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Thread: Measuring Pantoscopic Angle

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    Measuring Pantoscopic Angle

    Recently there was some discussion on how to measure pantoscopic angle. I mentioned that Zeiss will probably give you an instrument/gauge for this.
    If you don't have access to Zeiss various hardware and home supply tool departments have "Angle finder gauges" for sale. that will do the job as well or better. Through the week-end Harbour Frieght has one on sale for around $6.00.

    Chip

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    At AO we used to use a 29 cent plastic protractor, worked OK.
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    Shamir and KBCo have charts that are pretty good. The only problem with them is that they measure the angle of the frame itself, not the angle of the fit on the person. In most cases it will be the same, but then there are those people with ears in strange locations...
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    I'm looking for some chart or measuring unit for pantoscopic angle. Could you help me out?

    Is that some measuring unit or chart is good enough? I just remember that iwas the Zeiss measuring unit somewhere, but i can't find it again.

    How did you solve the cases, where people have ears in the strange location? individually ?

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    Quote Originally Posted by essegn View Post
    I'm looking for some chart or measuring unit for pantoscopic angle. Could you help me out?

    Is that some measuring unit or chart is good enough? I just remember that iwas the Zeiss measuring unit somewhere, but i can't find it again.

    How did you solve the cases, where people have ears in the strange location? individually ?
    You could make use of Zeiss Individual Panto and Vertex Tool (part #000-0139-15450).

    With a pre-adjusted frame and the patient standing in profile looking straight ahead, use the Zeiss IndividualTM Panto and Vertex Tool (part #000-0139-15450) to measure the pantoscopic tilt of the frame on their face. Place the vertical edge of the panto tool against the plane of the frame. The pendulum of the tool will automatically line up vertically and show the pantoscopic angle of the frame. Zeiss IndividualTM is suitable for pantoscopic tilt up to 30°. If no pantoscopic tilt is specified in the lens order an average value of 9° will be used.
    http://www.personalizedlens.com/imag...pense_0809.pdf

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    When we measure pantoscopic tilt (not angle...angle is the measurement between the temple and the front. Tilt is the measurement of the lens (frame front) plane with respect to the visual axis), keep in mind that the client's facial angle is EXTREMELY important. Head back or head forward tilts will give erroneous values. In reality what we really want is to discover the eye's center of rotation. When we measure pantoscopic tilt, the value or equations use make many small, hidden assumptions about vertex, corneal refletion, visual axis position, etc.

    Essilor VisioOffice purports to discover the eye's *effective* CR. Only time will tell if we're all getting too hung up in the minutiae of measuring.

    B

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    Quote Originally Posted by Barry Santini View Post
    When we measure pantoscopic tilt (not angle...angle is the measurement between the temple and the front. Tilt is the measurement of the lens (frame front) plane with respect to the visual axis), keep in mind that the client's facial angle is EXTREMELY important. Head back or head forward tilts will give erroneous values. In reality what we really want is to discover the eye's center of rotation. When we measure pantoscopic tilt, the value or equations use make many small, hidden assumptions about vertex, corneal refletion, visual axis position, etc.

    Essilor VisioOffice purports to discover the eye's *effective* CR. Only time will tell if we're all getting too hung up in the minutiae of measuring.

    B
    Barry, is there some authority that asserts what you've said about the "pantoscopic angle" vs. "pantoscopic tilt" nomenclature?

    I can understand how the "facial angle" (another term I suspect to be non-normative) is relevant if you are measuring the pantoscopic tilt relative to a normal to the Earth, but I don't see what that has to do with the center of rotation of the eye.

    Because a human is capable of holding his head at a range of angles while gazing afar, it seems to me that you'd really want to know what that angle is, and I gather that's what you mean by "facial angle". But I can imagine the center of rotation moving in any or all of three dimensions without that (the "facial angle") changing at all.

    And if I know the center of rotation of the eye, I don't see how that helps me determine the "facial angle"; how the patient holds his head seems to me to be independent of that (he can decide to tuck his chin a bit, and change the "facial angle" thereby, but that obviously wouldn't change the centers of rotation of his eyes - which, for that matter, could differ).

    I suppose if you know the center of rotation, and the pantoscopic tilt at far, you could determine the pantoscopic tilt at another "facial angle", as may be presented at near.

    To what do you think the "facial angle" is relative?

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    Quote Originally Posted by Barry Santini View Post
    Tilt is the measurement of the lens (frame front) plane with respect to the visual axis),

    B
    How do you measure where the visual axis is ?

    When the wearer look through the glasses to the 5-6m and then by placing the vertical edge of panto tool against the plane of the frame ?

