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Thread: Your Opinion: Prism Ground In vs Decentered

  1. #1
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    Your Opinion: Prism Ground In vs Decentered

    I have a script from a local OD for a young boy.
    +1.75 sph OU, 0.5 BI OU. There is a note that says to use ground-in prism only.
    I would NOT decenter an aspheric lens for prism, but I do not personally see any difference between ground-in prism versus decentered prism using a stock spherical lens. I wanted to consult with you all before moving forward, however. I called to check with the OD and when I told her there wasn't any difference, she said "oh yes there is, optically in the lens."
    What do you think? I can get a stock lens in the appropriate blank size so we won't end up with excess thickness.
    Do you see something I don't see? How would the doctor know if I cut these out from a lens that has the OC in the center or slightly (2.8 mm) away from the center?

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    There is no difference and I challenge anyone on a spherical lens to show proof that there is a difference.

    There "may" be an OC thickness difference, but it will be under 1mm.

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    Agreed, absolutely no difference whatsoever.

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    Bad address email on file DC Optix's Avatar
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    Quote Originally Posted by eyemanflying View Post
    Agreed, absolutely no difference whatsoever.

    +3

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    +4.....
    ....the refractionist may be worried about lens thickness, and to accomplish the perfect edge thickness, due to possible horizontal and vertical o.c. placement, surfaced lenses would create the ultimate result. If you can use a stock lens that is ultimate in edge and centre thickness....get er done!

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    +5

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    In our state (MASS) we would have to fill as written and surface with prism even though there is no difference, that's our law here.

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    Quote Originally Posted by cwinma View Post
    In our state (MASS) we would have to fill as written and surface with prism even though there is no difference, that's our law here.
    Meeeh....prism is prism, whether surfaced or induced by displacing the optical centre location. The requirement to surface for small amounts of prism(and charge for) is a lab myth. In other words, if you receive a job with the wrong PD from the lab, they induced prism...........FREE! LOL

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    If there is no difference, and there really is no difference, what's the difference in ground in or displaced? Nuthin boyze. No one can tell the difference in the finished product (not even a drunken legislator) so why bother to grind in if diplacement gives the same result? We are argueing about whether the coin is heads or is that Washington's profile. Even in MASS with it's odd politics, displacement of a sphere, or grinding in a sphere is exactly the same thing.

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    Quote Originally Posted by uncut View Post
    Meeeh....prism is prism, whether surfaced or induced by displacing the optical centre location. The requirement to surface for small amounts of prism(and charge for) is a lab myth. In other words, if you receive a job with the wrong PD from the lab, they induced prism...........FREE! LOL
    Yep.
    Wesley S. Scott, MBA, MIS, ABOM, NCLE-AC, LDO - SC & GA

    “As our circle of knowledge expands, so does the circumference of darkness surrounding it.” -Albert Einstein

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    Master OptiBoarder OptiBoard Silver Supporter Barry Santini's Avatar
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    Ah, but if you selected an optimized FFSV lens, such as Zeiss individual, there would most certainly be a difference. The global optimization performed accounts for the lens "tilt" induced by the prism. My prism clients all luv their FFSV lenses

    I grant the difference in this case is small. 1.5D is where i start to see prism correction via FF

    FWIW

    B

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    Quote Originally Posted by Barry Santini View Post
    Ah, but if you selected an optimized FFSV lens, such as Zeiss individual, there would most certainly be a difference. The global optimization performed accounts for the lens "tilt" induced by the prism. My prism clients all luv their FFSV lenses

    I grant the difference in this case is small. 1.5D is where i start to see prism correction via FF

    FWIW

    B
    That would be true if there were such a thing as a stock FF lens.

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    Master OptiBoarder OptiBoard Silver Supporter Barry Santini's Avatar
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    Oh, we're talking about stock? I don't differentiatye whether, in the past, it was stock, or surfaced and I decentered it anyway.

    B

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    Defer to the Dr. if he specifies... although in most cases on PD there will be no effective difference their may be other differences off Oc in periphery. We usually don't know the entire pathology, and the cost of guessing is more than the cost of a grinder.

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    Quote Originally Posted by EyeFitWell View Post
    I have a script from a local OD for a young boy.
    +1.75 sph OU, 0.5 BI OU. There is a note that says to use ground-in prism only.
    I would NOT decenter an aspheric lens for prism, but I do not personally see any difference between ground-in prism versus decentered prism using a stock spherical lens. I wanted to consult with you all before moving forward, however. I called to check with the OD and when I told her there wasn't any difference, she said "oh yes there is, optically in the lens."
    What do you think? I can get a stock lens in the appropriate blank size so we won't end up with excess thickness.
    Do you see something I don't see? How would the doctor know if I cut these out from a lens that has the OC in the center or slightly (2.8 mm) away from the center?
    So, what did you finally do?
    • Optician
    • Frame Maker/Designer
    • Teacher of the art of crafting handmade eyewear.

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    Quote Originally Posted by Barry Santini View Post
    Ah, but if you selected an optimized FFSV lens, such as Zeiss individual, there would most certainly be a difference. The global optimization performed accounts for the lens "tilt" induced by the prism. My prism clients all luv their FFSV lenses

    I grant the difference in this case is small. 1.5D is where i start to see prism correction via FF

    FWIW


    B
    Your not comparing apples to apples with a FFSV. The Optimized Rx would change everything anyway

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