"True" free form vs. "hybrid" free form

I have found bits and pieces here and there about the arguments against digitally surfaced molded progressives as "true" free form (Varilux, duh), but I want to explore the reasoning behind this stance. I understand that *if* you define free form as surfacing the entire lens design onto the backside of a spherical blank, then Varilux (and a few others') lenses don't qualify. However, "free form" seems in theses forums to be used interchangeably as a description of surfacing technique and a measure of quality. I have encountered numerous rebuttals of Essilor product as "not true free form", clearly implying they are inferior to "true" 100% backside free form designs.

One of the prime purported benefits of backside design is the "keyhole effect" and gain in near vision width of field. Maybe I'm a sucker for E propaganda, but they have both mathematically and clinically dispelled the myth of that benefit. What remains is the potential "freedom" of designing the entire lens freely on the backside, but that must still take into account the existing front curve. Since we're just designing with mathematical models, why should an existing progressive front curve provide excessive technical challenges over a merely spherical curve? The backside can compensate for anything on the front, and in E's theory existing frontside curves can compliment and enhance backside design for a greater combined effect than 100% backside alone.

I am as open to debate as anyone, but I have not encountered compelling arguments for 100% backside vs. hybrid in free form lenses. I know there are plenty of 100% backside proponents here; what's the definitive opticians' argument in favor of the backside vs. hybrid?

Good question - - Dan, a quick one for you. Do you currently wear a progressive? This isn't a question that is meant to be a "slam," but if you wear one, what is your opinion??

If not, then we can all talk about what the various manufacturers claim.

I have plenty of opinions, but wanted to get your wearing experience!

Cheers,

jim

You can digitally grind a poorly designed progressive backside or hybrid and, either way you have a poorly designed lens. That said, those with far more math skills than I have- said a backside lens will have wider field of view.

Here's my take. We can all talk about lens designs, etc., but at the end of the day, it is the wearer that has the final word. I wear progressives. Even though I look half my age!! LOL.

My experience: PHysio 360 (original) About as good as my conventional GT2. No better, but it has frontside progressive.

AOEasy HD - Not too shabby. Good Optics. Freeform from a SV Blank
ProFit XXXX - pretty good, nice optics, however ordered it, and the made it in China. good price, but I can get similar pricing here.
GT23D - Better, wider field of vision. Freeform from a SV blank
Kodak Unique. Really nice. Freeform from a SV Blank. Like it as much as my GT23D


Zeiss Individual - Hands down kicks all the above's collective butts. What induced astigmatism? Of course, freeform from a SV blank.

I think you can all see where I'm going here. As a wearer of these lenses, I honestly feel that my experience is that if the lens is ground/CNC'd (if that's a term) from a SV blank, you will get a better result. Why even waste time with older designs. There has been too much confusion in the marketplace from the manufacturers, specifically the ones who didn't start with a SV blank. Terms like "digital mold" "optimized" and the like don't do anything to help us. The only way to go is SV blank, IMHO. The word "freeform" kind of got *******ized over the past few years.

All that being said, we just fitted our first two "private label" freeform lenses from a lab in the Chicago area. Of course, they are SV blanks. Hey, if they have the machine, why not, right?? I will be personally testing them out in a week or so. The price is definitely right.

Cheers!

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Originally Posted by bigeyejim

Good question - - Dan, a quick one for you. Do you currently wear a progressive? This isn't a question that is meant to be a "slam," but if you wear one, what is your opinion??

If not, then we can all talk about what the various manufacturers claim.

I have plenty of opinions, but wanted to get your wearing experience!

Cheers,

jim

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I don't wear a progressive, but I have plenty of experience with what my customers like and don't like.

I'm not asking about wearer experience here, I'm questioning theories of lens design. If 100% backside is technically superior, there ought to be design arguments that support that. However, I have heard lots of them from reps, but none that withstand critique (IMO). That could very well be because brand reps don't know more about their product than technically minded and experienced opticians, and may just be supplying poor arguments. I'm hoping technically oriented professionals here will have more decisive arguments, especially since there seems to be a common consensus among the more vocal here that 100% backside is stright up better.

I'm with bigeyejim, true free-form is design+RX on a SV blank.

Essilor certainly has muddied the waters with their techno. mumbo-jumbo.

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Originally Posted by scriptfiller

I'm with bigeyejim, true free-form is design+RX on a SV blank.

Essilor certainly has muddied the waters with their techno. mumbo-jumbo.

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Originally Posted by DanLiv

Maybe I'm a sucker for E propaganda, but they have both mathematically and clinically dispelled the myth of that benefit. What remains is the potential "freedom" of designing the entire lens freely on the backside, but that must still take into account the existing front curve. Since we're just designing with mathematical models, why should an existing progressive front curve provide excessive technical challenges over a merely spherical curve? The backside can compensate for anything on the front, and in E's theory existing frontside curves can compliment and enhance backside design for a greater combined effect than 100% backside alone.

