EDITORIAL Driving with Parkinson’s Disease: More Than Meets the Eye Driving is one of the mainstays of modern life. Most members of our society use the automobile as their primary source of transportation,1,2 and driving oneself is a critical feature of daily living. Driving frequently defines an individual’s independence and competency, and driving cessation has been associated with depression and social isolation.1–3 What does the act of driving entail? Driving has been described as a combination of a continuous tracking task, a multiple-choice reaction time task, actions involving coordinated sequential motor movements of the limbs, and judgment, planning, perception, and attentional tasks.4 Safe automobile driving requires a driver to perform these multiple competing tasks, attend to a number of objects and ongoing events, and simultaneously monitor traffic with central and peripheral vision.1 Clearly, safe driving is not merely a function of vision. It is therefore remarkable that in most of the United States, the only testing requirements for legal driving in all the years that follow initial issue of a driving license relate to visual acuity and visual field.5 Furthermore, in many states, mandatory rescreening of even elementary visual functions is no longer required. In this setting of a relatively ambiguous legal environment that varies from state to state, physicians, especially neurologists and ophthalmologists, often find themselves in the proverbial driver’s seat when it comes to determining whether a patient is actually safe to drive. Most neurologists, especially those specialists who care for patients with Parkinson’s disease, do not even systematically test visual acuity and visual fields on their patients. Although these simple tests of visual function are readily available, they fall far short in determining a patient’s true ability to safely command a vehicle and the risk for crash involvement.1 The issue of driving safety in neurologically impaired individuals has been a particularly important area of investigation among patients with such common and progressive degenerative diseases as Alzheimer’s and Parkinson’s diseases.4,6 –12 In addition to motor dysfunction, Parkinson’s disease causes abnormalities in cognition, sleep regulation, autonomic function, visual processing, attention, and perception.13,14 Previous studies have confirmed impairments in driving safety among patients with Parkinson’s disease, as measured by epidemiological studies, driving simulators, and road tests.4,8 –12 The current article in Annals by Uc and colleagues15 from the University of Iowa takes us further down the road in our understanding of the degree of driving impairment, some of the mechanisms at play, and the predictive value of various standardized measures of visual, cognitive, and motor function among Parkinson’s disease patients. The authors used an instrumented vehicle to test the hypothesis that drivers with mild to moderate Parkinson’s disease have impairments on a landmark and traffic sign identification task and to investigate whether these impairments would increase the risk for safety errors and crash potential. A battery of visual, cognitive, and motor tests were performed to assess whether patient driving performance and safety errors could be predicted independently. The 79 drivers with Parkinson’s disease, compared with the 151 neurologically normal older adults, identified significantly fewer landmarks and traffic signs and committed more at-fault safety errors. The most important predictors of landmark and traffic sign identification rate were performances on Useful Field of View (which tests visual speed of processing and attention) and Complex Figure Test–Copy (which assesses visuospatial abilities). Although visual acuity measurements were included among the off-road battery of tests that correlated with poor performance on the onroad identification task, standardized visual field testing was not performed. Trail Making Test (B-A), a measure of cognitive flexibility independent of motor function, was the only independent predictor of at-fault safety errors in drivers with Parkinson’s disease. All Parkinson’s disease patients were tested in the “on” condition, and the total daily L-dopa–equivalent amount did not correlate with the performance on the search and recognition task or safety errors. As the authors conclude, cognitive and visual deficits associated with Parkinson’s disease result in impaired visual search and object recognition while driving, and the increased cognitive load resulting from this visual search task degrades these patients’ driving safety. Impairments in attentional control, working memory, executive functions, and visuospatial ability are present early in the course of Parkinson’s disease,14 even recognizing its taxonomy as a primarily motor disorder. The