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Thread: What is a FreeForm?

  1. #26
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    Quote Originally Posted by IC-UC View Post
    They told me they use spherical blanks, so i would asume they would have the ability to decentre the progressive which is seemingly not the case. How do you ascertain that they have in fact used/made a freeform lens? Anyway of a quick check?
    Many Free-form makers don't allow decentering because it increases the likelyhood of unwanted prism or reduced yields. If I have machinery that cost 2 Million, I would want to keep my yields high by making sure as many lenses as possible came off the line OK.

    Some Free-form manufacturers use pre-marked blanks to reduce laser time as well. They cant be decentered. Although Decentration is possible, it increases the chance of unwanted prism and the tool falling off the blank. There are also blocking issues as well. Its a business decision to keep speed and yields higher.

    If you want to check, what is the name of the lens? You can check it on Lensguru.com

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    I'm not sure how many folks out there will benefit from this, but I recently came up with the following information for staff training purposes...and to assist in patient education. It was my attempt to address the confusion surrounding freeform and digital lenses. I titled it "Understanding Digital and Freeform Lens Technology" and it's available in PDF form (with more details and brand-specific examples) if you're interested. Enjoy! -Roger Smith

    Q: What is a "digital" lens, and what makes it so special?
    A:The term "digital" refers to a newer and advanced PROCESS of surfacing a lens. A digital generator uses a computer-guided lathe that cuts and polishes the lens in one step utilizing a diamond point. This process yields a lens that is more accurate and made in less time than was previously possible with traditional lens manufacturing (which uses molds, a rougher cutting instrument, and a series of sanding/polishing stages).

    Q: What is a "freeform" lens, and what makes it so special
    A: In short, a freeform lens is "unique, ONE-OF-A-KIND, and notcookie-cutter". However, what makes it ONE-OF-A-KIND involves the 1) PROCESS and 2) DESIGN compensations.
    - PROCESS: Every SV and PAL freeform lens utilizes the digital lathe process for part or all of the lens
    - DESIGN compensations: This relates to computer software which provides instructions to the digital lathe generator. The software will create customized instructions for all SV and PAL freeform lenses based on lens shape and size (frame info). However, there are more sophisticated freeform designs which will incorporate optimized prescription information (i.e. Zeiss iScription), and the most sophisticated freeform designs will generate a compensated prescription & lenses based on all of the above PLUS the patient's "position of wear" measurements (panto, wrap, vertex).

    Q: So, in a nutshell, what's the difference between "digital"and "freeform"?
    A: "Digital" refers to the precise, computer-driven, diamondpoint lathe. It precisely and accurately follows the computer'sinstructions. "Freeform" refers to the computer programthat compensates the lens Rx and design before it gives thoseinstructions to the digital generator/lathe.

  3. #28
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    One more note...my Shamir rep told me today that all semi-finished lenses have the laser engravings on the front of the lens, and all "fully freeform" lenses have the laser engravings on the back of the lens. Just an FYI!

  4. #29
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    That is true for backside PAL designs, but a dual surface PAL may have markings on front, back, or both.
    RT

  5. #30
    Master OptiBoarder Darryl Meister's Avatar
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    In short, a freeform lens is "unique, ONE-OF-A-KIND, and notcookie-cutter". However, what makes it ONE-OF-A-KIND involves the 1) PROCESS and 2) DESIGN compensations
    Keep in mind that free-form technology is ultimately just a manufacturing process; it does not imply that free-form lenses are unique or "one of a kind," although some lens suppliers may have you believe otherwise.

    Unless the lens design has been specifically customized by lens design software, using design input parameters specific to the individual wearer, there is little if any inherent visual benefit to free-form technology for the wearer. And it is equally possible to make traditional progressive lenses using free-form surfacing by simply adding the basic lens design surface to the back Rx surface.

