# Optical Forums > Ophthalmic Optics >  Stick on prisms?

## mirandaok

ok, I know this is strange  but in all the years of  being an optician I never
came across having anything to do with stick on prism. Well, today I had my
first experience. I ordered the prisms and I need someone to tell me what the
heck to do with them or any information so I don't look like a fool when they
come in and the patient brings in his frame what do I do with them how are 
they used. I am a very quick learn and if you briefly explain or send me to information I'll catch on thanks.

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## Darryl Meister

Here's a good thread on the subject.

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## mhboptics

This is very easy. Looking at the Fesnal Prism you should be able to tell the direction of the base, if not, the outer ring has a marking. Then I lay the prism face down, remove the lens it's to be applied to, put the lens on the prism with the correct direction and trace it using a pen. Cut it a little on the inside of the line, clean the lens and prism and apply with a rubbing motion.

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## chip anderson

Save yourself the time of marking it.  Put it on the unmounted lens, trim with sissors.  Then finish trimming (as much to the inside of the bevel as possible or it will move when you mount the lens) with a single edge razor blade (pkg. of 100 cheap at Harbor Freight or office supply).


Chip

You can check the direction of the base with your fingernail, it will catch on the base side and slide over the apex side.  I cases of small lenses you can get two out of one fresnel for twice the profit if you are carefull.  Remember there is no center to these.

Chip

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## Ory

Also remember that there should be absolutely nowhere that the fresnel sticks out over the edge of the actual lens. That is just asking for it to get caught and peel off.


They will come off in certain circumstances, such as going from somewhere cold to somewhere warm, or if Chip Anderson applied them.:)   Always let your patient know this and ask them to bring it back to you rather than try to stick it back on yourself.

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## fjpod

The fresnel must be trimmed within the margin of the safety bevel.  If it's not, it will peel.  Rub the concave side of the spectacle lens and the smooth side of the fresnel with a conditioning solution such as Boston.  Rinse with water and apply to each other while still wet.  rub the fresnel from the center outward to eliminate bubbles.

BTW, the s in fresnel is silent.  So it is pronounced frenel.  It's a French thing.

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## Dave Nelson

You mentioned prisms, plural.  You do not normally split fresnel prisms. If the rx calls for 4bd right and 4bu left, you would normally do 8 down right or 8 up left.

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## chip anderson

Old Dave: 

 Not really, many patients will suppress the Fresnel eye if both eyes are not equally clouded by the ballanced frosted effect of  Fresnel prisms.  Ir is less expensive to do one eight, and less expensive for us to stock only one each.  Some patients actually prefer the cosmetic effects of ballanced fresnel's.

Chip

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## mhboptics

I agree with Chip, sometimes we use a Fresnel prism on both eye's, usually in vision thearpy, to make sure the amount of prism and direction is exactly right before spending the money on ground in prism.

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## HarryChiling

It helps to use alcohol to apply, it helps to dry on quicker(I picked that up from shutterfly).  I have also put them on under running water and then massaged the water out.  I agree with taking the lens out and tracing it.  This gives a more appealing look to the prism.

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## Dave Nelson

Dearest friends. While I don't entirely disagree with you regarding the use of fresnel prisms on both eyes, I find it to be questionable. I have never found monocular use of a fresnel prism to elicit suppression, even in a situation where suppression occurs due to the original alignment disorder. Au contraire, the stimulus to converge should over-ride any suppression tendancies. If you believe however, that the prism will contribute to suppression, you could apply to the more dominant eye. As for using them binocularly to tune the amount and direction of prism, I submit that the same can be accomlished by a singe prism, even in cases where the orientation is different for both eyes, by use of a singe, oblique angle prism. Success in this manner will mean success in splitting and grinding the prism later. The loss of acuity using fresnel prisms binocularly is not justified, IMHO. I certainly understand that there are other opinions on how to proceed, but I cannott see a situation where binocular use of press-ons is better than monocular. As an afterthought, however, I remember one patient who wore binocular press-ons PERMANANTLY. Would give no consideration to a grind. Who knew?

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## Darryl Meister

Just keep remember that the amount of scatter (by the ring edges) and the amount of chromatic aberration produced by Fresnel prisms depends on the total prism power in one lens. Though, since these prisms are often temporary, I don't know that the benefits of splitting the prism are really worth the cost and trouble...

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## Chris Bowers

For a really good looking press on prism you might want to try the following

Use a plastic plano lens and scribe a 180 line on the blank





Apply the prism to the back (while aligning the base reference to that prescribed) surface with static friction only





Block the lens on the datum line and put another plano lens behind. Now edge the lens the same shape as the real lens only makes it smaller, such that this new lens is just the size of the real lens without the bevel.

If you have an edger that can use the feature "bevel positioning" edge the lens so the prism has a nice taper to it.



When you disassemble these lenses you will have a very smooth cut and shape. Adhere to the real lens use techniques explained in these other replies. Or an alternate technique I like on very steep curves or permanent lens design is to use an optical adhesive and UV cure. If the curves are really steep you may have to make relief cuts, kind of like the old RK procedure used on the cornea. When ever possible mount prism while the lens is in the frame. It wont take much warping to dislodge the prism.

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