Although there is little evidence to support an association between vision and car accidents, a vision screening law in Florida that targets drivers age 80 and older seems to have reduced the number of adults in this age range who die from motor vehicle collisions. The findings are published in the November issue of Archives of Ophthalmology.

"Older drivers represent the fastest-growing segment of the driving population," write Gerald McGwin Jr., M.S., Ph.D. (University of Alabama at Birmingham) and colleagues. "As this segment of the population expands, so too have public safety concerns, given older drivers' increased rate of motor vehicle collision involvement per mile driven. Research has suggested that this increase may be partly attributed to medical, functional and cognitive impairments."

Visual acuity has not been firmly linked to involvement in motor vehicle collisions, but that did not stop the State of Florida from implementing a law that required vision tests for drivers 80 years and older before renewing licenses in 2004. This change in law combined with data from the National Highway Traffic Safety Administration and the U.S. Census Bureau on rates of motor vehicle collision deaths from 2001 to 2006 provided McGwin Jr. and colleagues the necessary tools for a quasi-experimental analysis. The researchers also looked at death rates from motor vehicle accidents in Alabama and Georgia, neighboring states that had no change in license renewal policy.

Between 2001 and 2006, Florida saw an overall but non-significant increase in its overall death rate from motor vehicle collisions. However, drivers age 80 and older demonstrated a linear decrease in this rate. Compared to the period before the law (from 2001 to 2003), the fatality rate in the period after the law (from 2004 to 2006) among all drivers increased from 14.61 per 100,000 persons per year to 14.75 per 100,000 - a 6% increase. The rate specific to older drivers decreased from 16.03 per 100,000 persons per year to 10.76 per 100,000 - a 17% decrease. In the comparison states, Alabama and Georgia, there was no change in death rates among older drivers.

The authors try to explain the decrease in the decrease in death rates among older Floridian drivers: "Perhaps the most apparent reason is that the screening law removed visually impairment drivers from the road...However, in reality, the situation is significantly more complex."

According to the authors, only 7% of drivers were unable to receive a license renewal. This means that only a small percentage of drivers were removed from the road because of failure to meet vision standards. In addition, it is possible that many drivers who did not pass the vision requirement sought vision care and were able to receive a license after being treated. This could have improved overall vision function of drivers. A third suggestion is that drivers with poor vision selected themselves to be removed from the road because they assumed that they would not receive a renewal.

"Ultimately, whether the vision screening law is responsible for the observed reduction in fatality rates because of the identification of visually impaired drivers or via another, yet related, mechanism may be inconsequential from a public safety perspective," conclude the researchers. "However, the importance of driving to the well-being of older adults suggests that isolating the true mechanism responsible for the decline is in fact important."

The Impact of a Vision Screening Law on Older Driver Fatality Rates
Gerald McGwin Jr; Scott A. Sarrels; Russell Griffin; Cynthia Owsley; Loring W. Rue III
Archives of Ophthalmology (2008). 126[11]: pp. 1544 - 1547.
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: Peter M Crosta

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