    Best regards,
    Darryl
    Darryl J. Meister, ABOM

  6. #31
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    We can't fully understand Free-form until we understand the problems associated with traditional grinders in progressives:

    DIGITAL: We use tools/laps to grind lenses, essentially with sand paper. On manufacturing, the average tool discrepency from true is .07 D, which means that even if I have the correct tool/lap the job starts off .07 D on average. A fully stocked lab has over 4000 tools, and if I have 1000 jobs in process it means half my tools/laps are missing at any give time. So I take my tray to the tool room, and my lab ticket gives me the best tool, the second and third best tools for that job. So I might be able to substitue a 1.67 tool for my CR-39 lens in a different power, but its not perfect. We start substituting tools for a lot of jobs. Of course I can make a tool, but that means I have to take a job off a generator to make a tool, slowing everything down (there is no money in tools). Or it could wait, and wait. And that post-it I left in the empty tool slot gets thrown away on Friday at 4pm. So that means in most cases we substitute, and most cases that tool is off power.

    A free-form generator has only one tool/blade, its always there. It self calibrates daily and it tells me when the tool/blade is about to wear to the point its no longer good.

    FREE-FORM: With ground lenses we have to make compromises. In a progressive, if I stocked every material, every add power, every Transistions or Polarized option, gray and brown and every base curve, I would need over 24,000 blanks. Just for one brand and model. We cant afford that so we start cutting corners, and the first thing we start cutting is reducing base curves from 45 to 5-6. Do you know from among those what factor has the greatest effect on DVA? Base curve. So when we stock only 5 or 6 base curves we only give 5 or 6 RXs perfect optics, everything else is a compromise. The first thing free-form lenses did was modify curves to give every lens the possibility of true/best form optics. Oblique Marginal Astigmatism is also a base curve issue really, affecting cylinder and astigmatism the same way. Only with Free-form optics can we solve base curve issues and give the patient a customized atoric back-side curve.

    So with Digitial Processing and Free-form optics we in one fell swoop solve the 2 most eggregarious problems caused by ground lenses and traditional cast blanks.

  7. #32
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    Darryl, when you say "parameters" do mean Panto, Vertex and Face-form? Or something else?

    Quote Originally Posted by Darryl Meister View Post
    using design input parameters specific to the individual wearer, there is little if any inherent visual benefit to free-form technology for the wearer. And it is equally possible to make traditional progressive lenses using free-form surfacing by simply adding the basic lens design surface to the back Rx surface.

    Best regards,
    Darryl

  8. #33
    Master OptiBoarder Darryl Meister's Avatar
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    Only with Free-form optics can we solve base curve issues and give the patient a customized atoric back-side curve.
    As I said, this is only true when free-form surfacing is utilized in conjunction with real-time lens design software that is capable of designing or optically optimizing a new lens design using input from the wearer, prior to fabrication. Otherwise, none of the advantages that you described really apply.

    Again, "free-form" or "digital" surfacing is just a lens fabrication technology. Although free-form surfacing can serve as a vehicle for the production of customized lens designs, as a surfacing technology it provides no inherent visual benefits to the wearer.

    Not all free-form technologies involve customized optics. Consequently, while many eyecare professionals are charging their patients an added premium for "free-form" lenses, the lenses that they are selling may or may not actually offer any real visual benefits to the wearer.

    I would always recommend a critical review of the lens manufacturer's patents, white papers, clinical studies, and other technical details in order to understand what your free-form lens brand of choice is providing to your patients in terms of clinically-relevant visual benefits.

    Darryl, when you say "parameters" do mean Panto, Vertex and Face-form? Or something else?
    When designing a truly "modern" progressive lens, optical ray tracing is typically utilized to improve optical performance for the wearer by modeling the lens-eye system. Minimally, this process requires a prescription, the position of wear of the lens, and the reading distance.

    For semi-finished lenses, an average position of wear for a median spherical prescription is typically assumed in order to deliver sufficiently good optical performance for broad categories of wearers. With fully customized free-form lenses, on the other hand, the values associated with the actual wearer can be utilized.

    Furthermore, for the more sophisticated real-time lens design applications, additional factors may be utilized to customize the lens design and the distribution of progressive optics for the wearer in other clinically useful ways, such as the fitting height, lifestyle, head movement propensity, et cetera.

    Best regards,
    Darryl
    Darryl J. Meister, ABOM

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