    I want to be sure that i'm understand right. Because i tried to measure the panto angle and tilt on Rudyproject Rydon and i've got these results:

    Pantoscopic angle=16° (angle between temples and lenses)
    Pantoscopic tilt=12° (the wearer had his glasses on and then i measured tilt of the lenses)

    is it correct ?

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    Master OptiBoarder OptiBoard Silver Supporter Barry Santini's Avatar
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    Quote Originally Posted by essegn View Post
    How do you measure where the visual axis is ?

    When the wearer look through the glasses to the 5-6m and then by placing the vertical edge of panto tool against the plane of the frame ?

    I want to be sure that i'm understand right. Because i tried to measure the panto angle and tilt on Rudyproject Rydon and i've got these results:

    Pantoscopic angle=16° (angle between temples and lenses)
    Pantoscopic tilt=12° (the wearer had his glasses on and then i measured tilt of the lenses)

    is it correct ?
    You are correct, assuming the cleint's *facial plane* was perperndicualr to the floor. This has nothing to do with observed or habitual posture.

    B
    Last edited by Barry Santini; 06-29-2010 at 08:56 AM.

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    Well remember, that this angle is relative to the fit of the eyewear.
    If by chance you have an individual with ear set slightly above their eyes the glasses would have a greater amount of angle to that of someone whose ears were set on plane or blow the relative plane of the orbit. The angle in which someone holds there head also obviously effects this measurement (As we have all seen in the fitting of conventional bifocals and PAL's).

    Thus we can reason that the Pantoscopic Angle is relative to the frame, the pantoscopic tilt is relative to the indivdual. So your measurements can very well be correct. What would be interesting would be to go back today and remeassure the tilt on the patient, then set the frame on a counter and measure the tilt as a relative control. I would be curious to see what the difference if would be and how that would ultimately fit an average wearer.

    For those looking for master's papers subjects that would be a fun one. "POW measurements and the effect on the average patients visual experience".
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    Quote Originally Posted by rinselberg View Post
    You could make use of Zeiss Individual Panto and Vertex Tool (part #000-0139-15450).

    http://www.personalizedlens.com/imag...pense_0809.pdf
    That's how I measure it. I would recommend measuring the distance visual point with the subject standing. The posture must be relaxed and typical. Triple check it.

    Alternatively, if you don't have a plumb line device, after measuring the distance visual point in the typical posture, have the subject raise their chin until the frame/lens is perpendicular to the floor, marking the lens for the new distance visual point. Measure the distance between the these two points and multiply by two. This is roughly equal to the pantoscopic tilt.
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    Master OptiBoarder OptiBoard Silver Supporter Barry Santini's Avatar
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    We use martin's Rule to ensure that the optical axis of a spherical, best form lens, or the design*pole* of a aspheric/atoric lens is properly oriented with repsect to the eye's center of rotation, since this best desscribes the expected/effective focal plane of the dynamic eye.

    Because the angle between the temple of the frame has, over time, become an incorrect stand-in for the angle of the lens in front of the eye, so the new differentiation and distinction between ther terms pantoscopic angle and pantoscopic tilt. I took these from a CE by Ed Degennero.

    "facial angle" is an attempt to define the appropriate position for a subject's head to be placed in order to use the various plumb devices, like the Zeiss tool, to ascertain the pantoscopic *tilt* of the frame/lens plane. because of all the dynamic postures a head may take, we need some sort of *base point* to which we attempt to relate the plane of the frame/lenses, from which, we mount the appropriate lens reference point with respect to a lien extending from the eye's CR to the interesection of said lens.

    Essilor and others have postulated that eyes with substantially different axial dimensions or other physiometric differences (say, asian, vs. indian, vs. caucasian) would possess CRs that may deviate in an appreciable way from the assumed Gullstrand coordinates. Therefore, with the current goal to obtaining ever finer lens performance (or, in the basence of that, giving the marketing department something to hang their position statements upon), attemtping to refine lens performance necessitates ever more precise ways of ensuring the ideal placement of the lens surface with respect to the ascribed/dynamic retinal plane. Whether this is valid or reasonable, I will let others speculate.

    In any event, the term (mine?) facial plane is defined as follows: A line drawn from the uppper orbital area, tangent, as closely as possible, to the lower orbital area, continuing through and utilizing the upper and lower jaw areas, as well as the chin perhaps, is used to define a subject's facial plane. When measuring pantoscopic tilt using a plumb device, one should try to make such plane as perpendicular as possible to the floor plane.

    Anyone else want to jump in hear and discuss this, please do. I'm here to learn.

    B
    Last edited by Barry Santini; 06-30-2010 at 06:47 AM.

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