# Optical Forums > General Optics and Eyecare Discussion Forum >  How do I use a Fresnel stick-on prism?

## VHB

I figured it would come with directions, but the only directions were for how to clean the lens!  I have absolutely no idea how I'm supposed to use it.  My customer is already wearing progressives with 3.5 base out o.u. and his doctor wants to see if he can tolerate an additional 3 base out on the left eye.  The package shows a picture of someone cutting the lens to the shape of the frame and applying it with water, but surely there's more to it than that.

This is a first for me in forty years in the business!  I will greatly appreciate your help!

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## TylerOpticians

Cut the prism how you want it. Typically the size of a ft 28 bifocal area.  

 Get a bowl of warm water and dip the prism piece into the water for a few minutes. Place it on the backside of the lens and squeeze it down.

 It should stay in place.

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## VHB

So it doesn't cover the whole lens? How do I know where to put it?  I'm sorry to sound so stupid!

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## TylerOpticians

It depends on the patient and the prism you are wanting to induce and which lens you are doing.

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## Dr. Bill Stacy

> So it doesn't cover the whole lens? How do I know where to put it?  I'm sorry to sound so stupid!


Disregard the 7x28 bifocal comment (really, there is no such thing as a 7x28 bifocal, and if the poster would read your post, nothing at all about a multifocal).  From your description, it should cover the whole lens.  Remove the recieving lens from the frame and clean it THOROUGHLY and make sure the Fresnel is clean as well.  Submerge both in water and simply press them together (smooth side of Fresnel against back side of lens), making sure the prism base is OUT and the lines are completely vertical, not tilted. Remove them from water and squeeze out any air bubbles.  Then take a sharp blade, scalpel or xacto knife and carefully trim the excess material from the Fresnel, angling the blade to make a nice bevel cut that's thinnest on the outer edge.  Then take it off and reinsert the lens into the frame, submerge the whole thing again and squeegie it again, and there you have it, just like Hillary did after her concussion.

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## CME4SPECS

The base of the  prism is marked on the side align the lines so they are perpendicular to the 180 line, the base going out on the entire inside surface of the lens. I take the lens out to do this. Cut around the edge of the lens with a slight angle, do that none of the prism overhangs the lens edge. Then take the cleaned lens and prism and dunk into warm water, squeeze out all of the air bubbles and let it set. Dab the lenses dry and it should be good to go.

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## rbaker

Follow directions on packaging.

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## Dr. Bill Stacy

> Follow directions on packaging.


True, and those will probably include a warning about being careful not to slice your fingers...

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## SharonB

I have found it more valuable to use CL (rigid) wetting solution rather than water.... it makes the Fresnel adhere better.

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## VHB

rbaker: that's my point--there were no directions!

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## VHB

CME4SPECS and Dr. Bill Stacy--Thank you both so much!  That's exactly the information that I needed!  Hugs and kisses to you both!

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## optical24/7

1. Determine which eye has better acuity. If both have the same, determine which eye is dominant. You'll want to apply it to the opposite eye. (Prism by itself, along with the material Fresnel's are made of induce higher LCA's and will drop acuity in that eye. Don't take it away from the better eye.)

2. If you have compound prism (both vertical and horizontal components ) Do not use two Fresnel's. (one direction in one eye, the other direction in the other eye) for the same reason listed in #1.

3. With compound prism, figure the resultant prism ( *P**² =  H*² *+**V* ² √) then it's orientation/axis ( *Tan ‾¹  = V/H )

* 4. Once you have the prism direction, place your lens on a protractor and make two marks on the lens front 90 degrees opposite the direction of prism orientation. ( by marking the lens 90 degrees opposite of direction you can use the lines on the Fresnel to align with your marks on the lens front.)

5. Clean both lens back and Fresnel's smooth side, dry. Orient the Fresnel on the back lens surface. (do this dry so the Fresnel doesn't move around). 

6. Use scissors to trim around the lens, cutting about 2-3mm's from the lens edge.

7. While still dry, hold the lens and Fresnel together in the middle tightly while you use a new razor to trim excess off. tilt the razor about 45 degrees. If the lens go into a plastic or metal frame you'll want to make sure you trim it well away from the bevel. If the frame contacts the Fresnel it will usually want to lift off the lens at that point.

