Originally Posted by
Darryl Meister
Also, are you using a focimeter (i.e., lensomter or vertometer or lensmeter) to measure your resultant prism? Have you tried using a lens clock to double-check? Are you certain the prism is wrong? Keep in mind that a 3.25 PD slab-off will only correct about half of the vertical imbalance that you would see in the bifocal segment with that prescription... (Even if the lens stop of the focimeter was right up at the bi/tri line, the center of the stop would still be roughly 15 mm below the distance optical center, which results in about 2.25 BD in the right and 2.25 BU in the left -- a difference of 1.25 PD once you subtract the 3.25 BU slab-off prism.) Consequently, you may in fact be getting the correct results.
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