Difference between revisions of Astigmatism

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==Reducing astigmatism==

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, 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.

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".

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 ==Reducing astigmatism==
-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, 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.
+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".