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What Does 20/20 Vision Mean?

POSTED ON June 20, 2011

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20/20 vision is considered normal. But what exactly does that mean? Image courtesy of AllAboutVision.com Let’s start with the eye chart. According to All About Vision, the classic example of an eye chart is the Snellen eye chart, developed by Dutch eye doctor Hermann Snellen in the 1860s.  There are many variations of the Snellen eye chart, but in general they show 11 rows ...

20/20 vision is considered normal. But what exactly does that mean?

Image courtesy of AllAboutVision.com

Let’s start with the eye chart. According to All About Vision, the classic example of an eye chart is the Snellen eye chart, developed by Dutch eye doctor Hermann Snellen in the 1860s.  There are many variations of the Snellen eye chart, but in general they show 11 rows of capital letters.  The top row contains one letter and the other rows contain letters that are progressively smaller.  During a comprehensive eye exam, Dr. Tavel will ask you to read the smallest line of text letters that you can make out.

The standard placement of the eye chart is on a wall that’s 20 feet away from your eyes.  In a room smaller than 20 feet the eye chart may hang behind your chair and the doctor will use mirrors to make it appear in front of you at a simulated distance of 20 feet.

Having 20/20 vision means you can read at 20 feet a letter that most human beings should be able to read at 20 feet.

If you can read the big E at the top of the eye chart but none of the letters lower than that, your vision is considered 20/200.  That means you can read at 20 feet a letter that people with “normal” vision can read at 200 feet.  In the United States you are considered “legally blind” if your visual acuity is 20/200 or worse.

Here’s an interesting fact: Many animals have much better visual acuity than people. Birds of prey have an estimated visual acuity of 20/5 or better.

To find out how you measure up, visit Dr. Tavel for your comprehensive eye exam.

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