What is 20/20 Vision?

Everyone has heard of 20/20 vision.

What does it mean? This is one of the most common questions I get asked when people find out I am an optometrist. If you have 20/20 vision you can see clearly at 20 feet what should normally be seen at that distance. How do we know what is normal? Back in the good ol’ days around 1862 (before Canada was an official county) an ophthalmologist named Herman Snellen asked people to stand at 20 feet and read the lowest line they could. Through experimentation he determined which lined that was and called it 20/20 vision. 20/100 vision would describe someone who has worse than 20/20 vision. A person with 20/100 vision has to stand at 20 ft to see what a person with normal vision can see at 100 feet.

Many people have better than 20/20 vision and it is common for people to see 20/15 vision. The best recorded vision ever recorded vision was that of an Australian man who could see 20/5. This means he could stand a 20 ft and see what normal people see at 5 feet!

20/20 is only a small part of what we check during an eye exam. 20/20 vision does not take into account eye diseases (many eye diseases do not affect vision until it is to late) or the eyes ability to focus (key in reading and learning) but these are topics for a later column!