The use of vision is key to all aspects of driving. Good near and distance vision are needed to identify road hazards, read signs and view your dashboard. There are several factors that can affect the health of your eyes. Awareness of vision-related changes and problems will help you continue to drive safely.
When your eye doctor asks you to read the letters on an eye chart, you are being tested for visual acuity, or how clearly or acutely you can see. People who have a history of eye conditions that may affect driving seem to have more crashes than others.
There are two types of visual acuity:
- Static visual acuity is the ability to see stationary objects clearly.
- Dynamic visual acuity is the ability to see objects in motion clearly.
Although many people can continue to see clearly as they get older, there are relatively larger changes in the ability to see moving objects over time.
Acuity problems may lead to a higher risk of crashes. There is also evidence that the lens of your eye becomes yellow and less transparent with age, and your pupils become smaller and less able to dilate in dim light. This can be particularly problematic when driving at dusk or dawn.
Color blindness may cause problems when identifying traffic signals or brake lights of other vehicles while driving. With cataracts, your ability to tell the difference between colors gradually decreases.
Contrast sensitivity is the visual ability to see objects that are not outlined clearly or do not stand out from their background. Poor contrast sensitivity can be a symptom of serious eye conditions. Examples of problems could include difficulty seeing pedestrians walking along poorly lit roads and road signs in fog or at night.
Useful Field of View
Useful field of view refers to the amount of visual information that can be processed in a brief glance using both eyes. It is directly related to our ability to process information quickly and accurately. It takes less time to simply see and identify a single object than it does to divide your attention between two or more objects.
For example, we can identify and react easily to a stop sign at an empty intersection. If you add a pedestrian crossing in front of you and an oncoming vehicle making a left turn into the intersection, it becomes much more complicated. Our ability to process information gradually slows with age, particularly for situations in which the environment is very complex.
Depth perception gives us the ability to judge the distance of objects in relation to ourselves, especially when those objects are moving toward or away from us. For example, depth perception is important in judging the distance and speed of approaching vehicles when merging or turning.
Peripheral vision is the ability to see outside your immediate field of view, such as seeing a vehicle approaching you from either side, without having to take your attention away from what is in front of you. Our ability to use depth perception and peripheral vision gradually weakens with age. This decline makes distances and speeds of vehicles more difficult to judge, and objects coming from each side of our field of vision may surprise us.