Difference between revisions of Astigmatism

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==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.

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==

* [[Astigmatism measurement]]

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

* [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]

@@ Line 65: / Line 65: @@
 ==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". The resulting spherical equivalent is not intended to compensate for the asymmetry of the lens, so it will introduce some directional blur.
+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==
 * [[Astigmatism measurement]]
-* [https://endmyopia.org/the-definitive-guide-astigmatism/ EndMyopia Blog - The Definitive Guide: What Is Astigmatism]
+* [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]