Drivers with glaucoma are reported to have reduced ability to detect traffic hazards and higher rates of motor vehicle collisions, though the underlying mechanisms are poorly understood.1 Visual field loss is undoubtedly a major contributor, but previous studies have suggested that scanning behavior, as explored by observing eye movement patterns, is also altered in glaucoma and that changes to visual field and eye movement patterns are inextricably linked. For example, Crabb et al. observed older drivers with glaucoma to have a higher rate of saccades when performing a hazard perception test, perhaps as a strategy to compensate for glaucomatous visual loss.2 The aim of Lee and colleagues' work was to evaluate eye movement patterns and performance of drivers with glaucoma compared to age-matched controls.
Visual search behavior was evaluated in 31 drivers with glaucoma and 25 controls, while performing DriveSafe, a slide recognition test purported to predict fitness to drive. The DriveSafe consists of 11 images of driving scenes presented on a computer screen. Participants are required to report the type, position and direction of travel of different road users shown in the scene. A score was assigned for the total number of correctly reported items and visual search during testing examined using an eye tracker.
Patients with glaucoma may have less effective visual scanning strategies, reducing their ability to identify potential hazards
Drivers with glaucoma were found to have significantly worse DriveSafe scores compared to controls, indicating greater difficulty in identifying and locating relevant objects. Differences in eye movement measures were also noted, including smaller amplitude saccades and the observation that those with glaucoma spent less time fixating on road users, with the rest of the time spent looking at less relevant objects. Longer fixation on road users was associated with better DriveSafe scores. According to the developer's recommended cut off score, only one participant failed the DriveSafe test, but this likely reflects the relatively mild visual field loss in the better eyes of participants (average mean deviation of -2.88 ± 3.17 dB).
Although it seems intuitive that drivers with glaucoma would spend more time fixating on road users, in order to maximize identification of potential obstacles, the opposite was true. The shorter time spent fixating on road users may have been due to the shorter saccadic amplitudes and short task time. This suggests that patients with glaucoma may have less effective visual scanning strategies, reducing their ability to identify potential hazards.
Although the DriveSafe test has not been validated for the evaluation of patients with visual impairment this study provides an important starting point and adds to the important work examining how glaucoma affects activities of daily living.