What is 20/20 vision?

20/20 vision is a term used to express normal vision (the clarity or sharpness of vision) from a distance of 20 feet. If you have a 20/20 vision it means if stand 20 feet away from the vision chart you can see what the "normal" human being can see. In other words, you vision is normal.

If you have a 20/40 vision, it means that when you stand 20 feet away form the vision chart you can see what a normal person can see from 40 feet away. Higher the denominator value weaker is your eye.

You can also have vision that is better than normal. A person can have a 20/10 vision, which means that what he can see from 20 feet away, a normal person can see it at a distance of 10 feet from the chart.

Some people can see well at a distance, but are unable to bring nearer objects into focus. This condition can be caused by hyperopia (farsightedness) or presbyopia (loss of focusing ability). Others can see items that are close, but cannot see those far away. This condition may be caused by myopia (nearsightedness).