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Thread: Stumped! Help!

  1. #1
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    Stumped! Help!

    I have a customer who is a high minus with a high astigmatism. He has a pair for reading and a pair for distance. The distance is fine, but for reading he says that when he rotates his head things seem clearer. I don't mean turning his head side to side I mean actually cocking his head to one side while looking at something. When he just tilts the glasses and looks out of them that actually makes it worse. I re-did the lenses in a different material (from 1.7 to 1.67) and that seemed to help but not totally. What is wrong with this guy? I don't think it's an axis issue.

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    Master OptiBoarder OptiBoard Gold Supporter DragonLensmanWV's Avatar
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    Quote Originally Posted by dweinstein View Post
    I have a customer who is a high minus with a high astigmatism. He has a pair for reading and a pair for distance. The distance is fine, but for reading he says that when he rotates his head things seem clearer. I don't mean turning his head side to side I mean actually cocking his head to one side while looking at something. When he just tilts the glasses and looks out of them that actually makes it worse. I re-did the lenses in a different material (from 1.7 to 1.67) and that seemed to help but not totally. What is wrong with this guy? I don't think it's an axis issue.
    Look carefully - is one eye lower than the other one? I generally place the OC lower than the 180 line for reading glasses, above for distance.
    Is he old enough to be starting cataracts? I'm starting some myself, and my vision in the upper field is noticeably poorer.
    DragonlensmanWV N.A.O.L.
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    Optical Clairvoyant OptiBoard Bronze Supporter Andrew Weiss's Avatar
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    I agree, it sounds like an O.C. issue. He may be sensitive to the induced prism. And I find it's not uncommon to find that folks have one eye lower than the other (I'm one of 'em).
    Andrew

    "One must remember that at the end of the road, there is a path" --- Fortune Cookie

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    Manuf. Lens Surface Treatments
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    Redhot Jumper Try to...........................

    Quote Originally Posted by DragonLensmanWV View Post
    Look carefully - is one eye lower than the other one? I generally place the OC lower than the 180 line for reading glasses, above for distance.
    Is he old enough to be starting cataracts? I'm starting some myself, and my vision in the upper field is noticeably poorer.
    Good advice.....................try to do the lenses in CR39

  5. #5
    OptiBoard Professional Ory's Avatar
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    It's also not uncommon for presbyopes to develop a significant exophoria. Often a head turn is a compensation for this. Check with the prescribing doc about potential need for prism; just make sure you haven't induced any as others have said above.

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    Checked old lenses

    I forgot to mention I checked everything on his old lenses. Base curve, OC, PD, etc. Everything matches. Only a slight change in the Rx. Any other suggestions?

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    Optical Clairvoyant OptiBoard Bronze Supporter Andrew Weiss's Avatar
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    Quote Originally Posted by dweinstein View Post
    I forgot to mention I checked everything on his old lenses. Base curve, OC, PD, etc. Everything matches. Only a slight change in the Rx. Any other suggestions?
    Are you simply putting new lenses in the frame he was already wearing for reading?
    Andrew

    "One must remember that at the end of the road, there is a path" --- Fortune Cookie

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    yup

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    Master OptiBoarder OptiBoard Gold Supporter DragonLensmanWV's Avatar
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    Quote Originally Posted by dweinstein View Post
    yup

    Ok then. Sounds like the customer is crazy - time to use that giant vat of acid in the back.:D
    DragonlensmanWV N.A.O.L.
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    Master OptiBoarder
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    What material was he wearing before? What was the PD in the old lenses?

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    What's up? drk's Avatar
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    Are you talking about the SVNO pair?

    Is the distance pair OK? I think you said "yes".

    And the axis of astigmatism is correct in both pairs?

    You need to run a monocular test:
    Take the near only pair, have him occlude the left eye, and see if reading material is clear at the prescribed working distance.

    Repeat for the left eye.

    If either one is blurry, have him tilt until it is correct, and make a mental note as to how the axis should be changed to compensate.

    If neither one is blurry individually, but binocularly, you need to go back to the prescriber (assuming the level MRPs are correct)...Is the add wrong? Does he have some eye muscle problem (including cyclorotary muscles)?

  12. #12
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    Do I see Poly raising it's ugly head here? High Myope, High astigmatism, humh? Also Do I see vertical centers not set correctly?

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    Optical Clairvoyant OptiBoard Bronze Supporter Andrew Weiss's Avatar
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    Quote Originally Posted by drk View Post
    Are you talking about the SVNO pair?

    Is the distance pair OK? I think you said "yes".

    And the axis of astigmatism is correct in both pairs?

    You need to run a monocular test:
    Take the near only pair, have him occlude the left eye, and see if reading material is clear at the prescribed working distance.

    Repeat for the left eye.

    If either one is blurry, have him tilt until it is correct, and make a mental note as to how the axis should be changed to compensate.

