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Thread: Seg height is the weak link in PAL fitting

  1. #1
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    Seg height is the weak link in PAL fitting

    As a novice I get the impression that the seg height measurement is the weak link or limiting factor in successful PAL fitting. After all, the P.D is easy to do properly with the pupillometer. I have read and applied many tips regarding "dotting the pupil" but still find it rather inaccurate. I have done it standing up while having them look at distance. I have measured sitting down with their elbows not on the table. Eye to eye etc. Nonetheless, for a measurement that has to be really precise I have not been impressed at the reproducibility of this. I have even had several staff members measure seg heights on the same patient and come up with answers that are 3mm apart. I have considered using a cut out with an occluder and a little hole in the middle and asking the patient to fixate on a letter on the wall chart until he sees it through the little hole (and then dotting at that point). Alernatively I have read about a mechanical device called the Y-touch that is being sold by Laramy K. Any advice would be appreciated since I think all my redo's are coming from this issue.

    ilan

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    No more...................

    Quote Originally Posted by ilanh
    Any advice would be appreciated since I think all my redo's are coming from this issue.
    ilan
    Learned this a long time ago..........................

    Let patient walk around the store naturally and he/she will assume to hold a normal head position. Then suddenly you tell them to freeze..................take measurement and you will have nore re-doos, if this was mainly the issue.

  3. #3
    What's up? drk's Avatar
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    I think you're partially right.

    Most avoidable problems with progressives seem to be from fitting height measurements being too high, in general. Assuming a reasonable head posture, avoiding parallax, and having the benefit of adjustable pads should be sufficient. I routinely measure to pupil center and subtract 1-2 mm. Yes, it may reduce near performance somewhat, but that's what HAS to be done. Note that longer-corridor lenses will require you to fit on pupil center, exactly.

    The other major issue is improper adjustment. Minimizing vertex and it's cousin "sufficient pantoscopic tilt" will get you through most dispenses.

    It doesn't need to be rocket science to make it work.

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    Cape Codger OptiBoard Gold Supporter hcjilson's Avatar
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    I use a device sold by Hilco, called Seg-Hi, or something like that. After removing the demo lens it fits in the groove of the eyewire. I install it and then start a conversation with the customer, telling to disregard the device.Once they relax a bit it is realatively simple to get a good measurement. Parallax can be another problem, but easily solved if you remember that you've got to see "eye to eye". When fitting rimless, or semi rimless, the dotting method works for me.
    "Always laugh when you can. It is a cheap medicine"
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  5. #5
    OptiWizard
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    Also make sure you adjust and fit the glasses before you take the measurements.
    :cheers: Life is too short to drink cheap beer.

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    I'm not in this business, but I just want to add that here in Denmark there is a computer machine (I think it is Zeiss) which determines the seg height. Don't you have them in the States?

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    Paper Shuffler GOS_Queen's Avatar
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    Definately pre-adjust the frame before measuring.

    I typically like to use the seg hi guage.

    My favorite thing to do is to have them look at me ... then I ask them to turn around and look at something (doesn't matter what ...) and then turn BACK around to me ... this usually makes them get out of the stiff "romper room" posture and into a more natural head position.

    HTH

    Karen

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    Pomposity! Spexvet's Avatar
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    Quote Originally Posted by ilanh
    ... I have read and applied many tips regarding "dotting the pupil" but still find it rather inaccurate.
    Compared against what standard?

    Quote Originally Posted by ilanh
    Any advice would be appreciated since I think all my redo's are coming from this issue.

    ilan
    What specific symptoms of your remakes lead you to believe that it's the seg ht that is causing them? Could it be that you are not setting expectations by educating the patient? Are you fitting poor candidates? Are you using the best PAL brands? Do other staff members have alot of remakes?
    ...Just ask me...

  9. #9
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    Also, make sure you measure the frame where they will wear the frame. Some people like the frame to sit lower. It does not matter how much you adjust it or tell them it should be higher that is where they will wear them so fit them there.

