I have a wrap compensation problem...

[drk]

This is for anyone, but especially Mr. DM, Mr. HC, or Mr. AW...

I had a thought...when wrap-compensating a spherocyl, you get a singular answer...

...but when wrap-compensating a multifocal you do not get a singular answer...you get a variety of answers!

In a BF, there is a different compensation for the add than for the distance sphere...

In a prog, there would be an "infinte" number of compensations throughout the corridor...

So, what's a common-sense solution?


I would say that the higher power portion of the lens should be wrap- compensated (e.g. the add on the low minus and plus power lenses, or the distance portion on a higher minus multifocal lens), and the lower power portion should be ignored...

...But the problem seems to be that the compensation to help the one section actually can aggravate the vision in the other...

...for example in a low minus spherocylinder with a high plus add has an axis compensation 2 degrees one way for the add, but 2 degrees the other way for the distance power....


Is the better solution with multifocals to simply not compensate at all?

[Barry Santini]

???????
Really, I'm not sure I follow....

Barry

[HarryChiling]

This is for anyone, but especially Mr. DM, Mr. HC, or Mr. AW...

I had a thought...when wrap-compensating a spherocyl, you get a singular answer...

...but when wrap-compensating a multifocal you do not get a singular answer...you get a variety of answers!

In a BF, there is a different compensation for the add than for the distance sphere...

In a prog, there would be an "infinte" number of compensations throughout the corridor...

So, what's a common-sense solution?


I would say that the higher power portion of the lens should be wrap- compensated (e.g. the add on the low minus and plus power lenses, or the distance portion on a higher minus multifocal lens), and the lower power portion should be ignored...

...But the problem seems to be that the compensation to help the one section actually can aggravate the vision in the other...

...for example in a low minus spherocylinder with a high plus add has an axis compensation 2 degrees one way for the add, but 2 degrees the other way for the distance power....


Is the better solution with multifocals to simply not compensate at all?

I know what you are saying and I don't think it's going to be a simple answer. Given the absolute nature of an add, the best idea would be to compensate both Rx's individually and then subtract them from one another, use the spherical equvalent of this difference as the add power and this could be a solution. Just a thought but of course any axis and risidual astigmatism left will not be accounted for, but the nature of wrap eyewear is comprimised optics in lieu of comprimised cosmetics. The nice thing abou wrap eyewear is that it usually ony applies to sunwear where the distance correctiong will be utilized a majority of the time so if any comprimise shoul be made I would say place that comprimise in the reading.

PS - I usually don't bother with any compensations untill the Rx goes over 2 diopters and I don't make them above a 5.

[drk]

Barry:
Run a wrap compensation for -0.50-1.50x180 and note the magnitude of change in sph, cyl and axis.

Then run the same calculation for the add portion, say +2.50, +2.00-1.50x180 and note the magnitude of change in sphere, cyl, axis.

You will find they do not agree...So which one do you compensate?

Harry says:
1.) Distance Rx for sunwear, perhaps
2.) Average the compensations and apply a "global compensation".

Cryptically, he doesn't correct over 5D. Maybe it's a bad idea to wrap that high an Rx, anyway...

[snowmonster]

I would say use the distance power and axis and just keep the original bifocal power. Although, Harry's point about performing near and distance conversions and subtracting seems to make sense. I just can't imagine that your add power would vary more than +/-0.25 from the original Rx. Does that amount of difference really matter with a PAL? Probably not.

Now with a FT, maybe it would matter a little more. I ran the numbers on the powers drk suggested and found a +2.50 add should probably be reduced by 0.25 D. That was with the KBco calculator, at least.

[HarryChiling]

Cryptically, he doesn't correct over 5D. Maybe it's a bad idea to wrap that high an Rx, anyway...

I tell them that there Rx won't be done if it's over a 5, it's just not worth it to us it's time consuming, I do the lenticulars in house and the rate of non adapt over 5 is too great fro me to waste a lot of time on these jobs, I am in the process of lookign for a lab to do the higher Rx's for our office, but not many labs are up to the challenge.

[AWTECH]

This is for anyone, but especially Mr. DM, Mr. HC, or Mr. AW...

