Why higher adds produce more "swim"...

[Uncle Fester]

From 2005- A Dr. Sheedy article on PAL's and Minkowitz's Theorem I find interesting and not found with a search of the OB.

Correct me if I'm wrong- but isn't this broadly speaking why Position of Wear compensated lenses are more often a better lens?

Can a guru chime in with a clarification of the last sentence from the website article? Is further reducing, not just redistributing, unwanted astigmatism the final frontier of progressives? Or just theory?


https://www.ncbi.nlm.nih.gov/pubmed/16276325

[Uncle Fester]

Here's a picture of what this is talking about from Darryl Meister's Progressive Optics tutorial---

[Chris Ryser]

Here's a picture of what this is talking about from Darryl Meister's Progressive Optics tutorial---

Very simple...................................

The higher the add, the narrower the intermediate and smaller the reading section, and the larger the distorted area, on whatever progressive and whatever brand or design.

Anybody in an older age group should think hard, to continue wearing progressive lenses, when they can have a ST lens with a 5 times larger reading section.

[Kwill212]

Just keep beating on that dead horse Chris. You will convince somebody, someday, maybe...but I doubt it. By this logic we should also abandon the FT28/7x28s and fit every single multifocal wearer in executive trifocals rights?

[Chris Ryser]

Just keep beating on that dead horse Chris. You will convince somebody, someday, maybe...but I doubt it.

That dead horse has been alive since 1955 and is still alive. On the drawings of the plus 3.00 addition lens above (Darryl Meister) there is just about 50% of unusable distortion with a very narrow progressive part and the clean crisp reading area is terribly small.

Taking into account that the old people, who already have problems adapting to the getting older, have to move their head around, to see and focus on some small print instead of having a crisp view of about a 30 centimeters wide.

[Kujiradesu]

That dead horse has been alive since 1955 and is still alive. On the drawings of the plus 3.00 addition lens above (Darryl Meister) there is just about 50% of unusable distortion with a very narrow progressive part and the clean crisp reading area is terribly small.

Taking into account that the old people, who already have problems adapting to the getting older, have to move their head around, to see and focus on some small print instead of having a crisp view of about a 30 centimeters wide.

I agree. If you have a +3.00 add in a PAL there should at least be a discussion about moving to a FT28 or FT35. Someone who's retired generally only needs two zones. 7x28 if you need an intermediate for something. Life's too short to suffer with such a small reading area.

[Chris Ryser]

Just keep beating on that dead horse Chris. You will convince somebody, someday, maybe...but I doubt it. By this logic we should also abandon the FT28/7x28s and fit every single multifocal wearer in executive trifocals rights?

That dead horse is still so much alive ..............................

All, this mumbo jumbo to sell progressives that have a minimal fraction of more clear reading area, and a creates larger distortive area that comes with it, is all to make a more expensive sale for the optical retailer.

When are opticians going to admit that the times of hokus pokus high priced glasses with a 50 percent distortion on each lens should be a thing of the past for elderly people.

[Uncle Fester]

And for deep divers the tour de force article...

http://64.50.176.246/cecourse.php?ur...essive_lenses/

[Kujiradesu]

And for deep divers the tour de force article...

http://64.50.176.246/cecourse.php?ur...essive_lenses/

Thanks for this. I found the example with the executive N-focal lens especially informative, its an excellent way to grok the whole concept and geometry of a PAL. (^_^ )

[DanLiv]

Thanks for this. I found the example with the executive N-focal lens especially informative, its an excellent way to grok the whole concept and geometry of a PAL. (^_^ )

YES agreed. I consider Darryl Meister's article necessary reading for every optician.

[DanLiv]

Correct me if I'm wrong- but isn't this broadly speaking why Position of Wear compensated lenses are more often a better lens?

I believe most of the advancements in progressive optics are in the digital design and surfacing alone. This is where designers can manipulate the distortions to best meet the particular wearers needs; like giving more or less priority to distance, or intermediate, or near; varying near vision inset and prism by Rx and PDs; varying corridor length by seg height. This is all the stuff that plays around with Minkwitz.

Position of wear is the next higher order customization, but if I understand it correctly POW values will not alter the lens design, they will simply refine the Rx as they would in a SV lens (and possible induce a little compensating prism for wrap).

