What does 20-20 Vision mean?

Often times when people talk about eyesight, they say that their vision is 20/20 or 20/40 or even 20/200. What does this really mean?

It is the measurement of your VA - Visual Acuity, which is (acuity from 'acute' meaning 'sharp') the sharpness of your vision. This is measured during an eye exam when you are looking at the eye chart that has the black letters on the white background. To have 20/20 vision does not necessarily mean perfect vision. There are other factors that enter into a full eye examination.

To have 20/20 vision means that you can see from 20 feet what the 'average' person can see from 20 feet. 20/40 means that you have to be 20 feet away from the chart to see what that average person can see from 40 feet away. To have 20/100 means that you have to be 20 feet away from the chart to see what that 'average' person can see at 100 feet or even closer still. That means you are nearsighted and see better when things are closer to you.

There is also the possibility of measuring 20/10, which would mean that you can see from 20 feet away what the other person has to be 10 feet away to see. This indicates farsightedness.

Eyeglass or contact lens prescriptions are used to bring people back to 20/20 vision. This formula and method of measuring VA dates back to 1861 and is credited to a Dr. Franciscus Cornelis Donders (1818- 1889) from the Netherlands.