This is possible through our ability to detect contrast, distinguish colour and perceive motion. We look for pedestrians, other vehicles and hazards on the road ahead.We don’t only read street signs while we are driving. We have many different visual abilities that help us to see the world around us. Other visual abilities help us to see the world around us
Visual acuity is relatively easy to measure, and is specified as one of the criteria for obtaining licences (such as for driving a car or piloting a plane) and for acceptance into some occupations such as the military or the police. It is important for reading books, labels, computer displays and signage. This measure of vision is called “visual acuity”. Similarly, 20/60 (6/18) letters have detail of 3’ (and are three times as big), and so forth. If you can only read letters that are twice as big (with detail of 2’) from the same distance, then you would have 20/40 (6/12) vision. If the letter “E” has detail within it of 0.07 inches (1.75mm) and you can read it from a distance of 20 feet (6m), then you are able to read the 20/20 (6/6) letters: The optometrist points to a letter “E” and asks you to state aloud what the letter is. The vision chart is set up at a distance of 20 feet (6m) from your eyes.
In practical terms: imagine you are having your eyes examined and you are looking at the vision chart on the wall. If you have 20/20 vision, then it means that you can discern detail of 1 minute of an arc (1’) at a distance of 20 feet (6 metres).
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