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Thread: Adding/Combining Cylinder Powers

  1. #1
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    Adding/Combining Cylinder Powers

    Hello Everyone,

    I was trying to build an excel spreadsheet to do vertex, wrap, & panto tilt compensation and I've gotten through calculating vertex, and the new sphere powers using Darryl's formula on pdf pg.74 of Intro to Ophthalmic Optics , but his formula only gives the induced cylinder power and not the "new" cylinder power that must be ordered.

    So the next thing I need to do is take the induced cylinder & axis(180 for panto & 90 for wrap) and add it to the patients cylinder and axis. I'm struggling to find the formula on how to do this.

    Example: Patients Cyl is -0.50 @135 and the induced cyl from panto tilt is -0.50 @ 180

    According to http://opticampus.opti.vision/tools/cylinders.php this would result in -.15 Sphere and -.71 Cylinder @158, but it doesn't explain how it arrives at it.
    Any help would be appreciated.
    Last edited by tyha; 07-26-2022 at 04:46 PM.

  2. #2
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    I don't have the exact answers for you but you can check this thread for how extremely complex it is to calculate powers for tilt and wrap at the same time. It's quite the rabbit hole you can go down if you can stomach the math. I don't think an excel spread sheet is going to cut it.

    https://www.optiboard.com/forums/sho...=oakley+secret

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    This might be the info I need. I found some of the formula's for combining obliquely crossed cylinders after posting, but as you mentioned doing both tilt and wrap at the same time might be over my head. I was originally planning on doing panto calculation first then feeding the new Rx it into the same formula for tilt (90 degrees off), but that would probably mess with the calculation as you should probably do the combination angle of wrap and tilt at the same time.

  4. #4
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    The formula and method for combining oblique cylinders can be found on page 320 in Systems 3rd edition. But as the other thread states and you correctly assume, you can not just independently calculate Tilt then use that to calculate Wrap.

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    The -0.50 induced cylinder due to panto will be increase power primarily towards the 180.

    Since Rx cylinder axis is true oblique, take half cylinder amount of induced -0.25 and half of the distance in degrees of 45 which is 22.5

    -0.50 @ 135 (+) -0.25 (approximated) = -0.75 compensated power Axis 135 + 22.5 = 157.5 or 180-22.5 = 157.5

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