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PALs Bi-Convex at Near?

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    I think that's the way to verify any front surface multifocal, even segmented. Right? Not that anyone does that. I don't think that's proof.


      The reason you turn a segmented lens around to check the power of the add is this eliminates the thickness of the lens which adds plus power to the seg. When you do this you must read the distance as well as the seg reversed and the difference is the power of the seg. The explanation from Andy makes no sense to me.


        For segmented multifocals I'd agree, that's also how I was taught to verify them, convex side facing down. Reading distance and near Rx separately, then deducting the difference to get the add.

        The lenses being discussed here are progressives, however, and not segmented multifocals.

        For progressives, be it manual or digital lens meters, with the old front surface designs I never saw issues verifying the add even with the concave side facing downwards towards the lens meter stop. The distance and near Rx consistently could be verified as such, even if the method was wrong.

        When everyone started moving progressive optics to the back surface, the add often read weaker than even the compensated/recalculated/etc modified Rx the labs provided for verification.

        Explanation given by the labs was that it was not a production defect. So we were told to flip the lens and verify the back surface progressive as if it was a segmented multifocal, for the reason as described in my first post.

        Doing so yielded verified Rx within tolerances, and wearers had good vision + feedback with the lenses on dispense, therefore I left it at that.