IMO 80% of the value is in upgrading to good digital progressives, the last 20% is in the POW. I fit digital progressives about 50/50 with and without POW, because for moderate Rxs I think almost all the benefit to be gained is satisfied by the digital design alone. Plus, to be cynical, there is so much distortion in even the best progressives that I think the benefits of "last mile" fine tuning of POW is pretty much obliterated for all but the highest Rxs or bizarre frame fits.

Can a guru chime in with a clarification of the last sentence. Is further reducing, not just redistributing, unwanted astigmatism the final frontier of progressives? Or just theory?

"In the end, it appears the unwanted astigmatism associated with a given power change along a given distance can be redistributed but probably not reduced."

That one? If there is a way to reduce unwanted astigmatism, no one's found it yet even a decade later. There are advancements that reduce other distortion, like Camber reduces distortion from base curve problems, higher ABBE materials reduce chromatic aberration, but those lens problems are not the unwanted astigmatism quantified by Minkwitz, those are extra problems we have in addition to it. I think it's a physics limitation of our progressive lens paradigm, and we won't be getting away from it until someone images an entirely new multifocal lens design concept.

[Robert Martellaro]

Position of wear is the next higher order customization, but if I understand it correctly POW values will not alter the lens design, they will simply refine the Rx as they would in a SV lens (and possible induce a little compensating prism for wrap).

Dan,

Some lens manufacturers have software that is capable of significantly modifying the PAL design. It's mostly centered around retaining the intended design regardless of Rx (see image below) including position of wear, for example, a shorter corridor for smaller values of wearer's vertex distance.

Plus, to be cynical, there is so much distortion in even the best progressives that I think the benefits of "last mile" fine tuning of POW is pretty much obliterated for all but the highest Rxs or bizarre frame fits.

It can be a tough call sometimes. We need to be skeptical, until we can obtain convincing data and experience fitting and wearing different designs, ensuring that our recommendations are in our client's best interest.

I think it's a physics limitation of our progressive lens paradigm, and we won't be getting away from it until someone images an entirely new multifocal lens design concept.

Probably electroactive eyeglasses, although med/science/pharma may come up with a way to delay or prevent presbyopia before that happens.

Best regards,

Robert Martellaro

[DanLiv]

Some lens manufacturers have software that is capable of significantly modifying the PAL design. It's mostly centered around retaining the intended design regardless of Rx (see image below) including position of wear, for example, a shorter corridor for smaller values of wearer's vertex distance.

Can you give me examples of who does? I understand the concept and that it should be possible, varying corridor based on vertex makes perfect sense, but I haven't read in any manufacturer literature that they exploit the technology to this extent. I'd love to know who's really using the tech to the fullest extent.

It can be a tough call sometimes. We need to be skeptical, until we can obtain convincing data and experience fitting and wearing different designs, ensuring that our recommendations are in our client's best interest.

I will always use POW compensation when I believe the Rx or POW warrants it, but in cases where neither of those are crazy I don't see how an Rx compensation of even 0.12D will overcome diopters of unwanted astigmatism. Perhaps a strict design which aim for as little distortion above the 180 as possible might get some advantage in distance, but in my experience even those designs don't actually seem to deliver on that claim. Softer designs, like Varilux, smear distortion all over the lens which makes them pretty easy to wear but makes it pretty unlikely the Rx compensation alone would have any discernible effect on the overall lens experience. I'm not yet a wearer so I'm just relying on my analysis of the internal logic of the system.

Thanks for the comments Robert!

[Robert Martellaro]

Can you give me examples of who does? I understand the concept and that it should be possible, varying corridor based on vertex makes perfect sense, but I haven't read in any manufacturer literature that they exploit the technology to this extent. I'd love to know who's really using the tech to the fullest extent.

Zeiss for sure.

https://www.zeiss.com/vision-care/en...hnologies.html

I will always use POW compensation when I believe the Rx or POW warrants it, but in cases where neither of those are crazy I don't see how an Rx compensation of even 0.12D will overcome diopters of unwanted astigmatism. Perhaps a strict design which aim for as little distortion above the 180 as possible might get some advantage in distance, but in my experience even those designs don't actually seem to deliver on that claim. Softer designs, like Varilux, smear distortion all over the lens which makes them pretty easy to wear but makes it pretty unlikely the Rx compensation alone would have any discernible effect on the overall lens experience. I'm not yet a wearer so I'm just relying on my analysis of the internal logic of the system.

