tone from a speaker on the blind side), the report notes. Scanning was quantified via the percentage of intersections at which an early large scan was performed (a scan with a head movement of at least 20° made before 30 meters from the intersection). Responses to motorcycles were quantified via the time to the first fixation and the time to the horn-press response.
A total of 16 participants completed the study, but 2 were excluded from the analysis. Data from the remaining 14 participants (median [IQR] age, 54 [36-66] years and 13 men [93%]) were included. The investigators found that stroke was the primary cause of the HH (10 participants [71%]). They also determined that 6 participants (43%) had right-sided HH.
Participants were more inclined to perform an early large scan to the blind side in drives with cues than in drives without cues (65% vs 45%; difference, 20% [95% CI, 5%-37%]; P <.001). When participants performed an early large scan to the blind side, they were faster to make their first fixation on blind-side motorcycles (mean [SD], 1.77 [1.34] vs 3.88 [1.17] seconds; difference, -2.11 [95% CI, −2.46 to −1.75] seconds; P <.001) and faster to press the horn (mean [SD], 2.54 [1.19] vs 4.54 [1.37] seconds; difference, -2.00 [95% CI, -2.38 to -1.62] seconds; P <.001) than when they did not perform an early scan.
The study reports several limitations. For one, the sample size is relatively small and heterogeneous. Also, detection was examined in relatively simple motorcycle-hazard scenarios and response times were based on horn-press instead of braking responses.
“This post hoc analysis suggests that auditory reminder cues may promote proactive scanning, which may be associated with faster responses to hazards,” according to the researchers. “This hypothesis should be considered in future prospective studies.”
Xu J, Emmermann B, Bowers AR. Auditory reminder cues to promote proactive scanning on approach to intersections in drivers with homonymous hemianopia. JAMA Ophthalmol. Published online November 24, 2021. doi:10.1001/jamaophthalmol.2021.5007