Options for high-plus add bifocals?

[snowmonster]

My Grandmother is getting into the low vision realm because of dry macular degeneration. One eye is functionally gone while the other is 20/60 to 20/80, depending on the day.

So I made a pair of SV readers with essentially +4.00 over her distance script based on Kestenbaum's rule and put 6 total prism diopters base-in (3 BI per eye) to offset the fact that her eyes will have to converge to 10" in front of her face.

Her distance Rx is roughly +0.50 -1.50 x 080 and +0.50 -1.00 x 120.

So what do I do when I go to make a pair of bifocals with a +4.00 add? Is there any way with a round seg or wider flat top or an exec to create no prism in the distance but induce 3 BI (each eye) at near?

Does anyone still make CR39 ribbon segs with high add powers?

I know Franklins are an option but was thinking there might just be a better way to do it all myself at least.

Thanks!

[braheem24]

One eye is functionally gone

Sorry to hear bro,

Why are you trying to fuse the images if one image is non-existant? I would teach her how to use the peripheral vision in the one eye; which would not only require no prism but also not force her to use her central vision which is probably not as good as her periphery.

Edit:Ever considered doing an HVF and placing the bifocal in the area of her best vision, probably temporally?

[snowmonster]

I was thinking about that while I was typing it, but something seemed weird about it with how much she would still have to converge with the one eye. You're probably right.

[Jacqui]

Do it the easy way, use a Franklin.

[braheem24]

If you want to play labtech for a day here's how I would do it...

Original Rx
+0.50 -1.50 x 080
+0.50 -1.00 x 120
4.00 3BI

interpret the rx at 180...

OD is a -1.00
OS is a plano

that would make the near...

OD +3.00
OS +4.00

For the OD, If you want 3BI on a +3.00 you would need 10mm decentration IN at the near.
For the OS, If you want 3BI on a +4.00 you would need 7mm decentration IN at the near.

Go back to the distance...
If you decenter the OD 10mm too much in the distance you will induce 1 diopter of prism BO.
If you decenter the OS 7mm too much in the distance you will get no prism since the OS is a plano at the 180.

Enter this into your lab program preferrably using a FT-45
+0.50 -1.50 x 080 1BI (1BI to counteract the 1BO you will be inducing)
+0.50 -1.00 x 120
4.00

At edging calculate as usual and add 10mm to the decentration for the OD and 7 for the OS.

If you want to make it symmetrical use the same concept and calculate for 8.5mm decentration each which should roughly be the same except you make have to use 0.85 BI instead of 1BI for the OD.

In the end you will have above rx with no prism in the distance and 6BI total in the near along with envy and a new found respect from your labtechs. :D

(ALL CALCS ARE A ROUGH ESTIMATE)


Good luck :cheers: