New research shows that one in ten drivers would fail a driving test if they re-took it today, because of poor eyesight.

Nigel Charlesworth, spokesman for motoring organisation Green Flag, said: "Though simple eye tests are a standard procedure at the Driving Test Centre, there is still no compulsory re-test of a driver's sight until the age of 70.

"Many motorists are unaware of, or perhaps choose not to do anything about, their fading vision, and therefore don't realise they are unfit to drive."

Eyesight deteriorates rapidly over the age of 45, but tests are recommended every two years for all adults. A recent Mori survey revealed that 23 per cent of people had not had an eye test for over two years and 14 per cent had either never had a test or not had one since they left school. Mr Charlesworth said: "As the number of cars on our roads continues to increase, having 100 per cent vision becomes even more important."

Green Flag has compiled a guide to keeping your eye on the road:

**We are required by law to ensure we can read a number plate from a distance of 20.5 metres (67 feet), that's about five car lengths. If you need glasses to do this, then you must wear them at all times when driving

**Every day, tens of thousands of short-sighted people take to our roads, having forgotten, or chosen not to wear their glasses: the majority not realising that in doing so, they are breaking the law. It is therefore advisable to always carry a spare pair in the car. Indeed, in some European countries, this is a legal requirement.

**Try to avoid driving at night if your night vision is poor

**If you wear contact lenses, the chances are your eyes will grow tired more quickly on a long journey, so consider switching to a pair of glasses, until reaching your destination

**To reduce glare from the sun, and from the lights from on-coming traffic, anti-reflection coatings can be applied to any lenses. This will help you to see more clearly

**The Highway Code states that tinted glasses, lenses and motorcycle helmet visors must never be worn after dark or in poor visibility such as heavy rain or fog. It also states that spray-on or other tinting materials should not be used on windows and windscreens

**Like alcohol, some medicines can impair vision and slow down reaction times. It is, therefore, worth checking with your doctor whether a prescription is safe before taking to the wheel.

Mr Charlesworth added: "The major problem is that in the majority of cases, motorists don't even realise their eye sight is posing a danger, not just to themselves, but to other road-users.

"If you find yourself suffering from headaches, having to squint or feeling particularly tired when driving, the best thing you can do is visit an optician. It could save your life."