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Thread: Measuring PD's?

  1. #1
    Sawptician PAkev's Avatar
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    Just curious about how most folks are measuring PD's of their clients.

    I have used a pupilometer for many years with OK results. Since now I am the one manufacturing the orders which I sell and dispense, I feel more comfortable actually seeing where I need to position the lenses and prefer the manual method. I also feel more confident and precise by dotting the PD's and segs for my PAL wearers without using the pupilometer. After edging the lens, I could lay the demo lens over the respective edged lens and the dots should be aligned over the fitting cross. Although it is easy to use and understand, I found a greater margin for error with the pupilometer if it was not positioned correctly, measurements were rounded up or down, or settings were not correct.

    Finally, I believe my clients feel they are truly receiving a custom product as you carefully exhibit your measuring skills rather than "Bing Bang - Look at the Light"

    How about the rest of you? What do you prefer and why?

    PAkev

  2. #2
    Christine
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    Redhot Jumper

    I use a PD stick.
    I trust my own judgement over anyone or anything!
    C.

  3. #3
    Bad address email on file Rich R's Avatar
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    I've used a p.d. stick and always will, I've also double checked others who have used the pupilometer and come up with slightly different results, and when we go back and recheck with marking the demo lenses the p.d. stick wins every time. I'm sure everyone has their own opinions. Rich R

  4. #4
    Master OptiBoarder Texas Ranger's Avatar
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    I believe that when you use the "pd stick" you lose accurate monocular measurements. Assuming that you desire a binocular measurement of the interpupillary distance, and not the monocular measurement of the patients visual axis, then the pd stick is ok. but the latter measurement works better when the rx is more than very basic powers, and especially with pals. spotting the demo lens is fine for monocular hts. unfortunately, we have built in "human" errors, well at least I do, maybe because i'm just old. Question: what do you do if the rx has a written PD on it that greatly differs with any of your measurements?

  5. #5
    Sawptician PAkev's Avatar
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    Al,

    Your mono PD theory sounds correct and is very important in PAL & SV fittings. However I found that dots exactly over the pupil bottoms don't tell any lies.

    As far as bifocal fitting goes, I guess there are Two schools of thought. The first being do you want the segs to be positioned OPTICALLY CORRECT and the second being do you want the segs to be positioned symetrical and COSMETICALLY CORRECT?

    I am in agreement that the first will provide optimum corrective vision but it has come to haunt me more than once. Especially when their previous pair was symetrical and they didn't have any problems with the positioning. Sometimes when they come in to make you aware of the problem and you pleasantly explain that they are specifically made that way, it is not what they want to hear and they interpret it as an excuse.

    I found this situation to leave me with two alternatives.

    1. Make it optically correct and take the chance of them realizing the difference and exhibit (what they consider) your "poor" workmanship to all their friends and perhaps even returning to have the lenses remade.

    2. Make it symetrical with anticipation they will tolerate minor differences.

    If the doc indicates a PD which is different from my findings my first responsibility is to advise him/her of my findings and if he/she insists they are correct, I use their measurements.

    Kevin, with a dusty pupillometer, Treat

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    OptiBoardaholic
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    I know that a lot of people might disagree with me, but I prefer the pupillometer for the following reasons.
    I have carried out a number of surveys of alternative PD methods with my final year opticianry students and have found the pupillometer to be more consistent, with fewer errors. There is less room for human error or parallax etc.
    Also, although the pupillometer does measure narrower than the PD rule (stick) or dotting pupil center, this is because it measures the distance between the visual axes (which is what we should measure) as opposed to pupil center. For a good explanation of this and an equally good diagram see Ralph Drew's last book, Present Day Realities (I think that is the title). You will also find similar diagrams in other books.

    With regard to the client's point of view, I also think that the pupillometer gives a very professional image (although, I agree that this would not be a good enough single reason for using it). The client has just been tested by the optometrist, usually with state of the art equipment, and then comes to be measured by the optician; at this point the PD rule creates quite a contrast with the optometrist's instruments.

    I'm also curious about the reference to the bottom of the pupil in the last message. Presumably this is your reference point for the PD measurement and not the progressive height.
    Sorry if I have tended to rave on a bit.

    David

  7. #7
    Christine
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    I have more confidence in a professional that relies on his own abilities above and beyond any state of the art technology. I believe that you should be much more than what you do. If the machines breaks he should be able to perform just as able or better than the machine.

