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This question already has an answer here:

I have just discovered that if I rotate my left spectacle lens about the vertical axis by 10 degrees in one direction, the vision in that eye becomes much crisper.

Note that the sphere and cylinder prescriptions in the (unrotated) lens were confirmed yesterday by an optometrist as being the best I could get -- but simply by yawing the lens I can see much better.

What is this rotation correcting? Is it physically possible to create a lens with the same correction but without the rotation?

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marked as duplicate by Qmechanic Aug 2 '13 at 16:03

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    $\begingroup$ possible duplicate of Why nearsighted people see better with their glasses *rotated*? $\endgroup$ – Mo_ Aug 2 '13 at 12:41
  • $\begingroup$ Thanks for the link -- it looks like I might be correcting horizontal coma in the eye. I'm still wondering how this works optically and whether a single unrotated lens can do the same job. $\endgroup$ – Tom Shaw Aug 2 '13 at 12:49
  • $\begingroup$ I have the same questions! I asked that question, and nobody has posted an acceptable answer yet. $\endgroup$ – Mo_ Aug 2 '13 at 12:54

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