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Thread: Some free-form questions

  1. #1
    OptiBoard Novice
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    Some free-form questions

    Hi, my name is Chris and I would like to know if anyone here has any experience in free-form PAL fitting, neutralizing, edging, and dispensing; that is, are there differences in how they are worked with?

    I have heard that there is a device that the patient is tested/measured with to take into account the higher order optical anomalies that FF's correct and for a customized fit. Has anyone worked with one of these and how much do they cost? If it is expensive, is the cost shared with the lens manufacturer?

    Any information would be gratefully received. I believe that FF's are the way of the future but we are now in its incipient stages so hard data seems to be difficult to come by. Thanks. - Chris

  2. #2
    Allen Weatherby
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    Freeform information

    Freeform lenses require the same exact measurements taken for a conventional lens plus some lens designs maybe able to optimize individual lens designs with additional information.

    Both single vision and progressives lenses can be produced using freeform machines but they may require some additional information, such as vertex distance, frame wrap angle, pantoscopic angle and reading distance. Doting the pupil on a demo lens in the frame in the as worn position provides much more information than a traditional prescription.

    Remember with freeform there are two major components, one the hardware needed to produce the lens and two the lens design software needed to generate the data the machines need to produce the surface. The information the software can manipulate depends on the complexity of the lens design software. Just providing additional information does nothing to optimize a lens design if the software does have the ability to utilize the additional information.

    Measuring this additional data such as frame wrap, pantoscopic tilt and then converting the original prescription to a compensated state involves getting correct information and each manufacturer may have a different device or system developed for this. The software from different companies may need similar information but their data entry fields maybe different. Therefore you may see different lens designs asking for different measurements.

    There will also be freeform designs that are very basic PAL designs and that is they may not take into account the wrap angle or pantoscopic tilt etc. For these there may not be the need for much additional data and they may still produce a superior lens compared to a traditional front side cast semi-finished traditional PAL.

    I believe the greatest challenge with freeform lens implementation is going to be exactly what your question addresses, and that is how do we as developers of freeform lens technology train our sales and service teams so that you as a dispenser can properly provide the correct data to the manufacturer. We also must train the dispenser to be able to communicate the benefits to the patient without being over technical.

    We currently require every frame to be sent to our facility and we produce, edge and fit the lens to the frame. We also make all of the frame measurements required in our lab. This way we have eliminated one of the greatest areas for mistakes. We had some resistance at first to this, however when we explained the problems of sending an uncut expensive lens that requires special edging and fitting techniques, our customers have understood that the risk of mistake is very high and this way we take full responsiblity.

    At ICE-TECH we currently utilize freeform to produce high front base curve polarized sunglass lenses for an extremely wide Rx range. We are developing unique freeform produced PAL designs.

    I hope this information answers your question. If you would like any additional information please ask. I will try to provide as much general knowledge as possible.

  3. #3
    ATO Member HarryChiling's Avatar
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    Free Form lenses take into account an average wearers parameters and offer you a lens with the back curve optimized to reduce or eliminate the abberations commonly found in proggressive lenses. You would measure it like a regular PAL. The companys that use Free Form lens technology will have all the tools available to create the lens that would be optimal for

    prescription
    thickness
    distance from the eye to the back vertex of the lens
    distance from the lens to the object
    object’s angular position in the eye’s field of vision
    pantoscopic tilt and face form tilt
    pupil distance

    You could get this data yourself with a ray tracing program, and common optical tools.

    prescription - from your doctor
    thickness - with saggita formula, Darryls Optics Lite, my online calculators
    distance from the eye to the back vertex of the lens - Darryls Optical Analysis
    distance from the lens to the object - Ruler, Yard Stick, Tape Measure
    object’s angular position in the eye’s field of vision - Darryls Optical Analysis I think

    pantoscopic tilt and face form tilt - has been discussed on previous threads, maybe a picture from above and from the side (not hoighly accurate)

    pupil distance - PD ruler

    I am sure that the big lens manufacturers use more sophisticated machines and optimize the lens to account for more errors, but this is the jist of what they are doing to optimize a lens.
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  4. #4
    Allen Weatherby
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    Follow up to the Post by Harry

    The data Harry is talking about is what is needed however each lens design software requires data input. As an example a program that requires the adjustment for frame wrap could use a combination of input data or pre measure the optical center and calculate the lens wrap angle from this point.

    My point is the same data gathering will not work for input data for different lens design programs. Each manufacturer may approach the same data gathering from a different point of view.

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