Will different power make SH look off?

**Paulie** · 08-08-2009, 06:53 PM

Hello, I have a pt who's Rx is OD -0.50 -100X130 OS +1.75 -1.00X035 with a +250 in a poly trifocal. Her complaint is that she sees the top of the seg on the OS sooner. I measure them and it's dead on and looking at them off her face it's symetrical across both lenses. But looking at them on her face, it does look like the left seg is 1mm higher. Any suggestion? Remake OS with a 1mm lower SH. thx

**DragonLensmanWV** · 08-08-2009, 07:08 PM

The higher add trifocal has a larger lip and thus is easier to see.

**braheem24** · 08-08-2009, 08:40 PM

Originally Posted by Paulie

But looking at them on her face, it does look like the left seg is 1mm higher.

...or her left eye is 1mm lower :p, if the lenses are on the large side try shaving the top of the OD and bottom of the OS to grind the left down. If not remake and specify OCs to the lab.

**harry a saake** · 08-09-2009, 05:57 PM

nothing much your going to do will help much, the problem is the ledge of the seg is being magnified in the os and demagnified in the od, so naturally she picks up that ledge easier.

you can try round segs and that would probaly eliminate the problem, if you can still find them

years ago, i think it was univis, came up with this bright idea of putting serrations across the top of their flattop segs, so they could be identified as being theirs, guess how many remakes their was with that, especially with the hyperopes

**Bob MacNeil** · 08-09-2009, 07:52 PM

Have they used a Bicentric before.... the reading could use some correction.

Bob

**Darryl Meister** · 08-10-2009, 06:33 PM

While a "hyper eye" (one eye at a different level than the other) will produce this effect, as well as a poorly adjusted frame, a significant difference in prescription powers will produce the same effect due to the difference in prism as the images of the bifocal segments are refracted through the lenses.

The other issue relates to the apparent "curve" of segment ledges on steeper base curves.

**mike.elmes** · 08-10-2009, 06:54 PM

I have had many customers over the years complain about seeing "the line" on one eye....even though it looks dead even with the other eye. This is due to the vertex distance being unequal. Adjust the frame to have a closer vertex distance on the eye that is noticing the line....