Spectacles For Vehicle Drivers

I would like to make a number of points regarding the dispensing of spectacles to motorists.

First, the frame should have thin rims and sides, so that it does not restrict peripheral vision. The eye size chosen should be as large as possible, bearing in mind the prescription, again to allow the widest field of view.

Lenses should be impact resistant, i.e. either plastics or toughened lenses should be used. If bifocals are required they should be dispensed with the smallest bifocal segment for driving spectacles. This is not to say that Executive bifocals are unsafe, after all, many people wear them when driving without any problems, but they may not be ideal.

Any bifocal or trifocal lens must be dispensed so that the reading portion does not encroach on the distance vision, i.e. fit the segment top low. Varifocals do not appear to be a problem for drivers if they are correctly dispensed. In fact, many drivers find them very useful when parking, as they can see the car bonnet clearly through the intermediate portion of the lens.

Ideally, tinted spectacles should not be worn for night driving, unless they are proven to be clinically necessary, nor should they be worn in conditions of poor visibility.
Tinted lenses for daytime driving may be considered under the following headings:

1. Photochromics; These do not work very well in vehicles as the ultraviolet light that activates them is absorbed by the windscreen and windows of the car. Heat also lightens the lenses. Hence, the lenses will not darken to their full potential inside a warm vehicle. They are most frequently made of glass, although plastics are available. Photochromics perform better than uncoated white crown glass by day but are worse at night.
2. Polarizing lenses; These are particularly effective in reducing the glare from the road surface when driving towards the sun. They give the greatest benefit in the evening and winter months, when the sun is low and the roads may be wet. However, problems may arise if the driver has a toughened glass windscreen or Triplex laminated glass, as the strain pattern will be clearly visible. Some drivers do not object to this pattern but others do not like it. Polarizing lenses are often thought to absorb the UV/blue end of the spectrum. However, this is not necessarily true.
3. UV/blue-absorbing lenses; These lenses absorbing wavelengths up to 500nm are useful for drivers. UV light is important because it causes fluorescence of the crystalline lens proteins. The visible light produced is then scattered over the retinal surface and reduces visibility.

A driver who wears sun spectacles with a deep tint is relatively more dark-adapted than the driver without sun spectacles. This means that if the sun spectacles are removed on entering a tunnel the driver will be able to see more clearly than the more light-adapted driver.