Using a driving simulator (DS) system, researchers discovered that advanced glaucoma patients with deficits in the inferior hemifield have a high incidence of collisions with oncoming vehicles.
Study Design
This prospective investigation compared the performances of 95 advanced glaucoma patients (defined as mean deviation less than -12 dB in both eyes) with 43 normal controls on a driving simulator (DS). Subjects completed 2 DS scenarios that involved avoiding an oncoming car. Investigators then assessed how specific visual field loss affected the likelihood of collisions.
Integrated visual fields (IVF) were calculated by merging monocular Humphrey visual field 24-2 tests from each eye. In the advanced glaucoma group, IVFs were further analyzed in the central area of the superior and inferior hemifields (0–12 degrees) and within 13–24 degrees of the fixation point.
Outcomes
The advanced glaucoma group was significantly more likely to be involved in at least one collision (80%) compared with the normal group (26%, P<0.001). Among glaucoma patients, those who experienced a simulated collision were older (P=0.050) and had worse visual acuity in their better seeing eye (P<0.001) than those who avoided collisions. In contrast, the control group showed no significant differences in age, VA, or mean deviation between those who had collisions and those who didn’t. Further analysis showed that worse mean deviation in the inferior central IVF was associated with collisions (OR 0.91); this was not noted for the superior IVF.
Limitations
There are inherent limitations to a study informed by a driving simulator rather than real-world situations. Also, this study focused on a specific driving situation rather than multiple scenarios. Last, patients in the advanced glaucoma group who were involved in collisions tended to be older, and it is possible that other factors associated with age (e.g., mild cataracts or dementia) were confounding variables.
Clinical significance
Each state in the U.S. has varying laws regarding visual fitness to obtain and maintain a driver’s license. While most states have a specific visual field requirement, these requirements are not universal and many seem arbitrary and confusing. Regardless of laws, with the information from this article—namely that inferior central visual field loss appears to be a risk factor for collisions—clinicians can advise patients on their risk of collisions based on their specific visual field abnormalities.