The unwanted/surface astigmatism is carefully managed to minimize disruption of the visual image. In this regard, PAL designers make assumptions about the POW, the distance to the center of rotation to the eye, etc., regardless it there's distance or near compensation, hoping that the intended design, sometimes clinically tested, reaches the end user.

OTOH, if the intended design is a bad one, it's still bad after fussing with the additional measurements. What I do is to single blind test the lenses in my Rx, sometimes with a test subject, to determine who has the best performing designs, knowing that the personalized and customized designs will be the best at keeping that level of performance over a wide range of Rxs and fitting values.

Thanks for the comments Robert!

I hope you find my thoughts useful to you.

Robert Martellaro

[Quince]

Zeiss for sure.

https://www.zeiss.com/vision-care/en...hnologies.html

The unwanted/surface astigmatism is carefully managed to minimize disruption of the visual image. In this regard, PAL designers make assumptions about the POW, the distance to the center of rotation to the eye, etc., regardless it there's distance or near compensation, hoping that the intended design, sometimes clinically tested, reaches the end user.

I hope you find my thoughts useful to you.

Robert Martellaro

What about Shamir Auto III? From what our rep explained- the "Eyepoint Technology" is set-up to work off of the 'keyhole' design (ADD power on the back) so that they can focus on how to adapt the Rx so that different Rxs have the same field of vision.



Robert, I personally always enjoys your view on things!

[Uncle Fester]

Thanks Dan for your reply! Getting my head around the optics of the myriad of progressive choices and their level of sophistication too often boggles this Luddites mind. Oh for the day when the Grohlman fitting device and an AO or Sola choice was about it for a progressive lens!!!

While I confess to being easily confused by much of this- I also created the thread to help newbies, lurkers, and the consumer appreciate what a progressive lens is.

I'd welcome some more "optical gold" from the likes of Robert Martellaro. Especially when it's putting into layman's terms what we are dealing with.

Harry C had a great post using a sandbox analogy. I think I'll dig for that...

Found it- From Harry Chiling in early 2009:

Think of a designing of a PAL like a sandbox, we know we want a 2 story castle in the top of the sandbox and our add of lets say +2.00 tells us that the castle on the south side of our sandbox must be 4 storys high. Now we have a limited amount of sand so we can't exactly create these castles without taking a bit of sand from other areas of the sandbox. So one company decides heye I'll build my castle with maots around them and the sand I take outta the moats will go towards building the castle, another company might say I'll skim the entire surface of the sandbox and use that skimmed sand to make my castles. One might say my castles better because it's got moats around them the other company says my castles are built on level foundations. The different designs are determined by what the designer thinks a patient might like. Even in Single Vision lenses you could have a point focal lens, a percival lens, or a minimal tangetial error lens, or reduce the RMS error. In progressi9ve lens design they are trading one charactersistic to gain in another and certain companies will employ better processes to finalize their design and include both objective (ray tracing) and subjective (user trials) to see what people really think of the lenses and then tweak their designs based on the further research.

The difference in design is going to be the biggest difference in the lens regardless of the processing techniques employed, even the best traditionally molded lens is going to give you similar optics to a FF lens on a select nnumber of Rx's, and some crappy FF desings are going to be no better or worst than a good traditionally molded design. The one big advantage to FF PAL's is that the deformed conicoidal surface is moved to the back of the lens alowing for a larger angle of view through a smaller surface of the lens this correlate to wider optics through the umbilic and other parts of the lens. Even the crappy designs like the SNL mentioned above will see an increase in clarity with FF just by moving the PAL surface to the back, also even a traditionally molded PAL will see improvments from non-optimal base curves in the series being cleaned up with atoric surfaces on the back surface.

Thanks again.

[golfnut]

Very simple...................................

The higher the add, the narrower the intermediate and smaller the reading section, and the larger the distorted area, on whatever progressive and whatever brand or design.

