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Thread: Transposition

  1. #1
    OptiBoardaholic OdTech's Avatar
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    Transposition

    Hello there, i want to know who exactly uses Cross Cylinder Transposition. The only conjecture comes to mind is either lab-tech, an ophthlamologist, and maybe optometrist.
    Even though i am an a apprentice optician i have lots of use with flat transposition since i can evaluate which eye defect a patient has, and with toric transposition its has most of use in surfacing the lens itself and then the lab will send it(the lens) to the optician. Furthermore, in theory i know and understand the Cross Cylinder Transposition but not in practice in the business sphere.

    Any sort and kind of feedback welcomed

  2. #2
    OptiBoardaholic OdTech's Avatar
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    Wow no replies

    Woow i can't imagine enough that people on this site don't know Who exactly uses CROSS CYLINDER TRANSPOSITION? and FOR what exactly it is used for?

    You may LOL but seriously what's the use for CCT?:(

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    Forever Liz's Dad Steve Machol's Avatar
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    Perhaps I've led a sheltered life but I haven't seen a Cross Cylinder Rx in over 25 years.


    OptiBoard Administrator
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    OptiBoard has been proudly serving the Eyecare Community since 1995.

  4. #4
    OptiBoardaholic OdTech's Avatar
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    Well Steve thanks for the reply but i 've got the book that has all the formulas an optiican in the lab would most certainly use but not in terms of making sales:D .

    Anyhow I'm sure in this website a excellent lab techs that maybe use the formula.
    I am looking forward to hearing from you all.

  5. #5
    Optical Educator
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    crossed cyls

    Hello,

    We still teach crossed cyls in our opticianry program...

    Although it is unlikely you will use it, it is still good to know. On occasion, given our geographic location, we receive prescriptions written in crossed cylinder form from South America. One of my Internet students from Equador tells me that they still work in crossed cyl form.

    If you are over-refracting and need to add cyl at a different axis, it is useful. Transposing and combining crossed cyls 90 degrees apart is easy...it is the obliques that take some time.

    Laurie

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    Post cross cyl or cross curve?

    Hello ODtech,
    Cross-Cyl is used in refractometry for refining axis and checking power of cylinder.
    If you are talking about lab,is that to do with sphere curve/base curve/cross curve transposition. However,you will get your answer in this forum.
    Regards,
    Shabbir

  7. #7
    OptiBoardaholic OdTech's Avatar
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    Wow thanks G-d somebody knows their things around opticianry world.

    Hello and well "Optom" you mistaken in this somewhat. This is not i guess the terminology . I am intersted only in Transposition not in 'Cross Cylinder' which is Jackson Cross Cylinder . I will agree with you with your 1st sentence. However lets clear it up.

    With CC Transposition you find 'Sphere' and 'Axis'
    so it looks like this Ex: -1.00x020 (*) +0.50x110
    (*)=means combined.

    This is not exactly what you get with Refraction, please correct me if i'm wrong and thanks very much for reply.

    Hello "Laurie" well you are on the right track. this is opticianry not refraction.

    What is usefulness of CCT? why the Flat transposition not good enough?

    As i explained before with FT i can know exactly which defect the patient has and how much of it, so i can service better to customer's needs. Lastly thanks for participation.

    Well once again feedback is welcomed. :D :cheers:

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    Post CC transposition

    Hello ODtech,
    You are right,I ve failed to comprehend you question well. Do you mean transposing cross cyl prescription into sphero-cylinder prescription and vice versa? If this is what you want to know I have the answer. I hope Lab experts from this board may be able to anwer your question.
    Regards,
    Optom

  9. #9
    Moderator - Joann Raytar Jo's Avatar
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    Hope this helps:
    Cataract & Refractive Surgery Today
    http://www.crstoday.com/02_current/crst1102_12.html


    The Bitoric and Cross-Cylinder Alternative
    Arturo Chayet, MD, of Chula Vista, California, and Paolo Vinciguerra, MD, of Milan, Italy, pioneered the techniques of bitoric and cross-cylinder ablations.3-5 Both techniques divide the pre-existing astigmatism into hyperopic and myopic components. The key difference is that the cross-cylinder technique divides the preoperative cylinder into equal myopic and hyperopic components and treats the spherical equivalent of the preoperative refraction. Dr. Chayet and his colleagues introduced the bitoric LASIK ablation profile in order to correct mixed and simple myopic astigmatism by dividing the preoperative astigmatism into unequal ratios of myopic and hyperopic cylinder. Theoretically, this technique avoids causing a hyperopic shift in the spherical component of the refraction.


    It is not surprising that both techniques were originally developed and patented6,7 by Nidek Co., Ltd., (Gamagori, Japan) for its EC-5000 excimer laser platform, because the circular ablation profile of the standard Nidek myopic cylinder ablation demonstrates greater hyperopic spherical coupling than other modern excimer laser platforms performing unimeridional (oval) ablation profiles. With the possible adoption of both of these ablation algorithms to the EC-5000, Nidek will be able to provide refractive surgeons with a detailed, cognitive, preoperative approach and one of the broadest astigmatic treatment ranges of any excimer laser platform currently available.


    The primary goal of the bitoric and cross-cylinder techniques is to create a more stable, predictable optical result with fewer of the side effects commonly associated with unimeridional myopic cylinder treatments (Figure 1). One of the best times to use these alternate approaches to astigmatism treatment is when correcting mixed astigmatism induced by prior refractive procedures. During the preoperative surgical planning, it is important to note that these techniques differ in regard to the location and quantity of corneal tissue ablated. My personal clinical experience is that a cross-cylinder ablation provides the highest quality mesopic/scotopic vision in high astigmatic corrections. The cross-cylinder (50/50 astigmatic split) ablation treats the spherical equivalent of the manifest refraction with the cylinder of the same sign. I generally treat the myopic component first. For example:
    Preoperative manifest refraction: -1.0 -5.0 X 180
    Treatment Parameters
    • First treatment: -3.50 -2.50 X 180
    • Second treatment: plano +2.50 X 90
    As a general rule, I will make my standard personalized-nomogram adjustments to each component of the treatment.
    The cross-cylinder ablation picks up where the unimeridional, compound/myopic astigmatic ablation falters. The other key benefit of the cross-cylinder ablation is manifest in the form of less regression/greater stability of the treatment effect with higher-magnitude cylinder corrections. Cross-cylinder ablations are also tremendously useful when treating mixed astigmatism. For example:
    Preoperative manifest refraction: +4.0 -6.0 X 180
    Treatment Parameters
    • First treatment: plano -3.0 X 180
    • Second treatment: +1.0 + 3.0 X 90 (spherical equivalent added to cylinder of same sign)
    The main caveat in using the cross-cylinder ablation approach is that it consumes more total tissue than the unimeridional treatment.

  10. #10
    Optical Educator
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    CCT

    Hi OdTech,

    The reason you cannot use flat transposition is because the prescription is not written in spherocylinderical form, but in crossed cylinder form (as mentioned by Shabbir).

    Assuming the spheres to be plano, the example you gave would combine as:

    +0.50 -1.50 x 020

    or

    -1.00 +1.50 x 110


    Is this what you are asking?

    : )

    (I can't resist a good optical geek question)

    Laurie

  11. #11
    OptiBoardaholic OdTech's Avatar
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    Welcome back and thanx for participation

    Optom u understood correctly. And Laurie thanx to you too that exactly what i wanted to know.
    :idea:

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