Visual acuity - Revision history

Vision at 11:47, 17 July 2023

2023-07-17T11:47:50Z

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			[[File:20-20novelgames.PNG\|thumb\|20/20 vision as diagnosed by [https://www.novelgames.com/en/eagleeye/ Eagle Eye on Novel Games]]]

	Visual acuity (VA) is the measurement of how well the entire vision system can recognize what it sees. Formally, it is defined as the reciprocal of the smallest angle that the visual system can resolve.		Visual acuity (VA) is the measurement of how well the entire vision system can recognize what it sees. Formally, it is defined as the reciprocal of the smallest angle that the visual system can resolve.

User: /* Reasons for differing visual acuity */

2022-03-09T17:48:53Z

Reasons for differing visual acuity

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	==Reasons for differing visual acuity==		==Reasons for differing visual acuity==
	[[~~Refraction~~]], which causes [[blur]] and [[double vision]], is only one factor 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]].		Non-zero [[refractive state]], which causes [[blur]] and [[double vision]], is only one factor 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]].

	==20/x==		==20/x==

User: /* Reasons differing visual acuity */

2022-03-09T17:47:13Z

Reasons differing visual acuity

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	which approaches 2, and we can be almost certain that if, with a good illumination, the acuity is only equal to 1, the eye presents defects sufficiently pronounced to be easily established.</blockquote>		which approaches 2, and we can be almost certain that if, with a good illumination, the acuity is only equal to 1, the eye presents defects sufficiently pronounced to be easily established.</blockquote>

	==Reasons differing visual acuity==		==Reasons for 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]], which causes [[blur]] and [[double vision]], is only one factor 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]].

	==20/x==		==20/x==

User at 17:29, 9 March 2022

2022-03-09T17:29:27Z

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	Visual acuity (VA) is the measurement of how well the entire vision system can recognize what it sees. Formally, it is defined as the reciprocal of the smallest angle that the visual system can resolve.		Visual acuity (VA) is the measurement of how well the entire vision system can recognize what it sees. Formally, it is defined as the reciprocal of the smallest angle that the visual system can resolve.

	It will depend on the amount of defocus that [[accommodation]] cannot overcome~~, as well as~~ other defects such as [[astigmatism]].		It will depend on the amount of defocus that [[accommodation]] cannot overcome because it is outside of the focus range or due to other defects such as [[astigmatism]]. Defocus causes [[blur]] and [[double vision]].

	For distance, 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. Lens or mirrors may be used to change the effective test distance in a smaller room.		For distance, 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. Lens or mirrors may be used to change the effective test distance in a smaller room.

User: /* Reading a Snellen chart */

2022-02-09T16:14:04Z

Reading a Snellen chart

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	With text that we are familiar with, the brain may clear up that text more than our vision would actually allow.		With text that we are familiar with, the brain may clear up that text more than our vision would actually allow.

	20/20 is "good enough" for most purposes, but not "perfect" in any way. Rather, 20/20 vision is slightly defective. It is possible to have 20/20 vision with 0.25 to 0.5 D of defocus, and 20/20 does not imply clear or sharp vision. As [[normalized]] correction typically ~~impose~~ 0.25 D of extra myopic defocus on [[20/20 correction]], it can be considered to be 0.25 to 0.75 D of undercorrection.		20/20 is "good enough" for most purposes, but not "perfect" in any way. Rather, 20/20 vision is slightly defective. It is possible to have 20/20 vision with 0.25 to 0.5 D of defocus, and 20/20 does not imply clear or sharp vision. As [[normalized]] correction typically imposes 0.25 D of extra myopic defocus on [[20/20 correction]], it can be considered to be 0.25 to 0.75 D of undercorrection.

	Tscherning writes in ''Physiologic Optics: Dioptrics of the Eye, Functions of the Retina, Ocular Movements and Binocular Vision'':		Tscherning writes in ''Physiologic Optics: Dioptrics of the Eye, Functions of the Retina, Ocular Movements and Binocular Vision'':

User: /* Reading a Snellen chart */

2022-02-09T16:05:20Z

Reading a Snellen chart

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	* 20/10 is excellent.		* 20/10 is excellent.

	The [[prescription]] for [[myopes]] and [[hyperopes]] is typically the weakest lens power required to achieve 20/20 or better vision measured at [[distance vision\|20 feet or 6 meters]]. The prescription for a [[presbyope]] is the smallest plus power added to the distance prescription to see 20/20 at 40 cm.		The [[prescription]] for [[myopes]] and [[hyperopes]] is typically the weakest lens power required to achieve 20/20 or better vision measured at [[distance vision\|20 feet or 6 meters]]. The prescription for a [[presbyope]] is the smallest plus power added to the distance prescription to see 20/20 at 40 cm. Emmetropic presbyopes have zero distance prescription, so their near prescription is simple spherical [[plus lenses]].