I had a thought...when wrap-compensating a spherocyl, you get a singular answer...

...but when wrap-compensating a multifocal you do not get a singular answer...you get a variety of answers!

In a BF, there is a different compensation for the add than for the distance sphere...

In a prog, there would be an "infinte" number of compensations throughout the corridor...

So, what's a common-sense solution?


I would say that the higher power portion of the lens should be wrap- compensated (e.g. the add on the low minus and plus power lenses, or the distance portion on a higher minus multifocal lens), and the lower power portion should be ignored...

...But the problem seems to be that the compensation to help the one section actually can aggravate the vision in the other...

...for example in a low minus spherocylinder with a high plus add has an axis compensation 2 degrees one way for the add, but 2 degrees the other way for the distance power....


Is the better solution with multifocals to simply not compensate at all?

You are right there is alot more to a PAL wrap than a single vision wrap. I don't think molded front side PALs lend themselves to wrap compensations very well. An individualized wrap PAL can manage the issues over the total lens surface with individual calculations to control power error and off axis problems due to wrap angle.

We choose to keep the add power rated as prescribed to avoid confusion, but the Add power is just that an add to the compensation we developed to produce a superior PAL wrap lens.

Lens corridor designs for wraps does matter.

We produce these everyday with very few non-adapts.

The results in vision for the patients who use these lenses prove that this works.

[snowmonster]

Allen:

Aside from the fact that the front curve is variable across the surface of the lens and therefore (at least theoretically) not fitting into the frame as well, does the new Younger Image Wrap 8.50 base lens really help with these issues or did they just decenter the lens for better cutout for large sunglass frames?

http://www.youngeroptics.com/product...rapnppoly.html

Thanks!

[AWTECH]

Allen:

Aside from the fact that the front curve is variable across the surface of the lens and therefore (at least theoretically) not fitting into the frame as well, does the new Younger Image Wrap 8.50 base lens really help with these issues or did they just decenter the lens for better cutout for large sunglass frames?

http://www.youngeroptics.com/product...rapnppoly.html

Thanks!

This approach allows a traditional method of surfacing to have a lens that will at least cut out and work better than a non-decentered. Obviously the PAL surface design is fixed for each frame angle and panto tilt as an example.

The best way is to base curve match the front curve to the frame and individualize the calculations of frame angle, tilt etc. and individualized the lens surface for the patients prescription combined with this information.

[Barry Santini]

Barry:
Cryptically, he doesn't correct over 5D. Maybe it's a bad idea to wrap that high an Rx, anyway...

DRK, I'm away till next week, so I don't have access to my comp prog. But, I've comp'ed Rxs as high as -9D in a 13 degree wrap with client "satisfaction".

Their are alot of variables. the importance of extreme peripheral acuity is not one of them, in my humble opinion.


Barry

[Laurie]

Hello 'boarders,

Have you considered, instead of trying to compensate complicated designs like PALs into a wrap compensation formula, trying a lens that was invented for this purpose?

The Shamir Attitude PAL was designed especially with wraps/PALs in mind. They add special asphericity into the design/mold, which conteracts and neutralizes the spherical aberration/distortion inherent in wrapping a PAL.

If you have not checked it out yet, you may want to consider it. It makes more sense than trying to put a square peg in a round hole.

: )

Laurie

[AWTECH]

Hello 'boarders,

Have you considered, instead of trying to compensate complicated designs like PALs into a wrap compensation formula, trying a lens that was invented for this purpose?

The Shamir Attitude PAL was designed especially with wraps/PALs in mind. They add special asphericity into the design/mold, which conteracts and neutralizes the spherical aberration/distortion inherent in wrapping a PAL.

If you have not checked it out yet, you may want to consider it. It makes more sense than trying to put a square peg in a round hole.

: )

Laurie

Good point Laurie: The solution you describe is much better than trying to get a PAL not designed for wraps to work in a wrap frame. The limitations to this approach is the front molded wrap product has to be designed for a specific frame angle and these wrap frame angles vary. So for the lab that has to surface there own this is a solution, but the best way is to individually design the lens for frame, this will make for better optics, better fit within the frame, a thinner lens, etc. etc.

