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Thread: High Index Lens Becoming More Curved

  1. #1
    OptiBoardaholic hip chic's Avatar
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    High Index Lens Becoming More Curved

    Hi Everyone,

    I have a customer who purchased glasses from me about 6 months ago. I fit him with 1.67 high index plastic lenses. The base curve of the demo lenses in the frame were 6. The customer liked the "wrap around" feel of the glasses and so I had his RX ground on a steeper base curve (clocked at 5 at dispense) than he was previously wearing (clocked at 3.5). The center thickness of his new lenses was 1 millimeter.

    The RX is:

    OD) -6.00 -0.25 x 135
    OS) -4.25 -2.00 x 180

    He brought the glasses in a few weeks ago because they'd become more curved causing blurred vision. The lenses HAVE in fact become more curved. The right lens clocks at 6.25 and the left 8.5. Any thoughts as to why the lenses (especially the left) would curve so much more than the original curve of the frame??

    The lab is suggesting new lenses (same material) with a center thickness of at least 2 mm.

    I'm just wondering if anyone else has had this problem and what your thoughts are.

    Thanks,
    Hip Chic

  2. #2
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    Many lenses, especially thin ones will warp with tension, heat, stress, and time. Can be from an chord mount having the chord shrink the above.
    Can be from the frame shrinking, lens having been mounted under too much stress.
    Sometimes you can correct this by heating the lens in the air warmer and placeing it concave down on a flat surface and pressing down.
    You might want to start inspecting jobs for stress in the colmascope (polariscope) when they come in from the lab. Sometimes this will reveal problems that will bite you later in advance.

    Chip

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    Master OptiBoarder optical24/7's Avatar
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    1. Lenses were subjected to too much heat.
    2. Lenses are too large/tight in the frame.
    3. Agree, increase the thickness
    4. I hate 1.67

  4. #4
    Master OptiBoarder OptiBoard Silver Supporter Now I See's Avatar
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    I know that cr39 lenses can warp if they get too hot...I've also seen warped lenses due to the lens being edged a little large, and "squeezed" into the frame....
    ___________________________________________

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    Redhot Jumper Can only be..................

    Quote Originally Posted by hip chic View Post
    The right lens clocks at 6.25 and the left 8.5. Any thoughts as to why the lenses (especially the left) would curve so much more than the original curve of the frame??
    An increase in the left base curve of 3.5 Diopters (50%) over a period of 6 month without doing anything to them can only be the work of the Hi Index fairy.

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    If the lenses have AR, don't heat them in a blower or salt bath. Heat them in some hot water, place them concave surface down on a piece of padding or a towel and put some weight on it...try not to press the optical center too much. You want to flatten the periphery... and let it sit til cool.

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    Manuf. Lens Surface Treatments
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    Blue Jumper Craze....................

    When lenses have AR and would change curvator shape, the AR would automatically craze and delaminate and be ready for the garbage,

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    If it's a plastic frame, the lenses were possibly too big. Put lenses in warm water to help them return to original shape. Then hand edge down a bit.

    Increasing CT to 2.0 would really negate the whole point of the 1.67, yes?Heck you might as well put him into a poly or Trivex instead.

    If you do remake the lenses, I'd suggest a flatter curve but a bevel closer to the frame curve. I'm the last person who should comment on base curves but a -6 on a 5.25BC lens seems a bit much

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    Anybody know which plastics used for lenses are linear and cross-linked?

    Chip

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    Master OptiBoarder OptiBoard Gold Supporter DragonLensmanWV's Avatar
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    1 mm CT for a 1.67 lens at that high a curve is a disaster, as you've found.Send the job to a wrap specialist lab.
    DragonlensmanWV N.A.O.L.
    "There is nothing patriotic about hating your government or pretending you can hate your government but love your country."

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    Master OptiBoarder snowmonster's Avatar
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    Quote Originally Posted by FullCircle View Post
    If you do remake the lenses, I'd suggest a flatter curve but a bevel closer to the frame curve. I'm the last person who should comment on base curves but a -6 on a 5.25BC lens seems a bit much
    I would agree with this, but there are a lot of labs that still routinely put Rx's like this on a 4 base, so a 5.25 isn't much of a stretch from that. We would typically run this ourselves on a 2 or 1 base lens but we run everything flatter than average.

    I think Trivex wouldn't be so hot for this job due to the fact that it will be a lot thicker, might recommend poly instead. It's at least got 0.06 more index of refraction to it's advantage.