	===Caveats===		===Caveats===

User: /* Reading a Snellen chart */

2022-02-09T16:02:52Z

Reading a Snellen chart

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	{{main\|Snellen chart}}		{{main\|Snellen chart}}
	* 20/200 would be very bad (possibly just [[myopic]]),		* 20/200 would be very bad (possibly just [[myopic]]),
	* 20/70 ~~(with best possible correction)~~ is a typical threshold of low vision,		* 20/70 is a typical threshold of low vision (being unable to read 20/70 with best possible correction),
	* 20/20 is good enough,		* 20/20 is good enough,
	* 20/15 is average, and		* 20/15 is average, and

User at 16:02, 9 February 2022

2022-02-09T16:02:07Z

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	For distance, 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. Lens or mirrors may be used to change the effective test distance in a smaller room.		For distance, 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. Lens or mirrors may be used to change the effective test distance in a smaller room.


	For near, this is typically measured with a near vision test chart at 40 cm.		For near, this is typically measured with a near vision test chart at 40 cm.

User at 16:00, 9 February 2022

2022-02-09T16:00:43Z

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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.		Visual acuity (VA) is the measurement of how well the entire vision system can recognize what it sees. Formally, it is defined as the reciprocal of the smallest angle that the visual system can resolve.

			It will depend on the amount of defocus that [[accommodation]] cannot overcome, as well as other defects such as [[astigmatism]].

			For distance, 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. Lens or mirrors may be used to change the effective test distance in a smaller room.


			For near, this is typically measured with a near vision test chart at 40 cm.

			20/20 (VA of 1) corresponds to an angle of 1 minute of arc. The 20/20 line is 5 minutes of arc in height and width, but the smallest detail subtends 1 arcmin. 20/200 (VA of 0.1) corresponds to 10 arcmin. 20/10 (VA of 2) corresponds to 0.5 arcmin.

	==Reading a Snellen chart==		==Reading a Snellen chart==
	{{main\|Snellen chart}}		{{main\|Snellen chart}}
	* 20/200 would be very bad (possibly just [[myopic]]),		* 20/200 would be very bad (possibly just [[myopic]]),
	* 20/20 is ~~(by definition) normal~~, and		* 20/70 (with best possible correction) is a typical threshold of low vision,
			* 20/20 is good enough,
			* 20/15 is average, and
	* 20/10 is excellent.		* 20/10 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~~.		The [[prescription]] for [[myopes]] and [[hyperopes]] is typically the weakest lens power required to achieve 20/20 or better vision measured at [[distance vision\|20 feet or 6 meters]]. The prescription for a [[presbyope]] is the smallest plus power added to the distance prescription to see 20/20 at 40 cm.

			===Caveats===
	With text that we are familiar with, the brain may clear up that text more than our vision would actually allow.		With text that we are familiar with, the brain may clear up that text more than our vision would actually allow.

			20/20 is "good enough" for most purposes, but not "perfect" in any way. Rather, 20/20 vision is slightly defective. It is possible to have 20/20 vision with 0.25 to 0.5 D of defocus, and 20/20 does not imply clear or sharp vision. As [[normalized]] correction typically impose 0.25 D of extra myopic defocus on [[20/20 correction]], it can be considered to be 0.25 to 0.75 D of undercorrection.

			Tscherning writes in ''Physiologic Optics: Dioptrics of the Eye, Functions of the Retina, Ocular Movements and Binocular Vision'':
			<blockquote>We have found also that the best eyes have a visual acuity
			which approaches 2, and we can be almost certain that if, with a good illumination, the acuity is only equal to 1, the eye presents defects sufficiently pronounced to be easily established.</blockquote>

	==Reasons differing visual acuity==		==Reasons differing visual acuity==
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	==20/x==		==20/x==
	Shorthand for 20 over a single digit, or considerably better than 20/20 vision.		Shorthand for 20 over a single digit (such as 20/9), or considerably better than 20/20 vision (VA > 2).

	==See Also==		==See Also==

User: /* Reading a Snellen chart */

2021-09-18T19:38:12Z

Reading a Snellen chart

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	==Reading a Snellen chart==		==Reading a Snellen chart==
	{{main\|Snellen chart}}		{{main\|Snellen chart}}
	* 10/~~400~~ would be very bad (possibly just [[myopic]]),		* 20/200 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.		* 20/10 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.