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Difference between revisions of Cylinder

 
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'''Cylinder''' lenses correct for [[astigmatism]]. It's represented as CYL on [[prescriptions]].
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'''Cylinder''' lenses correct for the most common kind of [[astigmatism]]. It's represented as CYL on [[prescriptions]]. The lens is shaped like a cylinder rather than a sphere, bending light in one direction, but not in the other.  The direction is specified by the [[Axis]].
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==Positive vs. Negative Cylinder==
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Eyecare professionals have individual preferences for writing out positive vs negative values for cyl.  For discussion with other EM participants, it is usually recommended to convert positive cylinder values into their negative equivalent, as the negative cylinder values are potentially more intuitive from a reduction point of view. 
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* For example, there are participants who get surprised [https://www.youtube.com/watch?v=AJQEdXwKiNA&t=1363s when they remove plus cylinder, and then find that the glasses they order are too strong].
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* [https://www.aclens.com/positive-cyl-converter There are tools that will convert between equivalent prescriptions of plus or negative cylinder]
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* [https://www.youtube.com/watch?v=0AyE1BmKUh8 Gemily's video explaining plus vs negative cylinder]
  
 
==References==
 
==References==

Latest revision as of 19:00, 10 October 2022

Cylinder lenses correct for the most common kind of astigmatism. It's represented as CYL on prescriptions. The lens is shaped like a cylinder rather than a sphere, bending light in one direction, but not in the other. The direction is specified by the Axis.

Positive vs. Negative Cylinder

Eyecare professionals have individual preferences for writing out positive vs negative values for cyl. For discussion with other EM participants, it is usually recommended to convert positive cylinder values into their negative equivalent, as the negative cylinder values are potentially more intuitive from a reduction point of view.

References