Jonathan Myers, MD, of the Wills Eye Hospital, discusses a study examining the rate of car accidents among glaucoma patients.
As the US population ages, problems with vision are becoming more and more common. Jonathan Myers, MD, director of Glaucoma Service at Wills Eye Hospital, sat down with MD Magazine® at the 2019 Annual Meeting of the Association for Research in Vision and Ophthalmology to discuss the results of a study that examined the association between glaucoma patients and the rate of car accidents.
They found that, despite not being legally blind, the rate of car accideents among glaucoma patients was nearly 3 times the national average. As a patient's vision begins to decline, doctors are often put in a position where they have to make difficult decisions regarding their patients' safety.
MD Mag: What is the prevalence of car accidents among glaucoma patients?
Myers: We prospectively looked at a group of about 120 patients with varying degrees of glaucoma. the study looked at many aspects including vision, visual field or, peripheral vision testing. It looked at their ability to do certain normal daily activities like matching socks looked at contrast sensitivity looking at the question of whether you can tell not just black or white but can you discriminate dark gray from light gray and these particular aspects of this study asked the patients each year, over five years, to tell us if they had been involved as a driver in any motor vehicle accidents. What we found was a lot of people were involved in motor vehicle accidents. Each year between 5 and 10% we started with about a 120 plus patients and by the end still had just under 100 patients. So, it had good retention but still each year about 5 to 10% of the patients and these patients were not legally blind and generally they were patients who had vision that qualified for driving. That's about twice, and maybe one could argue three times, the national average for motor vehicle accident rates. So, that's significantly more in these patients who have glaucoma again many of them most of them not severe glaucoma.
MD Mag: Are there any predictors that could indicate an increased risk of being in an accident, even if a patient is not legally blind.
Another thing we found in the study was that predictors of the patients who were more likely to have higher accidents were, in univariate analysis, things like the visual acuity, the binocular visual acuity — that makes sense you see less well. Interestingly, it was the peripheral vision in the worst eye that made the bigger difference. So, if you have the view of worst peripheral vision and in your worse eye that probably means that there's some blind spot out there that is a liability for driving. Again, not something that can be assessed outside of the ophthalmologist office.
MD Mag: Is it concerning that patients who are not legally blind are involved in more accidents?
It is concerning, both, for the safety of our patients and the safety of those around them. First of all, we have to consider what the legal requirements are for driving and those are somewhat historical and not entirely evidence-based. For most states, that is 20/40 vision for night driving and 20/70 vision for daytime driving although that part does vary some. 20/40 means that you can see at 20 feet what a normal person could see at 40 feet — so, about half as sharp. So, 20/70 even more so and you have to have at least a hundred twenty degrees of vision in the horizontal meridian. So, 120 degrees is about 12 times your fist at arm's length so it's quite a bit to either side. So, it's quite a bit of range; of course, people in primary care don't have the ability to assess visual field so those are the legal requirements and most of our patients and the vast majority met those legal requirements and still were a greater risk of having accidents.
MD Mag: Should ophthalmologists advise patients to stop driving, even if they are not yet considered legally blind?
It's a common predicament especially as we have an increasingly aging population. Of course, vision disturbances more common as we grow older. The most common causes of reduced vision in the order are cataracts, which can be fixed, followed by in a Caucasian population macular degeneration and in blacks or Hispanics, glaucoma. Those second, of course, not reversible. So, it's not uncommon to have these conversations, of course, driving isn't just about driving is about independence for a lot of elderly people who may not have other aspects of support so these can be very emotional conversations, very difficult. Most ophthalmologists did not go into ophthalmology because of the desire to do police work and so it's a very awkward business. Some states do have mandatory reporting laws if a patient does not make criteria for driving and so there is an obligation. Most patients will stop driving after continued counseling but, it's important for ophthalmologist have these discussions.
Of course, there are a lot of non-eye reasons to for a patient not to be able to drive not just orthopedic reasons but let's face it as we all get older our reaction times get slower and sometimes the patient's cognitive ability or their reactive ability is a big part of why they not may not be safe for driving and that may not be something the ophthalmologist should be making the call on.