    AMEN

  8. #8
    Sawptician PAkev's Avatar
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    I made this post with the understanding that there is a lot of objectivity for consideration.

    I believe the biggest piece of cheese is over maintaining the integrity and consistency of the information. For instance, the PD's taken by the fitter were accurate but the guy taking the frame PD measured and figured decentration incorrectly. The RX may still be within tolerance but where did all the accuracy get you? My point is that any helpful info. which could be conveyed to everyone/anyone involved in the manufacturing process will provide optimum results. This is where I find the dotting process for PD's and lines for segs to be helpful indicators on the demo lenses.

    I am not an opponent of the pupillometer and believe they have a place in every dispensary. However, in my specific situation, I personally have complete control over the job from fitting, to manufacturing, and finally dispensing. The PD rule enables me to see exactly where my measurements will be positioned in relation to the clients facial profile. I therefore develop a good picture of the situation in my mind when blocking up the lenses.

    Kevin, has a pupillometer with dead batteries, Treat

  9. #9
    Master OptiBoarder Darryl Meister's Avatar
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    I have to agree with David on this one. Here are my Top 10 reasons why pupillometers are better (for interpupillary distance measurements):

    1) Pupillometers eliminate parallax errors, which are almost unavoidable when your PD differs appreciably from the patient's.
    2) Pupillometers take monocular PDs quickly and easily.
    3) Pupillometers can also take vertex distance measurements.
    4) Pupillometers are easier to use with persons with dark irises, since they use a light reflex.
    5) Pupillometers allow you to take near PD measurements for a range of working distances.
    6) Pupillometers are more repeatable and consistent.
    7) Pupillometers are more accurate (As David pointed out, they measure the separation of the visual axes by using reflections off the corneas).
    8) Pupillometers allow you to occlude one of the patient's eyes while taking measurements of someone with strabismus.
    9) Pupillometers are more professional and give the patient a greater perception of accuracy when filling his/her Rx.
    10) And, drum roll please... It is much harder to be poked in the eye or the face with a pupillometer!

    Best regards,
    Darryl



  10. #10
    Master OptiBoarder Texas Ranger's Avatar
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    As someone with brand new pupillometer batteries, I'll give you a way to sort of incorporate both the P'meter and PD. First take the P'meter monocular readings. next transfer thos reading to the demo lens(we uses a sharpie ultra fine point narker. On no lines, we place a micro-dot at 22mm ht. now with those two dots on, we can compensate the seg hts(on pals) and assure ourselve that the mono pd's are indeed OK. the key though is that we are trying to place the optical center on the visual axis, just as the retinascope uses the visulal axis, which is off-center, in, of mid pupil to mid pupil. when monoculars are significantly different, we discuss this situation with the pt. BEFORE we make the lenses. then they don't think we're "making excuses for poor workmanship", they know that we are making an effort to help them "see their best". now, if they are very concerned with the "cosmetics" of the glasses, we'll keep them as before, if they're very concerned , why not just get a Pal? a pt. informed of exactly what to expect, usually has no problem with the final spex.

  11. #11
    Optical Curmudgeon EyeManFla's Avatar
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    about 20 some odd years ago, I got into a contest with the late Dan Studenberg, the Varilux rep for the DC area that I could measure PDs with my trusty old ruler just as well as with a pupilometer. Ok, so I was off 1/2mm on one person...........

    I use the pupilometer now because it looks more 'professional', people just love toys. Also, I am just getting too old and lazy o use the damn stick.....besides, with the ofice staff using the toy, you always want to set a good example......

    where the hell's my Grolmann when you need it........

  12. #12
    Sawptician PAkev's Avatar
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    Thanks for all the input. There have been some helpful suggestions for consideration of maintaining the use of a pupilometer. I must humble myself and admit that confidence could sometimes be your biggest enemy. I guess the chief reason I stopped using the pupilometer is that I got tired of lugging it around in my optical tool bag all day long in and out of nursing homes and became "Too" comfortable with my trusty PD stick.

    Kevin "buying fresh batteries for my pupilometer" Treat

  13. #13
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    I like the use of the pupilometer, but prefer a pd stick.

    Most often I use the pupilometer, to find any difference is axis, and if I find normal
    light axis, then I will turn off the pupilometer and use PD stick.

    I am more trusting of a pd stick, but think the pupilometer is great for catching those pupils with off center axis.

