What Does 20/20 Vision Mean?

This is a common question that people seem to always ask eye doctors at social events. Typically optometrists and ophthalmologists refer to visual acuity in terms of the Snellen acuity eye charts. The Snellen acuity eye charts displays letters which become progressively smaller from the top to the bottom. In terms of Snellen acuity, 20/20 is considered normal vision for most people. From a statistic point of view what does this mean? In basically means that approximately 68.2% of the normal healthy population is able to have their vision corrected to this level. It also however means that approximately 15.9% of the normal healthy population has correctable vision that is better than this and that 15.9% of the normal healthy population has correctable vision that is worse than this.

In general 20/20 means that a person sees the same line of letters at 20 feet that a normal person sees from 20 feet. If a person has 20/40 vision, than this means that they can see the same line of letters at 20 feet that a normal person sees from 40 feet away. Therefore their vision is worse than normal. If a person has 20/15 vision, than this means that they can see the same line of letters at 20 feet that a normal persons sees from 15 feet away. Therefore their vision is better than normal.

Recap:

20/20 – Top number is where you are standing and the bottom number is where a normal person stands to see the same sized object or line of letters.

Now you know!