Difference between revisions of Visual acuity

Jump to navigation Jump to search
m (adding a (possibly slightly gratuitous) linkification)
No edit summary
Line 1: Line 1:
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, so
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 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.
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]].



Revision as of 17:46, 14 June 2020

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

  • 10/400 would be very bad (possibly just myopic),
  • 20/20 is (by definition) normal, and
  • 40/20 is excellent.

Visual acuity for myopes is typically measured at 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.

See Also

References