Difference between revisions of Astigmatism

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Astigmatism often reduces spontaneously as myopia is corrected.

==Symptoms==

Uncorrected and uncompensated astigmatism appears as ''directional blur'' or ''[[double vision]]''. [[Transient astigmatism]] also occurs when making spherical reductions. According to EM, the [[visual cortex]] compensates for irregularities in the cornea. If the [[double vision]] is just a little bit, the visual cortex can learn to fuse double vision and change the compensation.

==Understanding astigmatism==

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As with myopia, astigmatism should be tackled in small steps when selecting lenses for [[differential]] or [[normalized]] glasses. If only a small amount of cylinder correction is present, say 0.25 [[diopters]], the cylinder correction can be dropped, with no other changes. Otherwise, cylinder should be reduced in small increments. If sphere is being reduced, cylinder should not be changed at the same time, and conversely, if cylinder is being reduced then sphere should not be changed. The only time that both sphere and cylinder should be changed, is when converting to the spherical equivalent.

The link between astigmatism strength and visual acuity is weak. How your eyes and [[visual cortex]] respond to astigmatism is a greater factor in visual acuity than the number of dipoters.<ref>{{Cite journal |last=Remón |first=Laura |last2=Tornel |first2=Marta |last3=Furlan |first3=Walter D. |date=2006-05 |title=Visual Acuity in Simple Myopic Astigmatism: Influence of Cylinder Axis |url=https://journals.lww.com/optvissci/Abstract/2006/05000/Visual_Acuity_in_Simple_Myopic_Astigmatism_.11.aspx |journal=Optometry and Vision Science |language=en-US |volume=83 |issue=5 |pages=311–315 |doi=10.1097/01.opx.0000216099.29968.36 |issn=1538-9235}}</ref> If the standard advice for correcting astigmatism does not work for you, you may need a more gradual reduction.

The average person with medium-to-high myopia should wait until having reduced norms/diffs twice each before reducing cylinder for the first time. Then wait a minimum of 8 weeks before introducing the next spherical reduction, and wait 6 months before introducing the next cylinder reduction.

Regardless of how the myope reduces their lenses, the goal of each reduction is to have a small amount of "useful blur", to be cleared up with [[active focus]] and good habits.

~~==Spherical equivalent==~~

The '''spherical equivalent''' of cylinder lenses may be useful, to simplify the reduced lens path. 0.50 cylinder means the power varies from 0D on one axis to 0.5D on the perpendicular axis. This can be substituted by the spherical power with the averaged value of 0.25D. For example, a full prescription of "-1.00 Sphere -1.50 Cylinder" could be converted to "-1.75 Sphere". The resulting spherical equivalent is not intended to compensate for the asymmetry of the lens, so it will introduce some directional blur.

===Axis===

When reducing cylinder value, you should never change the axis value if it has been consistent for some time. The axis only refers to the orientation in which the cylinder is affecting your eyes, and any reduction of cylinder will happen on this orientation.

==Spherical equivalent==

The '''spherical equivalent''' of cylinder lenses may be useful, to simplify the reduced lens path. 0.50 cylinder means the power varies from 0D on one axis to 0.5D on the perpendicular axis. This can be substituted by the spherical power with the averaged value of 0.25D. For example, a full prescription of "-1.00 Sphere -1.50 Cylinder" could be converted to "-1.75 Sphere".

A common [[reduction]] is to trade 0.5 cylinder to its spherical equivalent of 0.25 sphere (of the same sign).

* For example, -2 sph -1 cyl (equivalently, -3 +1) is reduced to -2.25 -0.5 or -2.75 +0.5.

The resulting spherical equivalent is not intended to compensate for the asymmetry of the lens, so it will introduce some directional blur.

==Resources==

* [https://endmyopia.org/the-definitive-guide-astigmatism/ EndMyopia Blog - The Definitive Guide: What Is Astigmatism]

* [[Astigmatism measurement]]

* [https://endmyopia.org/the-definitive-guide-astigmatism/ EndMyopia Blog - The Definitive Guide: What Is Astigmatism] (2013)

* [https://endmyopia.org/astigmatism-the-big-guide-summary/ EndMyopia Blog - Astigmatism: The Big Guide & Summary] (2021)

* [https://endmyopia.org/tag/astigmatism-2/ EndMyopia Blog - all astigmatism articles]

* [https://endmyopia.org/diy-tools-how-to-measure-your-astigmatism-diopters/ How To Measure Your Astigmatism Diopters]

* [https://visiontools.netlify.app/ Vision tool]

* [https://community.endmyopia.org/t/having-trouble-figuring-out-my-astigmatism/4843/6 Astigmatism Assasin's guide]

* [https://www.youtube.com/watch?v=KDgU4AoFsA4 Fixing Astigmatism - Jake Steiner]

* [https://drboulet.com/wp-content/uploads/2016/07/Forrest-a-new-model-of-functional-astigmatism.pdf Functional astigmatism]

