How can my vision be more than 100 %?

During routine eye exams, your eye doctor will always check how well you can see far. Sometimes they say that your vision is more than 100 %. How can that be?

There are many eye charts that can be used to measure vision, but the Snellen chart is the most common one. In America the doctors place the chart 20 feet away from the patient, in Europe that distance is 6 metres.

20/20 vision (1,0 or 100 % in Europe) means that a person 20 feet away from the chart sees the letters that a person with ‘normal’ vision should see from 20 feet away. 20/10 vision means that a person 20 feet away from the chart sees the letters that a person with ‘normal’ vision would see only 10 feet away from the chart. In case you only see the top line (the big E), your vision is 20/200 (0,1 in Europe).

Usually the line marking 20/20 vision on the chart is the fourth from the bottom. The ones after that mark 20/15, 20/10 and 20/5 vision – that means vision that is more than 100 %. There are not many people with vision that good, but for example most birds of prey have at least 20/5 vision!