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Thread: Inset in molded progressives

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    Master OptiBoarder OptiBoard Silver Supporter ak47's Avatar
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    Inset in molded progressives

    I realize that you can't specify inset in most progressives, although in some free-forms the inset will be "optimized" for distance power, pd, and add power...question I have is do molded progressives such Comfort, Creation, Ellipse have same standard inset (2.5 mm?) across all add powers or will some of these molded progressives have insets that are larger for higher add powers?

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    Quote Originally Posted by ak47 View Post
    I realize that you can't specify inset in most progressives, although in some free-forms the inset will be "optimized" for distance power, pd, and add power...question I have is do molded progressives such Comfort, Creation, Ellipse have same standard inset (2.5 mm?) across all add powers or will some of these molded progressives have insets that are larger for higher add powers?
    The mold insets are increased on the higher adds and steeper base curves (for high hyperopes) up to 4mm per eye.

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    Master OptiBoarder rbaker's Avatar
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    Which begs the question, why would you want to monkey around with the inset?

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    Master OptiBoarder OptiBoard Silver Supporter ak47's Avatar
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    What about low adds such as + 1.00? Is inset still set at 2.5 or is it reduced? Is it reduced from 2.5 in the flat base curves (less than 3.5 base)?

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    Quote Originally Posted by ak47 View Post
    What about low adds such as + 1.00? Is inset still set at 2.5 or is it reduced? Is it reduced from 2.5 in the flat base curves (less than 3.5 base)?
    For the lower adds, and flatter base curves (for myopes) less convergence is required at the near level. I believe the minimum inset on these lenses is most likely 1.5mm per eye.

    As for the exact numbers on inset, I have yet to see a blank manufacturer release this data. Hence why freeform progressives with full customized inset is best for all patients since everyone accomodates at a different rate.

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    Quote Originally Posted by Lab Insight View Post
    For the lower adds, and flatter base curves (for myopes) less convergence is required at the near level. I believe the minimum inset on these lenses is most likely 1.5mm per eye.

    As for the exact numbers on inset, I have yet to see a blank manufacturer release this data. Hence why freeform progressives with full customized inset is best for all patients since everyone accomodates at a different rate.
    I'm not so sure accommodation has anything to do with inset. Inset has to do with working distance...and a patient's initial (distance) PD.

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    Master OptiBoarder MakeOptics's Avatar
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    Accommodation and Convergence go hand in hand, with each individuals relationship being unique. I don't know that correcting an inset for base curve and add power like most molded lenses do, has a significant impact on quality. My reasoning is that at best it is a guesstimate based on an ideal scenario. Doctors are unique in the way in which they prescribe as well, some will leave a reserve of 50/50 others will have a 2/3 accommodative reserve. The manufacturer of the blank cannot know and produce the number of blanks to anticipate both these scenarios. The reason why the accommodative reserve is important is that the relationship between the accommodation and convergence system is going to rely on the amount of reserve the patient is using at near point. All that said this is the same problem with FF customized lenses, their just is no way to relay that information to the lab to produce the level of accuracy I think this post is looking for, to get a true measure of the inset would also be difficult for those thinking they know a trick.

    To properly fit a patient:
    I would start by taking the distance PD as a baseline.
    Place a trial frame with the near Rx and distance PD on the patient and taking a measurement of the near PD with the patient fixated at the near working distance.
    (this is where most would feel as though their work is done, but consider the above passage accommodation and convergence have a close relationship, so knowing that the likely scenario would be in a plus powered lens the distance PD in the trial frame is going to cause the patient to have to converge more a minus lens is going to cause the patient to converge less)
    Next I would set that same trial lens at the near PD and take another near PD.
    This process can be iterated until a certain threshold of accuracy is achieved.

    Here's the rub, this process would eat up enough an excruciating amount of time and provide very little benefit to a patient. In many cases if I see a convergence issue I like to fit the near PD and adjust the distant PD while using a fixed inset design.

    PS - Frames Data supplies a lens catalog that does list insets for various progressive lenses so the data is out there.
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    Quote Originally Posted by ak47 View Post
    I realize that you can't specify inset in most progressives, although in some free-forms the inset will be "optimized" for distance power, pd, and add power...question I have is do molded progressives such Comfort, Creation, Ellipse have same standard inset (2.5 mm?) across all add powers or will some of these molded progressives have insets that are larger for higher add powers?
    The near IPD at 40cm is about 4mm less than at infinity, slightly wider and narrower, by about .5mm, for larger and smaller distance IPDs respectively.

    Some PALs, regardless of the manufacturing platform, vary the inset by distance power and/or base curve. Add power is generally not relevant when determine inset, athough the PAL design might be modified as the add power changes. It's likely that the above lenses have an inset based on the base curve, and that they vary in design (astigmatism placement, corridor length, and zone widths) depending on base curve and add power.

    Lenses that are made on a free-form manufacturing platform may have the above optimizations, with the inset determined more by distance power than by base curve, and may or may not have additional optimizations.
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