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Thread: Ordering compound prism

  1. #1
    My Brain Hurts jpways's Avatar
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    Ordering compound prism

    So I received my first prescription with a compound prism. It was prescribed as "2 PD Base Down & Out @ Axis 135 OS only"

    After finding the proper conversion method, I figured out that it was 2.00PD @ 315 = 1.41 BD 1.41 BO and then I try to order it.

    So, I looked at Visionweb, Eyefinity, and the lab's website. None of them have a way to order prism with a Power and Axis only horizontal and Vertical. So, I try to order it as 1.41BD 1.41 BO and get kicked out on all 3 sites, the accuracy that the sites want is: Eyefinity to the nearest 0.50D, Visionweb to the nearest 0.25D, and the lab website to the nearest 1.00D.

    So, I order it as 1.50BD, 1.50BO (with notes saying what the prescribed prism was), so 2.12D @ 315, I believe this is within ANSI standards, but I still feel like I'm changing the prescription since I have a 0.12D difference.

    So, I called the lab and they're changing the order at their end to fill it as prescribed.

    My question is, does anyone know of a website that I can order the prism as Power/Axis?

    Also, am I just being overly cautious by not ordering it as 1.50BD 1.50 BO?
    Last edited by jpways; 08-21-2019 at 12:10 PM.

  2. #2
    What's up? drk's Avatar
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    Yeah, prism is like sailing a boat on choppy waters. That degree of accuracy is not needed.

    Think about the prescriber...if it were oh-so-accurate, what are the chances the patient needed "exactly 2" prism diopters, and at a hardly-rare meridian of 135?

    No, just do it the best you can. Heck, no one at the ophthalmology office probably has a lensometer, anyway, as if they could even use a manual one. They probably have an automated, and wouldn't know prism if it were wedged in their butt crack.

  3. #3
    Master OptiBoarder OptiBoard Silver Supporter lensmanmd's Avatar
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    2@135 is 1.41in/1.41up. Your calculations are correct @315. Your prescriber hasn’t a clue about yoking.
    I bend light. That is what I do.

  4. #4
    One eye sees, the other feels. OptiBoard Gold Supporter
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    Quote Originally Posted by jpways View Post
    So I received my first prescription with a compound prism. It was prescribed as "2 PD Base Down & Out @ Axis 135 OS only"
    They were reading it off the trial frame, except they forgot that there's 360˚ in a circle! However, if you wish to use 180 notation, note the eye, base up or down, and the axis. In this example it would be written as OS 2∆ BD @ 135. But, OS 2∆ @ 315 is preferred.

    After finding the proper conversion method, I figured out that it was 2.00PD @ 315 = 1.41 BD 1.41 BO and then I try to order it.

    So, I looked at Visionweb, Eyefinity, and the lab's website. None of them have a way to order prism with a Power and Axis only horizontal and Vertical. So, I try to order it as 1.41BD 1.41 BO and get kicked out on all 3 sites, the accuracy that the sites want is: Eyefinity to the nearest 0.50D, Visionweb to the nearest 0.25D, and the lab website to the nearest 1.00D.
    Labs use 360 notation. Maybe you could write it in the special instructions?

    Also, am I just being overly cautious by not ordering it as 1.50BD 1.50 BO?
    I can't read 1.41 in a lensometer, I would see 1.5∆ and use that value. Regardless, they should accept 360 notation, even if you have to pick up the phone and talk to them personally.

    Quote Originally Posted by drk View Post
    Heck, no one at the ophthalmology office probably has a lensometer, anyway, as if they could even use a manual one.
    Nowadays, true more often than not.

    Best regards,

    Robert Martellaro
    Roberts Optical Ltd.
    Wauwatosa Wi.
    www.roberts-optical.com
    ~~~~~~~~~~~~~~~~~~
    Science is a way of trying not to fool yourself. - Richard P. Feynman

  5. #5
    OptiBoard Novice teej's Avatar
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    Most digital lensometers can be switched from degrees to angle prism read. Humphrey, Nidek, and its too true that most ECP's dont know what a B&L tabletop lensometer even is.

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