To do this you need a lens produced like we do using ICE-TECH Advanced Lens Technology which optimizes each design. We have over 10 Million possible lens designs.

[Fezz]

Laurie brings up s good point:

Do lenses like Shamir Attitude, Younger's new Image for wraps, or KBCo's EOS wrap designed progressive benefit from rx optimization or compensation formulas? Or, does optimizing the rx in such designs wreck havoc on the finished optics?

[AWTECH]

Laurie brings up s good point:

Do lenses like Shamir Attitude, Younger's new Image for wraps, or KBCo's EOS wrap designed progressive benefit from rx optimization or compensation formulas? Or, does optimizing the rx in such designs wreck havoc on the finished optics?

Fezz: Good follow up. There is so much confussion about wraps in the market at this time. Our system is designed to make it easy. All the optican needs to do is send us the frame and give us the Seg height and other standard prescription information and we then optimize the design for the specific patient using their prescription information combined with the frame angle, frame trace etc. The we design the lens. The other solutions you mention design the lens base on an estimated use. So with any of these designs if one is used with a frame with an 19 degree frame angle and the same person wants a second frame with a 25 degree frame angle you are stuck using the same lens design for both. If one has a B measurement of 42mm and the other has a B measurement of 32mm then the same lens is design is used for both. With an individualized approach like ICE-TECH uses each of these would have a different design which would result in optimized optics and thickness for each.

[snowmonster]

I received my first pair of Younger Image Wrap in polycarb going into a zyl Oakley today. The decentered lens is perfect for this type of frame. I know, it's not a custom solution, but this guy isn't going to do a lot of reading in his polarized PAL's.

[HarryChiling]

Hello 'boarders,

Have you considered, instead of trying to compensate complicated designs like PALs into a wrap compensation formula, trying a lens that was invented for this purpose?

The Shamir Attitude PAL was designed especially with wraps/PALs in mind. They add special asphericity into the design/mold, which conteracts and neutralizes the spherical aberration/distortion inherent in wrapping a PAL.

If you have not checked it out yet, you may want to consider it. It makes more sense than trying to put a square peg in a round hole.

: )

Laurie

Thanks Laurie for the post, I love the idea of the Kbco and the Shamir having asphericity to counter the sph aberration/distortion, but sph aberration isn't a big concern as the stop size the pupil limits the amount of sph aberration allowed into the eye, but the off axis powrs created by these lenses is a big concern since most the powers are outside of their best form curves. I am glad to have both options available EOS and the Attitude, however the compensations are still necessary.

[drk]

Here's my take:

Progressives for wrap is an emerging "buzz" topic, and confusion exists, as has been already mentioned.

Decentering the progressive features in the lens blank helps, but only so much. That's not really "wrap compensated".

Shamir's 8-base Attitude series in Piccolo and Genesis is supposed to allow parameters -4 to +2, IIRC (over +2, 8 base is the normal choice, anyway, so normal lens designs suffice). I believe that they are trying to eliminate whatever aberration is induced by ignoring the corrected curve formulae.

This is partial wrap compensation, and is a big step forward. But as Harry says, this in no way compensates for the power changes that tilting induces; you'd have to run those as well, and include the prism, and then order it in the Attitude series, as Laurie notes.

As Allen mentions, there is another significant variable: frame wrap. You can easily go to your inventory and see 8-base plano lenses in varying degrees of frame wrap. So he's right, you must have a formula to compensate for that, as well. Of course, Darryl's program includes all these factors.

One factor that is difficult to compensate for with front surface molded progressives is loss of corridor width with lens tilt. I think Allen alludes to this. The solution is to begin with a wider corridor than needed so that tilt effect can be offset, and this may mean back surface progressive curves.

Add to this mess whatever errors may occur on a case-to-case basis from "non-individualized" designs (variable seg insets and error from using a non-atoric design in higher astigmats).

Summary of progressive wrap challenges:
I. Optical challenges (that I'm not an authority on)
A.) Induced aberration (of what kind, I never know) by going off corrected curve
B.) Lens tilt power changes and prism changes
C.) Confounding "non-individualized errors", when they exist
D.) Tilt-induced narrowing of corridor and potential loss of binocularity

II. Mechanical challenges (that I'm especially not an authority on)
A.) Blank size and cut out
B.) Excessive edge thickness and possible need for lenticulation
C.) Beveling and lens glazing issues


Any improvements to that summary?

