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Thread: what is the tolerance for axis - to what degree is it dispensable?

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    Confused what is the tolerance for axis - to what degree is it dispensable?

    wondering what others are doing out there if the frame turns out 2-3 degrees off axis? would you consider that dispensable?

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    Quote Originally Posted by chronometre View Post
    wondering what others are doing out there if the frame turns out 2-3 degrees off axis? would you consider that dispensable?
    Depends entirely on the amount of overall Rx and the specifically the amount of cylinder.

    Just had a guy pick up and pair last week where he's got like ~5 diopters of cylinder in each eye. One lens he wasn't happy with, I checked it on the lensometer found it off by 1 degree, adjusted the lens in the frame a bit to fix it and he was good to go. Someone who is, for example, -3.00 -0.25 isn't typically going to be sensitive to the exact axis, but if the Rx is -0.25 -3.00 then they likely will be.

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    Quote Originally Posted by Quig View Post
    Depends entirely on the amount of overall Rx and the specifically the amount of cylinder.

    Just had a guy pick up and pair last week where he's got like ~5 diopters of cylinder in each eye. One lens he wasn't happy with, I checked it on the lensometer found it off by 1 degree, adjusted the lens in the frame a bit to fix it and he was good to go. Someone who is, for example, -3.00 -0.25 isn't typically going to be sensitive to the exact axis, but if the Rx is -0.25 -3.00 then they likely will be.
    FT or PAL probably would not work even with a sphere. Anything else look at the z-80 standards

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    sub specie aeternitatis Pete Hanlin's Avatar
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    To Don and Quig's points, check your ANSI Z80 standards to determine if the lens falls within standards (at only 2-3 degrees off, it should unless the patient has considerable cylinder).

    If the lens is a PAL and falls within ANSI, the next question needs to be "What is off axis- the design or the power?" Remark the engraved circles, and determine if the design is mounted correctly in the lens. If the circles all fall on the 180, and the cylinder is within ANSI, I'd go for it. However, if the circles are NOT perfectly aligned on the 180, I would try adjusting the lenses to see if I can get them aligned (then remeasure to see if that also fixes the cylinder axis). As Don mentioned, if the design itself is off-axis, you are going to move the near zone of the lens- which can cause problems in a hurry.
    Pete Hanlin, ABOM
    Sr. Director Professional Solutions
    Essilor of America

    http://linkedin.com/in/pete-hanlin-72a3a74

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    I took the OP as how much a FRAME can be off axis. No? Like a pair of lenses were off axis and someone changed the frame axis so the lenses were on axis. My answer to that would be that it depends how obvious it is and does it affect the overall look. Some frames it would not be noticeable, others would be very noticeable.

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    What about a lab compensated Rx that falls outside of ansi standards? Do you trust the software that does the compensation and see if the patient can tolerate it or do you remake?

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    There's also the option of using profile of a surface, which controls the location (and form) of the physical surface.
    That kind of staff click site helps to do the things like that. You should also buy it on amazon or ebay.
    Last edited by Sendycrox; 09-25-2019 at 07:45 AM.

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    Quote Originally Posted by Alex Camblor View Post
    What about a lab compensated Rx that falls outside of ansi standards? Do you trust the software that does the compensation and see if the patient can tolerate it or do you remake?
    Use the compensated Rx as the starting point to determine if it is withing ANSI suggested tolerance. Same as you would if you adjusted the Rx for vertex power, or made a computer Rx from the patients full Rx, etc. Start with the final Rx produced and compare to ANSI.

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    Quote Originally Posted by Alex Camblor View Post
    What about a lab compensated Rx that falls outside of ansi standards? Do you trust the software that does the compensation and see if the patient can tolerate it or do you remake?
    Yes. Imagine applying Vertex calculations, tilt calculations and panoramic angle calculations, along with the index of refraction, and apply those to the prescribed RX, and you will see the change in fitted RX. This is what the software does, along with other formulas. You will then apply ANSI to the compensated RX. You are determining the accuracy to the fitted RX at this point, not the refracted RX.

    Every design will weigh the importance of each formula, assign values to it, and voila. Every wonder why IOT compensation is different from Hoya compensation is different from Shamir compensation is different from Zeiss compensation is different from Essilor compensation, and is different between designs within each of their portfolios?
    I bend light. That is what I do.

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