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Thread: Question For Pete Hanlin!

  1. #1
    Master OptiBoarder OptiBoard Silver Supporter Jubilee's Avatar
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    Question Question For Pete Hanlin!

    We recently have begun using the Ovations as a primary progressive lens. I had one of the opticians throw a fit cause we went with the recommended minimum fitting height of 17, and noticed that half the add was cut off. So we grabbed the cut out chart and placed the lens with the factory markings still on, and the circle on the lens was a good two mm below the position it was identified at on the chart. It isn't just this lens.. so far all the lenses I checked show the add being lower than the cut out chart.

    Why?

    I convinced her to use it anyway showing her that if I checked the add where the cut out chart shows it, that you still can read the full add. But I would like to be able to tell them why, cause now they are straying away from the lens and using others that are less lab friendly ;)

    Cassandra

  2. #2
    sub specie aeternitatis Pete Hanlin's Avatar
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    This issue gets brought up fairly often (i.e., is it okay to fit a PAL such that part or all of the near verification circle is removed)...

    The minimum fitting height for Ovation is 17mm. As you have noticed, if you actually fit Ovation at that height, part or all of the near verification circle is removed. To understand why, we have to look into exactly what the "Near Verification Circle" represents.

    On Ovation (and many PALs), the Near Verification Circle is placed in a theoretical position that is more or less ideal for verifying the near power of the lens with a lensometer. This is why the diameter of the circle approximates the diameter of the lens stop on your lensometer. In other words, this is the area of the lens that should provide a relatively spherical front surface for the lensometer.

    The "full add power" of the PAL may or may not correspond to the circle. For example, in the case of Panamic, the depth at which full reading power is reached varies by a couple of mm depending upon the add power and the ametropia of the wearer. Likewise, the inset of the add power also varies greatly depending on the same two factors. As a result, the "Near Verification Circle" on a Panamic is basically only good for checking the add power with a lensometer (which not many people do anyway- since the lenses have risen "engravings" to indicate the add). The circle on Panamic (and on Ovation, BTW) has very little relevence to the "minimum fitting height."

    Unfortunately, eyecare providers have been taught (by Essilor and others) to treat the Near Verification Circle like some sort of holy shrine. This probably came from the days when yes- most frame fits would accommodate the full circle. Let's be honest (imagine that) for a moment- it would be IDEAL to fit PALs at 22-24mm. After all, even if the reading zone begins at 12-15mm (as it does in Comfort, Panamic, Ovation, and Natural), it would be ideal to provide the patient with a large depth of reading area for near use.

    For example, a FT28 can be fit at 4mm. The patient will get the full addition at the bottom of the frame. Unfortunately, s/he won't have much depth of lens to read through- which will probably become restrictive. The question with PALs should be- [How quickly does the add progress to 85% of its power? Why 85%? Because when we read, we usually require about 85% of our add power to see the TOP of the page we're reading (which is usually tilted slightly away when held normally). What we're looking for is a progressive that quickly gets to 85% and then increases to 100% over the next few mm. This allows the reader to obtain the top of the page and still have useful vision over the entire reading surface.

    Essilor's designs reach 85% of the add at about 12-13mm below the fitting cross. Your patient will be able to read the top of a page at that point in the lens. Everything below 12.5mm is going to be reading area. Essilor advocates 17mm minimum fitting height, because you should provide your patient with at least 5mm of reading area for comfortable vision. Ideally, you should provide patients with 10mm reading area- but patients often refuse to fit (or opticians are simply reluctant to suggest) frames that provide this much reading area.

    Regarding "Short Corridor" designs, most of them have two disturbing characteristics- first, they begin their progression considerably above the fitting cross. This overplusses the patient at distance and narrows the far vision field. In effect, its just like fitting a "regular" progressive a bit high. Second, short corridor PALs tend to reach 85% of their add at about the same spot as they reach 100% (the progression is very steep in most short corridior PALs). In effect then, the patient is going to have to tilt the head further back to obtain clear vision on the top of the page when reading held objects.

    Sorry for rambling on... the basic answer to your quesiton is this. The Near Verification Circle is placed so the lab can verify the near power of the lens in a relatively spherical area. It does not indicate the minimum fitting height of the lens. For those ECPs who care to debate that "they've always been told" that the circle should cut out, explain that the term "Minimum Fitting Height" has changed over the years. It used to mean "Minimum Ideal Fitting Height." Today however, eveyone wants to know "exactly how low can I realistically fit this PAL," which is what MFH now represents. The MFH for Ovation is 17mm.

    Hope this was useful information...
    Pete Hanlin, ABOM
    Vice President Professional Services
    Essilor of America

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

  3. #3
    Master OptiBoarder OptiBoard Silver Supporter Jubilee's Avatar
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    Thanks Pete!!

