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Thread: How do I use a Fresnel stick-on prism?

  1. #26
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    Quote Originally Posted by Tallboy View Post
    If you ain't cheatin' you ain't tryin'!
    Amen!
    Quote Originally Posted by Dr. Bill Stacy View Post
    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?

  2. #27
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    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...

  3. #28
    One eye sees, the other feels OptiBoard Silver Supporter
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    Quote Originally Posted by Dr. Bill Stacy View Post
    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
    Attached Thumbnails Attached Thumbnails IMG_0529a.jpg   IMG_0527a.jpg  
    Last edited by Robert Martellaro; 01-14-2016 at 01:13 PM.
    Science is a way of trying not to fool yourself. - Richard P. Feynman

    Experience is the hardest teacher. She gives the test before the lesson.



  4. #29
    looking up the answers smallworld's Avatar
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    "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.

  5. #30
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    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...

  6. #31
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    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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    Quote Originally Posted by fjpod View Post
    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.

  8. #33
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    Quote Originally Posted by Dr. Bill Stacy View Post
    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.
    Science is a way of trying not to fool yourself. - Richard P. Feynman

    Experience is the hardest teacher. She gives the test before the lesson.



  9. #34
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    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.

  10. #35
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    And Robert is correct in material choice when made in Rx form: Trivex.

  11. #36
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    Alcohol can fog them up ! Permanently

  12. #37
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    Quote Originally Posted by rdcoach5 View Post
    Alcohol can fog them up ! Permanently
    Never, 41 years. Have I'd seen this.

  13. #38
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    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%.
    Ophthalmic Optician, Society to Advance Opticianry

  14. #39
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    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!

  15. #40
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    oh...and I used alcohol many, many times on fresnels and never had any problems.

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    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.

  17. #42
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    Quote Originally Posted by Uncle Fester View Post
    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.

  18. #43
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    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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    Compulsive Truthteller OptiBoard Gold Supporter Uncle Fester's Avatar
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    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

  20. #45
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    Quote Originally Posted by Dr. Bill Stacy View Post
    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?

  21. #46
    O.D. Almost Retired
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    California license # 5233T, in effect since 1971, graduated from UC School of Optometry, Berkeley. In current practice at www.folsomeye.com

  22. #47
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    Quote Originally Posted by Dr. Bill Stacy View Post
    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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