A 39-year-old member asked:
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what is the distance to measure nearsightedness at, and why?

1 doctor answer
Dr. Richard Bensinger
52 years experience Ophthalmology
20 feet: All lanes are corrected for distance to be equivalent to 20 feet which is the defined standard. In metric countries it is 6 meters. The snellen fraction 20/ over something, uses the 20 foot standard as part of the fraction. It is arbitrary but since a universal standard was needed for the optical industry, in the usa 20 feet is adopted for all to measure by.
Answered on Apr 25, 2013

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