What is Perfect Vision? Where does the phrase 20 / 20 vision come from?

The longest distance the human eye can see clearly is 20 feet away.

20/20 vision (or more correctly, 20/20 visual acuity) is considered “normal” vision. This means that you can read a letter at 20 feet on an eye chart that most human beings should be able to read at 20 feet.

Eye charts are set up in many different ways and come in different forms and sizes, however, normally if you can read the large E at the

top of the eye chart but none of the letters below that then your vision is considered 20/200. That means you can read at 20 feet a letter that people with “normal” vision can read at 200 feet. So at 20/200, your visual acuity is very poor.

Visual acuity is most commonly tested with the help of different eye charts. As you will be able to find out in the program, there are charts that test how well you can see and charts that help you see better.

The most popular chart used for testing vision acuity is the Snellen chart, which has written on it letters of different sizes. The chart is set at 20 feet from the patient when the eye exam is taken. 20/20 vision should not be thought as “perfect” but as “normal” vision. You will be able to see more on how charts work and even learn how to make your own in the program.

When saying “20/20 vision”, the first number (numerator) indicates the distance in feet between the person and the thing he looks at (in our case, the chart). The last number (denominator) indicates the size of the letters, not in feet but in a specific measurement that denotes something more technical! (if you must know it’s the separation at which the lines that make up those letters would be separated by a visual angle of 1 arc minute, which for the lowest line that is read by an eye with no refractive error, or the errors corrected is usually 20 feet.)

In Europe, people don’t say they have 20/20 vision, they say 6/6 vision, due to the fact that they use the metric system and 20 feet is equal to 6 meters. This is the 20-20 vision we talk about. However not everybody has 20-20 vision. This differs from eye to eye.

A person with 20-40 vision at 20 feet away from an object will see what an eye sees when it is 40 feet away from the object, for example. On the other hand, somebody with 20-10 vision, at 20 feet away from the target will see it just like that object would be only 10 feet away.

What this means is that 20/40 can be considered half the acuity for distance vision and 20/10 vision would be twice the normal acuity.

What people call 20/20 vision is in fact called 20/20 visual acuity.. This is what we would consider “normal” vision. It means that you can read at a letter 20 feet that most human beings should be able to read at 20 feet. To get a driver’s license in most of the United States, your best-corrected visual acuity must be at least 20/40.

In the United States you are considered “legally blind” if your best-corrected visual acuity (meaning, your best distance vision with eyeglasses or contact lenses) is 20/200 or worse.

There are many reasons some people do not have 20-20 vision. Some of them can be fixed due to technological developments in science, but some are not correctable. One such problem is that of the lazy eye (amblyopia). This is a trauma to the eye caused by reasons that will be explained in other blog posts.

One very important thing you should know about 20/20 vision and visual acuity: this 20/something number does not directly relate to the eyeglass prescription required to correct vision, because it does not say why you have a vision problem, it only says how accurate your sight is. So be aware about this when looking for a cure, and read more about it within the program.