UK drivers are being urged to test their eyesight after a DVLA survey suggested 50% of motorists were not aware of the minimum standards needed for a licence.
Drivers must be able to read a number plate from 20m (65ft) away.
But the agency's survey found only half of drivers knew about the eye test and used it to regularly self-check, as they are legally required to do.
Those who do not pass the test should visit an optician, a DVLA doctor said.
Learner drivers must pass the eye test as part of their practical exam - and are then legally obliged to ensure their sight remains good enough to drive thereafter.
The DVLA's Wyn Parry warned vision can "naturally deteriorate over time", adding that regular checks to ensure good eyesight were "essential for safe driving".