What does 20/20 vision mean?
Submitted by Josh Talkington on September 13, 2011
The most common way to measure visual acuity is with an eye chart of a certain size, viewed from 20 feet away. Most Ophthalmologists offices are not 20 feet long anymore, but will use mirrors to simulate a 20 foot distance.
The numbers 20/20 is a comparison of your vision to perfect or normal vision. Therefore, if what you can see at 20 feet away is the same as a person with perfect vision, you are considered 20/20. If what you can see at 20 feet away, a person with perfect vision can see at 40 feet away, your vision is 20/40, and so on. While 20/20 vision is considered “perfect” vision, it is possible to see better than 20/20.
While this convention works well for measuring distance vision, it does not work for measuring the ability to read at close range. Most Ophthalmologists use a scale called the Jaeger scale, which again is based on specific sized letters, held at approximately 16 to 18 inches away.