Difference between revisions of 20/20 correction

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-'''''20/20 correction''''' is a correction you normally get from a licensed optician, which corrects your eyesight up to a degree of [[visual acuity]] that an [[emmetropic]] (or "normal-seeing") person achieves on a [[Snellen Chart]]. The visual acuity is defined as the distance (usually 20ft or 6m but can be less), divided by the letter size, expressed as the distance at which the letter subtends an angle of 5 arc-minutes. (Or as multiples of the height at which the letter subtends 5 arc-minutes at a distance of 1.) (5 arc-minutes just means 5/60 of a degree.) So
+'''''20/20 correction''''' is a correction you normally get from a licensed optician, which corrects your eyesight up to a degree of [[visual acuity]] that an [[emmetropic]] (or "normal-seeing") person achieves on a [[Snellen Chart]].
-* 20/20 means 5 arc-minutes at 20 feet
-* 20/16 means 4 arc-minutes at 20 feet
-* 6/12 means 10 arc-minutes at 6m
 If you can see 20/15 or even better, this means that your are [[overcorrected]]. (It is not necessarily considered super-human actuity, but it is unnecessary to correct to this level.)