prism

[seeknowevil1]

I ran across a problem today at work and was not all the way sure what the answer was or for that matter is. My lab manager did not have the answer either. The problem is that a patient came in and said that she had been at one of our other stores 4 times and she still had problems seeing out of them. The RX was OD +150-50 OS Pl-25 2 BI Prism OU, She was wearing a Trifocal. My question is Should the OS be treated as a minus? My feeling is that it is and therefore the base would be opposite. Basically spotting up in the same position in the lensometer. It was spotting up 2 BI on each lens therefore opposite sides in the the lensometer. Anyone have any advice they can share?

[braheem24]

Lensometer mires should be deviating towards the nosepads on both sides; no matter plus or minus rx.

Left mires should resemble image below, image below only has 1BI OS

[standarduck]

You'll find the base is always in the same direction, regardless of +/- powers. It's the decentration which is in the opposite direction.

[jonathan barber]

What had she previously been wearing (rx, lens style, PD/Seg Measurments, base curves, lens material, frame size)? Are the position of wear measurements (face form/pantoscopic tilt) similar? Is prismatic correction new to her? Is it a clarity issue (near or far) or is it distorted/doubled?