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Functional Assessment of the Older Driver

by David B. Carr, MD, Peggy P. Barco, MS, BSW, OT/L

Functional assessment involves assessment of a patient’s visual, physical, and cognitive abilities. Adequate function in these areas is needed to drive safely. Most of a functional assessment can be done by primary health care practitioners, but specialists (eg, ophthalmologists, neuropsychologists, subspecialists, occupational and physical therapists, driving rehabilitation specialists) may need to be consulted. Identified deficits may require interventions (see Interventions with the Older Driver), including driving rehabilitation, assistive devices, reporting to the state Department of Motor Vehicles, driving restrictions or cessation, or a combination. Some complicated cases may be referred to state medical advisory boards. One useful resource is the American Geriatrics Society's Physician's Guide to Assessing and Counseling Older Drivers .

Visual function

Visual function is vital to safe driving. Age-related and pathologic changes in vision are common and can contribute to driving impairment.

Changes with aging include

  • Decreased retinal illuminance (amount of light reaching the retina), visual acuity, and peripheral vision

  • Presbyopia (decreased ability to accommodate), which impairs depth perception

  • Decreased ability to adapt to changes in light and heightened sensitivity to glare, which impair night driving

Ocular diseases common with aging include

  • Age-related macular degeneration

  • Cataracts

  • Glaucoma

  • Diabetic retinopathy

In many states, central visual acuity and peripheral vision are routinely tested by the Department of Motor Vehicles when a license is renewed. Most states require 20/40 visual acuity in at least one eye for unrestricted licensing (glasses or contacts are allowed). However, in some states, practitioners can extend the requirement pending medical justification. Additionally, some states have approved use of bioptics (a lens system with a telescope attached to a pair of glasses) for people with severely reduced vision. For horizontal peripheral vision, safe driving thresholds vary widely among states from no requirement to about 140°.

Tests of useful field of view (spatial area from which visual stimuli can be acquired during a single fixed glance) provide integrated measures of visual performance (eg, visual-processing speeds, visual-spatial attention, visual memory) and can be used to predict a higher risk of MVC. For example, the incidence of MVCs is 6 times higher when useful field of view is reduced by > 40%. However, field-of-view tests are not yet widely available for the in-office practitioner.

Older drivers often require referral to an ophthalmologist for comprehensive testing.

Physical function

Various parameters of physical function can be assessed in the office.

  • Motor speed, balance, and coordination can be assessed with the rapid-pace walk test. The patient is asked to walk a 3-m (10-ft) path, turn around, and walk back to the starting point as quickly as possible. If the patient normally walks with a walker or cane, it should be used during the test. A time of > 9 sec may indicate an increased risk of an MVC. Practitioners should try to determine the reason for impairment (eg, parkinsonism, arthritis) in order to create a treatment plan.

  • Range of motion should be tested in the cervical region and in all joints of the upper and lower extremities. Decreased cervical range of motion impairs ability to turn the head and scan for traffic (particularly in the blind spot). Older adults should have ≥ 30° of lateral rotation to each side; if range of motion is less, they can be referred to a physical therapist to improve range of motion or to a driving rehabilitation specialist for installation of larger, wide-angle mirrors in the vehicle. Decreased range of motion in the extremities impairs ability to operate vehicle controls.

  • Strength in upper and lower extremities should be assessed qualitatively (in terms of meeting the needs of driving a vehicle). Grip strength can be measured with a dynamometer. A grip strength of < 16 kg for men or < 14 kg for women may reflect decreased ability to manipulate the steering wheel.

  • Lower extremity proprioception and peripheral sensory function should be tested. Decreased sensation can impair ability to modulate pressure on foot controls.

Physical and occupational therapists who specialize in driving rehabilitation can provide comprehensive testing of motor function related to driving ability. A rehabilitation driving assessment sometimes also involves the specialist going out in a vehicle with the patient to evaluate actual driving skills. The vehicle used during the evaluation should be equipped with features that allow the specialist to maintain safe control (eg, passenger-side brake). Driving rehabilitation specialists can be located by contacting local rehabilitation facilities or going to www.driver-ed.org . However, in most states, the cost of a rehabilitation driving assessment is not covered by insurance (Medicare or private) and may be an out-of-pocket cost.

Cognitive function

The incidence of cognitive impairment increases in people ≥ 65. People with cognitive impairment often do not recognize their limitations and are at higher risk of MVCs; risk increases with severity of impairment. Although no one test has been found to completely and accurately predict driving safety, some tests are able to provide some level of predictability regarding impaired driving performance in older adults. These tests include the following:

  • The Clock Drawing Test: This brief test screens for visual perception, visuospatial skills, selective attention, and executive skills.

  • The Trail-Making Test (Part B): This test assesses attention and visual scanning. Part B assesses alternating attention and executive function. Part B can be found at the National Highway Traffic Safety Administration web site . Drivers with an abnormal score on Part B (eg, > 180 sec) may be candidates for more specialized testing by a driving rehabilitation specialist.

  • The Mini-Mental State Examination: Examination of mental status (see Examination of Mental Status) screens for cognitive impairments. However, this test has not been validated for use in determining driving privileges, and traffic safety experts do not agree whether it is a useful for this purpose.

  • Maze tests: Various maze tests (eg, the Snellgrove Maze Test) require people to navigate through a maze printed on paper. These tests help assess visual search and executive skills.

Drivers with mild cognitive impairment should be considered for referral for more precise neuropsychologic assessment.

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