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Thread: backside curves

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    backside curves

    hello everyone,
    Friday I had a pt who was previously in a Physio. For his new glasses I wanted to use and Auto 2. I was curious to know if his previous pair was a physio or a physio 360. I understand the markings on both are the same. I read the thread on how to distinguish the two lenses. One of the replies talked about measuring the back curve of the lens with a lens clock. Traditional surfacing creates a spherical or toric surface and Freeform surfacing creates a aspheric or atoric back curve. Could someone please explain the diffrence to me and tell me how to use the lens clock to determine the diffrence. I read that U move the lens clock across the back of the lens, does that mean rotate the clock or what I am confused.
    thanx,
    jamie

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    Eyes eastward... Uilleann's Avatar
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    I've never heard of the ability to discern the difference between a regular Physio and the 360's with just a lens clock. I wouldn't think that was possible. Best thing to do would be to contact the original lab who made the things if at all possible. But a lens clock (I would have to think) would be nowhere near accurate enough to distinguish between a digitally surfaced vs conventionally surfaces lens. Perhaps I'm wrong though...

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    Using the lens clock . . .

    To get an accurate reading using the lens clock it is best to place the center post of the clock at the center of the lens and then slowly rotate either the clock or the lens on that center post axis.
    The difference between the lowest reading to the highest will tell you the amount of cylinder correction on the back of that lens. It may or may not be the total amount of cylinder correction the lens produces based on whether or not the lens has any cylinder correction ground or formed on the front side (pretty rare).

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    Determining asphericity using a lens clock . . .

    I am not sure that this proves how the lens was surfaced but to determine asphericity using a lens clock, place the lens clock with the clock's center post at the center of the lens. Do not rotate the lens but instead slowly move the lens toward the edge of the lens in a perfectly straight line in line of the clock's 3 posts.
    You will see the needle drop slightly if the lens is aspheric.

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    Uillean,
    According to the thread that I read it is possible I do not know how to pull up the thread and place it in my reply but I found it searchin physio 360 markings. Anyway, do you know of any way to know besides calling the lab or previous optical?
    jamie

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    Master OptiBoarder optical24/7's Avatar
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    The 360 series of lenses are not atoric. They are also not a FF surfaced lens. It is simply a digitally surfaced lens. (all 360's)

    All Physio's are digitally molded front surface.

    The only way to tell if you have a 360 is if you work in the lab that produced them. ( there are no special markings or way to decerne the difference with a lens clock nor lensometer)

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    Quote Originally Posted by opticalpig View Post
    I am not sure that this proves how the lens was surfaced but to determine asphericity using a lens clock, place the lens clock with the clock's center post at the center of the lens. Do not rotate the lens but instead slowly move the lens toward the edge of the lens in a perfectly straight line in line of the clock's 3 posts.
    You will see the needle drop slightly if the lens is aspheric.
    Almost correct, if the lenses are aspheric or atoric rather than spherical or toric like their conventional version you can tell the difference using a lens clock and lensometer.

    First - Using the lensometer mark the meridians of the lens.
    Second - Placing your lens clock on the back surface along the marked meridian if you move the lens along that marke meridian if the clock reading changes then your lens is more than likely the 360 version. Make sure to measure both meridians when making your determination.

    Potential Faults - If the lens was surfaced too thin, if the material is too soft, etc. a warped surface can give the impression of asphericity. Also the lens may be too small in diameter to move the clock across the surface and determine if any aspehricity is present.

    The physio short has since corrected this issue and I have heard that eventually all the 360 designs will have a marking to differentiate the conventional vs the 360. It was a very poor choice to not differentiate markings.

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    Quote Originally Posted by jamie w View Post
    hello everyone,
    Friday I had a pt who was previously in a Physio. For his new glasses I wanted to use and Auto 2. I was curious to know if his previous pair was a physio or a physio 360. I understand the markings on both are the same. I read the thread on how to distinguish the two lenses. One of the replies talked about measuring the back curve of the lens with a lens clock. Traditional surfacing creates a spherical or toric surface and Freeform surfacing creates a aspheric or atoric back curve. Could someone please explain the diffrence to me and tell me how to use the lens clock to determine the diffrence. I read that U move the lens clock across the back of the lens, does that mean rotate the clock or what I am confused.
    thanx,
    jamie
    Jamie,

    Rotating the lens clock will tell you the degree of toricity, e.g. a 1.0 DC Rx will show a one diopter difference between the steepest and flatest back curve, it can not show if the surface is aspheric, unless it has a very high degree of asphericity that you'll find on five drop cataract lenses, but not on the very small amount asphericity found on the 360.

    Quote Originally Posted by optical24/7 View Post
    The 360 series of lenses are not atoric. They are also not a FF surfaced lens. It is simply a digitally surfaced lens. (all 360's)

    All Physio's are digitally molded front surface.

    The only way to tell if you have a 360 is if you work in the lab that produced them. ( there are no special markings or way to decerne the difference with a lens clock nor lensometer)
    Right, although the 360 does use free-form technology, it doesn't take advantage of all that can be done with this technology. Free-form lite so to speak.
    Science is a way of trying not to fool yourself. - Richard P. Feynman

    Experience is the hardest teacher. She gives the test before the lesson.



