Adjusting OC for Bifocal FT28 Surgey Loops Help!

I was handed an older pair of sv surgery glasses with loops attached to the bridge and asked to make it into a pair of lined bifocals. My question is concerning the PD/OC and seg measurements. These loops are set inwards slightly and flip down over the front of the glasses. If I dot the center of the back of the lenses like a bullseye, where the loops rest, it's going to be about 10 mm above where the ft28 line could comfortably start as to not be in the line of sight when looking through them. I don't want to induce prism or unwanted astigmatism. They also sit towards the bottom of the glasses, it's double bridge style of frame and my doctor has an rx with astigmatism and -3.00 with a +2.00 add.

1. Should I specify an OC height of this bullseye marking with the lab and a separate seg height? I know std OC is set 5 mm above FT28 typically. OR should I set the oc height instead of the center of the loops circle, but just above the bottom viewing rim instead, as I know most people don't like looking below their oc but are okay looking above on a sv pair typically. Or leave it alone and just specify seg and be done with it.

2. Should I measure and use the pd from the pen markings of the center of each bullseye or use a normal far pd? Would this produce possible errors in decentration if i used the far pd? I don't have the near pd on file.

Any guidance would be greatly appreciated!

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Originally Posted by Crystalpluto

I was handed an older pair of sv surgery glasses with loops attached to the bridge and asked to make it into a pair of lined bifocals. My question is concerning the PD/OC and seg measurements. These loops are set inwards slightly and flip down over the front of the glasses. If I dot the center of the back of the lenses like a bullseye, where the loops rest, it's going to be about 10 mm above where the ft28 line could comfortably start as to not be in the line of sight when looking through them. I don't want to induce prism or unwanted astigmatism. They also sit towards the bottom of the glasses, it's double bridge style of frame and my doctor has an rx with astigmatism and -3.00 with a +2.00 add.

1. Should I specify an OC height of this bullseye marking with the lab and a separate seg height? I know std OC is set 5 mm above FT28 typically. OR should I set the oc height instead of the center of the loops circle, but just above the bottom viewing rim instead, as I know most people don't like looking below their oc but are okay looking above on a sv pair typically. Or leave it alone and just specify seg and be done with it.

2. Should I measure and use the pd from the pen markings of the center of each bullseye or use a normal far pd? Would this produce possible errors in decentration if i used the far pd? I don't have the near pd on file.

Any guidance would be greatly appreciated!

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You need to find out what the surgeon is going to be looking at with the bifocal. Presumably his tools mostly in the near and screens at the distance. Also, what kind of surgeon (Can determine positioning.) Were the sv lenses before for distance, intermediate, or near vision? Once you know those, we can find a comfortable position for the bifocal. You can tell the lab to make the OC 10 mm above the seg, that would avoid any unwanted prism, as long as they are not trying to use them outside of surgery. If they are, you'll be okay keeping it at normal OC.

You need to know how he's using those. I don't think many loupes have a "flip-up" function (most kinds I've seen are more fixed, but can loosen a screw and move it around). Therefore I'm guessing he's leaving them down all the time and looking through them for procedures. That's step one.

Next, if he's going to look around the loupe (below it), what's he trying to do? Look at his watch? A puddle of intestines on a table? What add power would that require? I'd assume you'd want that segment line right up against the bottom of the loupe, then.

(Pariah's right...oops)

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Originally Posted by drk

You need to know how he's using those. I don't think many loupes have a "flip-up" function (most kinds I've seen are more fixed, but can loosen a screw and move it around). Therefore I'm guessing he's leaving them down all the time and looking through them for procedures. That's step one.

Next, if he's going to look around the loupe (below it), what's he trying to do? Look at his watch? A puddle of intestines on a table? What add power would that require? I'd assume you'd want that segment line right up against the bottom of the loupe, then.


(Pariah's right...oops)

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lol Great minds think alike! I've noticed more and more oral surgeons wearing the flip ups actually.

Flip ups would be the best.

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Originally Posted by drk

Flip ups would be the best.

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They're so much easier to fit for prescription as well.