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Driving with Parkinson's disease More than meets the eye.

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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
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
Annals of Neurology
Vol 60
No 4
October 2006
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meet, disease, morel, parkinson, eye, driving
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