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Thread: Base Curve Problem

  1. #1
    OptiBoardaholic OdTech's Avatar
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    Base Curve Problem

    Hello there

    You know there are stylish frames that have "wraparound" shape of the frames. When you look from the top of the frame you'll see that lens are too curved.

    If you careless somehow, you will have lots of problems with edging and putting it into frame.

    The best solution? i want to know

    a) Do you send to the lab?
    b) Do it Yourself?

    I know that the standard base curve is '6' but if it's more than that.

    feed back appreciated

  2. #2
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    Without knowing your equipment or experience, I cannot say whether or not it would be easier to do these yourself.

    However, if you choose to order the pair from the lab it is important to provide them with the frame as well. Or, at the very least, indicate when ordering, the demo Base Curve and that a wrap frame will follow. (Please do not order these "lenes only" as nearly all wrap frames require some form of hand work on the lenses that is not an edger capablility.) The lab will be able to determine if:
    A) a thick enough lens blank is available, based on the material and lens style you've requested
    B) Your power is feasible on an 8BC lens (i.e. goodbye Mr OH MY Myope)
    C) Is your patient going to accept a V-bevel, if necessary, at the tempral and/or nasal area.

    These are just the first things that came to MY mind. I'm sure there are tons of Jeff Trails out there who can come up with others.

    Does this help? Rhonda Boman
    Hoya-Seattle, QA

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    OptiBoardaholic OdTech's Avatar
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    Well "Jane" you clearly stated that in the case of wrap around frames i should send it to lab but not do myself. the rest is true of what you told me.
    Thank you

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    Bad address email on file dfisher's Avatar
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    The problem with putting an rx in such a frame is more than lense retention and cosmetics. Because of the wrap there is a lot of distortion when moving your eyes behind those lenses because of the astigmatism induced when looking off-center.

    For best results in a high wrap frame, try the Spazio lenses from Sola Technologies currently availabe with many options but in single vision only.

  5. #5
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    I like to try and do most of the wraps on a 6 Base and set the edger to put a bevel on that corresponds to the demo's base.
    If the Rx is not compattable with a 6 base and needs to be on a lower base, I use a 4 base and again set the edger for as high a base as the lense will accept.
    Joseph Felker
    AllentownOptical.com

  6. #6
    sub specie aeternitatis Pete Hanlin's Avatar
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    Actually, having looked at the profile of many of today's frames, I believe manufacturers are assuming that either a.) most patients are myopes (which they are) or b.) aspheric lenses- with flatter curves- are being widely used. Most dress frames seem to come out of the box ready to accept a 4 base lens.

    However, wrap frames- as you noted- still call for an 8 (or sometimes higher) base curve if the frame's profile is to be maintained. There are a number of ways to address this... You could order the lens on an 8 base, which will work if you aren't above a -2.00. If the Rx is > -2.00, try a 6 base and make sure the lens is edged on an edger that traces the frame 3 dimensionally (like a Santinelli 3D). Given some edge thickness (which a lens > -2.00 is likely to have), the edger can compensate somewhat for the steep frame curve.

    If you choose to reshape the frame to accept a "reasonable" base curve (which will likely be flatter than the original profile of the frame), you will notice that it changes the fit of the frame (i.e., it doesn't wrap as much anymore). Some patients will be dissatisfied with the frame if it doesn't wrap the way it did when they tried it on. For folks like this, you can try a wrap frame with an insert (although, from my -4.75 days I have to admit this never appealed to me- looking through two sets of lenses never felt very comfortable).

    In any case, if you have a 3D edger try ordering the lenses uncut from the lab and specify the geometry of the lens (BC; edge thickness; A, B, ED; etc.). Otherwise, send the job out for edging.
    Pete Hanlin, ABOM
    Vice President Professional Services
    Essilor of America

    http://linkedin.com/in/pete-hanlin-72a3a74

  7. #7
    Bad address email on file dfisher's Avatar
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    True, Pete. What you are discussing, however, is for the most part just getting the lenses to stay in the frame with acceptable cosmetics.

    If you script a high wrap frame your chances of having to eat that one are pretty good. Folks just do not like the distortion in those situations even if they decide to keep the rx because of style.