predictors of performance on the landmark and traffic identification task demonstrated in this study are consistent with the cognitive processes required for normal visual search, such as planning, visuospatial abilities, and attention.13,16 It should be noted that a subset of drivers with Parkinson’s disease performed relatively well on the identi- © 2006 American Neurological Association Published by Wiley-Liss, Inc., through Wiley Subscription Services 387 fication task, and about 17% of them made no safety errors.15 How can we as neurologists determine who among our Parkinson’s disease patients are safe to drive? From this study it would appear that certain available standardized neuropsychological and visual tests provide indices of some of the key functional abilities in Parkinson’s disease patients that are important for driving. This may obviate the need for all patients with neurological impairment to undergo sophisticated on-road testing to determine their driving safety. Clearly, however, simple tests of primary visual functions such as visual acuity and visual field are not sufficient in that regard. Indeed, the currently prevalent indices for determining driving legality, and presumably safety, among drivers in the United States is woefully inadequate, especially in the setting of neurological disease that affects attention, cognition, planning, spatial working memory, and visual search. This study confirms that drivers with Parkinson’s disease are significantly less safe than age-matched control drivers. One of the most obvious implications of this and other studies4,8 –12 is that drivers with this diagnosis require education regarding their driving capabilities, as well as continuous monitoring for progression of their deficits. It is unrealistic to expect Parkinson’s disease patients to fully recognize their limitations in this regard. The question remains whether early identification and application of rehabilitation targeted to those aspects of driving most troublesome for this group of patients would improve their driving performance and prolong their independence, without risking their safety and the safety of others. This study was supported by the NEI core grant P30-EY06360, and by Research to Prevent Blindness. Nancy J. Newman, MD Departments of Ophthalmology, Neurology, and Neurological Surgery Emory University School of Medicine Atlanta, GA 388 Annals of Neurology Vol 60 No 4 October 2006 References 1. Owsley C, McGwin G. Vision impairment and driving. Surv Ophthalmol 1999;43:535–550. 2. DeCarlo DK, Scilley K, Wells J, Owsley C. Driving habits and health-related quality of life in patients with age-related maculopathy. Optom Vis Sci 2003;80:207–213. 3. Marottoli RA, Mendes de Leon CF, Glass TA, et al. Driving cessation and increased depressive symptoms: prospective evidence from the New Haven EPESE. J Am Geriatr Soc 1997; 45:202–206. 4. Dubinsky RM, Gray C, Husted D, et al. Driving in Parkinson’s disease. Neurology 1991;41:517–520. 5. American Association of Motor Vehicle Administrators. Summary of medical advisory board practices in the United States (June 18, 2003). Available at: http://www.aamva.org/searchresults. htm?query⫽vision. Accessed September 5, 2006. 6. Uc EY, Rizzo M, Anderson SW, et al. Driver route-following and safety errors in early Alzheimer disease. Neurology 2004; 63:832– 837. 7. Uc EY, Rizzo M, Anderson SW, et al. Driver landmark and traffic sign identification in early Alzheimer’s disease. J Neurol Neurosurg Psychiatry 2005;76:764 –768. 8. Zesiewiczs TA, Cimino CR, Malek AR, et al. Driving safety in Parkinson’s disease. Neurology 2002;59:1787–1788. 9. Meindorfner C, Korner Y, Moller JC, et al. Driving in Parkinson’s disease: mobility, accidents, and sudden onset of sleep at the wheel. Mov Disord 2005;20:832– 842. 10. Stolwyk RJ, Triggs TJ, Charlton JL, et al. Impact of internal versus external cueing on driving performance in people with Parkinson’s disease. Mov Disord 2005;20:846 – 857. 11. Wood JM, Worringham C, Kerr G, et al. Quantitative assessment of driving performance in Parkinson’s disease. J Neurol Neurosurg Psychiatry 2005;76:176 –180. 12. Worringham CJ, Wood JM, Kerr GK, Silburn PA. Predictors of driving assessment outcome in Parkinson’s disease. Mov Disord 2005;21:230 –235. 13. Poliakoff E, O’Boyle DJ, Moore AP, et al. Orienting of attention and Parkinson’s disease: tactile inhibition of return and response inhibition. Brain 2003;126:2081–2092. 14. Uc EY, Rizzo M, Anderson SW, et al. Visual dysfunction in Parkinson disease without dementia. Neurology 2005;65: 1907–1913. 15. Uc EY, Rizzo M, Anderson SW, et al. Impaired visual search in drivers with Parkinson’s disease. Ann Neurol 2006;60: 407– 413. 16. Kennard C. Scanpaths: the path to understanding abnormal cognitive processing in neurological disease. Ann N Y Acad Sci 2002;956:242–249.