Functional Assessment of the Older Driver

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, contrast sensitivity, 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 relax the requirements 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 and range from no requirement to about 140°.

Older drivers often require referral to an ophthalmologist for comprehensive testing if visual issues related to driving are present.

Changes to motor function with aging include

• Decreased flexibility, strength, and balance

• Slowed gait speed and reaction time

Medical conditions that can impact motor function include

• Neurologic impairment (eg, due to stroke, Parkinson disease, amyotrophic lateral sclerosis, or brain tumor)

• Diabetes that causes sensorimotor impairment and/or amputation

• Arthritic conditions

• Frailty and weakness from normal aging or medical disorders

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

• Motor speed, reaction time, 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 seconds may indicate an increased risk of an MVC. Practitioners should try to determine the reason for impairment (eg, parkinsonism, arthritis) 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 or when backing up. 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. Many newer vehicles come equipped with blind spot detection mirrors to assist drivers in monitoring their blind spot during lane changes. Decreased range of motion in the extremities may impair ability to operate vehicle controls safely and efficiently.

• Strength in upper and lower extremities should be assessed qualitatively (in terms of meeting the needs of driving a vehicle). Strength can be assessed by muscle strength testing on physical examination; decreased lower extremity strength on the right side has the potential to impair ability to operate foot controls and react quickly to driving situations.

• Lower extremity proprioception and sensation should be evaluated. Decreased sensation, particularly in the right lower extremity, can impair ability to safely operate the foot pedals.

• Tremor and other neurologic deficits should be noted and the need for referral to a neurologist determined.

Practitioners should consider motor function not only in relation to driving a vehicle but also in relation to patients' ability to get in and out of a vehicle and to function safely at the destination. Driving is just one part of patients getting to where they need to go. 

Referral to physical and occupational therapy may help determine whether interventions are required to improve motor function. Occupational therapists who specialize in driving rehabilitation can provide comprehensive testing of motor function related to driving ability. Recommendations for those who have motor deficits may include use of specialized adapted driving equipment (eg, hand controls, steering wheel spinner knobs).

Changes in cognitive function with aging that may affect driving include

• Declines in aspects of cognition that impact working and/or semantic memory

• Slowed speed of processing

• Decreased basic and complex attention skills (eg, sustained and divided attention)

• Decreased executive function (eg, trip planning, working memory)

• Decreased visual processing and perceptual skills

Medical conditions (including use of drugs needed to treat them) that can impact cognitive function include

• Psychologic factors (eg, anxiety, depression)

• Neurologic disorders (eg, stroke, Parkinson disease, mild cognitive impairment, Alzheimer disease and related dementias, traumatic brain injury, multiple sclerosis)

• Sleep disorders

• Cardiac disorders

• Diabetes

The incidence of cognitive impairment increases in people ≥ 65. People with cognitive impairment often do not recognize their limitations, do not modify or restrict their driving, and are at higher risk of MVCs; risk increases with severity of impairment. Those with insight into their cognitive limitations often modify their driving to better accommodate their limitations (eg, driving in familiar areas, at less busy times of the day, and during daytime hours), resulting in safer driving.

Although no one screening test has been found to completely and accurately predict driving safety, some are able to provide some level of predictability regarding the potential for impaired driving performance in older adults, can be done in the practitioner's office, and can be used to determine who may need to be referred to a driving rehabilitation specialist. Combinations of some of the following screening tests help improve prediction accuracy:

• The Freund Clock Drawing Test: This brief test is used to screen for visual perception, visuospatial skills, selective attention, semantic memory, and executive skills. Scores of 4 and under indicate potential concern related to driving.

• The Trail-Making Test: These tests are used to assess attention and visual scanning. Part A is easier and should always be given prior to part B. Part B is more challenging and assesses alternating attention and executive function. Drivers with an abnormal score on Part B (eg, > 180 seconds) may be candidates for more specialized testing by a driving rehabilitation specialist.

• The Mini-Mental State Examination: Examination of mental status is done to screen 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.

• Montreal Cognitive Assessment (MoCA): This 30-item test is used to screen for mild cognitive impairment in older adults by testing attention, concentration, executive functions, memory, language, visuospatial skills, abstraction, calculation, and orientation. Low scores have been associated with increased risk of driving impairment. It should be noted that practitioners must be trained and certified to give the MoCA.

Multi-model approaches that include a combination of screening tests are more useful in predicting driving performance in older adults with medical impairments, but none approaches 100% accuracy in prediction. Most of these multi-model screening tools (eg, probability calculator for dementia or stroke, 4 C’s) are easily administered in most office settings and provide an outcome score that is more predictive of risk of unsafe driving and need for driving intervention. Further information on multi-model approaches can be found in the American Geriatrics Society’s Clinician’s Guide to Assessing and Counseling Older Drivers, 4th Edition.

People with mild cognitive impairment may benefit from referral to occupational therapists or speech pathologists to help provide various interventions to improve function (eg, compensatory strategies). Additionally, referral may be indicated for neuropsychologic assessment to assist in determining underlying diagnoses and further recommendations.