WHAT DOES 20/20 MEAN? By Dr. James Ivanoski, Optometrist at Lakeshore Eye Care Professionals with offices in Mequon & Saukville, Wisconsin

By user-admin
July 17, 2017
What does 20/20 vision actually mean?  The measurement of visual acuity is usually stated as 20 with some other number.  20/20 is considered normal vision.  If the bottom number is larger than 20, the visual acuity is worse.  For example, a person with 20/200 visual acuity has worse visual acuity than somebody with 20/30 visual acuity.  A lot of fortunate people can see better than 20/20 (20/15 or even 20/10).  The best visual acuity thought achievable by a human is 20/8. 

The minimum separation the average person can see between two lines is 1 second of arc or 1/60 of a degree.  Using a mathematical formula, it can be calculated that this translates to a letter size of 8.75 mm or 0.35 inches high is what the average person should be able to see 20 feet away.  So a person that can see 20/20 can see as small as a 0.35 inch letter at 20 feet.  A person that sees 20/100 can only distinguish a 1.75 inch or larger letter 20 feet away.  In other words, what a 20/20 seeing individual can see at 100 feet, a 20/100 seeing individual would have to be 20 feet away (5 times closer) to see the same thing.

The visual acuity charts that we use are all based on these letter sizing calculations.  Herman Snellen was the ophthalmologist that invented the first standardized eye chart in 1862.  We still use similar charts to measure vision today.  Our vision charts are projected or digital, and we use a mirror to simulate a 20 foot long room.  At Lakeshore Eye Professionals our passion is to try to keep everybody seeing as close to 20/20 as possible for their entire life, especially now that you know what it means!

Dr. James Ivanoski

Dr. James Ivanoski is an Optometrist practicing at Lakeshore Eye Care Professionals with Dr. Martha Jay and Dr. Mark German. He welcomes patients of all ages into his practice and accepts most insurance plans.  For more eye care information, call 262-241-1919 or visit www.LakeShoreVision.com

Dr. James Ivanoski's Blogs, General Eye Care, Medical and Surgical Eye Care, Our Doctor's Blogs

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