‘Legal’ doesn’t always mean ‘safe’ in drivers’ vision

June 13, 2019
Glaucoma patients were five times as likely to get in a motor vehicle accident compared to similarly aged drivers, per a new study that illustrates a glaring problem with drivers’ vision requirements.

'Safe' is in the eye of the beholder when it comes to how states' legally define drivers' vision versus how patients actually see the road, discrepancies all the more consequential with new research concerning glaucoma patients.

Presented at The Association for Research in Vision and Ophthalmology's annual meeting this past April, a research paper from Wills Eye Hospital in Philadelphia found the rate of motor vehicle accidents (MVAs) among patients with moderate glaucoma and mild vision loss was nearly five times higher than expected for drivers of similar age. Moreover, these patients still technically met legal requirements for driving. Such findings demonstrate a common, poignant discussion about when patients should give up their keys, especially when state laws say otherwise.

Established independently by each state, legal standards for vision and driving always begin with best-corrected visual acuity (BCVA) requirements. That said, not every state takes the extra step to include peripheral vision or other considerations, such as night vision, visual perception and eye movements.

Pennsylvania, the residence of this particular study cohort, is one such state where vision requirements go beyond simple BCVA to include a horizontal field of view of at least 120 degrees, as well as other restrictions for drivers with less than 20/60 BCVA. Still, among the 161 patients with moderate open-angle glaucoma studied over the course of four years, researchers found an increased rate of MVAs despite their having legally qualified vision.

Per a hospital news release, researchers found between 5 and 10% of these glaucoma patients reported MVAs during the study period as compared with a 1.1% rate of similarly aged (61-65 years old) Pennsylvanians reporting MVAs in 2017. But, that's not all.

"One finding that stood out was that, interestingly, it was the peripheral vision in the worst eye that made the biggest difference," notes study presenter Jonathan Myers, M.D., chief of the Wills Eye Hospital Glaucoma Service. "That suggests that in some patients, significant blind spots existed, which could have been a liability for driving."

Significantly, this isn't the first study to reach such a conclusion. A 2016 study published in JAMA Ophthalmology examined the association between glaucoma and MVAs, and found impaired visual field was independently associated with at-fault MVA involvement whereas visual acuity and binocular contrast sensitivity impairments do not. That's particularly concerning as many state laws mandate BCVA and, sometimes, contrast sensitivity for drivers' licensing.

While researchers note further study is necessary, this evidence—compounded by data that shows Americans are living longer than ever with the over-65 group projected to more than double by 2060—suggests eye doctors be prepared to stand firm when having the talk. That is, the safe driving talk.

A difficult conversation

In some cases, these patients will present as a result of failing a DMV visual screening test and they may have received a form for their eye doctor to complete before they can legally receive their license renewal. In other cases, an examination may reveal vision loss, or a family member may approach the doctor about the patient's diminishing vision capabilities. As outlined in a 2015 AOA Focus article on the subject, determining whether a patient is legally fit to drive involves a number of steps:

  1. Assess why vision is declining. Determine whether the cause is natural or disease-related, and what interventions might be able to slow, stop or reverse these changes.

  2. Perform tests. Use a battery of tests to determine if a patient is still safe to drive, including a standard visual acuity chart; contrast sensitivity testing; glare sensitivity response; and other functional tests that may help determine a patient's visual awareness and ability to process information in a specific visual area without eye or head movement.

  3. Discuss vision changes with the patient. Consider framing these vision changes as they relate to everyday activities, including driving, to help the patient understand their potential impact. So, too, tactfully break the news to patients when they can't drive. Emphasize that it's your responsibility as their eye doctor to inform them when they no longer meet vision requirements and report it to the DMV.

    "Whatever course of action is taken, it is important for the optometrist to openly and truthfully explain to the patient the potential risks and dangers to the driver and others when vision and health become compromised," concludes the AOA Ethics Forum case study on vision and driving. "The reality of removing driving privileges often has significant consequences as this represents a significant loss of independence.

    "The optometrist has the obligation to weigh all of the components of the case to create an appropriate treatment plan and convey the findings to the patient."
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