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92 EW GLAUCOMA March 2013 February 2011 Advanced glaucoma patients at the wheel by Maxine Lipner EyeWorld Senior Contributing Writer How visual field loss affects road safety J ust because a patient has advanced glaucoma does not necessarily mean he or she has been precluded from driving. However, even those who handily pass traditional Snellen motor vehicle eye tests may be a hazard on the road, according to Shiho KunimatsuSanuki, M.D., assistant professor of ophthalmology, Tohoku University Graduate School of Medicine, Sendai, Japan. Dr. Kunimatsu-Sanuki recently led a first-of-its-kind study considering whether visual field loss correlates with frequency of collision. This found that advanced glaucoma patients were about twice as likely to have accidents as normal controls. Troubling standards Dr. Kunimatsu-Sanuki and colleagues undertook the study spurred by the knowledge that driving standards involving vision are often incomplete. "Patients with good (Snellen) visual acuity have no minimum visual field requirement in the current law," Dr. Kunimatsu-Sanuki said. In Japan, she pointed out the standard for a driver's license demands binocular visual acuity of 20/30 or more or monocular visual acuity of 10/30 or more. "Only if the subject has monocular vision of less than 10/30 is a horizontal visual field of 150 degrees or more required in the better eye," she said. This can leave potentially dangerous drivers on the road. "Currently, even advanced glaucoma patients can retain a driver's license if their (Snellen) visual acuity is good," Dr. Kunimatsu-Sanuki said. However, she pointed out that many of the patients have expressed a lack of confidence in continuing to drive in cases where there is no clear standard. Those with 20/20 Snellen acuity may, for example, have peripheral field loss as the result of glaucoma. This restricts the ability of drivers to see what is coming from the left or the right, Dr. Kunimatsu-Sanuki explained. "For example, some glaucoma patients said that, 'It is difficult to see a right turn signal of an The study used a driving simulator to determine how subjects would react to real-world situations, such as when a child rushes out in front of a car, as seen here. Source: Shiho Kunimatsu-Sanuki, M.D. oncoming car at the intersection or on the street, and when I was driving I was surprised when an oncoming car suddenly made a right turn,'" Dr. Kunimatsu-Sanuki said. "Some motor vehicle collisions seemed to be happening due to visual field restriction." Spurred by this, Dr. Kunimatsu-Sanuki set out to study the correlation between visual field defects and motor vehicle collision. "The question that we asked was, 'Are visual field defects associated with an increased risk of motor vehicle collisions?'" Dr. KunimatsuSanuki said. She noted that the literature on this had been inconsistent and often centered on patients who suffered only mild visual field defects. "We wanted to study the characteristics of patients with glaucoma specifically and used only subjects with advanced glaucoma to obtain clearer results," Dr. KunimatsuSanuki said. In the study, which included 36 patients with advanced glaucoma and 36 age-matched controls, a driving simulator was used to determine how subjects would react to realworld situations. Each subject was given two minutes to get familiarized with the driving simulator and to practice on the training course, which included 18 different scenarios. Included here were a myriad of potential trouble spots such as a child running out into the street or unexpected road hazards, as well as mundane stop signs and traffic lights. Breaking, response times, and the number of collisions were all recorded here. In terms of collision frequency, investigators found significant differences between the advanced glaucoma patients and the controls. The number of collisions that occurred for those with glaucoma was 222 as opposed to 118 for controls. Those with glaucoma were also less apt to break during a collision. In 44 of the accidents involving those with advanced glaucoma, the break was never applied compared with only 10 instances involving normal control drivers. Accident patterns The study also honed in on what could be expected with different types of visual field loss, with some interesting findings, Dr. KunimatsuSanuki observed. "Patients with the loss of the upper part of the field had motor vehicle collisions related to their inability to see stop signs," she said. "Meanwhile, patients with loss of the lower part of the field had motor vehicle collisions caused by their inability to see people and cars coming into their field of view." All of the situations were of deep potential concern but some were particularly troubling. "We found that the most dangerous scenarios were when oncoming cars turned in front of the driver or when children rushed out in front of the car," Dr. Kunimatsu-Sanuki said. One unexpected scenario of concern occurred for those with lower visual field loss. When their eyes were directed at the traffic lights above them, they lost track of what was going on in the road in front of them, Dr. Kunimatsu-Sanuki noted. Investigators concluded that those with advanced field loss tended to be at increased risk of hazardous driving. "We found an overall correlation between field loss and dangerous driving as well as specific dangerous scenarios for different types of field loss," Dr. KunimatsuSanuki said. She urged practitioners to broach the subject with their glaucoma patients. "It is necessary to make the patients aware of their visual field loss and for the practitioner to explain specific dangerous situations while driving," she said. Going forward, Dr. KunimatsuSanuki hopes that some of the technology used for the study can be put to use in the field. In addition, she would like glaucoma patients alerted to the possibility of driving impairment. "We would like to see the use of driving simulators in driver's licensing examinations as well as training for those with mild symptoms to help them become aware of their limits," she said. EW Editors' note: Dr. Kunimatsu-Sanuki has no financial interests related to this article. Contact information Kunimatsu-Sanuki: shihok-tky@umin.ac.jp