[HarryChiling]

Summary of progressive wrap challenges:
I. Optical challenges (that I'm not an authority on)
A.) Induced aberration (of what kind, I never know) by going off corrected curve
B.) Lens tilt power changes and prism changes
C.) Confounding "non-individualized errors", when they exist
D.) Tilt-induced narrowing of corridor and potential loss of binocularity

II. Mechanical challenges (that I'm especially not an authority on)
A.) Blank size and cut out
B.) Excessive edge thickness and possible need for lenticulation
C.) Beveling and lens glazing issues

Great summary drk, that about covers it. Of course we are leaving the refraction out of this so we start from the choice of eyewear with a prescription and it's up to the optician to choose an option. I don't particularly like doing progressive wraps, it's too much in my opinion to throw inthe mix. I know many here say the can d it, but the remakes make it not worth while and the outcoem is usually accetable not great, but when we do it here are some considerations that will help overcome soe of the issues in your summary:

Optical Challenges

A.)Induced Aberrations - going off corrected curve measn that the power off the axis is going to quickly change in an unpleaseing manner for the patient, Darryl's program or Mo Jalies program from his book will allow you to see how far off axis one needs to go to see significant changes in astigmatism and power. This should be corrected, however also keep in mind that designs are usually optimized for a set degree of ocular rotation and all the wraps I fit have very short vertex distances, this decrese in vertex distance changes the measure off the axis one needs to go to acheive the same degree of ocular rotation as one would need in a flat front frame, this works in our favor and gives us some leeway in off axis power so it's not all bad. The previously mentioned options such as EOS and Attitude are great in the fact that they have differing degree's of asphericity to compensate for the amount of power change that will occur so now our best form is corrected.

B.)Lens Tilt Power changes and Prism Changes - Thes formulas can be found in both a paper from Dr. Keating and from Dr. Blendowski that further refines Keatings formula and introduces prism compensation. Thes formulas are bassically taking into account that the optical axis changes with the tilt of the lens, in essence they are taking the Rx as written and placing it on a tilted (x_tilt,y_tilt,z_tilt) coordinate system and then comparing and coming up with formulas to find out what this lens woud be if it were ont he coordinate system that the doctor refracts on (x,y,z). The formulas are only accurate to 30^o of tilt so they are not perfect in any way, actual ray tracings using software would come up with way more accurate results but fro our purposes these average formulas are sufficient, the prism compenation that gets introduced is due to the front surface and the angle of incidence, by tilting the lens we change the angl of incidence of light entering the lens so this compensated for this change. Lens tilt and frame tilt this is a common issue that has been brought up lately and computations from frame tilt to lens tilt are so simple they are often done by me before usign a program, which is why it has not been incorporated into my program. Their is an old rule that we use to move the OC 1mm down for every 2^o of tilt, reverse this rule so that you subtract or add, dependeing on the direction of decentration; 2^o of tilt from the frame tilt, this can be done for both the horizontal meridian and the vertical meridian before compenstion this difference now becoes your lens tilt that should be compensated through further calculations. This is not a very difficult step. In a program you will see a more accurate version that can take the vertex into consideration when calculating the lens tilt this is because the rule of 2 to 1 with lens tilt is only an average hat is meant to be easy to remember, in previosu post I have outlined the exact formulas for the lens tilt, happy hunting if your interested or just lokup how the 2 to 1 tilt rule was derived.

