Bifocal Inset and Prism

[DazeyReign]

Doc presented Optical with this quandary:

Post Cat Patient's Rx is: +0.50 -1.25 x 158 Add 2.25 3.50 BU prism seg 11
(FT 35) +0.25 -0.50 x 27 Add 2.25 3.50 BD prism seg 13
This Rx has her clear at Distance but double in the near.

She refracts at 3 BI OU/10 BU OD in the distance and 14 BI OU/15 BU OD. He is wondering what we would do to fix it. We all agree on an inset Doc is thinking 7. My math (I'm new at this and an English major to boot!) shows more like 6 - 6.5. Seems like that amount of prism you'd want as much accuracy as possible.

Does it matter? Is there another soulution?

Thanks for any input!

[obxeyeguy]

????? Can't make out exactly what you need here. If you are trying to induce base in, seg only, 3-5 mm more with a +2.25 add induces minimal.

[Robert Martellaro]

She refracts at 3 BI OU/10 BU OD in the distance and 14 BI OU/15 BU OD.

If you mean 3∆ BI total distance, and 14∆ BI total near, then the prism seg in one eye should be 11∆ BI. The vertical prism at near may be a prism seg of 5∆ BU in the right, or 5∆ BD in the left, depending on which eye gets the BI prism seg.

Use unequal seg heights due to the distance vertical prism.

Prism segs are usually about 22mm in width.

Consider separates if applicable. If so, consider a Fresnel press-on prism on one eye for all of the prism for the SV readers.

[DazeyReign]

I agree that seperate distance and reading spectacles are the actual answer but "Patient wants bifocals, since it's all she's ever worn, so that's what we're going to give her."

[Robert Martellaro]

I agree that seperate distance and reading spectacles are the actual answer but "Patient wants bifocals, since it's all she's ever worn, so that's what we're going to give her."

One workaround that might be worth evaluating is to position the segment line very high, at least as high as a trifocal, minimizing the degree of ocular rotation required for near, maybe enough to allow the client to see near objects, for short periods of time, without diplopia.

If this works, supplement with SV readers, for sustained close tasks, as needed.

There's risk of rejection from the high seg though. OTOH, prism segs (and Franklins for the most part) are not cosmetically pleasing, are expensive, and also require adaptation.

Please follow up with the results after the final fitting.