If a person's vision changes and isn't questioned upon renewal of their license, drivers may be on the road without meeting vision criteria.

Once people start to become visually impaired, it’s usually time to have them consider not driving anymore, especially if they don’t meet the necessary requirements to have a driver’s license in the first place. In a recent study, researchers aimed to determine the proportion of these patients who continue to drive despite not meeting license criteria.

A total of 335 adults with low vision took a driving habits survey. Visual acuity and contrast sensitivity were measured, and the team compared license and driving status against vision criteria for a driver’s license in each participant’s home state.

Of the participants with a valid driver’s license, 141 (55%) had good enough vision to meet their home state’s license criteria. Of the 134 current drivers, 95 (70%) met their home state’s license criteria, while the rest were driving outside the bounds of license criteria in their state.

“This proportion grows even larger if severe to profound contrast sensitivity reduction was considered as disqualifying criteria,” the authors noted. “By comparison, a previous study reported that 77% of Alabamian drivers with age-related maculopathy would not meet vision criteria.”

Neglecting an applicant’s visual function at renewal allows some drivers to maintain their license despite a vision change. Some patients reported in previous studies that they have not had their vision tested for many license renewals.

“In some cases, this gap in testing may represent decades of potential visual degradation which goes unaccounted for in considering driving fitness and issuing license renewals,” the authors noted. “It is important to note that some subjects may have experienced vision loss within their most recent licensing cycle, giving their state licensing body no chance to detect the driver’s change in vision even with appropriate testing at each renewal.”

Among those who have a license, being a current driver was associated with younger age, better visual acuity and better contrast sensitivity.

The study concluded that many drivers do not possess adequate vision for a license renewal and that changes to licensure qualification and renewal procedures may be needed.