8. Once fully trimmed dry, it's time to apply it. There are several ways, one is to submerge both lens and Fresnel fully into a bowl of water, brush any small air bubbles off the two, press together, remove from the water and keep compressing with a paper towel or cleaning cloth. The Fresnel my have moved while doing all of this so check it prior to fully drying it. You can still move it slightly until it is centered and away from the lens edge or bevel.

9. Alternative to water is alcohol. You don't need to submerge it, just pour some into the concave side up. Press the Fresnel down from the center letting the alcohol run off as doing so. Press and dry and orient the same as #8. 


10. Re-insert lens in frame. Carefully clean the lens (pat dry only the Fresnel side.) Be sure to go over cleaning instructions with your patient. Until the water between the Fresnel and lens evaporates, the prism can become dislodged easily. Let the patient know that tiny air bubbles may show up over the 1st day or so. It's just the water evaporating and will go away soon.


That's why I prefer to use alcohol applying Fresnel's. It dehydrates faster than water. I hope this helps, good luck!

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## rbaker

> rbaker: that's my point--there were no directions!


_"The package shows a picture of someone cutting the lens to the shape of the frame and applying it with water, but surely there's more to it than that."_

No, that's all there is to it. It is that simple, particularly for someone with forty years in the trenches!

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## Dr. Bill Stacy

> 1. Determine which eye has better acuity. If both have the same, determine which eye is dominant. You'll want to apply it to the opposite eye. (Prism by itself, along with the material Fresnel's are made of induce higher LCA's and will drop acuity in that eye. Don't take it away from the better eye.)
> 
> 10. Re-insert lens in frame.


On # 1 if you are going to switch the prism from the prescribed side to the other, if it's got any vertical component, don't forget to change that vertical prism by 90 degrees.

On #10, I like to insert the lens alone first into the frame esp if any heat is involved, but also because you might need to do a little more trimming if the Fresnel contacts any part of the frame.

Otherwise, a good recipe.

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## optical24/7

> On # 1 if you are going to switch the prism from the prescribed side to the other, if it's got any vertical component, don't forget to change that vertical prism by 90 degrees.
> 
>  .


Yep, failed to mention that if it's prescribed BU-OD you'd apply BD of putting the prism on the OS. Good catch!

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## VHB

Thanks, everyone.  The doctor specified using the Fresnel on the left lens.  And, mercifully, it isn't a compound prism!

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## fjpod

> I have found it more valuable to use CL (rigid) wetting solution rather than water.... it makes the Fresnel adhere better.


+1

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## Uncle Fester

> Thanks, everyone.  The doctor specified using the Fresnel on the left lens.  And, mercifully, it isn't a compound prism!


http://www.opticampus.com/tools/compounding.php

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## optical24/7

> http://www.opticampus.com/tools/compounding.php



That's cheating!  :Eek:

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## obxeyeguy

> I have found it more valuable to use CL (rigid) wetting solution rather than water.... it makes the Fresnel adhere better.


I was taught 40 years ago to clean them this way, but water to apply.  When I switched from a bead heater to a hilco air, I put it in there on air only to dry it.

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## Robert Martellaro

The instructions from 3M/Fresnel that I remember was to clean both surfaces with a hard lens cleaner, typically LC65 or Lobob, then a light, steady stream of water between surfaces as it's applied from corner to corner or nasal to temporal depending on the ocular curve, or as desired. Don't forget to check the final product before dispense. Consider surfacing the prism for better optics.

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## Dr. Bill Stacy

> . Consider surfacing the prism for better optics.


Of course.  The only possible reason for a Fresnel is a temporary reduction/elimination of diplopia and/or a test run to see if it actually works.  I recommend no more than 1 or 2 weeks.  If still good at that point, grind it in...

Oh, and sorry, I think a permanent Fresnel is probably warranted in high prisms, like 10 P.D. or more, although in a small frame more than 10 might be successfully surfaced.

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## CCGREEN

I'm amazed that VHB got 40 years in before ever touching a fresnel. Hats off to you.
I have spent half my 35 years with OMD's so I have done a few fresnel's. 
And I prefer to use alcohol on them.

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## Tallboy

> That's cheating!


If you ain't cheatin' you ain't tryin'!

