Press-on prism over/under ground prism

**TLG** · 03-21-2013, 01:00 PM

Hey Everyone,
I have a guy currently wearing 6BO OU prism ground into his lenses. He has Graves disease and recently had surgery to decompress pressure in his eyes to reduce bulging.

His newest Rx requires an additional 26 BO total and I need some help getting my brain around this one.
1. If I place press-on prisms over his current 6BO will the result be additive?
2. I have a pair of 12's so I can easily provide the first 24. After applying them to the back, I'll still be a little short so I'm hoping to (temporarily at least, to achieve full prism) put a pair of 1's on the front. But I'm starting to think about all this stacked on top of each other -> 1pd on top of a ground 6pd and another 12pd stuck on the back. Is that gonna get me there?

We have prism bars so I should be able to check the accuracy, but I'm trying to anticipate any contingences ahead of time.

I'm open for any other ideas that don't involve grinding lenses at this time.

Thanks!!

**HindSight2020** · 03-21-2013, 01:07 PM

Originally Posted by TLG

Hey Everyone,
I have a guy currently wearing 6BO OU prism ground into his lenses. He has Graves disease and recently had surgery to decompress pressure in his eyes to reduce bulging.

His newest Rx requires an additional 26 BO total and I need some help getting my brain around this one.
1. If I place press-on prisms over his current 6BO will the result be additive?
2. I have a pair of 12's so I can easily provide the first 24. After applying them to the back, I'll still be a little short so I'm hoping to (temporarily at least, to achieve full prism) put a pair of 1's on the front. But I'm starting to think about all this stacked on top of each other -> 1pd on top of a ground 6pd and another 12pd stuck on the back. Is that gonna get me there?

We have prism bars so I should be able to check the accuracy, but I'm trying to anticipate any contingences ahead of time.

I'm open for any other ideas that don't involve grinding lenses at this time.

Thanks!!

Any additional prism over existing lenses would be additive. If memory serves me correctly, you can still get a 20D Fresnel which would sure beat cutting and stacking all of them up on top of each other.

**Mick** · 03-21-2013, 01:17 PM

don't forget the decrease in acuity with press on's. Stacking them would make it even worse.

**TLG** · 03-21-2013, 01:35 PM

Originally Posted by HindSight2020

Any additional prism over existing lenses would be additive. If memory serves me correctly, you can still get a 20D Fresnel which would sure beat cutting and stacking all of them up on top of each other.

Thanks. I even have a 20 but would prefer to split evenly...for now anyway ;), but good point as that might be a solution if stacking creates problems.

This is gonna seem like looking thru filthy glasses I'm afraid...

**MakeOptics** · 03-21-2013, 01:44 PM

Originally Posted by TLG

Thanks. I even have a 20 but would prefer to split evenly...for now anyway ;), but good point as that might be a solution if stacking creates problems.

This is gonna seem like looking thru filthy glasses I'm afraid...

Additive if the bases are oriented in the same direction and rather than splitting the other 2 diopters between the two eye's I would put it all in the least dominant eye, or the eye with the worst visual acuity on the front. Not a particularly handsome solution but it would work. There will definately be a loss in visual acuity looking through 2 Fresnel prism so just apply to the weaker eye.

**optical24/7** · 03-21-2013, 01:50 PM

Originally Posted by PhiTrace

Additive if the bases are oriented in the same direction and rather than splitting the other 2 diopters between the two eye's I would put it all in the least dominant eye, or the eye with the worst visual acuity on the front. Not a particularly handsome solution but it would work. There will definately be a loss in visual acuity looking through 2 Fresnel prism so just apply to the weaker eye.

Agreed. Also; They make a 25D fresnel (no 26), but that should work. Don't try to stack or apply to both side, just use one 25D on their weaker eye as Phi sugests. Also, keep in mind this much prism will displace his pupil over 7mm more (towards the apex) than it is now already with an additional 25 of prism. If he's in a PAL it will become useless to him in that eye. Good luck Tony!

**TLG** · 03-21-2013, 04:11 PM

PhiTrace,
Yeah, I'm starting to think the same; that too many layers is going to pile on problems. Doc likes to split prism when that's the way they've worn it so I think I might be too hung up on that.
Thanks for taking time to reply!

24/7,
Your comment made me take a second look at my stock and I actually have a 25 I hadn't seen before. Based on replies and consideration, I'm going to start with that in the non-dominant eye. That will get me in the ballpark and hopefully over my angst about not splitting it. They're flattop 35's so I think we'll be ok with the displacement you mentioned.
Thanks as always for your thoughtful reply...I owe you a broccoli.