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Thread: Plus lens and toric; how thick?

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    Plus lens and toric; how thick?

    Today I had a customer with the following prescription:
    OD: Plano+4.00X90

    OS: This eye had a very low acuity and wasn´t used by the customer.

    Question 1? What spheric power (no toricity consideration was necessary)should I choose for the left eye in order to make that eye equal in size with the right eye.

    Question 2? Is there any "thickness formula" for transforming toric lenses to spheric lenses considering only the optical center of the lens?Maybe the lens thickness is proportional to the spherical equalization?

    I would be very grateful for any answer from you experienced people. I graduated recently and would be a humble listener to any suggestion.

    Leon

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    Why bother trying to figure out what sphere power would make the left look the same as the right? Just order a balance lens, or the same rx for the left as for the right. That way you're sure they'll look the same and you don't have to worry about it. :D

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    Quote Originally Posted by AdmiralKnight View Post
    Why bother trying to figure out what sphere power would make the left look the same as the right? Just order a balance lens, or the same rx for the left as for the right. That way you're sure they'll look the same and you don't have to worry about it. :D
    :cheers:

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    ATO Member HarryChiling's Avatar
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    OD: Plano+4.00X90
    If your trying to use a stock lens for the left and not pay for a surfaced lens why not do a +2.00 +2.00 x 090, that's still stock and the meridian with the hihest power still matches. Or you could do a plano +2.00 x 090 so that the other meridian matches, but I would probably go with the +2.00 +2.00 x 090, that way the power along the 180 which is usually the longest box sizing matches and the thickness along the nasal and temporal edges match, the top and bottom won't matter as much as the power is low enough and frame sizes along the B are small enough (compared to the A size) that it won't look too off.
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    Quote Originally Posted by AdmiralKnight View Post
    Why bother trying to figure out what sphere power would make the left look the same as the right? Just order a balance lens, or the same rx for the left as for the right. That way you're sure they'll look the same and you don't have to worry about it. :D
    Thanks for your suggestions. The problem is more complex. A lens with a high cylinder is more expensiv and the balance therefore has to be spheric. Even if both lenses had the prescription with the high cylinder I am not sure how thick it will be. Is it equal with +4,00, +2,00 D, plano or something else? I believe it is the meridian of greatest power that controls the thickness of the lens but I am not sure. Because of that I cannot decide whether the customer would benefit of an high index lens with the purpose to minimize the magnification.
    Leon

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    Ah, I guess I'm just spoiled, our lab gives us 50% off balance lenses, so even though they're not stock prices they're still cheap. I'll bow to Harry on this one for suggestions :)

  7. #7
    ATO Member HarryChiling's Avatar
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    Quote Originally Posted by AdmiralKnight View Post
    Ah, I guess I'm just spoiled, our lab gives us 50% off balance lenses, so even though they're not stock prices they're still cheap. I'll bow to Harry on this one for suggestions :)
    Bow to me! Your the one with an Awesome lab. :cheers:

    Quote Originally Posted by Leon from Sweden
    I believe it is the meridian of greatest power that controls the thickness of the lens but I am not sure.
    Yes and No, the size also factors into the thickness so in certain cases you will have to make a blank thicker for cutout. For example if this Rx was plano +4.00 x 180, then using a +2.00 +2.00 x 180 for the other lens might not match the thickness as the +4.00 would lie on the 90 meridian which woud be afffected by the B size and the +2.00 would lie along the 180 which would be the A size. Since most frame have a larger A to B ratio the A size might dictate the lens be made thicker so that could cut out.
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