Difference between revisions of 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 '''spherical equivalent''' of cylinder lenses may be useful, to simplify the reduced lens path. 0.50 cylinder ~~is equivalent~~ to 0.~~25 sphere~~. 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 ~~perfectly tailored~~ for the ~~astigmatic blur~~, so it ~~leaves a small amount of "useful~~ 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". The resulting spherical equivalent is not intended to compensate for the asymmetry of the lens, so it will introduce some directional blur.

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.

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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 '''spherical equivalent''' of cylinder lenses may be useful, to simplify the reduced lens path. 0.50 cylinder is equivalent to 0.25 sphere. 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 perfectly tailored for the astigmatic blur, so it leaves a small amount of "useful 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". The resulting spherical equivalent is not intended to compensate for the asymmetry of the lens, so it will introduce some directional blur.
 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.