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Thread: Digital Progressives and Base Curve Selection

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    Master OptiBoarder AngeHamm's Avatar
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    Digital Progressives and Base Curve Selection

    I'm old enough to have been in this business when digital surfacing was just being introduced. In the training seminar where all the Manhattan Lenscrafters were having digital generators installed, I vividly remember the presenters extolling the extreme flexibility of the technology, claiming that we would be able to basically throw a hockeypuck in and have any RX made for any frame.

    Obviously the reality of the technology is just a ​little bit more restrictive than that. However, I am finding my understanding of the technology at odds with one of my labs, who insist that the software that plots the digital progressives specifies certain base curves for certain prescriptions. Specifically, I feel like my requests for 8BC sunglasses are hitting a wall, and I'm forced to dump out of superior lens designs into 15-year-old technology for the very prescriptions and frames that are most likely to create peripheral distortion. I'm pretty frustrated with having to put some of my patients with insurance restrictions into a Physio when there are several generations of improvements hypothetically available.

    I thought the whole point of digital surfacing was flexibility, not inflexibility. Can my surfacing lab peeps edumacate me here?
    Last edited by AngeHamm; 11-03-2022 at 01:03 PM.
    I'm Andrew Hamm and I approve this message.

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    OptiWizard
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    You and your lab are both correct. Most designs are fixed in their base curve selection that is for best optical performance. Some will allow you to deviate one step from normal. There are several designs that are specifically made for wrap frames that should be your choice. Just changing the base curve might allow the lenses to fit the frame but not be the best optics for the wearer. The designs made for that purpose will satisfy you and the wearer.

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    What's up? drk's Avatar
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    You are old school, Ange. Just marry a lens company and use their dumbed-down products. They're awesome but you don't get to be involved.

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    Master OptiBoarder AngeHamm's Avatar
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    Quote Originally Posted by Lensman11 View Post
    You and your lab are both correct. Most designs are fixed in their base curve selection that is for best optical performance. Some will allow you to deviate one step from normal. There are several designs that are specifically made for wrap frames that should be your choice. Just changing the base curve might allow the lenses to fit the frame but not be the best optics for the wearer. The designs made for that purpose will satisfy you and the wearer.
    I understand not wanting to make a choice with compromised optics, but what I'm being told is that under no circumstances can a base curve be specified for these digital lenses. That's the detail that flies in the face of what I thought to be true. I feel like an 8BC lens is going to provide compromised optics for most prescriptions, so why woudn't we be able to minimize that with a freeform lens design?
    I'm Andrew Hamm and I approve this message.

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    Quote Originally Posted by AngeHamm View Post
    I understand not wanting to make a choice with compromised optics, but what I'm being told is that under no circumstances can a base curve be specified for these digital lenses. That's the detail that flies in the face of what I thought to be true. I feel like an 8BC lens is going to provide compromised optics for most prescriptions, so why woudn't we be able to minimize that with a freeform lens design?
    It's just a bad lab or the wrong lens design. This is easily doable. Obviously a -6.00 on an 8 base is going to compromise the optics to an extent, but a freeform lens design with the proper POW measurements and compensations is going to worlds better than a non-compensated one.

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    Master OptiBoarder OptiBoard Silver Supporter Barry Santini's Avatar
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    Depends on a number of target goals for the design in question. Sometimes such restrictions are optical. Othertimes logistical. And yet others are based cosmetics. And sometimes a combination of all three. You don’t know and can’t know.

    OEM designs are usually best performance for wraps.

    Barry

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    OptiBoardaholic IIxIPariahIxII's Avatar
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    Quote Originally Posted by AngeHamm View Post
    I understand not wanting to make a choice with compromised optics, but what I'm being told is that under no circumstances can a base curve be specified for these digital lenses. That's the detail that flies in the face of what I thought to be true. I feel like an 8BC lens is going to provide compromised optics for most prescriptions, so why woudn't we be able to minimize that with a freeform lens design?

    If the concern is compromised optics in an 8bc lens due to sun wrap, the digital process is going to help alleviate those issues. But the system is going to optimize the lens for the best possible optics in the given frame design. If you're wanting an 8bc so the frame doesn't flatten, if they're a high minus then usually the system is going to pull it out of a flat base based on the frame parameters. It probably won't be an 8bc but it'll be a bit more doable. Just gotta make sure the frame is a bit more adjustable and they should be fine. Obviously the Mauis and Oakleys of the world have max ranges and probably can't do it.

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    Digital lens designs are calculated with a digital engine usually based in a cloud network. The calc engine uses Rx information to point to a specific base curve and almost always a lens that is only available from that same manufacture. Hense limiting the ability to specify base curves. Barry is correct in suggesting a wrap lens design. You could also use a Toric design as most LMS have the ability for a wide range of customization. Of note is that a few years back most calculation engines, both Toric and digital, threw out best lens design in favor of cosmetics. The frames available today have a much flatter factory bevel making higher base curves fit poorly. It has been about 6 years since I collected that data on hundreds of thousands bevel frames and they averaged about 3.50 base curve.



    Chris

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