    That was very useful information.. I nkow I had always been taught that the circle was where the add comes in its clearest, and the location of the so-called "sweet spot"

    I began to suspect something like what you explained.. when I showed her that the add was coming in above the circle. Of course she thought we were limiting the channel width and depth.

    I will be happy to pass this information on to the rest of my region!

    Cassandra

  4. #4
    Master OptiBoarder OptiBoard Silver Supporter varmint's Avatar
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    Progressive Advice

    Pete since you are here giving progressive advice, I would like your recommendation on which lens design to use for an order I took yesterday.
    Rx OD -11.00 -.50 x 97
    OS -8.75 -.1.00 87
    ADD +2.25
    frame Marchon 53/19 B= 45 ED= 55
    He wants the same frame he wears reordered and is a bit too big for this Rx, but I must not be a good enough salesman to get him to change.
    Pt is currently wearing a poly Varilux, but I can't identify the marks. He would like something other than poly as he was not happy with the way tinting turned out on them. Funny when I called our local Varilux source, they told me Varilux progressives are not available in any power over -8.00 diopters. I know this isn't true, but I couldn't get the recommendation I needed from that lab.
    He actually came in carrying a Phoenix lens brochure, but the BC's for that product would be prohibitive for this job. I'd like to recommend something state of the art for him. Any advice?

  5. #5
    Master OptiBoarder OptiBoard Silver Supporter varmint's Avatar
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    OK Pete, I know you havent had a chance to see this & respond, but I spoke with the local lab mgr & his suggestion is the Varilux 1.6 "thin-n-lite" in the comfort design. Would you agree, or would you consider the Panamic instead?
    Anyone else have any thoughts on designs are welcome, Mr Ranger sir?

  6. #6
    sub specie aeternitatis Pete Hanlin's Avatar
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    Varmint,

    The Panamic 1.67 Thin & Lite (as I recall, Comfort 1.67 won't be out for a little while yet), comes in a 1.75 base curve that can be processed to a -12.00 total power. Therefore, it should work just fine for the Rx you indicated.

    While I would suggest going with a Panamic (unless that patient is already wearing Comfort), it should be noted that the Comfort 1.60 does come in a 1.00 base curve (which is also indicated out to a total of -12.00).

    Regarding markings- if the tilted "e" is encompassed by a football shape, you have a Comfort. A Comfort polycarbonate lens will have a "P" after the symbol. If the tilted "e" is bracketed with these symbols "<e>" you have a Panamic.

    Hope this helps...
    Pete Hanlin, ABOM
    Vice President Professional Services
    Essilor of America

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

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    Pete - thanks for that great info! Could you also give some advise on checking in PALs for power, axis, etc? This is an area of high returns and redos for the lab, so prepare to be quoted :idea: Thanks in advance.

    shutterbug

  8. #8
    Master OptiBoarder OptiBoard Silver Supporter varmint's Avatar
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    Thanks Pete, I meant to say I can't find the markings to identify the lens style. His old poly's were tinted & marks not readable.
    We were hoping for a newer design for him, but decided to use the Comfort in 1.60. His only complaint on the old pair was the tint darkness on the old poly.

  9. #9
    One eye sees, the other feels OptiBoard Silver Supporter
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    Varmit,

    As you probably know the 1.60 will be significantly heavier than poly. I have fit a fair number scripts around -9.00 with the vip gold (spectralite). This higher abbe lens allows a much cleaner image on the downgaze and on the distance periphery. Just a tad heavier than poly. The +.50 base *might* make this doable up to -11.25.

    Robert

  10. #10
    sub specie aeternitatis Pete Hanlin's Avatar
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    Pete - thanks for that great info! Could you also give some advise on checking in PALs for power, axis, etc?
    I'm not sure what advice can be given regarding verification of PALs except for the following:

    Verifying prism (or the lack thereof) in a PAL has historically been the issue of greatest misunderstanding. Prism must be checked at the PRP (prism reference point), which is the dot at the 180 line. On some PALs, this dot is 2mm below the fitting cross- for Essilor/Varilux designs, this dot is 4mm below the fitting cross. Prism thinning is now routinely used to control edge thickness on plus (and low minus) PAL lenses. Prism thinning is always yoked (the same amount and direction in both eyes), and should never exceed 2/3 of the dioptric ADD power. If no prism has been prescribed, the amount of prism thinning should read within 1/3 diopter between the PRP of each lens, and (IMHO) should never exceed 2 diopters. Prism thinning is always oriented base down.