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    Master OptiBoarder Jedi's Avatar
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    Ditto, on having them walk around, and pre-adjustment is a must. If they having previously worn PALs make sure you dot up their existing pair to see where they are fitting. Ask a lot of questions too, where you happy with your last pair? what are you using them for? how big of a monitor do you work on and is it adjustable? I often fit sunglasses a few mm lower than clear if they are predominately used for distance.
    "It's not impossible. I used to bull's-eye womp rats in my T-16 back home."


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    The weak link in any opthalmic product or proceedure is the dispenser.

    Either for not having used the product properly or useing the wrong product.

    And no matter how much we promote newer products vision is better with segmented bifocals, preferably glass. This is why most progressives are sold with a warranty that the lens will be re-made as a bi-focal (segmented) if the patient is not happy.

    Chip

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    Quote Originally Posted by chip anderson
    The weak link in any opthalmic product or proceedure is the dispenser.

    Either for not having used the product properly or useing the wrong product.

    And no matter how much we promote newer products vision is better with segmented bifocals, preferably glass. This is why most progressives are sold with a warranty that the lens will be re-made as a bi-focal (segmented) if the patient is not happy.

    Chip
    I do not have non-adapts in my dispensery (maybe one or two in the past five years).

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    It is surprising to hear about "only 2 non-adapts in 5 years" or other situations in which the dispensers almost never have PAL issues. The fact of the matter is that failed PAL fittings is a huge concern to the industry. The labs and manufacturers structure their pricing and warranty policies around this problem. Part of the high costs that some of us are paying to finishing labs comes from the built-in "insurance" that they have to charge for a high number of returns of costly PAL lenses. Likewise, the exorbitant costs of these lenses from the manufacturers is also partly due to the fact that they have to provide full warrantys. Open any pricing package from any lab and you will see prominently displayed in BOLD type their "progressive re-do" policies. When speaking to patients I am also struck by how many of them have heard of friends, co-workers or family members who have had "problems with progressive lenses." I would guess that most of these problems are caused by us and not by patient brain/eye non-coordination. A successful fitting involves proper frame selection, meticulous fitting of the frame, accurate PD and seg height markings, lay-out confirmation on sending out and receiving back the job, fitting it properly when it arrives and proper education of the patient. A mistake anywhere down this chain can lead to a "redo" at best, or a patient who will grudgingly put up with awkward vision and head movements for the next 3 years.

    ilan

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    Pomposity! Spexvet's Avatar
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    Quote Originally Posted by ilanh
    It is surprising to hear about "only 2 non-adapts in 5 years" or other situations in which the dispensers almost never have PAL issues.
    ...
    A successful fitting involves proper frame selection, meticulous fitting of the frame, accurate PD and seg height markings, lay-out confirmation on sending out and receiving back the job, fitting it properly when it arrives and proper education of the patient. A mistake anywhere down this chain can lead to a "redo" at best, or a patient who will grudgingly put up with awkward vision and head movements for the next 3 years.

    ilan
    You are correct in all that you said. However, you attribute your high remakes to your ability to take accurate fitting hts. I am not so sure that this is the reason, it could be other factors, so:

    Quote Originally Posted by Spexvet
    What specific symptoms of your remakes lead you to believe that it's the seg ht that is causing them? Could it be that you are not setting expectations by educating the patient? Are you fitting poor candidates? Are you using the best PAL brands? Do other staff members have alot of remakes?
    ...Just ask me...

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    Bad address email on file sunoptik's Avatar
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    Zeiss RVT

    Anyone here know something about Zeiss RVT video centering system for fitting progressive lenses? I have seen many instruments that are installed here in Europe but nobody here tell about them.
    Have you an opinion about computerized fitting method?
    Excuse me but this is my first message here I don't know if it works fine.

