When your Doctor says you have 20/20 Vision, That’s Perfect Right?

Well, That's great news! But, it's not really perfect. We thought we would kick of the year 2020 with a little info about 20/20 vision. If you have 20/20 vision it means your eyesight is “normal” What is normal?  When your eye doctor administers a standard test and you are able to read what most people can read at 20 feet, your eyesight is considered normal or, 20/20.
 
Although there have been other tests developed through the years, one that is easily recognizable by many was developed in 1862 by Dutch ophthalmologist Herman Snellen. You are probably familiar with his chart where you read progressively smaller lines of letters. You have probably seen the chart on the left.

In the United States, your eye doctor, an optometrist or ophthalmologist, will set up the chart 20 feet from your eyes  (sometimes they use mirrors that create the equivalent of 20 feet when they don’t have rooms over 20 feet long.)
They will have you read the chart until you can no longer differentiate the letters. This tests is used to gage the visual acuity or clarity of your sight on a relative scale. 

Doctors and scientists do use other charts for various reason like for children who do not yet know letters or when more accuracy is called for, eye doctors and scientists may use a chart called the LogMAR chart developed in the 1970’s. There are others but for now we will stick to our 20/20 topic.

Using the chart Snelling developed, If you can read the big “E” at the top of the chart and no other letters below it, your vision would be 20/200. That means that you would be able to read at 20 feet what a person with 20/20 vision could read at 200 feet. 20/200 would mean your eyesight is very poor and in the United States you would be considered “legally blind".

Usually if you can read the 4th line up from the bottom your eye doctor would consider your eyesight as 20/20. The lines below represent 20/15, 20/10, and 20/5. For comparison, It is rare that a person would have 20/10. It is estimated that birds of prey could have a visual acuity of 20/5 or better.

So, when you take an eye exam and they tell you your vision is 20/20, it does not mean your eyesight is perfect. 20/20 is visual acuity that is good, normal and what most people would have. When an eye doctor prescribes corrective lenses, she is helping you see as clearly as someone with 20/20 vision.

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