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## Dr. Bill Stacy

> I'm amazed that VHB got 40 years in before ever touching a fresnel. Hats off to you.
> I have spent half my 35 years with OMD's so I have done a few fresnel's. 
> And I prefer to use alcohol on them.



In my 40 + years, one thing has amazed me is how little O.D.s and M.D.s seem to prescribe prism at all.  I'm thinking maybe they don't quite get the binocular vision coursework we got back in the day.  One doc I know decided to take out the prism (4^ base out o.u.) because he didn't think it was doing much.  

Of course the patient who had been happy as a clam got instant diplopia that persisted for the entire time he was encouraged to "give it a try".  What part of binocular vision aren't they getting taught?

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## Lelarep

> If you ain't cheatin' you ain't tryin'!


  Amen!   


> In my 40 + years, one thing has amazed me is how little O.D.s and M.D.s seem to prescribe prism at all.  I'm thinking maybe they don't quite get the binocular vision coursework we got back in the day.  One doc I know decided to take out the prism (4^ base out o.u.) because he didn't think it was doing much.    Of course the patient who had been happy as a clam got instant diplopia that persisted for the entire time he was encouraged to "give it a try".  What part of binocular vision aren't they getting taught?


I have a small prism due to an organic injury, and my OD refused to put any prism in my Rx to correct it since he said "You'll get dependent on it", "Its a crutch". Maybe other providers think similarly?

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## Dr. Bill Stacy

Yes, that's something I've heard many times.  But the same docs have no problem prescribing the biggest crutch of them all:  specs.  

And the doc I mentioned above has no problems yanking both crutches out from under the poor ususpecting patient...

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## Robert Martellaro

> Of course.  The only possible reason for a Fresnel is a temporary reduction/elimination of diplopia and/or a test run to see if it actually works.  I recommend no more than 1 or 2 weeks.  If still good at that point, grind it in...


I skip the "try" part and go right to surfacing. My rational is that adaptation might be faster due to the improved optics, and because I rarely see prism remakes from the prescribers in my area. I see about 30 prism Rxs a year.




> Oh, and sorry, I think a permanent Fresnel is probably warranted in high prisms, like 10 P.D. or more, although in a small frame more than 10 might be successfully surfaced.


I've found 10∆ total to be very manageable, even with standard size frames, unless the focal power is very high. The pics below are about 25∆ total BO, SV Trivex low minus.

http://www.fresnel-prism.com/_mod_fi...M_Press_On.pdf

It looks like Fresnel removed the above link from their website.

https://books.google.com/books?id=sV...0apply&f=false

http://www.eyeline.co.nz/uploads/pdfs/3m.pdf

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## smallworld

"I skip the "try" part and go right to surfacing. My rational is that adaptation might be faster due to the improved optics, and because I rarely see prism remakes from the prescribers in my area. I see about 30 prism Rxs a year."

+1 -to me this patient would adapt easier to ground in prism than a Fresnel. Split between the eyes vs testing on OS.

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## Dr. Bill Stacy

Yeah, I meant 10^ *each eye* is pretty much my upper limit.  But I try to go cr39 to reduce the color dispersal. I once tried a pair of trivex with only 2^ base in o.u. and the 3d effects on my computer screen were pretty dramatic. For all high prism I do try to push as much as possible to the non-dominant eye and if there is any significant supression or amblyopia I'll often use a permanent fresnel.  Patients can learn to clean them and re-install pretty easily.  Sometimes I split them and make 2 per fresnel, scotsman that I am...

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## fjpod

We are also doing fewer Fresnels and going right to surfacing, especially if the prism is reasonable and the lenses are SV.  Surfaced prism barely costs more than a regular lens...at least at our lab.  A single Fresnel costs more...

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## Dr. Bill Stacy

> We are also doing fewer Fresnels and going right to surfacing, especially if the prism is reasonable and the lenses are SV.  Surfaced prism barely costs more than a regular lens...at least at our lab.  A single Fresnel costs more...


true, but the real reason for fresnel is not the price.  2mm or so is better than 10 mm or so, and the pt can take them off and on as needed if the visual demands are varied.  That said I only use a pair a year or so.

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## Robert Martellaro

> Yeah, I meant 10^ *each eye* is pretty much my upper limit.