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My humble opinion. "E" sell lens blanks, and if we all go in the full backside designs, no more lens blanks, only click fees for the designs. As designs become more available, and useage go's up, other companieswill be content with click fees, as they will be getting more of them, not E. I swithed to a "generic" digital, full backside design months ago, and no real problems from previous varilux wearers.

Scriptfiller nailed it.

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Originally Posted by DanLiv

I don't wear a progressive, but I have plenty of experience with what my customers like and don't like.

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Someday, you will join the ranks!!!! LOL!:smile: But you do wear a freeform SV, right????????

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Originally Posted by DanLiv

I'm not asking about wearer experience here, I'm questioning theories of lens design. If 100% backside is technically superior, there ought to be design arguments that support that. However, I have heard lots of them from reps, but none that withstand critique (IMO). That could very well be because brand reps don't know more about their product than technically minded and experienced opticians, and may just be supplying poor arguments. I'm hoping technically oriented professionals here will have more decisive arguments, especially since there seems to be a common consensus among the more vocal here that 100% backside is stright up better.

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If Darryl Meister (Zeiss) would only chime in here. There is another gentleman from Essilor whose name escapes me as well on the forum. Yrage (sp) can argue technical points until your eyes bleed. They are great sources. As is Barry.

That being said, we can only provide wearing experience. If cost is a factor, then if I can get GT2 3D at the same cost as conventional surfaced GT2, then why bother with conventional. The full backside GT2 3D is that much better, and Zeiss doesn't even have a "hybrid" that I know of.

But I think I finally saw your real concern, and that is that the reps can't fully explain it from a technical standpoint. The nitty gritty. There are many on here who can, most notably the three I mentioned above.

Good luck!

jim

Pete Hanlin from Essilor could probably help too, although I think Darryl Meister is THE expert here.

I wear progressives, and my rx calls for so much total prism (vertical and horizontal) that the lens blank is too thick to be made with the "hockey puck, true freeform designs" even though I have tried my share of the modified types. It's been my experience that my eyes see no difference between modified freeforms and old way to surface progressives, but they see a huge difference in designs of progressives.
As far as the real reason I am writing concerning this subject, however, has nothing to do with the differences in true freeforms versus modified freeforms. The thing that got me to write in this thread was your statement "Maybe I'm a sucker for E propaganda, but they have both mathematically and clinically dispelled the myth of that benefit." My experience that is germane to this sentnce is back in the year 2000 Essilor invited eyecare professionals throughout the USA to Tampa for 3 days. Their theme was :Presybyiopia 2000" if I remember it correctly. I happened to be one of those that attended this lavish 3 day event. It was actually for the intoruction of their new lens design called Panamic. We sat through 2 days of listening to French scientist, in their hard to understand brogue, talk about how they had done a double blind study in France and at the University of Indiana Optometry school, if my remberances are correct. In any event they went on to espouse the greatness of their new lens, where it beat the comfort in every quadrant in their double blind study. They even made up a pair of eyeglasses with Panamics, I remember at the time I thought they were worse than the comfort for my eyes. I think we all know how the Panamic turned out in real life situations. So much for E's scientific clinical trials, wouldn't you say?

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Originally Posted by THE MEB

They even made up a pair of eyeglasses with Panamics, I remember at the time I thought they were worse than the comfort for my eyes. I think we all know how the Panamic turned out in real life situations. So much for E's scientific clinical trials, wouldn't you say?

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"O.25 seconds better peripheral recognition"

(Quote from the original Panamic benefit literature)

B

Here is another way of looking at the issue.

Why do we call Progressives Multifocals "Progressives"? Its because they "progress" smoothly from distance to reading. Its the most defining aspect of the lens. This "progression" then by definition is the most important curve after the corrective surfaces of the lens. In hybrid lenses this progression is cast on the front exactly the same as it is for a regular grinder.

This curve (on a standard front-add cast grinder) goes from a convex flat surface and then "progresses" to a steep concave surface and then back to a steep convex surface at the add. All along the way the non-symetrical curves create what they call now "unwanted astigmatism" but I prefer the old term, junk. Most of the junk created by progressive lenses is created by this curve. If I have a +2.50 add, with a 12mm corridor, this lens is changing a high amount of power in only 6 mm, and then changing it back again to something else.

In an old front add lens this "progressive" curve is cast on the front, and is not optomized for each RX or patient. Its a catch all middle of the road design that has inherant cast flaws.

If I digitally process this curve on the back, with a free-form design, I can optomize this curve for each RX, and each patient. In addition the curve path changes, its more symetrical reducing unwanted astigmatism.

In a grinder its: Flat Convex, Steep Concave, Steeper Convex, Steep Concave, Flat Convex. Like a fun-house mirror.
In a Backside Free-form its: Steep Concave, Moderate Concave, Flat Concave, Moderate Concave, Steep Concave. Smoother.

So in a backside free-form with the most important curves, I can improve surface accuracy, customize RX, perfect shape and location, and reduce the "wave".

In a front side grinder or "hybrid" lens, I cannot.

sharpstick777, thank you. That is a case I have not heard before and makes good sense.