    We had a CR39 job warp like this recently with our stock lenses we use. It's the first time I could remember it happening, but we surfaced the new lens with a 2.5 CT and haven't had a problem since then.
    -Steve

  12. #12
    Master OptiBoarder LENNY's Avatar
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    Make A measurment 1mm smaller!
    Or cut it down by hand.

    This is the problem I always face when cutting 6-8 base minus lenses especialy with a higher astigmatism.
    Hopefully you have an edger that can adjust A measurment only!!

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    [quote=LENNY;260821]Make A measurment 1mm smaller!
    Or cut it down by hand.quote]

    and the B larger, or it will be too small. Right?

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    Put a 6 base in the frame!

    Quote Originally Posted by hip chic View Post
    Hi Everyone,

    I have a customer who purchased glasses from me about 6 months ago. I fit him with 1.67 high index plastic lenses. The base curve of the demo lenses in the frame were 6. The customer liked the "wrap around" feel of the glasses and so I had his RX ground on a steeper base curve (clocked at 5 at dispense) than he was previously wearing (clocked at 3.5). The center thickness of his new lenses was 1 millimeter.

    The RX is:

    OD) -6.00 -0.25 x 135
    OS) -4.25 -2.00 x 180

    He brought the glasses in a few weeks ago because they'd become more curved causing blurred vision. The lenses HAVE in fact become more curved. The right lens clocks at 6.25 and the left 8.5. Any thoughts as to why the lenses (especially the left) would curve so much more than the original curve of the frame??

    The lab is suggesting new lenses (same material) with a center thickness of at least 2 mm.

    I'm just wondering if anyone else has had this problem and what your thoughts are.

    Thanks,
    Hip Chic
    We base curve match all of our jobs and in a thick frame like Chrome Hearts zyl, the heat will cause the lens to be overtaken by the frame curve. If you put them in a 6 base to start; all problems will vanish.
    Just remember to compensate for the curve and if you use the Autograph Attitude on a 6 base, you should have a job optically and cosmetically correct.
    It needs to be edged on a machine without wheels to ensure the curve/bevel are correct; this is essential on a 6 base thick zyl for cosmetics.

    Hope it helps and how is Rochester!

    Craig

  15. #15
    ATO Member HarryChiling's Avatar
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    The issue is mechanical, the frame bevel on a wrap is usually at an angle similar to the wrap angle. The bevel on the lens comes out of most edgers with the bevel and lens edge at 90 degrees to the front suface where it was blocked, over time a soft lens such as Poly, or a Eurathane (Hi-Index) will warp. The correct solution is not to cut smaller, or use thicker it's to relieve that pressure caused by the back ledge of the lens and the angle of the frames bevel. Multiple correct solutions:

    1. Lenticular - There are lenses out there that can make the edge of the lens thin enough that the back ledge of the frame is not there to interact with the frame, these lenses come in both traditional and a blended lenticular.
    2. Heavy Bevel - Hand edge the side of the lens that is causeing the issue to match the angle of the frame bevel, this will release the pressure and eliminate the issue.
    3. Frame Modification - This could void the warranty so might suggest it as a last resort, modify the bevel of the frame so that the frames angle matches the lens angle, this could also be done with a bit of hand beveling where both lens and frame are modfied slightly as a hybrid solution.
    DON'T - try to warp the lenses back into shape this is horrible suggestion, if you heat up hi index as suggested and place a weight on it you don't know what the outcome would be except warped lenses.

  16. #16
    Master OptiBoarder OptiBoard Silver Supporter Barry Santini's Avatar
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    Confirm warpage by using lens clock and

    check the vertical (90th) meridian. If the curve there is not as steep, the lenses are warping, for the reasons listed above.

    Barry

  17. #17
    Optical Clairvoyant OptiBoard Bronze Supporter Andrew Weiss's Avatar
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    I agree with Harry C mostly. I'd just add that most jobs I see these days are made too large. If you use a polariscope on all your jobs for a week, you'll see what I mean. So I will bet that your lenses are stretching that frame. Correct sizing and matching the rear bevel to the frame bezel should do the job. And of course you'll need new lenses, although I'd suggest a 1.5 center instead of 2.0.
    Andrew

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    OptiBoardaholic hip chic's Avatar
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    Thanks for all of your replies. I'm sorry I didn't get back to you sooner about the frame style. I was away from my computer for a few days.