Anybody in an older age group should think hard, to continue wearing progressive lenses, when they can have a ST lens with a 5 times larger reading section.

And no intermediate..
🤔

[Chris Ryser]

And no intermediate..
樂

Not needed ...........................

...........at old age you use two pairs of glasses one for daily all around glasses, and another pair on your desk in front of the computer.

When you get older everything becomes more complicated even little daily things, so making it simpler is helping getting these complications simplified.

[Tallboy]

Not needed ...........................

...........at old age you use two pairs of glasses one for daily all around glasses, and another pair on your desk in front of the computer.

When you get older everything becomes more complicated even little daily things, so making it simpler is helping getting these complications simplified.

I've had ophthalmologists from Johns Hopkins tell me to take their patients out of the flat tops I put them in and put them into a +3.50 Auto III, and the patients were very happy with their vision, because of the variable depth of field in the reading. Obviously it wasn't my first choice, because I like you know what "happens" in a +3.50 add progressive, however the proof is in the pudding with the people who feel progressives solve their presbyopia better - I've seen it.

[Chris Ryser]

I've had ophthalmologists from Johns Hopkins tell me to take their patients out of the flat topsI put them in and put them into a +3.50 Auto III, and the patients were very happy with their vision, because of the variable depth of field in the reading. Obviously it wasn't my first choice, because I like you know what "happens" in a +3.50 add progressive, however the proof is in the pudding with the people who feel progressives solve their presbyopia better - I've seen it.

Anybody wearing a +3.50 addition is as old as they can get, and are probably not even aware that their progressive lenses have about 60% of pure distortion to the sides.

Those people have probably been wearing progressives for the last 40 years and know nothing than that.

Anybody promoting such lenses is doing so for their own benefit.

[Robert Martellaro]

I've had ophthalmologists from Johns Hopkins tell me to take their patients out of the flat tops I put them in and put them into a +3.50 Auto III, and the patients were very happy with their vision, because of the variable depth of field in the reading.

It sounds like the Shamir rep worked over the MD pretty good. Your mission, if you choose to accept it, is to reeducate the prescriber. As always, should you be harmed in any way, I will disavow any knowledge of your actions. This post will self-delete in five/ten seconds. Good luck, Tallboy.

[lensmanmd]

It sounds like the Shamir rep worked over the MD pretty good. Your mission, if you choose to accept it, is to reeducate the prescriber. As always, should you be harmed in any way, I will disavow any knowledge of your actions. This post will self-delete in five/ten seconds. Good luck, Tallboy.

For veteran PAL wearers, i don't think this is much of an issue. They have worn PALs for decades and understand the limitations. Compensated FF designs do make it more comfortable to wear, regardless of add. That said, I would never take someone out of a 7/28 and put them into a PAL over +2.50 add.

We provide Zeiss FF up to +3.50 and IOT Alpha 45 up to +4.00 add without any issues. Our patients expect the swim, but the cosmetics outweigh the limitations, *as long as they are current PAL wearers. Notice the disclaimer?

[golfnut]

Not needed ...........................

...........at old age you use two pairs of glasses one for daily all around glasses, and another pair on your desk in front of the computer.

When you get older everything becomes more complicated even little daily things, so making it simpler is helping getting these complications simplified.

That is a very close minded view on what is best for older people...its called convenience... the use of one pr for reading and one for distances actually MORE difficult than pal's...certainlyif you are going to sit and read a novel or work on the cpu for extended hours then a dedicated pair would be best...i tell all my customers that pals are your swiss army knife...good at most things
But not great for any one thing. Ive worn flat tops and they are terrible for walking around in...you are just consumed with the fact that you think pals just don't work from what ive read...i have tremendous success with them and when (on rare occasions) people can't handle pals then i suggest the distance only/reading only option.

[Kwill212]

Every older person should use a flip phone with oversized buttons that only can only make phone calls because they don't need any other features. /s

[Happylady]

I really don't think it would go over very well if I told all my patients with more than a 2.00 add they needed to switch to a flat top out of progressives.

I have a 2.50 add and I love my progressives. I have zero issues with them. Just cause YOU don't like progressives Chris doesn't mean that millions of people are having problems and are unhappy with them.