    If neither one is blurry individually, but binocularly, you need to go back to the prescriber (assuming the level MRPs are correct)...Is the add wrong? Does he have some eye muscle problem (including cyclorotary muscles)?
    Ditto.
    Andrew

    "One must remember that at the end of the road, there is a path" --- Fortune Cookie

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    One eye sees, the other feels OptiBoard Silver Supporter
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    Quote Originally Posted by DragonLensmanWV View Post
    Look carefully - is one eye lower than the other one? I generally place the OC lower than the 180 line for reading glasses, above for distance.
    Yup, especially with high power and lower Abbe materials. If he's right dominant and tilts his head to the right, he's effectively lowering the right oc to better align with the pupil, and inducing BI prism. I would look at the vertical centers- if they are well above the pupil on the down gaze then consider lowering the OCs about 3mm or so and/or find a frame that positions the 180 line as low as possible, something like a wide bridged P-3 shape, as well as using a higher Abbe material. You can check this by having him raise the reading card higher and see if the vision clears.
    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.



  15. #15
    What's up? drk's Avatar
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    FASCINATING.

    You guys are "the bomb".

    So, you modify the OC height based on the purpose of the glasses?

    1.) I question the utility of raising the level MRP in distance only glasses...dot the pupil, then 1 mm drop per 2 degrees of panto. How much better can you get than that? Or, are you saying, Dragon, that you don't specify level MRP in SV, but you do "fudge" upwards as a cheap imitation?

    2.) Lowering the MRP to the pupil center for some "standardized downgaze angle", like 10 mm below distance MRP, or lowering the MRP to a customized level (assuming you can use mirrors to view and measure, etc.) is a nifty idea.

    a.) it would more completely eliminate prismatic imbalance on anisometropes on SVNO. That does occur occasionally, and would be a nice "fine tuning".

    b.) it would eliminate chromatic and other aberrations from looking off-center on high Rx SVNO lenses (+/-4.00?).

    How often does that come into play, though? How often are we doing SVNO high plus (it's a killer) or SVNO high minus? I guess as often as anisometropia.

  16. #16
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    Quote Originally Posted by DragonLensmanWV View Post
    Ok then. Sounds like the customer is crazy - time to use that giant vat of acid in the back.:D
    That quote has made my day!!!!!! LOL!

  17. #17
    One eye sees, the other feels OptiBoard Silver Supporter
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    Quote Originally Posted by drk View Post
    FASCINATING.

    You guys are "the bomb".
    Tick,tick,tick...

    So, you modify the OC height based on the purpose of the glasses?
    Yup. Position of gaze, Rx, etc.

    1.) I question the utility of raising the level MRP in distance only glasses...dot the pupil, then 1 mm drop per 2 degrees of panto. How much better can you get than that? Or, are you saying, Dragon, that you don't specify level MRP in SV, but you do "fudge" upwards as a cheap imitation?
    You put it where it induces the least prism/VI, power error/astigmatism, and chromatic aberration, not necessarily in that order.

    2.) Lowering the MRP to the pupil center for some "standardized downgaze angle", like 10 mm below distance MRP, or lowering the MRP to a customized level (assuming you can use mirrors to view and measure, etc.) is a nifty idea.
    You usually don't want to vertically decenter much more than 3mm or so for weight and thickness reasons. Better to select a frame that places the geometric center in a more favorable position. Probably should increase the panto if the OC is placed much more than 5mm below the pupil.

    a.)it would more completely eliminate prismatic imbalance on anisometropes on SVNO. That does occur occasionally, and would be a nice "fine tuning".
    It's fundamental, but fine tuning is a good thing too.

    b.) it would eliminate chromatic and other aberrations from looking off-center on high Rx SVNO lenses (+/-4.00?).
    In addition, we could use higher Abbe lenses.

    How often does that come into play, though? How often are we doing SVNO high plus (it's a killer) or SVNO high minus? I guess as often as anisometropia
    I'm seeing a lot more low vision (us boomers are getting older and grumpier) and aspherics need optimal vertical positioning. I'll also use long corridor PALs for general use on strong RXs, then use SVRO for prolonged near tasks.

    =========================================================

    dweinstein:

    Another thought- consider using the distance PD instead of the near PD for the readers. This induces BI prism that myopes usually get when they read with distance glasses- add a 3 or 4 degrees of face form to compensate optically for wide PD. {I believe I got this last part wrong- if the horizontal OC is equal to the distance PD, then there is no need to modify the face form.}

    Quote Originally Posted by ScottV View Post
    That quote has made my day!!!!!! LOL!
    I've been fond of the trap door under the chair treatment, unfortunately that just recycles them back into the ophthalmic community. But an acid bath...wow! You're outta here, gone, no more, fini. I like it.
    Last edited by Robert Martellaro; 05-11-2007 at 12:22 PM.
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  18. #18
    What's up? drk's Avatar
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    Well, now that I think about it a little more, the 10mm downgaze position would never occur in a SVNO situation. Most people are more likely to depress their heads when there's no MF in the lens. (I'll have to ask the Varilux Ipseo people :)).

