Drivers look set to face more stringent assessments of their fitness before getting behind the wheel under proposals being considered by the DVLA. The move is likely to include frequent eye tests to pick up some of the four million or so drivers thought to be breaking the law because they can't see properly. Yet it won't just be their safety and that of their fellow road users that is likely to benefit - regular eye tests have many other advantages, including spotting silent dangers such as diabetes and high blood pressure.

At the moment drivers need to have their eyes tested only for licensing purposes twice over their driving career: once when they take their test and again when they reach the age of 70. To pass you need only to be able to read a normal-sized numberplate in good daylight, with glasses or contact lenses if worn, at a distance of 20m. It is not so much the primitive nature of this test that is the problem as how often it is performed - twice in 53 years is simply not enough.

Free eye checks performed on thousands of visitors to the International Motor Show over the past decade suggest that 15 to 25 per cent of drivers fail the numberplate test. Even if you extrapolate the lower of the two figures to the 35 million drivers on British roads, it still suggests that at least four million cars are being piloted by people who haven't got a clear view of what is coming the other way.

It's not necessarily an issue of age. Substandard vision is mainly a problem in older drivers, in whom it is often compounded by slower reflexes (breaking distances have been revealed to be 20 per cent longer in the over-55s), but it is by no means restricted to them. Half of those over 60 surveyed may have failed the test, but so did one teenager in ten.

Although you are likely to be formally tested only twice in your driving career, the criterion of being able to pass the numberplate test applies throughout, and, as with all laws, ignorance - “I didn't know I had a problem, officer” - is no defence. So get your eyes checked regularly and if you do need to wear glasses or contact lenses to pass the numberplate test then please wear them when you are driving - failing to do so should, in my opinion, be an offence that is treated with the same gravity as drinking and driving. It is just as stupid and at least as dangerous.

But your safety on the road isn't the only thing likely to benefit from regular eye tests. Your eyes may not be true windows to the soul, but they do provide a unique insight into the inner workings of the body, and a skilled optometrist can often pick up early telltale signs of silent but potentially devastating illnesses. These range from raised pressure in the eyeball (glaucoma) and retinal damage, to problems originating in other parts of the body, including diabetes, dangerous cholesterol levels, high blood pressure and even brain tumours.

And it is not just the adult eye that needs monitoring. As many as one schoolchild in ten struggles to see properly because easily corrected eye problems - from squints to short-sightedness - are being missed, according to the Association of Optometrists, which has called for parents to make better use of the free eye tests available on the NHS.

In theory all children should have their eyes screened when they enter primary school, but in practice the service offered varies tremendously across the UK and many children are slipping through the net.

There is still a continuing debate about who should be screened and when, but parents ought to be aware of the importance of regular checks, and there is no need to wait for the establishment of a proper national programme.

A checkup by a high street optometrist is likely to be more thorough than a standard NHS screening test, and free to everyone under the age of 16. So what have you got to lose? A sensible regimen would be to get your child's eyes tested before he or she enters primary school, again between the ages of 7 and 8, and again when they enter secondary school.

For adults, the Royal National Institute for Blind People advises eye tests every two years from the age of 16, and then annually from the age of 60. Although its latest data suggests that fewer than half the population over 60 get close to this recommendation, and the figure is likely to be considerably lower for younger adults, many of whom have never had their eyes tested.

A thorough eye test takes around half an hour and costs £20 to £30 unless you are eligible for free assessments under the NHS (everyone under 16 or over 60, anyone living in Scotland and a long list of others). Type “free eye test” in the search box at nhs.uk for full details.