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Thread: prism on single vision ?

  1. #1
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    prism on single vision ?

    Help , a patient came in with sv r= -1.00 , L= -4.00 -1.00 x 80 . the doc wrote slab off grind but did not indicate any diopters. I haven't done one on sv , only ft and progs. Any advice ? Also does it still go on the higher minus ? left eye ? Thanks

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    You should contact the prescriber to see what he or she had in mind. Slab off can be done in SV lenses but if the patient is able to alter the gaze point on the lenses slab off won’t be needed. If they have a special situation where they have to look thru the upper or lower part of the lenses then shift the o.c. Up or down accommodate the situation.

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    Quote Originally Posted by Lensman11 View Post
    You should contact the prescriber ...........
    Possibly just omitted the bifocal add?

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    Single Slab Off is a solution for those with limited motion an unable to maintain gaze through the OC's typically looking below lens centers for near tasks.

    As with FT-28 Slab Off reading depth or location of gaze below single vision OC's must be measured in order to calculate vertical prism. For easy calculations assume 10 mm creating approximately 3 diopters of imbalance. Typically via free form machine processing the least minus eye is selected as base down prism is required.

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    Quote Originally Posted by waynegilpin View Post
    Possibly just omitted the bifocal add?
    I would agree... this would be the most likely situation since SV slab is more rare

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    Quote Originally Posted by mervinek View Post
    I would agree... this would be the most likely situation since SV slab is more rare
    "When you hear hoofbeats. Think horses, not zebras."

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    Quote Originally Posted by rkjr2222 View Post
    Help , a patient came in with sv r= -1.00 , L= -4.00 -1.00 x 80 . the doc wrote slab off grind but did not indicate any diopters. I haven't done one on sv , only ft and progs. Any advice ? Also does it still go on the higher minus ? left eye ? Thanks
    Most minus if custom slab. Get a freeform generated and a traditionally surfaced slab sample before you choose- the freeform is less noticeable appearence-wise, but has a wide blur zone, whereas the traditionally surfaced slab has a sharp junction zone.

    Quote Originally Posted by waynegilpin View Post
    "When you hear hoofbeats. Think horses, not zebras."
    Right, unless if you live in Africa. See Occam's razor.

    Best regards,

    Robert Martellaro
    Last edited by Robert Martellaro; 07-14-2021 at 02:14 PM.
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    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.



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    SV slabs are rare. Typically for sports, think cyclists, or therapeutics.
    The prescriber, IMO, is relying on your expertise, as he/she isn’t.
    Slab value for SV is dependent not only on RX, but down gaze. Unlike multifocals, the “10mm” rule does not apply.
    Making matters worse is determining where to place the slab. On center? Pupil height? Then measuring down gaze to calculate the prism value.
    Fresnels are the best option to trial before ordering the final pair.

    Contacting the prescriber would be wise before starting on this journey. It will save you a lot of headaches and $$$
    I bend light. That is what I do.

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