C.)Confounding Non-Individualized change - This is an interestign topic, the base curves available from manufacturers were not chosen arbitrarily. The base curves chosen by various manufacturers are done so that they can fit a wide range of Rx's on a set number of curves by introduceing a degree of aberration that is deemed acceptable. I find this interesting because at a point in time amount of aberration present in todays lenses would nto have been acceptable, but times have changed and so has technology, keep in mind that the introduction of these errors is a way of keeping costs down for the manufacturers and would ultimately be passed on to the dispenser and the genral public or at least that was the cry as our standards were slowly degenerated from what they were to what they are, now we are hearing the opposite that the once acceptable amount of aberration is no longer acceptable, this to me is a slap in the face, but they are right the amount of aberration present is no longer acceptable, but when it as my bills never went down and now with this new technolgoy they are tellign m my bills are going up? No one else is thinkign WTF? The marketing about accuracy basically says lets take the lenses back to what they were in the 60's which is fine by me, but they were the ones that told us we didn't need that level of accuracy in the first place. So now it coes down to this, how do you know when the lens is going to wreak havoc on your patients Rx? Well if the lens has a spherical upper portion you could still use best form to and if your power falls on that curve then you are good to go, if your power falls between two curves then you are in the area that needs to have correction (if you think that the aberrations that were acceptabel are no longer acceptable). If the lens has two different powers that vary greatly (high astigmats) then even if one meridian is on the corrected curve the other meridian 90 away will need something different (this is also one of the reaon why progressive lenses have a range of -2.00 astigmatism, doesn't mean that the curve to create higher powers cannot be surfaced int the blank it just means that the amount of aberrations goes outside of the manufacturers comfort zone of provideing adequate vision). Free Form is a great option to help eliminate these aberration however thes aberrations will not be present in every prescription and this is where I feel some manufacturers are being deceptive, if the patients Rx happens to fall on the correct base curve that's available in a varilux comfort, they will more than likely not see a significant improvement if they were to use the varilux comfort 360. The easy answer here, use FF technology on what we knwo defiantely needs correcting high degrees of differign power (high astigmats).

D.)Tilt Induced narrowing of corridor and loss of binocularity - If you tilt the lens yes it will narrow the corridor, FF can and will correct this by bringing the corridor to the back surface, couple this with the prism or cutting into the lens at an angle and this can be corrected this way, but again this will only present a real problem on higher add progressives lenses as with the lower adds the amount of narrowing can be compared to a hgiher add without tilt. Thisis an area that needs to be quantified better IMO. As for binocularity if the lens gets tilted so too does the inset, this coul wreack havoc on binocular vision, I haven't looked at that and matter of fact have only really considered that now as you bring it up, I do know that if you were to superimpose the clear right lens area with a clear left lens reading area you will more than likely be dissapointed as this tilt would probably leave a small useable are to read through, again I think in lower add and hard designs with larger areas this can be acceptable but I would need more data to confirm that.

Mechanical Challenges

A.)Blank Size and Cut Out - In single vision sperical lenses it's fairly simple decenter when blockig or surfaceing and you get more room for cut out in progressives lenses it's a whole different story, you can't decenter a progressive cause th corridor ont he fron is set, this is similar for an aspheric lens decentering is not an option so lenses such as the Younger wrap lens with a decentered design give mroe room for larger lenses. This is a great idea because often the wraps are large and require large blank sizes to make work. FF also has advantages her in that the progressive is designed ontot he back surface so the lens can be decentered.

B.)Excessive Edge Thickness and possible need for lenticulation - This is the fun stuff, this can be done both on FF and on traditional generators and has been done. Lenticulation is a great tool to reduce the thickness and weight of the lenses, this is a simple process once understood, on traditional equipment their will be a line present were the optic zone and the peripheral carrier meet, but coupled with a morrior coating this line vanishes from the front and with a good AR all but vanishes from the back. Thsi carrier curve can be used to eliminate thickness at the temporal edge and if decentered or prosm adjusted can eliminate the thickness on both the nasal and temporal edge of the lens. This is an area of wrpas taht I have been focusing my attention on as this is where we can currently improve. To date no one, NO ONE has been doing FF lenticulation on wraps that I am aware of, but this will be anice option that when applied will give a seamless look to the lens.

