Study: Visual field loss impacts driving performance

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Results of a randomized study show both superior and inferior visual field defects impair drivers’ performance on the computerized Hazard Perception Test. However, superior visual field loss is associated with significantly greater worsening than inferior visual field loss.

Dr. Glen

By Cheryl Guttman Krader; Reviewed by Fiona C. Glen, PhD

London-Visual field loss can affect driving performance, but the extent of impairment varies depending on the location of the defect, according to the results of a study reported by Fiona C. Glen, PhD and colleagues.

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To test their hypothesis, that the impact of a visual field defect on driving performance depends on its location, the investigators conducted a trial in which 30 participants with healthy vision completed the driving Hazard Perception Test (HPT). The HPT, a required component of the driving exam for new drivers in the United Kingdom, is a computer-based test measuring response times for detecting hazards appearing in real-life driving videos. Participants performed the HPT three times in random order. One test served as a baseline and was performed without any modifications. In the two other test situations, novel software was used to simulate superior or inferior visual field defects that were linked to the user’s real-time gaze.

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Outcomes

The results showed that the participants’ mean HPT score exceeded the passing mark in the baseline-testing situation, but not when the testing was performed with either simulated visual field defect.

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Compared to the baseline testing without visual field modification, HPT test scores fell 18% when the driving exam was done with the simulated superior defect and by 12% with the simulated inferior defect. Statistical analysis showed the effect of both visual field defects was statistically significant and also showed the impact of the superior visual field defect was significantly greater than the effect of the inferior visual field defect.

“Binocular visual field loss has been linked to subject-reported driving difficulties and risk of motor vehicle accidents,” said Dr. Glen, postdoctoral research assistant, Department of Optometry and Visual Science, School of Health Sciences, City University London. “The results of our study suggest that driving performance and potentially rates of vehicular accidents does not depend simply on the presence of binocular loss but rather on the location of the defect.”

She explained that interest in undertaking this study was motivated by the relative paucity of data on how different types and locations of visual field defect impact driving performance.

“The lack of good scientific evidence in this area was particularly surprising considering that driver’s license eligibility requirements in the United Kingdom include some complicated criteria relating to locations of visual field defects. However, the existing standards, which are being used to make what is a life-altering decision, have never been documented to actually impair driving performance.

“Furthermore, the use of the binocular visual field test to assess fitness to drive is questionable since it was never developed for that purpose and has many specifications that are not necessarily relevant to driving,” she said.

NEXT: Examining further

Examining further

Dr. Glen noted that the study’s finding of significantly worse performance on the HPT when testing was done with the simulated superior visual field defect compared to the inferior visual field defect is not surprising considering that the superior field of view is more relevant to the driving scene.

“However, it is an important finding because the visual field test that is used for determining driving eligibility in the United Kingdom is weighted toward the inferior visual field,” she said.  “Therefore, our study brings into question the appropriateness of using that test to determine fitness to drive.

“Our research was sponsored by the International Glaucoma Association, a patient-based charity that is very much interested in improving methods for assessing driving fitness.  Our research is a first step toward understanding which visual field defect locations are most important for driving and in turn devising better tests for assessing fitness to drive in the future,” Dr. Glen concluded.

Fiona C. Glen, PhD

E: fiona.glen.2@city.ac.uk

This article is adapted from Dr. Glen’s presentation at the 2014 meeting of the Association for Research in Vision and Ophthalmology. Dr. Glen has no financial interest in the subject matter.