Recent surveys show that one driver in five has a vision defect which might affect driving performance. Fortunately, with appropriate optometric care nearly all licensed drivers can reach the visual standards necessary for safe driving. Good driver vision is a crucial factor in road safety - 90 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 busier than ever before.
1. Distance acuity.
This is probably the most important vision 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 second. If your distance acuity is poor you may not even see a stop sign until you are almost upon it and you may not have 0.4 second in which to react. The faster you travel the less time you have available to act upon what you see. Poor distance acuity becomes more and more dangerous as speed increases.
2. Depth perception.
Passing and changing lanes in busy traffic requires accurate judgement of distances between moving objects. Both eyes need to function properly as a tearn for reliable depth perception. Depth perception deficiencies are common in drivers and the problem gets 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 half a horizontal circle or 180 degrees. It is reduced with increasing speed and is only 40 degrees (one-ninth of a circle) at speeds of 100 kilometres an hour.
4. Muscle balance.
Good muscle balance means that both eyes can easily be pointed simultaneously at a given object. It is essential for good two-eyed vision, depth perception and field of vision. Although drivers can usually 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 can become unmanageable.
5. Accommodation.
A driver needs to be able 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. Night 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 being in 20 to 30 year old drivers. Older drivers can compensate to some extent for the reduction in quality of their night vision by driving more slowly. 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 various colours and distinguish them from others. Drivers who are aware of colour vision deficiencies can learn to distinguish traffic signal lights by their position and differences in brightness. Changes in vision too often go unnoticed by drivers. Most drivers have defects which once detected can be corrected or for which they can compensate.
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. The introduction of uniform driver vision standards in all Australian States and Territories has been repeatedly urged. Your optometrist makes the following recommendations for drivers:
-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 cut down on night driving.
-compensate for poor field of vision by making good use of side and rear-view mirrors and turning your head to see objects at the side.
-if your depth perception is inadequate use extra care in passing other cars.
-remove objects from your rear-view mirror and see that it is correctly adjusted. make sure that your windshield and rear window are clean and tree from scratches or pitting that can increase glare.
-check headlights periodically so that they provide maximum light with each beam in the proper position.
-slow down. Most vision problems are accentuated by high speeds.