Functional assessment involves assessment of a patient’s visual, motor, and cognitive abilities. (See also Overview of the Older Driver.)
Adequate function in these areas is needed to drive safely. Most of these assessments 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 driving-related interventions, 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. A useful resource is the National Highway Traffic Safety Administration's Clinician's Guide to Assessing and Counseling Older Drivers, 4th edition.
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
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°.
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
Medical conditions that can impact motor function include
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) in order to determine its effect on driving and 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. 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.
Referral to physical and occupational therapy may help determine if 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
Medical conditions (including use of drugs needed to treat them) that can impact cognitive function include
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, during daytime hours), resulting in safer driving. Although no one test has been found to completely and accurately predict driving safety, some screening tests are able to provide some level of predictability regarding the potential for impaired driving performance in older adults and can be used to determine who may need to be referred to a driving rehabilitation specialist. These tests include the following:
The Freund Clock Drawing Test: This brief test screens 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 (Parts A and B): These tests 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 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.
Multi-model approaches that include a combination of brief screens are more useful in predicting driving performance in older adults with medical impairments, but none of these approaches is 100% accurate in prediction. Most of these multi-model screening tools (eg, probability calculator for dementia, 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 Chapter 3 of the National Highway Traffic Safety Administration'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.