C.)Beveling and Lens Glazing Issues - This is where some labs shine over tohers, the use of MEI edgers to tilt the application of the bevel is fantastic for wrap lenses as this is often where issues with lens retention pop up or out I should say. Cut on traditional machines wrap lenses will sit intheir bevel at an angle coule that with a zyl frame the back of the bevel will exert force on the lens puching it forward or bowing it for problems with lens retention. Many here have probably seen the lens that wants to pop out of the eyewire at the top. This could be corrected with a machine such as the MEI which allows for the tilt of the bevel, it will also be corrected by use of lenticulation as the lens will be thinned down so that it seats corractly in the bevel, it coud also be taken to the hand stone to corrct the lens with a slight roll of the lens, also and this is not recommended for the light of heart on zyl frame the back of the frame can be modified with file, buffing and acetone polish to get rid of the back lip of the frame creatign this force. Ultimately a combination of the previously mentioned techniques will provide a suitabl outcome.

I am currently workign on a paper that will outline a premium lens that can be traditionally surfaced that will fit the wrap solution, I use them in my office and my patients love them. When I'm done I will add all the functionality to my wrap program so that everyone can use them.

[Laurie]

Hi Harry...

You are correct...it is not just spherical aberration and marginal astigmatism, it is off center errors, and others. Thanks for briging that up.

The Attitude design also deals with those errors, I did not mention them specifically.

My point: you shouldn't have to do additional compensation when the design considers the variables and counter-acts them in the mold itself.

Instead of compensating, I would simply start with a design optimized for wrap, like the Attitude (available in SV and PAL).

: )

Laurie

: )

Laurie

[drk]

Stating the problem is one thing, but providing solutions is another. Nice commentary.

I have forgotten to add the most daunting optical challenge that is the original point of the thread: Need for variable lens tilt power compensation for a variable power lens!

I do think there would be a mathematical solution to that problem that could be incorporated in digital software, someday.

[HarryChiling]

Stating the problem is one thing, but providing solutions is another. Nice commentary.

I have forgotten to add the most daunting optical challenge that is the original point of the thread: Need for variable lens tilt power compensation for a variable power lens!

I do think there would be a mathematical solution to that problem that could be incorporated in digital software, someday.

Your right, and I don't know thatanyone has given any attention to the difference in compensation required for both the distance and near. I don't think it would be as simple as an add with astigmatism incorporated into the bottom portion of the lens as it will vary in axis. I would think that the FF option would be the only real solution to this, although I don't think anyones doing anything like this yet. I wonder if the future holds compensation for everything or if we're just being picky?

[AWTECH]

Stating the problem is one thing, but providing solutions is another. Nice commentary.

I have forgotten to add the most daunting optical challenge that is the original point of the thread: Need for variable lens tilt power compensation for a variable power lens!

I do think there would be a mathematical solution to that problem that could be incorporated in digital software, someday.

drk:

Someday is today for ICE-TECH. We use correct optical solutions that take into account all of the significant issues you have raised. Our results tell that this works. We have an exceptional adaptation rate, 99%+.

[drk]

Allen, this is as good a time as any to give us more information...

1. Obviously, your nice website shows that you provide your own line of plano sunwear...and I don't doubt that you can Rx those, but the retail optical would need to stock them, right?

2. Secondly, I assume that you can take any optical-supplied frame and make the lenses.

3. Thirdly, is a price sheet available upon request?

4. (Don't shoot the messenger) How do you deal with vision plan patients? I would assume that you are not a vision plan lab...we submit as "special lenses" like MJ lab, Oakley lab, etc.

[HarryChiling]

drk:

Someday is today for ICE-TECH. We use correct optical solutions that take into account all of the significant issues you have raised. Our results tell that this works. We have an exceptional adaptation rate, 99%+.

I was disappointed that your lab does not make progressives with blended peripheral curves.

[AWTECH]

Allen, this is as good a time as any to give us more information...

1. Obviously, your nice website shows that you provide your own line of plano sunwear...and I don't doubt that you can Rx those, but the retail optical would need to stock them, right?

Yes if you want to carry our brand. (Not required at this time)

2. Secondly, I assume that you can take any optical-supplied frame and make the lenses.

Correct

3. Thirdly, is a price sheet available upon request?

YES

4. (Don't shoot the messenger) How do you deal with vision plan patients? I would assume that you are not a vision plan lab...we submit as "special lenses" like MJ lab, Oakley lab, etc.

We are not a vision plan lab, so if you have a good solution for these patients then you have a way to deal with these patients.