Driving and Vision

Driving is a skill that is reliant on good vision. The majority of decisions we make behind the wheel are influenced by what we see on the road. These days vision for driving is more crucial due to higher numbers of other cars on the roads, and other factors such as brighter oncoming headlights. Ensure your vision is up the the task so that you drive safely and comfortably in all situations with a consultation with one of the optometrists at Innovative Eye Care.

It is important to have your eyes thoroughly check at regular intervals if you are a driver. This is because there are a number of visual skills that are are vital for safe driving:

DISTANCE ACUITY

This is probably the most important visual skill for driving. Distance acuity is the ability to focus and see clearly at far distances. Even the simplest reactions in driving take at least 0.4 seconds. If your distance acuity is poor, you might not see a stop sign until you are almost on it—and you may not have 0.4 seconds in which to react. Seeing debris on the road surface or spotting someone planning to cross the road in front of you is also dependent on your visual acuity. The faster you travel, the less time you have available to react to what you see.

Having your glasses or contact lenses working well will give you the best chance of seeing everything clearly on the roads. If you need your contact lenses or spectacles to meet this standard you should wear these at all times when driving. Drivers with a normal personal license need to see the 6/12 line of letters with both eyes open, meaning that if you have a weaker eye, you may still pass the standard. Commercial drivers have a stricter standard and need to see well to the 6/9 line with both eyes individually.

Drivers who use overnight orthokeratology contact lenses to see clearly the next day should wear their lenses every night to ensure their vision is sharp enough when behind the wheel. Your optometrist can give you a letter that can be left in your glovebox that explains your form of vision correction to anyone concerned.

A typical vision chart showing the size difference between 'normal' vision and the level you need to see to meet the driving standards and drive safely.

DEPTH PERCEPTION

Passing and changing lanes in busy traffic require accurate judgement of distances between moving objects. Both eyes need to function properly as a team for reliable depth perception. Depth perception deficiencies are common in drivers and get worse as speed increases. Even if you meet the driving standard without glasses or contact lenses, having these on when driving may make you safer on the road because they improve depth perception.

FIELD OF VISION

The ability to ‘see out of the corner of your eye’—to see over a large area without moving your eyes or head— is an important part of safe driving. It enables a driver to see cross-road traffic and pedestrians at the roadside without looking away from the road ahead. Normally, the field of vision is about l80 degrees, reduced with increasing speed, and is only 40 degrees for distant objects at speeds of 100 kilometres an hour.

To meet the driving standard you need to see with both eyes at least 110 degress horisontally, with no visual field problems within 20 degrees of where your eyes point. This means patients with vision in only one eye may still meet the driving standard but with require a period of time (usually 3 months) to adapt to only using one eye first if it is a new condition. Patients with conditions like glaucoma may not meet this standard due to loss of their peripheral vision. At Innovative Eye Care we have special visual field testing machines that can check if you meet this driving standard.

MUSCLE BALANCE

Good muscle balance means that both eyes can be pointed easily and simultaneously at a given object. It is essential for good two-eyed vision, depth perception and field of vision. Although drivers usually can compensate for muscle imbalance under favourable driving conditions, the effort involved may take its toll in fatigue and discomfort. Alcohol, tiredness and drugs can upset muscle balance so that a slight imbalance becomes unmanageable. Visual training may improve the muscle balance of someone with a condition that affects their muscle balance.

You are not allowed to drive if you see double. This may happen if you suffer a nerve palsy for example. Temporary prisms attached to you glasses may alleviate the double vision while your condition improves, allowing you to continue driving.

ACCOMMODATION

A driver has to change focus quickly and easily from the road to the dashboard and back again. This ability to change focus from a far object to a near object, and vice versa, is called accommodation. As we get older presbyopia sets in and we cannot change our focus so easily. Spectacle lenses such as progressive multifocal lenses can give focus for both distance and intermediate areas such as the dashboard.

GLARE

As we get older the tissues of our eyes become more opaque, causing conditions such as cataract. A cloudy lens will cause glare as the light from sun and headlights will be scattered rather than focused well. Some younger patients who are fair will also have issues with glare due to the lack of light-absorbing tissues in their eyes.

If glare becomes more problematic then shielding your eyes from light during the day with quality sunglasses can be helpful. The anti-reflective coating on the modern lenses that we use at Innovative Eye Care will also reduce the reflections of light within your lens, especially from behind you, which makes driving easier.

An illustration to show how a spectacle lens with an anti-reflective coating (right) can reduce glare at night.

Some recommendations from Innovative Eye Care for safe driving:

  • Have your vision examined regularly, with special attention to the needs of driving.
  • If spectacles have been prescribed for driving, make sure you wear them.
  • If you are troubled by glare, minimise your night driving and look into sunglass options for the daytime.
  • Compensate for poor field of vision by making good use of offside and rear -view mirrors and by turning your head to see objects at the side.
  • If your depth perception is inadequate, take extra care when passing other cars.
  • Remove objects from your rear-view mirror and ensure that it is correctly adjusted.
  • Ensure that your windows are clean and free from scratches or pitting that can increase glare.
  • Check headlights periodically, so that they provide maximum light, with each beam properly positioned.
  • Slow down. Most vision problems are accentuated by high speed.