B What does "1 diopter of astigmatism" mean?

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One diopter of astigmatism refers to the measurement of the difference in optical power between two principal axes of a lens. This measurement indicates how much correction is needed to address the distortion caused by astigmatism. The concept can be visualized by slicing a lens along its axes to create circularly symmetric lenses, with the power difference reflecting the astigmatism level. Additionally, prescriptions may denote astigmatism using a cylinder measurement, such as 0.4Cyl, along with an angle. Understanding these terms is crucial for effective vision correction.
KayT256
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The measurement for astigmatism is diopter. But what does 1 diopter of astigmatism mean?
Thanks a lot if you help me figure this out!
 
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Do you know what astigmatism is and what a diopter is?
 
Ibix said:
Do you know what astigmatism is and what a diopter is?
Yes, I do. I know about diopters when I studied optical lenses, and I have also done some research about astigmatism.
 
Then it's the difference in optical power along the two principal axes.

Slice the lens through parallel to one axis and make a circularly symmetric (i.e. non-astigmatic) lens with the profile you see. Slice the lens through parallel to the other axis and make another circular lens with this profile. The difference in power of the two circular lenses will be the number of diopters of astigmatism in the original lens.
 
Ibix said:
Then it's the difference in optical power along the two principal axes.

Slice the lens through parallel to one axis and make a circularly symmetric (i.e. non-astigmatic) lens with the profile you see. Slice the lens through parallel to the other axis and make another circular lens with this profile. The difference in power of the two circular lenses will be the number of diopters of astigmatism in the original lens.
An alternative description is the addition of a cylinder with focal length 1m (as I remember). On my prescription they write 0.4Cyl and the angle.
 
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