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Thread: Prism at near by bifocal segment decentration.

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    Prism at near by bifocal segment decentration.

    Hi everyone.
    I have a patient with the following Rx.

    OD -6.25/-1.00 x 120 ADD +3.00
    OS -5.25/ -1.50 x 52 ADD +3.00

    Patient requires 1.00 BASE IN for near only in both eyes.

    Can this be done using a D 45 seg decentred by 3.3mm?

    Or will it need a prism controlled bifocal?

    Thanks in advance.

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    Master OptiBoarder optical24/7's Avatar
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    Yes, you can decenter in an extra 3.3mm on each eye from their NPD to get 1^ in OU. Remember to keep your DPD the same as measured and inform the surfacing lab why you are requesting the PD's the way you are.

    Welcome to OB!

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    One eye sees, the other feels OptiBoard Silver Supporter
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    35mm should be wide enough, and with less segment ledge to boot.

    Double check if the prism is total or each eye. Get it in writing.

    About 1∆ BI is induced in each eye as the eyes converge behind the distance Rx. Make sure the prescriber understands this, especially if SVNO is required at some point.

    Hope this helps,

    Robert Martellaro
    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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    Quote Originally Posted by Robert Martellaro View Post
    35mm should be wide enough, and with less segment ledge to boot.

    Double check if the prism is total or each eye. Get it in writing.

    About 1∆ BI is induced in each eye as the eyes converge behind the distance Rx. Make sure the prescriber understands this, especially if SVNO is required at some point.

    Hope this helps,

    Robert Martellaro

    +1

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    Many thanks for your replies.
    I was having a discussion with a lab technician colleague who debated whether we could do this job in house via this method but you have both confirmed I was correct.

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