Difference between revisions of Visual acuity

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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, so
* 10/400 would be very bad,
* 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 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.


[[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 02:30, 11 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, so

  • 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.

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