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Thread: Patient complaining of thickness of 1.67 lenses

  1. #1
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    Patient complaining of thickness of 1.67 lenses

    I recently prescribed a pair of 1.67 hi index lenses for a patient with an Rx of about -8.00. The patient came back furious after receiving her lenses and complained that although she paid a "fortune" they were much thicker than her older pair of glasses. I took a lot at her older pair and agreed that they looked a lot thinner. I found out that they were polycarbonate and were called "polythin". I was quite surprised at this having always thought that 1.67 was the superior option at this range.

    On a related topic: I noticed over the last few weeks that my optician was frequently prescribing polycarbonate lenses to patients who are in a low myopic or hyperopic range eg: -1.25. My feeling about this is that if there is no compelling reason to use polycarb ie: thick or heavy lenses, sports, kids etc then why not use CR39 which has a better clarity. My optician was previously trained to sell Polycarb to almost everyone on the basis of built in scratch and UV protection, thin/lite, and impact resistance. I am not sure if I am exaggerating the abbe concept but I do wonder if it is right to dispense it polycarb so liberally.

    Last point to make: ANyone aware of polycarb that's better than other polycarb

  2. #2
    OptiWizard OptiJim's Avatar
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    Polycarbonate material does not = built in scratch protection. Without the coating, Poly will scratch if you just look at it wrong.

    IMO, if poly is not needed for the complelling reasons you described besides the scratch resistence, cr-39 is a superior product, optically.

    Good Luck.

    Jim

  3. #3
    Manuf. Lens Surface Treatments
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    Redhot Jumper Polycarbonate Materials......................

    Quote Originally Posted by ilanh
    ...........................but I do wonder if it is right to dispense it polycarb so liberally.

    Last point to make: ANyone aware of polycarb that's better than other polycarb
    Polycarbonate is one of the most commonly used plastics today. It is used to make motorcycle windshields, hockey helmets, kitchen utensils and your imagination can name item that are made of that material. You can see the properties of poly on a page of my website at http://optochemicals.com/polycarbonate_properties.htm

    Polycarbonate comes in plastic pebbles and is the injection molded into racks of 6 to 8 lenses every few seconds...........which makes it the cheapest manufacturing process for optical lenses ever invented.

    It is actually one of the cheapest and sturdiest materials in the way of resisting breakage as long as its finished chemical structure is not disturbed by chemical solvents or fumes which may make it craze and self destruct.

    It is also one of the softest materials in the plastics field. ...................you can actually scratch it with your finger nail. Therefore it has to be hard coated on both sides for optical lenses. These hard coats are very problematic to tint in the dye pot and can only be tinted fast to dark shades using the new micro-tint system.

    Polycarbonate lenses have only become really popular since some of the major optical corporations have purchased polycarb lens manufacturers like Gentex and others and have started major brainwash advertising towards the trade and public.

    For all the good qualities polycarbonate lenses display, they are heavily overprized as they are by far the cheapest item to produce in the optical field.

    Compare this to good old CR39 which is much more labor intensive to produce by filling the glass molds with monomer, then curing it for hours.........open the mold...............remove the lens ..................and clean the mould for the next use.

    CR39 sells for less..............but does not have to be hard coated if not wanted............has better optical qualities (is the closest plastic lens to the old glass lenses), can easily be tinted for colors and UV, does not need special edgers and tools to work it.

    To the last point..................Polycarbonate is Polycarbonate.........unless the lens design is different there is no difference in the material. They all have the same advantages or disadvantages.

  4. #4
    Optician Extraordinaire
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    Polycarb is very soft without a hardcoat, but you can only buy it with a hardcoat. It is not offered without one.

    The 1.67 might be thicker for several reasons. Is the frame bigger or wider? Is the prescription stonger? Is the center thickness thicker? Is the pd on her old glasses wider? Just how much thicker are the new glasses?

    All things being egual the 1.67 will be a little thinner, so something is different.

