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Thread: prism decentraion of astigmatic lens

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  1. #1
    OptiBoard Novice
    Join Date
    Mar 2012
    new zealand

    prism decentraion of astigmatic lens

    RE: +6.50/-4.00 *130
    LE: +7.50/-5.00 *45

    How to calculate the expected phoria at a near visual point 2mm in and 20mm down in both eye.

  2. #2
    Master OptiBoarder Darryl Meister's Avatar
    Join Date
    May 2000
    Kansas City, Kansas, United States
    Lens Manufacturer
    The mathematics are a bit tedious. It would be easier to use - Induced Prism or, since you are specifically interested in vertical imbalance at near, - Vertical Imbalance. According to the vertical imbalance calculator, these lenses require a net vertical prism compensation of 0.41 prism diopters base up, right eye, at 20 mm down and 2 mm in.

    This would be the amount to order for a slab-off, although vertical imbalance compensation is really not necessary for this particular job.

    Best regards,
    Darryl J. Meister, ABOM

  3. #3
    Join Date
    Jun 2000
    Only City in the World built over a Volcano
    Dispensing Optician
    SV patients seldom if ever need a slab off or any sort of prism compensation. Especially vertically.

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