Difference between revisions of Visual acuity
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Visual | Visual acuity is the measurement of how well the vision system as a whole is recognizing what it sees. This is typically measured with a [[Snellen chart]] and expressed as the distance you need to be from the chart to recognize the characters over the distance that someone with normal vision can recognize the characters. | ||
==Reading a Snellen chart== | |||
{{main|Snellen chart}} | |||
* 10/400 would be very bad (possibly just [[myopic]]), | * 10/400 would be very bad (possibly just [[myopic]]), | ||
* 20/20 is (by definition) normal, and | * 20/20 is (by definition) normal, and | ||
* 40/20 is excellent. | * 40/20 is excellent. | ||
Visual | Visual acuity for [[myopes]] is typically measured at [[distance vision|20 feet or 6 meters]]. Lens or mirror tricks may be used to change the effective test distance in a smaller room. Visual acuity for [[hyperopes]] is typically measured at 36cm, and a [[presbyope]] would be measured at both distances. | ||
==Reasons differing visual acuity== | |||
[[Refraction]] is only one part of visual acuity. Various medical conditions can cause physical blockage/dispersion of light in the eye, problems detecting light in the eye, or problems with the visual processing that turns a series of electrochemical signals into a picture in our mind's eye. See an [[optometrist]] if your vision can't be corrected with [[refraction]]. | [[Refraction]] is only one part of visual acuity. Various medical conditions can cause physical blockage/dispersion of light in the eye, problems detecting light in the eye, or problems with the visual processing that turns a series of electrochemical signals into a picture in our mind's eye. See an [[optometrist]] if your vision can't be corrected with [[refraction]]. | ||