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    Bad address email on file QDO1's Avatar
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    Quote Originally Posted by Happylady
    Polycarb is very soft without a hardcoat, but you can only buy it with a hardcoat. It is not offered without one.

    The 1.67 might be thicker for several reasons. Is the frame bigger or wider? Is the prescription stonger? Is the center thickness thicker? Is the pd on her old glasses wider? Just how much thicker are the new glasses?

    All things being egual the 1.67 will be a little thinner, so something is different.
    Polycarb without a hardcoat.. maybee 15 years ago..we all know better now.. as you say it isnt offered without one. more to the point, what about the crap abbe value

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    Bad address email on file jbiggs114's Avatar
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    Optima "Resolution" seems to be a better poly. Better clarity.
    1.67 is the lense I would have used over poly. How about the A, B, DBL and ED? Was it larger than the previous frame? Maybe the lab goofed and they didn't turn them down at inspection for thickness because of the cost to remake them. Did the lab have accurate measurments before computing the job to start on it? If both rx's are close in power and frame size, did you measure the center thickness on the old pair and state to the lab the center thickness you wanted? The lab doesn't know what you will accept if you give them no guidelines and all they use is a ANSI standard chart.

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    Poly is Poly

    I think the concensus so far is that Poly is Poly.

    But the question is: How can it be thinner than the lenses you prescribed her, right? How can 1.59 index be thinner than 1.67? I would like some professionals to help answer this question also.

    You did not mention eye sizes between the two pairs of glasses.

    Did the Rx change very much?

    How did your ascertain that her lenses were poly? By looking at the invoice or by testing it's pitch against one of your stock poly's?

    How did you ascertain that your lenses were 1.67? Is it possible that the lab pulled a fast one on you?


    paremyd, OD

    *I don't have lab experience (like the pros here), except troubleshooting so this is intriguing to me. And I want to find out because 10 years ago, a lab pulled a fast one on me.

  8. #8
    Bad address email on file QDO1's Avatar
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    Quote Originally Posted by paremyd
    But the question is: How can it be thinner than the lenses you prescribed her, right? How can 1.59 index be thinner than 1.67? I would like some professionals to help answer this question also..
    Simple a poly job could be thinner than a 1.67 job if:
    • the centre thickness was thinner
    • the effective diameter was smaller
    • the Poly was very aspheric, and the 1.67 was not
    • the frame shape combined with the cyl direction was unsympathetic in the thicker job, when the frame shape and cyl direction was complimentry in the thinner
    Look at the CT's, Heights, OC's and Asphericity of the two jobs, you will find the answer there

    The darker answer to the question is that the job has been surfaced poorly, or the original lens was not Poly, but a higher index lens...

  9. #9
    Manuf. Lens Surface Treatments
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    After surfacing...............

    Quote Originally Posted by Happylady
    Polycarb is very soft without a hardcoat, but you can only buy it with a hardcoat. It is not offered without one.
    That is correct.............but if a lab surfaces a lens ...............there will be no more hardcoat on the minus side....................and will have to be re-applied.

  10. #10
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    Unhappy 1.67 thicker than Poly

    With regard to previous questions:

    -The prescriptions for the poly and 1.67 lenses were almost identical. I checked both personally.
    -I do not have precise frame measurements but the frames looked almost identical in size, material and style. The poly job looked thinner and better.
    -No, I did not specify a center thickness. I never do. I have always assumed that my lab would make every pair of lenses as thin as they could. Should I specify center thickness? How do I decide on this? Isn't it logical to assume that for a high minus lens the lab would use every trick they have to make it look its best?

    -I verified that the poly lens was polycarb by its sound and by checking the previous records. However, I do not know how to check if the 1.67 was indeed 1.67 (is there a simple way to check this?)
    -I did not ask for asphericity or atoricity in my order. Once again, I did not know that this has to be specified. We occasionally use stock Poly and hi-index lenses and I was told by the company that sells them that "all our poly and hi-index are aspheric". This job, however, was theoretically surfaced.