  16. #16
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    Confused

    Plus, is that Y Stick worth $349 if you know what you're doing?
    Do your best and give it your all. Everyday. :)

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    I use a penlight and marker. I shine the penlight into the eye and dot the corneal reflex. I draw a line at the bottom of the dot and that is where I usually put the fitting height. Of course, I preadjust the frame and make sure I am level with the patient.

    I usually dot up their present glasses to see how they are being worn, too.

  18. #18
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    Quote Originally Posted by drk View Post
    Most avoidable problems with progressives seem to be from fitting height measurements being too high, in general. Assuming a reasonable head posture, avoiding parallax, and having the benefit of adjustable pads should be sufficient. I routinely measure to pupil center and subtract 1-2 mm.
    I do the same here. Most of my PAL remakes the first six months or so of practice were because I actually fit them where they were supposed to be, but that turned out to be too high. I've since gone to a method like yours and have had no problems.

  19. #19
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    The only time we have SH problems is with TF. THese weareres are picky and many times they don't like them "by the book"

    Progressives = no problem.

    Your fitter/frame consultant is too short! She needs a drafter's stool!;)

  20. #20
    Master OptiBoarder OptiBoard Silver Supporter Barry Santini's Avatar
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    Another perspective on progressive fitting height sensitivity:

    If the Rxs we receive *are*, as discussed elsewhere, somewhat overplussed in power, this, IMHO, is *definitely* a contributing factor to progressive-height sensitivity, especially with adds that are borderline strong. Don't forget the latest crop of fast-sloping, smaller fitting height designs compound the problem.

    FWIW

    Barry

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    OptiBoard Professional LadyDie's Avatar
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    I have very few remakes also. Sure wouldn't say never cause there are always a few.
    I also dot a little lower than the pupil, maybe the lower edge of the pupil unless of course they are dilated or have unusually large pupils.
    I will have them walk around occasionally, but usually find if after I dot them I ask them a question about their work or family something to get them out of their Romper Room/military position, then suddenly say "freeze" I get a much more natural position.
    All of these things were mentioned above along with more good suggestions.
    For some manufacturers I don't trust there recommended seg. hts. One brand in particular says 18mm but if you have ever done one at that ht. and then saw the markings on it over half of the reading circle is cut off. I also feel that if it is a zyl frame that measurement is even more important because if half the reading circle is cut off the thicker frame hides another milimeter or 2 of that circle and can make it really difficult to use.
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    Quote Originally Posted by LadyDie View Post
    I have very few remakes also. Sure wouldn't say never cause there are always a few.
    I also dot a little lower than the pupil, maybe the lower edge of the pupil unless of course they are dilated or have unusually large pupils.
    I will have them walk around occasionally, but usually find if after I dot them I ask them a question about their work or family something to get them out of their Romper Room/military position, then suddenly say "freeze" I get a much more natural position.
    All of these things were mentioned above along with more good suggestions.
    For some manufacturers I don't trust there recommended seg. hts. One brand in particular says 18mm but if you have ever done one at that ht. and then saw the markings on it over half of the reading circle is cut off. I also feel that if it is a zyl frame that measurement is even more important because if half the reading circle is cut off the thicker frame hides another milimeter or 2 of that circle and can make it really difficult to use.



    These are all good suggestions but unfortunately a lot of so called opticians in our field don't fallow them. Especially the boxes and large chains.

  23. #23
    Just An Optician jediron1's Avatar
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    Quote Originally Posted by Newyorkoptician View Post
    These are all good suggestions but unfortunately a lot of so called opticians in our field don't fallow them. Especially the boxes and large chains.


    Couldn't have said it any better!

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    If we have "brands in particular" that don't measure up to stated specs. Why are we afraid to mention the brand?

    Don't we have this board to help each other. Or are we afraid we might offend "the brand" ?


    Chp

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    Master OptiBoarder optigrrl's Avatar
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    I always tried to learn about the various PaL designs and how they translated to the pt's RX and lifestyle. Then fit, then adjust then measure. Very low redo rate.

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