Poor eyesight is an inconvenience, but in drivers it can be lethal. A new campaign is seeking to get motorists out of the driving seat and into the optician's chair.
"I didn't see him, officer" is a common cry at the scene of a road accident, and is open to all kinds of interpretation.
But new figures suggest many drivers could mean it quite literally, because 13 million - one in three - in the UK are taking to the roads without having had a recent eye test.
Although it's illegal to drive with uncorrected poor vision - carrying a fine of up to £1,000, three penalty points and possible disqualification - drivers are complacent, says the report from the Royal National Institute of the Blind (RNIB).
1. Drivers with cataracts have cloudy vision and are particularly affected by glare from headlights at night
2. Myopia, or short-sightedness, affects 20% of the population. Inability to focus on objects in the distance causes blurring
3. Untreated glaucoma causes loss of peripheral vision. The brain 'fills in' what's missing so the sufferer may be unaware for a while
These images are only indications of a selection of eye conditions - all drivers are advised to have a full eye test every two years
Are Britain's road jammed with people who can't see properly?
We don't know for sure how many fuzzy-visioned motorists are out on the roads, and although forces carry out local crackdowns police don't collate national figures on the number caught out during checks.
A study in 1999 suggested one in 10 drivers' eyesight failed to meet the legal minimum standard, while one in 10 had never had a test, said road safety campaign Brake.
So should we be worried? Yes, say optometrists, and not just for our safety on the roads, but for our long-term eye health.
A day of action on Wednesday by the RNIB focuses on the perils of driving with poor eyesight, but every year it has to hammer home the message that eye tests should be carried out every two years.
As a nation we are still failing to take heed, leaving us and others particularly vulnerable when it comes to navigating a vehicle around Britain's roads.
Both young and old are shrugging the responsibility of getting their sight checked, says optometrist Marek Karas, although a recent RNIB survey found the worst offenders were drivers aged 25-44 years, 43% of whom admitted to not having had a test in the previous two years.
Legs cut off
"The public doesn't understand how sight loss happens," says Mr Karas.
"Even though people think their vision is good it's all quite subjective."
Even if your sight is good, an eye check will detect conditions such as high blood pressure, early diabetes, age-related sight loss, and a range of neurological conditions.
One in 10 of the over-65s are likely to register some kind of sight loss, rising to one in four in the over-75s, and yet at 70 drivers are only required to self-certify to the DVLA that they are fit to drive.
Some people cite vanity as their reason for avoiding an eye test
The only circumstances in which a driving test is re-taken - which includes a rudimentary sight test - is when a magistrate orders it in the event of an accident coming to court, says the Driving Standards Agency.
Optometrist and chairman of charity the Eyecare Trust, Iain Anderson, says he believes all drivers should have to prove to the DVLA, every five years, they've taken a recent test.
"People kill people in cars, if it could save a few it would be worth it."
When the charity took part in a spot-check exercise with the police Mr Anderson witnessed an older man who couldn't read the number plate of the officer's car, although he was leaning on its boot.
"He was driving a van and a trailer, and knew perfectly well he couldn't see. They didn't let him drive away, I think his wife was quite pleased."
RULES OF THE ROAD
Drivers must be able to read, in a good light, a number plate from 20.5m (67.3ft)
Driving with uncorrected defective vision is an offence
Drivers who need glasses or contacts should always wear them while driving
Most in his field could cite a similar extreme case, but all drivers should be taking responsibility for their ability to drive safely and legally.
"The older ones often don't come because they are worried they will be stopped from driving. They would feel as if they had had their legs cut off. But I don't understand it with the younger people. They need to realise these problems can creep up on you."
One major turn-off is cost - sight tests range from £17 to £30 - concedes Mr Karas, although many don't realise they might be eligible for a free test.
But people may be squeamish about eyes or had vanity in mind, he adds. In additional research done for the RNIB's report at Warwick University on people who don't wear glasses, 65% of those who failed a basic eye chart test were drivers. A third of the total sample who failed said they were not surprised and had suspicions their sight was not perfect.
"Many said they felt squeamish about it, or that getting glasses might interfere with their social activities."