    The bottom line is that I do not really know what I got or if this was properly surfaced. I do know, however, that I paid a premium for this lens (as did the patient) and we were both disappointed.

  11. #11
    Bad address email on file QDO1's Avatar
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    Quote Originally Posted by ilanh
    With regard to previous questions:

    -No, I did not specify a center thickness. I never do. I have always assumed that my lab would make every pair of lenses as thin as they could.
    Dont assume anything

    Quote Originally Posted by ilanh
    Should I specify center thickness? How do I decide on this? Isn't it logical to assume that for a high minus lens the lab would use every trick they have to make it look its best?
    You can specify a thickness to be thicker, but in general the lab will surface each material to its own pre-determined thickness, usually that thickness is determined by saftey issues, and manufacturing issues. Labs sometimes miss-calculate the thickness. One measures it with thickness calipers

    Quote Originally Posted by ilanh
    -I verified that the poly lens was polycarb by its sound and by checking the previous records. However, I do not know how to check if the 1.67 was indeed 1.67 (is there a simple way to check this?)
    Use a base curve clock, and work the surface powers out

    Quote Originally Posted by ilanh
    --I did not ask for asphericity or atoricity in my order. Once again, I did not know that this has to be specified. We occasionally use stock Poly and hi-index lenses and I was told by the company that sells them that "all our poly and hi-index are aspheric". This job, however, was theoretically surfaced.
    Sounds like you havent a clue what was supplied, and furthermore, you probrably cant be certain what the previous order was. You ought to know if you are dispensing an aspheric, as they have a different need for dispensing measurements. You may be able to tell if the lenses are aspheric, by checking the front surface with a lens clock

    Quote Originally Posted by ilanh
    --The bottom line is that I do not really know what I got or if this was properly surfaced. I do know, however, that I paid a premium for this lens (as did the patient) and we were both disappointed.
    Why are you dispensing what you cant check? Ring the lab up and ask them what blanks they used for your order

  12. #12
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    Use a base curve clock, and work the surface powers out



    Why are you dispensing what you cant check? Ring the lab up and ask them what blanks they used for your order[/QUOTE]

    Obviously we called the lab and they assured us that they used 1.67. However, you are right...I don't know how to figure out if the material in front of me is 1.60, 1.67 or regular CR 39. I would be most interested in learning verification techniques. My optician does not know how to verify this either.

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    Bad address email on file QDO1's Avatar
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    Quote Originally Posted by ilanh
    Obviously we called the lab and they assured us that they used 1.67. However, you are right...I don't know how to figure out if the material in front of me is 1.60, 1.67 or regular CR 39. I would be most interested in learning verification techniques. My optician does not know how to verify this either.
    You guys should book on a Ophthalmic optics course, and get a few good textbooks

  14. #14
    Master OptiBoarder rbaker's Avatar
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    Prior to performing a task one should have the required knowledge and skill. Prior to supervising or commenting on a task one should also have the required knowledge and skill. I suggest closing your doors until you have achieved the basic skill set to practice or supervise a dispensary. This may be hard news to take but it is unfortunately true. There are far too many unqualified people working in opticianry. This, combined with ineffective education, licensing, regulations and enforcement has reduced the craft to little more than burger shuffling without the grease.

    The ground of the optical vineyard is very fertile for the growth of incompetence and ignorance. Thankfully, the public is seldom physically harmed by the incompetence of the optician. Thankfully, you can fool most of the people most of the time.


  15. #15
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    Two frames can look almost the same in size and not be. Measure across one of the lenses and the bridge and then do the same on the other frame. Often there can be several millimeters difference on two frames that look similar.

    I bet the center thickness of the 1.67 will measure thicker, too. A mm thicker in the center will make the edge a mm thicker and that will look like a lot on a finished job.

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