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Driving and Vision

Surveys show that one driver in five has a vision defect that could affect driving performance. Fortunately, with appropriate optometric care nearly all licensed drivers can reach the vision standards necessary for safe driving. Good driver vision is a crucial factor in road safety. Ninety per cent of the critical decisions made by drivers are based on sight. Most drivers are not sufficiently aware of the relationship between good vision and good driving. Today’s driver tackles an increasingly complex task on roads that are becoming busier.

Seven visual skills are vital for safe driving.

1. 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.

The faster you travel, the less time you have available to react to what you see. Poor distance acuity becomes dangerous as speed increases.

2. 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.

3. 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.

4. 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.

5. Accomodation

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.

6. Colour Vision

Safe driving at night requires the ability to see in the low light beyond the range of the car headlights. It also requires the ability to recover quickly from the glare of oncoming headlights.

Night vision deteriorates rapidly after 40 years of age. The best glare resistance is in the 23-30 year old drivers. By driving more slowly, older drivers compensate to some extent for the reduction in quality of their night vision.

Sunglasses should never be worn while driving at night because they dangerously reduce the ability to discern cars, pedestrians and road hazards.

7. Colour Vision

Colour plays an important part in road safety. Drivers need to recognise and distinguish colours. Drivers who are aware of colour vision deficiencies can learn to distinguish traffic signal lights by their position and by differences in brightness.

Too often, changes in vision go unnoticed by drivers. Most drivers have defects that, once detected, can be corrected or for which they can compensate.

Regular eye examinations

Optometrists have consistently drawn attention to the need for comprehensive vision tests during driver licensing examinations and at regular intervals during the life of a driver.

Your Heming Scott & Donald optometrist recommends:

• 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.
• 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.

The above information was largely produced by the Optometrist Association Australia