Motor vehicle collision injuries and sensory impairments of older drivers

Age and Ageing, July, 1994 by Lon W. McCloskey, Thomas D. Koepsell, Marsha E. Wolf, David M. Buchner

Summary

To determine whether ocular disease, impaired vision, or diminished hearing might increase the risk of motor vehicle collision injuries in older drivers, we conducted a population-based case-control study at a large Health Maintenance Organization (HMO). All study subjects were HMO members who were licensed drivers age 65 or over. Cases were drivers treated for injuries sustained in a police-reported collision that occurred in 1987 or 1988. Controls were drivers who experienced no such injury during the study years and were matched to cases by age, sex, and county of residence.

We found no clear evidence that ocular diseases or impaired visual acuity, as customarily recorded in the medical record, increased the risk of an injury collision. Although there was no significant association between impaired hearing and injury collision, we found that subjects who used hearing aids while driving had about twice the risk of others (adjusted RR 2.1; 95% CI 1.2-3.8).

We conclude that mild reductions in static visual acuity have little effect on the risk of injury collisions for older drivers. Moreover, the types of vision tests needed to identify elderly drivers at increased risk are not those that are generally administrered during routine optometry examinations or at the time of licence renewal. Further research is needed to verify a possible increase in risk among elderly drivers using hearing aids.

Introduction

Involvement in motor vehicle collisions steadily declines with age, both in absolute numbers of collisions and in age-specific collision rates (1)(2). Compared with 40-year-old drivers, 80-year-old drivers are less than half as likely to have a motor vehicle collision (MVC) whereas 18-year-old drivers have more than twice the risk (1). This continuous decline in crash involvement with advancing age appears to result from reductions in annual miles driven by the older cohorts. When expressed as the number of collisions per million miles driven, the relationship of the MVC rate to age graphically describes a U-shaped pattern in which the risk of crash involvement is lowest for drivers 40-55 years old and is highest for both the youngest and the oldest drivers. Collision rates increase appreciably at about age 70 and more rapidly after age 80 (1)(2) until the MVC rate in the oldest drivers exceeds that of 20-year-olds. Although there do not appear to be substantial differences in crash severity by age, the consequences of an MVC are more serious for aged drivers. The fatality rates for drivers sustaining severe injuries increase significantly after age 70 and driver mortality rates per mile driven rise sharply after age 75 (1).

Driving is a complex task that depends on sensory acuity, ability to process multiple environmental stimuli at once, cognitive capacity to draw correct inferences from incoming information and to formulate an appropriate response, and motor capacity to operate the vehicle's controls. Although impairments in any of these faculties might increase the crash risk, some investigators propose that the presence of sensory impairments is particularly important (3). It is well known that the prevalence of impaired vision and hearing increases with age (4). Tests of static visual acuity are frequently administered and the results are readily obtainable from the medical records of most elderly persons--a convenient, pragmatic source of information that might be used to predict a driver's risk of injury collision if it could be established that these tests can actually identify individuals at increased risk. To evaluate the roles of impaired static visual acuity, ocular disorders, and impaired hearing as potential risk factors for motor vehicle injury collisions, we studied a population of elderly, licensed drivers in Washington State.

Methods

We concluded a matched case-control study using members of Group Health Cooperative of Puget Sound (GHC), a consumer-owned HMO in Washington State having an enrolment of more than 400000. Study subjects were elderly, licensed drivers who resided in eight Washington counties and who received their medical care at GHC facilities located in King, Pierce, Snohomish, Thurston or Kitsap county. For purposes of eligibility determination and record review, all subjects had a reference date. For cases this was the date of the index motor vehicle collision, and for controls it was the reference date for the corresponding case. All study subjects were required to be licensed, active drivers as of the reference date.

The cases were drivers who sought medical care, within 7 days, for injuries sustained in an MVC that was reported to the police and that occurred when they were aged 65 or older. In Washington State, the legal criteria for reporting an MVC to the police were physical damage of $300 or more to any single vehicle or any injury to any person in any of the involved vehicles. The law defines injury in this context as subjective complaints, not dependent on physician or paramedical evaluations. We initially identified potential cases from police reports of motor vehicle collisions in 1987 and 1988 and then confirmed each case's eligibility by examining GHC medical records. Cases had to have on record at least one prior visit to a GHC physician in order to qualify. For those initially treated at facilities outside the Group Health system, we confirmed eligibility by reviewing either the summary reports of treatment or charges for such treatment on file in their GHC records.