    Which is nice, if Dr. does not specify.

    J Parker

  14. #14
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    Darryl has summed up my views better than I did, but, leaving the pupillometer aside for a moment, I have noticed that technology generally seems to be getting a lot of (in my view unfair) bad press. While I don't doubt the skills of opticians or optometrists (or any professionals, for that matter) I would feel more comfortable having my cataracts removed by an ophthalmologist using the latest phakoemulsification equipment than the older, less technologically enhanced, method. I would also back the results of the latest breed of patternless edgers over most people using hand edgers.
    Having said all that, I don't deny the need for more manual skills and I am certainly a strong believer in people having a sound understanding of what happens when they 'push the button'. Manufacturers, too, are aware of the need for maintaining the knowledge level as is evidenced by their continual release of high-tech lenses produced by emerging technologies, and the fact that they employ people like Darryl. You don't have to be a optical wiz to market lenses but, gee, it helps.
    Technology needs to be seen as a vehicle for improving what we do and not feared as an opportunity to de-skill a profession. The quality of the posts on OptiBoard would suggest to me that de-skilling is not a major concern (at least among OptiBoarders).
    As an interesting aside, this debate would not be possible without the technology of computers and the internet, yet a lot of business people still refuse to use computers for their record keeping etc for the same reasons that people criticize the pupillometer (sorry, I couldn't resist returning to the pupillometer).
    Enough of the preaching for now.
    Regards
    David

    [This message has been edited by David Wilson (edited 08-08-2000).]

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    I personally use a PD stick or dot the lenses. I do not mind the older pupillometers but do not like the new digital ones. I have found them not to be as accurate. I have never seen so many people with 3 and 4 millimeter difference on mono PD's this compares to 1 and 2 millimeter on the older model.

    Jerry

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    I prefer a pupillometer myself But one other thing I take into consideration is the PD in the old pair of glasses. Too big a difference can create quite a problem .But then that opens up a whole new can of worms

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    PD stick for binocular.

    Pupilometer for monocular.

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    Let me throw a wrench into this controversy..

    What do all of you pupilometer fans do when you have a small child come into your Optical
    with a PD too narrow for the pupilometer?
    Monocular? PD Stick? I am curious. I use both for double the accuracy and have rarely had to re-make a lens due to PD measurement error.


  19. #19
    opti-tipster harry a saake's Avatar
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    I agree about the usage of both , but more often then not will use the pupilometer. However the best system i have seen we apparently dont have over here in the states. I saw a system in France were a photo was taken, with two white lines running straight up, one in the center of each pupil, and the mono pd printed on the bottom.I also think that too much is made of being that accurate. If your within a .5 mm are you not satisfied? its kind of like the guy who sends in a seg ht of 25.5, and the "B" measurement is 40.5, Is the lab going to realistically split that into 1/4 of a mm.?

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    Thumbs up

    both but i prefer pupilometer if available. it's also equally important to have them calibrated once in a while.

    don A.

  21. #21
    sub specie aeternitatis Pete Hanlin's Avatar
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    Thumbs up

    Provided the pupillometer is kept CLEAN, I like the pupillometer (seems like most of the pupillometers I see in dispensaries have make-up caked on them ).

    I have seen very weird monoculars from dispensers using pupillometers. I think it is a result of the device being improperly placed on the patient.

    For PAL fitting, I admit I like the "penlight, tape, and dot" method. This allows me to measure actual "in frame" positions (after all, a frame doesn't always fit perfectly centered on the face). I usually verify the results with a pupillometer. Also, I find the pd stick works perfectly well for most "run of the mill" Rxs (< 3 diopters)- and it's just easier to use.

    I think a measurement with larger implications is the OC height. The few opticians I've observed who actually specify OCs generally move the OC to pupil height- disregarding the pantoscopic tilt of the frame. Fortunately, the small frames of current fashions are forgiving to lens design and placement. I wonder what will happen when they start becoming larger again...?

    Pete

  22. #22
    Master OptiBoarder Darryl Meister's Avatar
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    Hi Pete,

    Not only does this disregard the relationship between pantoscopic tilt and optical performance, but it also detracts from the cosmesis of the eyewear. Raising the optical centers, which increases the minimum blank size, increases the thickness and weight of the lenses. Moreover, since this practice is often done with high-index lenses, it kind of defeats the purpose for using these thinner, lighter lenses in the first place.

    Best regards,
    Darryl

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