    So, maybe, maybe lowering the level MRP on a SVNO is useful, to a degree, as you say. You use about a 3 mm drop?

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    Master OptiBoarder snowmonster's Avatar
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    I'm going with the axis on the new glasses being off. I've got -1.50 cyl in each eye and I notice that if I tilt my head right and left (towards opposite shoulders), my vision will either get better or worse.

    -Steve

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    Master OptiBoarder OptiBoard Gold Supporter DragonLensmanWV's Avatar
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    Quote Originally Posted by drk View Post
    Well, now that I think about it a little more, the 10mm downgaze position would never occur in a SVNO situation. Most people are more likely to depress their heads when there's no MF in the lens. (I'll have to ask the Varilux Ipseo people :)).

    So, maybe, maybe lowering the level MRP on a SVNO is useful, to a degree, as you say. You use about a 3 mm drop?
    Depends a bit on the frame. Usually not that much unless it sits really low.It's not needed as drastically now with the smaller frames, but boy, those old 60 eye aviators - if you didn't decenter up on those you could get into some real messes!
    DragonlensmanWV N.A.O.L.
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    Optical Clairvoyant OptiBoard Bronze Supporter Andrew Weiss's Avatar
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    Interesting. On higher-power SV lenses, particularly in high-index materials (including poly and Trivex), I routinely vertically decenter the OC to match the patient's viewing angle in that particular frame. My goal is to get the OC over the pupil as closely as possible, especially with aspheric designs.

    Robert, I think your limit of 3mm up or down may answer why I've occasionally had problems with my approach. Thanks much.:cheers:
    Andrew

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  22. #22
    One eye sees, the other feels OptiBoard Silver Supporter
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    Quote Originally Posted by drk View Post
    Well, now that I think about it a little more, the 10mm downgaze position would never occur in a SVNO situation. Most people are more likely to depress their heads when there's no MF in the lens. (I'll have to ask the Varilux Ipseo people :)).
    It varies from one person to another. Best to measure it with the frame on, and then have them hold a book or magazine. It would be helpful if the MDs did this when they prescribe the Add power!

    So, maybe, maybe lowering the level MRP on a SVNO is useful, to a degree, as you say. You use about a 3 mm drop?
    Beyond satisfying Martin's rule (typically 3mm to 5mm- best achieved by proper frame selection) vertical decentration may be helpful if there is a power disparity in the vertical meridian, as long as it doesn't introduce significant power or astigmatic errors, although increasing the panto angle should compensate for the lower OC.
    Science is a way of trying not to fool yourself. - Richard P. Feynman

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  23. #23
    What's up? drk's Avatar
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    I've never heard of Martin's Rule, so you'll have to fill me in.

    It sounds like, and I'm roughly estimating, "Choose a frame where the eye's distance to the upper eyewire is about 1/3 of the vertical dimension, and the distance to the lower eyewire is about 2/3 the vertical dimension."

    What is it?

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    Doh! braheem24's Avatar
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    Anyone got a trial frame?

    -Adjust the OC, PD, Panto, axis all you want plus it already has the best Abbe value.

    Can you please post the old and new NVRX, I have a feeling it's not the glasses.

  25. #25
    Allen Weatherby
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    Pupil and optical center location for a lens

    Andrew Weiss said:
    Interesting. On higher-power SV lenses, particularly in high-index materials (including poly and Trivex), I routinely vertically decenter the OC to match the patient's viewing angle in that particular frame. My goal is to get the OC over the pupil as closely as possible, especially with aspheric designs.
    I was not trained as an optician but I have come to learn the many Opticians believe that fitting a single vision does not require an OC height. I did not understand this, so I kept asking for the optics and math that says a single vision is always fitted at 1/2 the "B", yet a PAL is very sensitive to being fitted exactly infront of the pupil for good far vision. Not one optician that I asked could tell me why it was OK to split the "B" on single vision yet a PAL required much more precision. (I understand the channel and the add need to also be correctly positioned). My conclusion is this is the result of historical eye rim shapes vs. todays shapes. Original spectical lenses were designed as round frames with pupil located in the middle of the frame. This lead to single vison being fitted at 1/2 of the "B". Aviator styles have been mentioned in this tread and of course the lens optical center would need to be located exactly over the pupil, not 1/2 of the "B".

    Our PAL design has a very small spherical area at the optical center of the far vision. This is fitted directly over the pupil and the aspheric design of the lens begins approximately 14 to 16 mm outside this spherical area. With any lens looking straight ahead through a spherical lens of the correct power is the best lens for accuity. Obviously fitting this design at 1/2 the "B" on any frame would not work well.

    With high power single vision lenses the location of the optical center in relation to the pupil is very critical.

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