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Peter, If your refraction is -0.75 Cyl, this means that you need a cylindrical or astigmatic lens at a certain axis which should be also specified on your prescription. Any correcting lens of this type will (should) have one or two engraved lines on the periphery which indicate the orientation of the lenses in the mount. Astigmatic (or toric) lenses are orientation sensitive.
I suspect that 0.75 Dioptrix lenses will be +spherical form, which can be easily duplicated by racking the eyepiece in a millimetre or so, and won't correct for astigmatism. Check with your supplier of the Dioptrix before laying out the cash.
If you have any doubts, take the lenses to your prescriber for verification.
OOPs, See below.
Last edited by GraemeT; 06-06-2013 at 08:04 PM.
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