_Now_ I understand.




> But I try to go cr39 to reduce the color dispersal.


I try to minimize weight and chromatic aberration, and maximize chip and crack resistance. Most of the binocular disorders that I see are with the elderly, with sensitive skin around the nose, and sometimes not steady on their feet. The aforementioned high prism case lost only a few letters compared to the trial frame, better than expected, but typical for somewhat lower levels of prescribed prism. 




> I once tried a pair of trivex with only 2^ base in o.u. and the 3d effects on my computer screen were pretty dramatic.


That was due to the prism (spatial distortion), not from chromatic aberration. You should see the same effect from hand-held crown glass trial prism lenses. Anecdotally, mid-forty Abbe lens materials seem to have low enough dispersion levels to provide very good vision for high to occasionally very high levels of prescribed prism.

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## optical24/7

I have a significant patient base that has diplopia. We see multiple patients weekly. ( I have an MD that gets referrals from multiple sources) Many times, sudden onset from stroke. I've seen plenty of patients have upwards of 20D + that needed the prism temporarily, that have a spontaneous recovery (similar to some homogenous hemianopia's). A month or so ago we had a patient that had 24D BO that recovered completely.

I have a direct account with the Fresnel Prism CO. and stock every prism diopter made, from 1 to 40D. The 40's are used to make Peli type prism aids.

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## optical24/7

And Robert is correct in material choice when made in Rx form: Trivex.

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## rdcoach5

Alcohol can fog them up ! Permanently

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## optical24/7

> Alcohol can fog them up ! Permanently


Never, 41 years. Have I'd seen this.

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## Johns

With our new clinic in a large hospital, we also got a direct account with Fresnel, and stock them deep.  The (former chain store) opticians had never seen one, and now they can cut and slap them on faster than changing a push on nosepad!

Have never had an issue with alcohol fogging the prisms.   I use isopropyl 70%.

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## mervinek

I worked in a chain store for a short time while I was in graduate school... I remember a patient coming in with a slab off and the staff brought the guy's glasses back to the lab for me to see the "horrible defect" in his lens.  They kept saying how bad it was that someone let those pass inspection.  So I had to explain that a slab off is not a defect and it is prescribed.  It doesn't surprise me that they don't know what a Fresnel is!

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## mervinek

oh...and I used alcohol many, many times on fresnels and never had any problems.

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## Uncle Fester

Peli type prism aid???

Never mind! Found it on Wiki!!!

Glad to see it was developed in 1999. To me that's a new development.  :Eek:

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## optical24/7

> Peli type prism aid???
> 
> Never mind! Found it on Wiki!!!
> 
> Glad to see it was developed in 1999. To me that's a new development.


I've had limited success with them on Hemianopic patients, but better results than cemented prisms put temporally.

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## Lelarep

Ugh, I wish I had known about this after my iatrogenic neural injury, I had the worst diplopia, and didn't want to get a new Rx with prism since it was likely to go away (still have a little bit, about 0.5 D prism BD when gazing down from a neutral head position, but I'm a head mover due to being used to keeping gaze in the center of the lens, so its a non-issue)

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## Uncle Fester

I have no association with Chadwick Optical but found the site interesting.

Note the research paper at the top of the home page. There's some meat on that bone!

I plan to save the site!!!


http://www.chadwickoptical.com/index.htm

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## Speed

> Of course.  The only possible reason for a Fresnel is a temporary reduction/elimination of diplopia and/or a test run to see if it actually works.  I recommend no more than 1 or 2 weeks.  If still good at that point, grind it in...
> 
> Oh, and sorry, I think a permanent Fresnel is probably warranted in high prisms, like 10 P.D. or more, although in a small frame more than 10 might be successfully surfaced.


Are you _REALLY_ an OD?

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## Dr. Bill Stacy

California license # 5233T, in effect since 1971, graduated from UC School of Optometry, Berkeley. In current practice at www.folsomeye.com

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## Speed

> California license # 5233T, in effect since 1971, graduated from UC School of Optometry, Berkeley. In current practice at www.folsomeye.com


'71.  That explains a lot.  You seem like a real down to earth person.  Too bad you are not closer to us.  You'd make a great wholesale customer.

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