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Thread: Best method for measuring PD

  1. #1
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    Best method for measuring PD

    I'm curious about both your opinion and any research anyone may be aware of into what method for measuring monocular and binocular PD respectively is best.

    What are your views and what the research says on pupillometer, autorefractor, ruler, apps (and anything else you might use)
    Last edited by Alfred001; 05-10-2019 at 09:19 AM.

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    Welcome to Optiboard. I'm curious what your background in this field is.

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    Quote Originally Posted by Alfred001 View Post
    I'm curious about both your opinion and any research anyone may be aware of into what method for measuring monocular and binocular PD respectively is best.

    What are your views and what the research says on pupillometer, autorefractor, ruler, apps (and anything else you might use)
    Never used an autorefractor. App and pupilometer gave almost same results and both work off the same principle assuming the app works on reflection.

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    Autorefractors are not very accurate and dont provide mono pd's.

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    Master OptiBoarder rbaker's Avatar
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    The Gold Standard is a muscle light and a metric ruler.

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    One eye sees, the other feels. OptiBoard Gold Supporter
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    Alfred,

    A Pupilometer is the standard, but is unable to account for face turns and other physical anomalies.

    https://healthpartnersohpe.files.wor...ns-handout.pdf

    I use the client's preadjusted frame in situ with narrow vertical ink lines bisecting the corneal reflex. Adjust for differences between measurer's IPD and wearer's IPD. Use a PAL verification chart to read the results.

    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

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    Compulsive Truthteller OptiBoard Gold Supporter Uncle Fester's Avatar
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    "I use the client's preadjusted frame in situ with narrow vertical ink lines bisecting the corneal reflex. Adjust for differences between measurer's IPD and wearer's IPD. Use a PAL verification chart to read the results."

    Robert- Does this explain why my wide PD'd eyes tend to ruler measure a millimeter or so larger than other colleagues as well as a pupilometer?

    Can you expand on the last sentence? Verification chart???

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    Quote Originally Posted by Uncle Fester View Post

    Can you expand on the last sentence? Verification chart???
    Draw a vertical line at the corneal reflext right onto the glasses that you are planning to put lense into. Super impose the frame onto the chart with the center of the bridge aligned to the center of this chart. Read PD's off the scale.
    Click image for larger version. 

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  9. #9
    One eye sees, the other feels. OptiBoard Gold Supporter
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    Quote Originally Posted by Uncle Fester View Post
    "I use the client's preadjusted frame in situ with narrow vertical ink lines bisecting the corneal reflex. Adjust for differences between measurer's IPD and wearer's IPD. Use a PAL verification chart to read the results."

    Robert- Does this explain why my wide PD'd eyes tend to ruler measure a millimeter or so larger than other colleagues as well as a pupilometer?

    Can you expand on the last sentence? Verification chart???
    For every 1mm diference between the PD of the fitter and the subject, the fitter will over-estimate
    the subject's PD by 1/16 mm if the fitters PD is larger than that of the subject.
    -Probably Jalie.

    If your binocular IPD is 74mm and the subject is 58mm, and you don't compensate, your result will be off 1mm on the high side. Not usually an issue, but when it is, the compensation is typically .5mm to 1mm, maybe a little more if the subject is a very young child.

    Keep in mind that these errors are additive, if the lab is 1mm wide on each lens, and your measurement method is 1mm wide per lens, and the lens power converges the eyes 1mm more per eye at the near point than the lens design anticipates, and/or if there is prescribed horizontal prism imbalance (base out in this example), we'll be looking at errors of 2mm to 4mm or more wide per eye! Admittedly that's the worse case but you get the idea- this can go very bad really fast if we're not paying attention.

    ************************************************************ ******************

    If you're not using a pupilometer, Use this chart to determine the near PD if the work distance is less than 16"/40cm.

    If stop distance equals 27mm, the near multiplier for a work distance of
    40cm is .937
    35cm is .928
    30cm is .925
    25cm is .903
    20cm is .881


    Quote Originally Posted by Oscar View Post
    Draw a vertical line at the corneal reflext right onto the glasses that you are planning to put lense into. Super impose the frame onto the chart with the center of the bridge aligned to the center of this chart. Read PD's off the scale.
    Click image for larger version. 

Name:	test.png 
Views:	14 
Size:	63.9 KB 
ID:	14308
    That's it. Position accurately and eliminate errors due to parallax.

    Hope this helps,

    Robert Martellaro
    Last edited by Robert Martellaro; 05-21-2019 at 10:32 AM.
    Roberts Optical Ltd.
    Wauwatosa Wi.
    www.roberts-optical.com
    ~~~~~~~~~~~~~~~~~~
    Science is a way of trying not to fool yourself. - Richard P. Feynman

  10. #10
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    Quote Originally Posted by Robert Martellaro View Post
    For every 1mm diference between the PD of the fitter and the subject, the fitter will over-estimate
    the subject's PD by 1/16 mm if the fitters PD is larger than that of the subject.
    -Probably Jalie.

    If your binocular IPD is 74mm and the subject is 58mm, and you don't compensate, your result will be off 1mm on the high side. Not usually an issue, but when it is, the compensation is typically .5mm to 1mm, maybe a little more if the subject is a very young child.

    Keep in mind that these errors are additive, if the lab is 1mm wide on each lens, and your measurement method is 1mm wide per lens, and the lens power converges the eyes 1mm more per eye at the near point than the lens design anticipates, and/or if there is horizontal prism imbalance (base out in this example), we'll be looking at errors of 2mm to 4mm or more wide per eye! Admittedly that's the worse case but you get the idea- this can go very bad really fast if we're not paying attention.

    ************************************************************ ******************

    If you're not using a pupilometer, Use this chart to determine the near PD if the work distance is less than 16"/40cm.

    If stop distance equals 27mm, the near multiplier for a work distance of
    40cm is .937
    35cm is .928
    30cm is .925
    25cm is .903
    20cm is .881



    Robert Martellaro

    Is it possible to avoid making these calculations by just having the dispenser shift their position so that the eye's line up with the patient? dispenser uses left eye and lines up with patient's right eye and measures "0". Dispenser uses right eye and shifts their body to line up with patient's left eye and measures binocular. Repeat step 1 to correct alignment of PD ruler. Check bridge for monocular measurement.

  11. #11
    One eye sees, the other feels. OptiBoard Gold Supporter
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    Quote Originally Posted by Oscar View Post
    Is it possible to avoid making these calculations by just having the dispenser shift their position so that the eye's line up with the patient? dispenser uses left eye and lines up with patient's right eye and measures "0". Dispenser uses right eye and shifts their body to line up with patient's left eye and measures binocular. Repeat step 1 to correct alignment of PD ruler. Check bridge for monocular measurement.
    That may introduce errors, I think. If you move more for one eye than the fellow eye we might change the binocular PD, which is arguably more important then the monocular PD. A simple rule of thumb would probably suffice- modify by .5mm for differentials of 6mm to 10mm, and 1mm for larger differences. Or use a pupilometer, which eliminates parallax errors (but not errors due to face/head turns).

    Note to pupilometer users- clean with 70% isopropyl alcohol after every use, especially during flu season. Calibrate routinely, especially after hard use.

    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

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