    Verifying distance Rx should be done in the center of the distance verification circle. For obvious reasons, any prism noted should be disregarded, and I would recommend using a lensometer with a prism neutralization dial. If using a Humphrey Lens Analyzer, the equipment should be set to the PAL setting and the lens should be manipulated to a central reading point indicated by the screen. I would suggest that PALs which read incorrectly on a Humphrey should be re-verified by a manual lensometer before being returned. Auto-lensometers are still subject to being fooled occasionally (again, IMHO). For PALs with very low powered Rx (particularly those with a significant ADD power), there may be a small amount of unwanted cylindrical power evident in the center of the distance verification zone. Attempt to read the lens from several points within the distance verification zone before returning, as this is a phenomenon common to PAL designs.

    Verification of near power can be made from the near verification circle. Again, having a method of neutralizing the prism will be invaluable in reading the lens- since there can be quite a lot of prism in the reading zone of a PAL. To be honest, the "engravings" (which are actually raised areas) can be used with confidence to verify the near addition. These markings are part of the mold that was used to create the lens, and should never be wrong- if they were, every lens made from that mold would be incorrect (and that would be noticed extremely quickly by the manufacturer's QA department). If an add power seems to be incorrect, examine the lens for a wave. The edge of the surfacing block usually corresponds with the reading area, and therefore this zone is susceptible to an optical wave if the lens has been improperly processed. You can also check for irregularities with an Arc Lamp- but thankfully very few ECPs (or even labs) have this device. I say thankfully, because those who do have it tend to use it as an inspection tool- which is not what it is intended for.

    I hope this is the information you required. To sum, prism is checked at the PRP (and only at the PRP). Distance power is checked in the large circle above the fitting cross. Near power can be verified with the engravings, or at the near verification circle.

    Note that some PAL designs will not "read correctly" in the near verification circle. This is because some manufacturers design their lenses with consideration given to the pantoscopic and vertex distance at which the lens will be worn.
    Pete Hanlin, ABOM
    Vice President Professional Services
    Essilor of America

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

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    Thanks Pete. You covered the part I wanted - the little cyl that shows up in low powers and screws up the axis or power readings. Since this is part of the design I hope we'll get fewer returns :-). In my humble opinion it is best to let the patient wear it before assuming it is wrong.

    shutterbug

  12. #12
    sub specie aeternitatis Pete Hanlin's Avatar
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    Shutterbug,

    Actually, I was flying home last night reading an article on lenses, and it occurred to me that I hadn't completely explained the presence of trace amounts of cylinder in the far zone of PALs.

    Marginal Astigmatism is another reason you may notice a small amount of cylinder in the distance portion of a PAL. As we all know, marginal astigmatism is a naturally occurring aberration when light travels through a point in the lens away from the Optical Center.

    On a PAL, the OC is actually the PRP (Prism Reference Point). This point is usually 4mm below the fitting cross (on Essilor and other products), and the distance verification zone is another 3 or so mm above the fitting cross! Therefore, when we verify distance power, we are looking at a point approximately 21 degrees (or 7mm) away from the OC. It shouldn't be surprising, then to detect a small amount of astigmatism- especially on lenses with strong powers.

    Sorry for neglecting to include this on the original post- slipped my mind.
    Pete Hanlin, ABOM
    Vice President Professional Services
    Essilor of America

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

  13. #13
    Bad address email on file Susan Henault's Avatar
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    I'd like to throw in one more plug for the use of 'prism rings' or prism neutralizers as Pete called them. These devices are specifically designed to give a true reading, when checking the power well off of the OC. Those small traces of cyl often disappear and the target becomes crisp and sharp when you use a prism ring to verify the power of a progressive lens.

    Also, though I don't know if it is still commonly practiced, we used to double check the add from the BACK surface, if it seemed to be a little off. This method usually proved the add to be accurate. Not only that, but it really helps to use only one set of "lines" in the target (we always used the most vertical lines, be they the sphere lines or cyl) when verifying the add (or the difference in power between the distance and the near) in an old style lensometer. If you were not taught this, give it a try. You will like what you see!

    Lastly, I advise caution when fitting general purpose PALs at 17mm seg heights, versus using a well designed short corridor lens. While it is true that some general purpose PALs achieve 85% of the add in the first 12 or 13 mm, whether that provides the patient with 5mm of "full reading" (at a 17mm fitting height) is debatable. I encourage you to consider what you would do with a FT-28 that came in from the lab only reading 85% of the +2.00 add you prescribed.

    Truly, some short corridor designs are more of a compromise than others, but in my opinion even the worst "true" short corridor progressive, provides more "prescribed reading" than the best general purpose lens fit at 17mm. Remember, it really is only my opinion.
    Last edited by Susan Henault; 09-22-2003 at 11:20 AM.

  14. #14
    OptiBoard Apprentice Gov't Mule's Avatar
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    HOYA Summit CD Progressive

    Hoya Summit CD

    Consider this lens with small frames and extremly low fitting heights.

    Minimum height: 14mm.

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