    I agree, again, with you Pete that reducing the wrap helps to eliminate some of the inherent problems, but if you reduce the wrap enough to put lenses in their proper plane in relation to the eye it totally defeats the purpose of the customer selecting the wrap style in the first place.

  8. #8
    sub specie aeternitatis Pete Hanlin's Avatar
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    ...if you reduce the wrap enough to put lenses in their proper plane in relation to the eye it totally defeats the purpose of the customer selecting the wrap style in the first place.
    I agree, that's why I pointed out that patients are often disappointed with the finished product when you Rx a wrap frame.

    ...for the most part just getting the lenses to stay in the frame with acceptable cosmetics.
    As for keeping the lens mounted, that's another thing that a 3D trace and edge can help with. Consider what happens when you trace a 2D image of a frame. Since a 2D tracer does not take into account the depth of the design, it sizes the frame with an A measurement that is too small. Also, since the bevel a 2D trace and edge will place on a lens is too flat, the superior and inferior edges of the lens will always be trying to exit the back of the frame.

    Folks just do not like the distortion in those situations even if they decide to keep the rx because of style.
    Good point... when you have a patient that wants to try an expensive lens in a wrap frame (e.g., a polarized or PAL), I recommend having a SFSV lens surfaced into the parameters necessary to dispense the frame. It takes an extra trip and a little time for the customer, but placing a clear SV lens with the modified curve in the frame affords an opportunity for the patient to see if the vision will be acceptable. If not, another frame can be selected before too much money is invested. That's just a piece of advice from someone who has seen patients reject mirrored, polarized PAL lenses before...
    :(
    Pete Hanlin, ABOM
    Vice President Professional Services
    Essilor of America

    http://linkedin.com/in/pete-hanlin-72a3a74

  9. #9
    Master OptiBoarder Jeff Trail's Avatar
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    I usually push it two ways with the accounts, one being not EVERY RX works in a wrap so tell people this :), second they do have "wrap" frames where the frame has a wrap look but the bevel is not wrapped in the 8.75 base curve.. I would think every optical should have a few of these on hand for those who want a wrap, doesen't matter if they are a -5
    Tracking the bevel to match the curve..oh yea hasn't everyone done this trick a time or two.. the only problem is that if you are mounting a polarized the bevel has to track the curve or if the bevel gets behind the sheet, cosmetically it looks like ****, and the first thing out of the techs and or patients mouth is "this has gaps"..
    Your selling a high index polarized lens, you can't charge premium prices and the job looks fudged.. being in FL. I think I do far more than my fair share of polarized and using a frame that has the wrapped look but a unwrapped bevel :) is the best answer...both in visual acuity and cosmetics..
    I wish I had a quater for every time an account told me that they wanted it in a wrap and they "understood" putting that -3.75 on an 8 would look thicker than "normal" and the patient understands as well...than you do it and tada.. the patient will NOT take it and the OD is calling me wanting full credit for that "junky" looking job..
    Common sense and EDUCATION works a long way solving a lot of these problems..If it were up to me EVERY optical who likes to push sunglass style wraps would have a number of the wrap designs with the flatter bevel..
    BTW I have 5 trays sitting on my desk right now with wraps , pending the OD calling back when I told them putting a -7.50 in a 9.75 base wrap is not really a good "thing" to do :) (power ranges from -5.5 to that -7.50) ... the patient is NOT always right..I always
    thought that was one of the reasons (among many) we opticians were there was to "guide" the patient in choices that worked well..maybe I'm to old fashioned ... Is it me or the frame designers are getting FURTHER away from actually designing frames that "work" and last more than a week before falling apart, breaking, or excluding about 90% of the RX's we have to deal with? ...
    I get one more -10 with 3 cyl. in a drill mount with a "b" of 28mm and they want a PAL and they complain when it breaks two days later..arrrggg.. I just did that RX SEVEN times for the same OD and patient.. with the last excuse being "I had them in my pocket for only a second" (she was doing gardening and was told how fragile they were, after the other 6 times breaking them, so she placed them in her pocket to "protect" them) ... no matter how well we make a pair of glasses it will NOT increase the IQ of some of these bean heads

    Jeff "no wonder optics has a high burn out rate" Trail

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