    The frame is full metal stainless steel frame. The lenses are grooved to sit inside the frame.

    hip chic

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    Quote Originally Posted by HarryChiling View Post
    The issue is mechanical, the frame bevel on a wrap is usually at an angle similar to the wrap angle. The bevel on the lens comes out of most edgers with the bevel and lens edge at 90 degrees to the front suface where it was blocked, over time a soft lens such as Poly, or a Eurathane (Hi-Index) will warp. The correct solution is not to cut smaller, or use thicker it's to relieve that pressure caused by the back ledge of the lens and the angle of the frames bevel. Multiple correct solutions:

    1. Lenticular - There are lenses out there that can make the edge of the lens thin enough that the back ledge of the frame is not there to interact with the frame, these lenses come in both traditional and a blended lenticular.
    2. Heavy Bevel - Hand edge the side of the lens that is causeing the issue to match the angle of the frame bevel, this will release the pressure and eliminate the issue.
    3. Frame Modification - This could void the warranty so might suggest it as a last resort, modify the bevel of the frame so that the frames angle matches the lens angle, this could also be done with a bit of hand beveling where both lens and frame are modfied slightly as a hybrid solution.
    DON'T - try to warp the lenses back into shape this is horrible suggestion, if you heat up hi index as suggested and place a weight on it you don't know what the outcome would be except warped lenses.
    Delete.
    Last edited by Metronome; 05-18-2009 at 02:04 AM. Reason: Delete.

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    Quote Originally Posted by Andro View Post
    Welcome to the forum, Harry!

    ;):cheers::cheers::cheers::D

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    Quote Originally Posted by Craig View Post
    We base curve match all of our jobs and in a thick frame like Chrome Hearts zyl, the heat will cause the lens to be overtaken by the frame curve. If you put them in a 6 base to start; all problems will vanish. Just remember to compensate for the curve and if you use the Autograph Attitude on a 6 base, you should have a job optically and cosmetically correct. It needs to be edged on a machine without wheels to ensure the curve/bevel are correct; this is essential on a 6 base thick zyl for cosmetics.
    While not a 'lab tech', I believe you match a base curve to the RX and NOT to the frame. Do you truly understand the theory behind a corrected curve (best curve series) lens, Tscherlings & Oshwalt (sp?) ellipses, unwanted lens abberations, Vogel's formula for base curve selection? Darryl??

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    Quote Originally Posted by tmorse View Post
    While not a 'lab tech', I believe you match a base curve to the RX and NOT to the frame. Do you truly understand the theory behind a corrected curve (best curve series) lens, Tscherlings & Oshwalt (sp?) ellipses, unwanted lens abberations, Vogel's formula for base curve selection? Darryl??
    Barry Santini covered the whole base curve thing here: http://www.optiboard.com/forums/show...t=31241&page=2

    The ability to change base curves for the frame is part of what makes the whole sunglass wrap lenses available to us. Now, putting a -3.00 -3.00 in a wrapped 8BC RayBan is much easier and ends with a every usable product for the patient.

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    Quote Originally Posted by FullCircle View Post
    Barry Santini covered the whole base curve thing here: http://www.optiboard.com/forums/show...t=31241&page=2

    The ability to change base curves for the frame is part of what makes the whole sunglass wrap lenses available to us. Now, putting a -3.00 -3.00 in a wrapped 8BC RayBan is much easier and ends with a every usable product for the patient.
    I stand by what I have said. If you want good, useful optics throughout the lens you are just asking for peripheral trouble by using a +6.00 base curve on a -6.00 lens. Why would you lens surfacers sacrifice optics for cosmetics.... just because you can? Where's Darryl on this issue?

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    Master OptiBoarder snowmonster's Avatar
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    Quote Originally Posted by tmorse View Post
    I stand by what I have said. If you want good, useful optics throughout the lens you are just asking for peripheral trouble by using a +6.00 base curve on a -6.00 lens. Why would you lens surfacers sacrifice optics for cosmetics.... just because you can? Where's Darryl on this issue?
    I think this is sort of the difference between being "book smart" and "real world smart." There has to be a little give in the realm of optics, and in my experience, patients rarely complain of BC-related issues or symptoms. The fact is that an OGI 2-base frame won't look or fit great with an 8-base lens in it, so jobs get run flatter. The same is true for a wrapped frame with a minus Rx.
    -Steve

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    Quote Originally Posted by snowmonster View Post
    I think this is sort of the difference between being "book smart" and "real world smart." There has to be a little give in the realm of optics, and in my experience, patients rarely complain of BC-related issues or symptoms. The fact is that an OGI 2-base frame won't look or fit great with an 8-base lens in it, so jobs get run flatter. The same is true for a wrapped frame with a minus Rx.
    And I suppose you have of idea what an iseikonic lens is/does...

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