Test Shows Visual Field Loss Reduces Vehicle Control

When patients with glaucoma completed a driving simulation, poor vehicle control was independently associated with greater visual field (VF) loss and worse neurocognitive performance, according to research published in BMC Ophthalmology. The researchers suggest that both factors must be considered when developing models of poor vehicle control in patients with glaucoma.

Patients with glaucoma are often unaware that visual field loss restricts their ability to detect objects in their periphery, and that affects their perception of the real world. Researchers have linked severe visual field loss to higher motor vehicle crash rates, which are more than 4 times higher in patients diagnosed with moderate-to-severe glaucoma than in healthy patients, according to research. However, neurocognitive performance is a strong predictor of driving safety in healthy drivers, which until now, had been understudied in drivers with glaucoma, according to investigators.

In the current study, researchers sought to understand the relationship between binocular VF loss, global neurocognitive performance, and quantitative measures of motor vehicle control by conducting a driving simulator study of licensed, actively driving glaucoma patients. 

Researchers recruited 43 subjects. Because the subjects with glaucoma (69.8 ± 11.3; n = 25) were significantly older than the subjects suspected of having the disease (60.3 ± 13.1; n = 18), the investigators included age as a separate factor in their statistical models. All of the subjects had greater than 20/40 best corrected visual acuity in each eye and were experienced field takers, with at least 3 stable (reliability > 20%) fields in the last 2 years. Those who had been diagnosed with a neurological disorder or cognitive impairment were excluded.

Driving performance was evaluated using a driving simulator with a 290-degree panoramic field of view constructed around a full-sized automotive cab. Vehicle control metrics, such as lateral acceleration variability and steering wheel variability, were calculated using vehicle sensor data collected while patients drove on a straight, two-lane rural road. Linear mixed models were developed to analyze associations between driving performance and clinical characteristics.

The study found that drivers with glaucoma who had a range of binocular VF loss demonstrated significantly worse lane position control, marked by a more than 3-fold increase in lateral acceleration and steering wheel variability as compared with subjects without VF loss. It also revealed that greater lateral acceleration variability was associated with greater binocular visual field loss, worse neurocognitive performance, and worse self-reported driving performance. Finally, the study found greater binocular VF loss was associated with greater lateral acceleration and steering wheel variability on a straight, hazard-free highway.

Subjects with glaucoma showed greater steering wheel variability (P =.0001) and lateral acceleration variability (P <.0001) compared with healthy controls. Greater steering wheel variability was independently associated with OU-VFI (P =.0069), MoCA total scores (P =.028), and VFQ driving subscores (P =.0087), but not age (P =.61).

The investigators acknowledge that how glaucomatous VF loss contributes to predictors of increased crash risk remain unclear. They suggest that one reason may be that peripheral VF loss causes poor lane boundary tracking and, by consequence, poor lane maintenance, and vehicle control.

To further validate the pilot study’s findings, the researchers say that their results must be translated to on-road driving studies. 

Limitations of the study include its relatively small sample size. Further, subjects suspected of having glaucoma were recruited as the control group because they presented with the same pathophysiologic risk factors of glaucoma without VF loss. In future studies, the investigators say, enrolling an additional healthy control group will provide further support that these findings are related to VF loss, not glaucoma-related risk factors. 

Reference

Anderson DE, Bader JP, Boes EA, et al. Glaucomatous visual fields and neurocognitive function are independently associated with poor lane maintenance during driving simulation. BMC Ophthalmol. Published online October 20, 2020. doi: 10.1186/s12886-020-01682-9.