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]] | {{For|the the condition of eyes having perfect vision|emmetropia}} | ||
'''''20/20 correction''''' ('''''full correction''''' rounded to weaker 0.25 D step) 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]], putting your [[blur horizon]] within 0.25 D of the chart. | |||
If you can see 20/15 or even better, this | If you can see 20/15 or even better, this might mean that you are [[overcorrected]] ('''''full correction''''' rounded towards stronger 0.25 D step). (It is not necessarily considered super-human acuity, but it is unnecessary to correct to this level. Also, 20/15 isn't always a good measurement, as some people can sometimes see 20/20 with blur horizon 0.5 D away or even 20/10 with overcorrection on a bright Snellen) | ||
It is very difficult or impossible to perform [[Active Focus]] at this level of correction, as there is not enough of a [[blur horizon]] to produce [[stimulus]] - see [[Distance vision]], unless there is some sort of [[Guide:Reducing lens complexity|cylinder reduction]] or [[transient astigmatism]] involved. | |||
A good [[normalized]] might be a further 0.25 D reduction from 20/20 correction, resulting in a 0.25 to 0.5 D undercorrection, or even a 0.5 D reduction, resulting in 0.5 D to 0.75 D of undercorrection. | |||
==See also== | ==See also== | ||
[[20/x vision]] | [[20/x vision]] | ||
Latest revision as of 17:55, 9 March 2022
20/20 correction (full correction rounded to weaker 0.25 D step) 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, putting your blur horizon within 0.25 D of the chart.
If you can see 20/15 or even better, this might mean that you are overcorrected (full correction rounded towards stronger 0.25 D step). (It is not necessarily considered super-human acuity, but it is unnecessary to correct to this level. Also, 20/15 isn't always a good measurement, as some people can sometimes see 20/20 with blur horizon 0.5 D away or even 20/10 with overcorrection on a bright Snellen)
It is very difficult or impossible to perform Active Focus at this level of correction, as there is not enough of a blur horizon to produce stimulus - see Distance vision, unless there is some sort of cylinder reduction or transient astigmatism involved.
A good normalized might be a further 0.25 D reduction from 20/20 correction, resulting in a 0.25 to 0.5 D undercorrection, or even a 0.5 D reduction, resulting in 0.5 D to 0.75 D of undercorrection.