What Does 20/20 Really Mean?
Posted October 2012
20/20 vision means that a person can read the small letters on the standard eye chart at 20 feet away. As the second number gets larger, it means the person’s vision is worse. So a person with 20/40 vision can only see the larger 20/40 size letters at 20 feet, and the smaller rows are too blurry to see clearly. A person with 20/400 vision can only see the large ‘E’ at the top of the chart, and everything below is blurry. Most standard eye charts have the 20/400 at the top of the chart. If the person cannot see the “Big E”, then vision is recorded as worse than 20/400, or the person is moved closer to the chart until they report seeing the 20/400 letter (i.e. 20/400 at 5ft). Some eye charts even have a row smaller than 20/20 which is 20/15, and is usually the smallest row that can be resolved by the normal human eye at 20 feet.
Most of the time, vision can be correctable to at least 20/20. If not, there should be a clinical reason such as cataracts, lazy eye, or some other disease/condition that causes the vision to be less than 20/20, even with the best powered lens in front of the eye.
Dr. Carney is available for all your eye care needs by appointment at Wallace Eye Associates by calling (318) 448-0221.