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To be optically equivalent, the lens made from lower index of refraction material needs to be thicker. My guess is that your optician thinks the metal grooved frames you want won't work well with ...
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#1: Initial revision
by
Olin Lathrop
·
2021-02-25T21:50:14Z (over 3 years ago)
To be optically equivalent, the lens made from lower index of refraction material needs to be thicker. My guess is that your optician thinks the metal grooved frames you want won't work well with the outer thickness of the lenses. Note that he's not saying 1.74 index is bad, but just that it's somewhat incompatible <i>with the particular frames you have chosen</i>. -7 and even -6 is rather extreme. This limits other tradeoffs.