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Thread: Slab off AND prism

  1. #1
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    Confused Slab off AND prism

    Hi everyone. I need a little advice. I received an Rx from an MD.
    He is prescribing prism for the bifocal only AND a slab off. He wants a progressive bifocal. Doesn't the slab off eliminate the need for the prism? And, is it possible to have the prism just in the seg? After talking to this MD, I am doubting myself!! Please help! The prism he is prescribing is .50 base out O.U. I know (or thought I knew ) that the slab off is base down. There is a 6 diopter difference between the lenses for reading. The Dr. did not prescribe slab-off or prism initially. The patient returned to the Dr. after I explained slab-off, and the MD gave her a new script that said "slab-off if desired". That's when I called him to verify his request. Any help woud be appreciated.

    Thanks,
    Mary

  2. #2
    Bad address email on file Rich R's Avatar
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    Hi Mary, I never heard of grinding prism in seg on progressive lenses, except for slab prism which you are correct would be base down. With 6 diop difference I think the slab would be much more important that .5 base out prism
    Rich R

  3. #3
    since 1964 Homer's Avatar
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    Back to basics ....

    Let's start over.

    What is the RX?

    When you say the Doctor want prism in the segment only are you talking about .5 PD BO OU? That sounds a bit strange?

    We'll all be able to comment more accurately if we can; 1) see the complete Rx, 2) know what the patient is wearing now, 3) Has anything happened since the last Rx, trauma, surgery, stroke ??,

  4. #4
    Master OptiBoarder Jeff Trail's Avatar
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    One thing is that you CAN NOT get that .50^ OU BO in the reading only in a PAL.. Don't care who or what lab you are.. the only way would be to use Fresnel. That .50 OU in "reading only"is not even worth diddling with if you are dealing with 6 degree's of slab anyway.
    Sounds like you ran into a problem I have seen many times over the years, the OD or MD or optician dropped the ball on that imbalance due to power and they are splitting in the reading and the OD or MD comes up with this "oh they "may" need a slab" and to make it really sound like that "oh and .50 OU BO in the reading" would really mean a thing is just the ole "cover your A$$" policy.
    Do the slab (which you were correct prism in the 90) and forget that .50 OU in the near.... and no one will ever know the difference.
    No matter what we do at ties can NOT fill an RX due to the restraints of designs, materials or frames, just have to tell him/her that that .50 OU in the reading only in a PAL is impossible without using Fresnel and dollars to doughnuts bet he/she just tells you "well than just slab it".. it sounds like to me that's the only problem worth worrying about here anyway is that 6 degree's of imbablance.
    Oh and if he/she really insists on that .50 OU than explain it has to be a hard seg only that can be used to get this effect..unless they want Fresnel.

    Jeff "no matter what sometimes we just can't do the impossible" Trail

  5. #5
    Master OptiBoarder Joann Raytar's Avatar
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    Jeff,

    This is going to be a stab in the dark but ...

    Is it possible with spherical powers in the distance the doctor would be applying a technique that would have been used when PAL's were designed symmetrically on center and you used to have to rotate the lens to postition the add in place like a round seg or blended?

  6. #6
    since 1964 Homer's Avatar
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    I think this whole question is a "slab in the dark" until Mary decides to give us more information.

    I can't imagine a person needing a 6D slaf-off having great binocular vision in either distance or near. Would love to know the corrected visual acuities in addition to the things I asked for above.

  7. #7
    Master OptiBoarder Jeff Trail's Avatar
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    Jo,

    You are going back pretty far talking about the old AO's where we "tilted" it to get a OD/OS? Boy was that a crappie lens and I remember all the complaints I had when we did use those lens..
    I guess you could do it with that lens.. but the main problem I run into often is the OD is using a trial lens set and they are tinkering with the distant and near independently. Since you are working in a full field lens with trial sets.. than when you combine the powers and than start to split do to imbalance of power in relation to the design they want to just "add" on the slab.
    It's the burden we have to live with when the OD's and MD's are not familiar with the parameters we have to work in to try to reproduce the results they got using something that does "NOT" translate in a one field combination.
    you have a total of 1OU of convergence prism.. which is not really that big of an item and with all the fluctuations in power points in a PAL anyway you could just about wave that anyway.
    Homer is looking for more information but just from the face value of the posting once you said 6 degree's of imbalance that .50 in the near is really just nothing.
    Now the trick will be where to place the slab line in the PAL which I would be more worried about than that .5 ^ BI


    Jeff "sometimes the forest is missed when just zeroing in on one tree" Trail

  8. #8
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    Slab Off

    Jeff,
    I appreciate your knowledge about slab off. I am going to ask you for help as well. I am an opticianry student working in a small optical office. We have a patient that one of our OD's is seriously thinking about having her order filled with Slab off. Our patient will be returning for her final RX check etc. in a couple of weeks. She's wearing CL's first time wearer, this is for her CL follow-up appt.

    1. Will I have to do anything special when I send this order to our lab?
    2. Should I stay with a frame with a short or deep B Measurement?
    3. Progressive only? I think you're saying no Flat top and no Single Vision.
    4. Material something that we should take into consideration as well?
    5. Anything else I should be made aware of?

    Thank You,
    ICU2020

    Quote Originally Posted by Jeff Trail View Post
    One thing is that you CAN NOT get that .50^ OU BO in the reading only in a PAL.. Don't care who or what lab you are.. the only way would be to use Fresnel. That .50 OU in "reading only"is not even worth diddling with if you are dealing with 6 degree's of slab anyway.
    Sounds like you ran into a problem I have seen many times over the years, the OD or MD or optician dropped the ball on that imbalance due to power and they are splitting in the reading and the OD or MD comes up with this "oh they "may" need a slab" and to make it really sound like that "oh and .50 OU BO in the reading" would really mean a thing is just the ole "cover your A$$" policy.
    Do the slab (which you were correct prism in the 90) and forget that .50 OU in the near.... and no one will ever know the difference.
    No matter what we do at ties can NOT fill an RX due to the restraints of designs, materials or frames, just have to tell him/her that that .50 OU in the reading only in a PAL is impossible without using Fresnel and dollars to doughnuts bet he/she just tells you "well than just slab it".. it sounds like to me that's the only problem worth worrying about here anyway is that 6 degree's of imbablance.
    Oh and if he/she really insists on that .50 OU than explain it has to be a hard seg only that can be used to get this effect..unless they want Fresnel.

    Jeff "no matter what sometimes we just can't do the impossible" Trail

  9. #9
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    2002? Really?
    Last edited by Speed; 10-20-2012 at 07:59 PM.

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