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Thread: Manual Mounting prism in glasses

  1. #1
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    Manual Mounting prism in glasses

    Good afternoon,
    Actually I want to make a research about mounting prism in glasses, but I have a lot of difficulties, I tried to visit a lot of libraries in my city, but as I didn't expect, there is no book concerning steps of mounting and measurements to take, I want to ask you some questions: what are the measures that the optician must take from patient ? are there the same like others types of glasses (measuring the seg hight, the seg width and the half inter-pupillary distance) or there is another measurements to take ?
    And also, if you can tell me for all the steps that a good optician must follow to arrive in a good manual mounting prism in glasses, I have no idea about this mounting.
    thank you very much.
    Sorry if i commit a lot of mistakes, I try to improve my english.

  2. #2
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    Prism is a prescription that is ground into the lenses and not mounted. The exception being a fresnel prism, which is a "stick on" temporary prism. So any procedures to grind the prescription would be similar to grinding any kind of eyeglass lens.

  3. #3
    One eye sees, the other feels. OptiBoard Gold Supporter
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    Welcome to OB.

    Adding to Mervinek's discussion,

    Prisms can also be cemented onto the lenses, sometimes for when the deviation varies depending on the angle of gaze, typically the primary and near gaze, or to expand or change the field of vision in localized areas (see Hemianopsia).

    https://cvt123.files.wordpress.com/2012/05/prism-dispensing-final.pdf

    Hope this helps,

    Robert Martellaro
    Roberts Optical Ltd.
    Wauwatosa Wi.
    www.roberts-optical.com
    ~~~~~~~~~~~~~~~~~~
    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.



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    Thank you very much Mr Mervinek and Mr Robert Martellaro, your precious informations that you have given to me will help me a lot.
    but I have a question about the real prismatic lens and not the prism results with decentration of a single vision lens, for exemple: when an optician reads the prismatic lenses power on the lensometer and dot's his lenses with the ink marker of the lensometer, we have for example a patient who suffers from strabismus, what the dot on lens that must be in the front of his pupil ? I mean the exact location of the lens in front of the pupil, is it the center of the lenses ? Does it necessits a calculation? that's what I realy want to know,
    I hope I haven't bothered you with so many questions
    Thank you very much

  5. #5
    What's up? drk's Avatar
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    (I'm assuming you are a "dispensing optician" that works with patients and not a lab optician that makes glasses. Correct me if I'm wrong.)

    To keep the concepts simple (which is always the way to do things) think this way:

    TO MEASURE:
    Take interpupillary distances as usual on a strabismic patient: use a pupillometer with one eye occluded, then the other. (If you don't use a pupillometer, let me know.) This tells you where the eyes are IF/WHEN they're straight in everyday life. (In some cases, only one eye is going to ever be straight. In some strabismic cases, both will, for a while. In other cases, one or the other but never both at the same time. You'll never know without an in-depth report, but you don't need to know.)

    TO ORDER:
    Then order the lenses with that p.d. value. It's that simple.

    TO VERIFY:
    Now, when looking at the results on the lensometer, measure with a ruler the split p.d. from the center of the bridge of the frame, and put a mark. Put that mark over the lensometer stop; it will tell you the amount of prism that the patient will be looking through, and the power the patient will be looking through. It should match what was prescribed. Done!



    DISCUSSION:
    Now, what happens if you do it another way? You'll get confused. If you center the lensometer mires so they're in the center of the reticule (or scale) and dot the lens, you are finding something other than what the patient is looking through. You are finding where the "optical center" of the lens is...that is, where there is zero prism*. This is useless information.

    But if you want to make the useless information become useful, yes, you have to use a formula to calculate how many millimeters away from the optical center is the spot on the lens where there is the prescribed prism amount, and then compare that spot to the p.d. you ordered.

    This is way too much work, and the first method is far, far easier.

    (In fact, one could adopt this method for any and all glasses...it's more intuitive. You just mark where a patient's eyes are going to be, and then read what they're going to see!)



    *But not all prismatic lenses have zero prism...some have no "optical center" at all, no matter how hard you look.
    Last edited by drk; 08-18-2020 at 10:08 AM.

  6. #6
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    Thank you very much Mister drk for your informations, that will helps me a lot,
    No I am not a dispensing optician, I an just a student and I am doing a research about how to mountain prismatic lenses on glasses with all the steps from order to glasses (reading power with lensometer...etc) I started my research by gathering all bibliographic sources, but what I notice is that there is no book that contains how to do the real job of the optician, like the mountain of glasses with details, so I started a statistic study in my city to know more about prismatic lenses from professionals, but the majority use the decentration of a single vision lenses or the press-on, I contacte a lot of other professionals in other countries but every one has his own way to proceed, for exemple what I understood from them is that the prismatic lens doesn't necessit IPD the lenses comes from laboratory with all of this parameters.
    Thank you very much

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