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    Ok.

    Hopefully you have a Physio layout chart. Dot the progressive markings, and draw on the distance and reading circles.

    Put the lens clock in the center of the distance circle. Move the clock straight down to the reading. If the needle moves, it's a 360. If not, it's not.

    The 360's are not a true Free Form design, rather a digitally designed lens with a split add. Part of the add is on the front, the rest surfaced into the back. (A true Free Form design will have a completely spherical front, and all power, distance and reading, surfaced into the back.)

    Rotating the lens clock on the back surface in the center of the distance area will give you a fair approximation of the cylinder power and axis.

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    Quote Originally Posted by WFruit View Post
    (A true Free Form design will have a completely spherical front, and all power, distance and reading, surfaced into the back.)
    What about the Hoya Id?

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    Rochester Optical WFruit's Avatar
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    Quote Originally Posted by Fezz View Post
    What about the Hoya Id?
    I will be the first to admit that my experience with the ID is limited. What I've heard/read about it, however, both on Hoya's site and in talking with people, is that it is a dual add lens. Better designed (possibly the best digitally designed) than most, but still having some power on the front and the rest on the back. Thus it is digitally designed, digitally surfaced, but not free form.

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    Wfruit,

    What is free form?

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    Quote Originally Posted by View Post
    Ok.


    The 360's are not a true Free Form design, rather a digitally designed lens with a split add. Part of the add is on the front, the rest surfaced into the back.

    .
    I don't think that the 360 is a split add design. The 360 starts out with a regular Physio blank (pre-engraved, hence no distinguishing factors in the markings)

    If a lens is marked "20" then there is a +2.00 add already on the front surface. If they "duel added" the back we would recieve a lens with an add greater than +2.00.

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    Quote Originally Posted by WFruit View Post
    I will be the first to admit that my experience with the ID is limited. What I've heard/read about it, however, both on Hoya's site and in talking with people, is that it is a dual add lens. Better designed (possibly the best digitally designed) than most, but still having some power on the front and the rest on the back. Thus it is digitally designed, digitally surfaced, but not free form.
    Ok, this post just set me back at least 5 years of learning. And from a lab guy at that.:hammer:

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    Quote Originally Posted by WFruit View Post
    I will be the first to admit that my experience with the ID is limited.
    http://www.optometry.co.uk/articles/...ie20050617.pdf

    Scroll down to "Hoya Lens".

    ...two plano cylinders that have been combined at right angles to one another.

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    Another tidbit for Wfruit about the Hoya ID Mystyle offering.

    http://www.hoyaluxid.com/index.php?S...&page_id=17491

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    Quote Originally Posted by Fezz View Post
    Another tidbit for Wfruit about the Hoya ID Mystyle offering.

    http://www.hoyaluxid.com/index.php?S...&page_id=17491
    Last I heard we'll get it (in the US) in the spring of 2010. Note that there are three levels of softness and three corridor lengths. Hopefully we'll be able to overide the MyStyle iDentifier recommendations, and won't be forced to purchase the Mystyler “all-in-one” measurement tool to dispense this design.
    Science is a way of trying not to fool yourself. - Richard P. Feynman

    Experience is the hardest teacher. She gives the test before the lesson.



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    Quote Originally Posted by Fezz View Post
    Wfruit,

    What is free form?
    http://patft.uspto.gov/netacgi/nph-P...&RS=PN/7159980

    The patent says that's what Free Form is. In simpler language, it's a progressive addtion lens having a spherical front curve, and all power on the back surface.

    Thank you all for the links on the Hoya ID lens. I stand educated.

    I don't think that the 360 is a split add design. The 360 starts out with a regular Physio blank (pre-engraved, hence no distinguishing factors in the markings)

    If a lens is marked "20" then there is a +2.00 add already on the front surface. If they "duel added" the back we would recieve a lens with an add greater than +2.00.
    If this were true, wouldn't you just end up with a regular Physio? There would be no optical difference between a Physio and a Physio 360. Or did I just spoil Varilux's marketing.....

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    Quote Originally Posted by WFruit View Post
    If this were true, wouldn't you just end up with a regular Physio? There would be no optical difference between a Physio and a Physio 360. Or did I just spoil Varilux's marketing.....

    ;):cheers::cheers::cheers:

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    Quote Originally Posted by WFruit View Post
    http://patft.uspto.gov/netacgi/nph-P...&RS=PN/7159980

    The patent says that's what Free Form is. In simpler language, it's a progressive addtion lens having a spherical front curve, and all power on the back surface.
    That's just one example. We can use free-form generators/polishers to create almost any kind of lens/surface, including single vision.

    Thank you all for the links on the Hoya ID lens. I stand educated.
    37 years and I'm learning something new almost every day.

    If this were true, wouldn't you just end up with a regular Physio? There would be no optical difference between a Physio and a Physio 360. Or did I just spoil Varilux's marketing.....
    The ocular (back) curve on the 360 lenses is aspheric. There can be reduced off-axis power error and somewhat reduced marginal astigmatism compared to what you will get with the spherical/toric surface on the regular Physio.
    Science is a way of trying not to fool yourself. - Richard P. Feynman

    Experience is the hardest teacher. She gives the test before the lesson.



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