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Progressive with high prism

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    Progressive with high prism

    I have a patient who currently wears a Varilux Comfort DRx with 8D base out OU. With her new script, the prism is now 13D base out OU. Our lab is telling us that that amount of prism is too high for a progressive. I am reluctant to put the patient in a FT28 because of her balance issues. Our lab is telling us that the best option for this patient is single vision. I know there has to be a lab out there with the expertise to be able to do her new script with the prism. Her distance Rx is very mild, but she does have 25D esotropia. Any help will be appreciated.

    #2
    That's quite a shift. Did you try a fresnel first? Just curious when the change is so great.

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      #3
      Fresnel goes in 5D increments after 10D, so not an option. I can get a 12D, but I don't think the Dr wants to back down on the prism due to the big shift in patient's esotropia.

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        #4
        You could induce the split prism, then place a fresnell over the non dominate eye in the amount that is needed to create the overall prism effect., That should make it a 10d fresnell for the non dominate eye going with the current 8D base out OU in the current rx.
        Roy W. Jackson, Sr. ABOC

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          #5
          13∆ total? That's doable on a semi-finished Comfort. Some labs will try it on a freeform generator but the results vision-wise are typically very poor.

          Make sure to check (likely) the need to modify the IPD to anticipate the eyes turn towards the prism apex by .3mm per prism diopter.

          Keep auxiliary segmented or SVNO on the table for those with above average close tasks.

          Use small, round frames that will accommodate increased levels of prescribed prism in the years ahead.

          Hope this helps,

          Robert Martellaro
          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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            #6
            26 total prism. 13 out in each eye.

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              #7
              26 is a lot for a progressive tbh.

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                #8
                Originally posted by Jalane View Post
                26 total prism. 13 out in each eye.
                Ouch. Fresnel then, if a PAL. The highest I've gone is a pair of -8's with 16∆ out total, but in SVDO with Chemistrie power clip over for near.

                Best regards,

                Roberts Martellaro
                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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                  #9
                  From my conversation with the rep at the Luxexcel booth at VEE a couple years ago, that's the sort of thing they will be able to make using a 3D printing process. As I recall, they're doing some limited processing at a lab in NC.

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                    #10
                    Originally posted by Robert Martellaro View Post
                    Make sure to check (likely) the need to modify the IPD to anticipate the eyes turn towards the prism apex by .3mm per prism diopter.


                    Robert Martellaro
                    You are so good at this stuff, Robert.


                    OK, let's flesh out your recommendation. This whole exercise is how to convert monocular p.d.s taken with a pupillometer-accuracy-level device, with ALTERNATE OCCLUSION of the fellow eye (that is, not measuring it in the binocular state).

                    Let's say someone has the more typical 2^ in each eye. Let's say it's BI.

                    So you're saying that the inset needs modified for the progressive corridor and near zone.

                    It is true that prism allows the eye to go towards its rest position. In the case of an exo deviation as is the case in the example, each eye would want to go 2^ out (which isn't an angular or linear amount, but you've converted that to a linear amount at the spectacle plane...0.3mm per prism diopter).

                    Therefore we would outset the whole lens via the p.d. (if single vision, segmented, or PAL) by 2^ X 0.3mm = 0.6 mm/eye.

                    That's within measurement error for low prism amounts.




                    Take the example to a less common amount, say, 6^ BO OU.

                    6^ x 0.3mm = 1.8mm inset per eye. That is not insignificant.



                    I have not done this, ever. Shame on me.

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                      #11
                      Yes Drk. This is laid out and explained in chapter 20 of Systems for Ophthalmic Dispensing 3rd edition.

                      The summary table can be seen here along with the table describing how and when to alter the amount of prescribed prism, which is described in detail in the preceding pages.

                      https://www.google.com/books/edition/System_for_Ophthalmic_Dispensing_E_Book/sV5PAQAAQBAJ?hl=en&gbpv=1&dq=system+for+ophthalmic+dispensin g+box+20-4&pg=PA486&printsec=frontcover


                      Originally posted by drk View Post
                      Therefore we would outset the whole lens via the p.d. (if single vision, segmented, or PAL) by 2^ X 0.3mm = 0.6 mm/eye.
                      That's within measurement error for low prism amounts.

                      For a PAL it is important to keep the eye path in the corridor to receive the most usable area of an already narrow mid range view. Not adjusting the PD for prism displacement will reduce the usable int/near area, regardless if it within measurement error for low prism amounts.
                      Last edited by Kwill212; 05-13-2021, 09:26 AM.

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                        #12
                        I like it!

                        Screenshotted it.

                        Funny that Brooks and Borish's conclusion used some of the same ideas and numbers I did!

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                          #13
                          OK, here's where I go nuts....Do labs already do this automatically? What about digital lens softwares?

                          In general, if it's a software-based lens, I don't monkey. If it's a "grinder" then I'm the software.

                          Click image for larger version

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                            #14
                            There is no lab or lens software that I am aware of that will do this automatically for you.

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                              #15
                              Originally posted by drk View Post
                              OK, here's where I go nuts....Do labs already do this automatically? What about digital lens softwares?
                              No, and no.

                              Dick Cook at Benson Optical Co., circa late 80's, showed me why my segment heights were misaligned when there was prescribed vertical prism. 10∆ vertical on a segmented is 3mm off, more if there is physical asymmetry in the facial structure. I could see the error from across the room, not just sitting face-to-face at the dispensing table.

                              Best regards,

                              Robert Martellaro
                              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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