Have a patient whose most previous Rx was
+2.25 +1.00 180
+2.25 DS
Add: +2.75
New Refraction improves VA on the left eye to 20/30
+2.50 +1.00 180
+1.75 DS
Add: +2.75
Alas, we have a new issue of prismatic imbalance. To boot, my patient likes low segs in her FT28s, so I estimate her reading line to be 12-13mm below her distance gaze.
The lit I've read says to worry about prismatic differentials on the 90 above 1.50D/cm. Me and my calculator have her at ~2.2D.
A small slab off is possible, but I'm wondering if differing ADDs (assuming the doc's ok with it) would address this issue more cosmetically?
I've seen a rule of thumb of .25 bump in add power per 4 diopters difference in [adjusted] sphere powers. That would suggest a fairly minute differential of add powers for my patient and perhaps not all that feasible.
Not sure what "the real" equation is here--figured there's 2 dozen eyeballs attached to genius brains around these parts who can tell me if and why I'm on a dead-end tangent.
I might be lucky enough that one of them does!
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