==References==

@@ Line 2: / Line 2: @@
 Astigmatism often reduces spontaneously as myopia is corrected.
+==Symptoms==
+Uncorrected and uncompensated astigmatism appears as ''directional blur'' or ''[[double vision]]''. [[Transient astigmatism]] also occurs when making spherical reductions. According to EM, the [[visual cortex]] compensates for irregularities in the cornea. If the [[double vision]] is just a little bit, the visual cortex can learn to fuse double vision and change the compensation.
 ==Understanding astigmatism==
@@ Line 50: / Line 53: @@
 As with myopia, astigmatism should be tackled in small steps when selecting lenses for [[differential]] or [[normalized]] glasses. If only a small amount of cylinder correction is present, say 0.25 [[diopters]], the cylinder correction can be dropped, with no other changes. Otherwise, cylinder should be reduced in small increments. If sphere is being reduced, cylinder should not be changed at the same time, and conversely, if cylinder is being reduced then sphere should not be changed. The only time that both sphere and cylinder should be changed, is when converting to the spherical equivalent.
 The link between astigmatism strength and visual acuity is weak.  How your eyes and [[visual cortex]] respond to astigmatism is a greater factor in visual acuity than the number of dipoters.<ref>{{Cite journal |last=Remón |first=Laura |last2=Tornel |first2=Marta |last3=Furlan |first3=Walter D. |date=2006-05 |title=Visual Acuity in Simple Myopic Astigmatism: Influence of Cylinder Axis |url=https://journals.lww.com/optvissci/Abstract/2006/05000/Visual_Acuity_in_Simple_Myopic_Astigmatism_.11.aspx |journal=Optometry and Vision Science |language=en-US |volume=83 |issue=5 |pages=311–315 |doi=10.1097/01.opx.0000216099.29968.36 |issn=1538-9235}}</ref>  If the standard advice for correcting astigmatism does not work for you, you may need a more gradual reduction.
+The average person with medium-to-high myopia should wait until having reduced norms/diffs twice each before reducing cylinder for the first time.  Then wait a minimum of 8 weeks before introducing the next spherical reduction, and wait 6 months before introducing the next cylinder reduction.
 Regardless of how the myope reduces their lenses, the goal of each reduction is to have a small amount of "useful blur", to be cleared up with [[active focus]] and good habits.
-==Spherical equivalent==
-The '''spherical equivalent''' of cylinder lenses may be useful, to simplify the reduced lens path. 0.50 cylinder means the power varies from 0D on one axis to 0.5D on the perpendicular axis. This can be substituted by the spherical power with the averaged value of 0.25D. For example, a full prescription of "-1.00 Sphere -1.50 Cylinder" could be converted to "-1.75 Sphere". The resulting spherical equivalent is not intended to compensate for the asymmetry of the lens, so it will introduce some directional blur.
 ===Axis===
 {{Main|Axis}}
 When reducing cylinder value, you should never change the axis value if it has been consistent for some time. The axis only refers to the orientation in which the cylinder is affecting your eyes, and any reduction of cylinder will happen on this orientation.
+==Spherical equivalent==
+{{Main|Diopters#Spherical Equivalent}}
+The '''spherical equivalent''' of cylinder lenses may be useful, to simplify the reduced lens path. 0.50 cylinder means the power varies from 0D on one axis to 0.5D on the perpendicular axis. This can be substituted by the spherical power with the averaged value of 0.25D. For example, a full prescription of "-1.00 Sphere -1.50 Cylinder" could be converted to "-1.75 Sphere".
+A common [[reduction]] is to trade 0.5 cylinder to its spherical equivalent of 0.25 sphere (of the same sign).
+* For example, -2 sph -1 cyl (equivalently, -3 +1) is reduced to -2.25 -0.5 or -2.75 +0.5.
+The resulting spherical equivalent is not intended to compensate for the asymmetry of the lens, so it will introduce some directional blur.
 ==Resources==
-* [https://endmyopia.org/the-definitive-guide-astigmatism/ EndMyopia Blog - The Definitive Guide: What Is Astigmatism]
+* [[Astigmatism measurement]]
+* [https://endmyopia.org/the-definitive-guide-astigmatism/ EndMyopia Blog - The Definitive Guide: What Is Astigmatism] (2013)
+* [https://endmyopia.org/astigmatism-the-big-guide-summary/ EndMyopia Blog - Astigmatism: The Big Guide & Summary] (2021)
 * [https://endmyopia.org/tag/astigmatism-2/ EndMyopia Blog - all astigmatism articles]
 * [https://endmyopia.org/diy-tools-how-to-measure-your-astigmatism-diopters/ How To Measure Your Astigmatism Diopters]
 * [https://visiontools.netlify.app/ Vision tool]
-* [https://community.endmyopia.org/t/having-trouble-figuring-out-my-astigmatism/4843/6 Astigmatism Assasin's guide]
+<!-- * [https://community.endmyopia.org/t/having-trouble-figuring-out-my-astigmatism/4843/6 Astigmatism Assasin's guide] forum access required; not a public link -->
 * [https://www.youtube.com/watch?v=KDgU4AoFsA4 Fixing Astigmatism - Jake Steiner]
+* [https://drboulet.com/wp-content/uploads/2016/07/Forrest-a-new-model-of-functional-astigmatism.pdf Functional astigmatism]
 ==References==