What Lens are truly Freeform?

[hyperoptic]

Kurt, could you please clarify what you define as "compensated"? There is some word in the market that only Free-form lenses that offer "customized" vertex, face form and panto calculations are truly better. However, I have seen usage studies from both manufacturers and universities where only about 11% of patients benefit from those advanced compensations (Essilors says 9%).

All true-free form are compenstated with at atoric, base curve, ect, and most use standard averages of tilt and vertex. So when you say "compenstated" are refering to the standard ones, or the fully customized ones?

And if you mean that only the highly customized compensated lenses are better, do you have any usage studies your company has done (or at least read) to support that? Right now the ones I have seen do not.

By compensated I am referring to ether using an average value, or individual measurments to compensate for, at least in the case of IOT Digital Ray Path technology the oblique aberration experienced by a wearer, our non compensated designs do not take these values into consideration when calculating the back surface of a lens thus providing a digitally surfaced progressive that supplies prescribed power, not compensated power.

As far as the effect of compensation by percentage, to my knowledge there have been no published independent studies about the effects of compensation but I will ask our Designers and if they have a link Ill provide it here for your pleasure, however if we as optical people take an objective look at this technology I think we can all see that someone who is a -.25 sph will not see benefits from compensation the same way a person with a -8.00 -2.25 x142 with a +2.25 would in a standard ophthalmic frame. Wrap frames are a different story of course be cause the light incoming to the lens is farther from perpendicular to the eye.

I generally use a rule of 3's. If the sum distance power is greater that a +3.00 or -3.00 then patients will begin to see benefit from compensation and this sum power value decreases as the angles of the frame become more extreme.

Its also important to note that certain Rx's are not the best choice for digital lenses over conventional. example Rx:+4.00 with a +2.00 add, in a conventional lens we would choose a 6 base with a 2.00 add. That conventional blank front would be ~6.00 at the top and ~8.00 BC at the near portion with a ~2.00 curve on the back, now being done on a SV blank and surfaced digitally we have ~6.00 on the whole front surface meaning we have a ~2.00 rear curve at the top, and ~ 0.00 at the near. This has a negative effect on the visual acuity of the near area unless a steeper base curve is used (like an 8 base).

Sharpstick I hope this answered your question.

[sharpstick777]

Yes... There is some rhetoric out now that for a lens to be "truly" free-form it must include wearer measured and customized face-form, panto, and tilt. I am just trying to crush that rhetoric.

As well, your points on plus power I have noted in other forums but is seldom discussed, there are limits to FF advantage on higher plus powers.

By compensated I am referring to ether using an average value, or individual measurments to compensate for, at least in the case of IOT Digital Ray Path technology the oblique aberration experienced by a wearer, our non compensated designs do not take these values into consideration when calculating the back surface of a lens thus providing a digitally surfaced progressive that supplies prescribed power, not compensated power.

As far as the effect of compensation by percentage, to my knowledge there have been no published independent studies about the effects of compensation but I will ask our Designers and if they have a link Ill provide it here for your pleasure, however if we as optical people take an objective look at this technology I think we can all see that someone who is a -.25 sph will not see benefits from compensation the same way a person with a -8.00 -2.25 x142 with a +2.25 would in a standard ophthalmic frame. Wrap frames are a different story of course be cause the light incoming to the lens is farther from perpendicular to the eye.

I generally use a rule of 3's. If the sum distance power is greater that a +3.00 or -3.00 then patients will begin to see benefit from compensation and this sum power value decreases as the angles of the frame become more extreme.

Its also important to note that certain Rx's are not the best choice for digital lenses over conventional. example Rx:+4.00 with a +2.00 add, in a conventional lens we would choose a 6 base with a 2.00 add. That conventional blank front would be ~6.00 at the top and ~8.00 BC at the near portion with a ~2.00 curve on the back, now being done on a SV blank and surfaced digitally we have ~6.00 on the whole front surface meaning we have a ~2.00 rear curve at the top, and ~ 0.00 at the near. This has a negative effect on the visual acuity of the near area unless a steeper base curve is used (like an 8 base).

Sharpstick I hope this answered your question.

[sharpstick777]

I don't think they are 100% freeform. Just because freeform surfacing is used doesn't mean you get a freeform lens. You also need a lens blank and design. :)

Free-form is any progressive where any lens has curves modified in any area to improve VA over standard curve powers. Although Shamir trademarked the name, Zeiss first used it 1997 to explain the Zeiss Individual (which later became the "i", and back to the individual). At that time the only Free-form curve was customized atoric compensation for cyl power. Digital CNC lathe surfacing is now the standard way of producing FF but it has been made with thermo micro casting (2C Optics 1996, Warelite Currently) or a "router" type surfacing machine.

Both the Varilux Physio DRx and Enhanced Fit are back side only lenses with the entire RX processed digitally including distance and add. Essilor uses standard measurments for the DRx for axial length, pupil size, listings law, vertex, and face form, but those are calculated based on human averages. The Enhanced Fit included POW measurements including Face-form, vertex and panto that are specifically measured for each patient.

Whether they are good or not is another question, but they are without a doubt Free-form.

[GokhanSF]

Ok, I got your point. I think we have a different understanding of the term freeform.

Free-form is any progressive where any lens has curves modified in any area to improve VA over standard curve powers. Although Shamir trademarked the name, Zeiss first used it 1997 to explain the Zeiss Individual (which later became the "i", and back to the individual). At that time the only Free-form curve was customized atoric compensation for cyl power. Digital CNC lathe surfacing is now the standard way of producing FF but it has been made with thermo micro casting (2C Optics 1996, Warelite Currently) or a "router" type surfacing machine.

Both the Varilux Physio DRx and Enhanced Fit are back side only lenses with the entire RX processed digitally including distance and add. Essilor uses standard measurments for the DRx for axial length, pupil size, listings law, vertex, and face form, but those are calculated based on human averages. The Enhanced Fit included POW measurements including Face-form, vertex and panto that are specifically measured for each patient.

Whether they are good or not is another question, but they are without a doubt Free-form.

[Fezz]

As well, your points on plus power I have noted in other forums but is seldom discussed, there are limits to FF advantage on higher plus powers.

Why?

[hyperoptic]

Why?

Hi Fezz,

Basically its because to use digital designs on plus patients the base curve selection must be made using the highest plus power, cosmetically there would be a mutiny if some one who is a +4.00 +200 add was given an 8 or even 10 base lens to cope with the negative effects of the flatter near vision (this will cause a smaller "sweet spot" and reduce the magnification factor of the NV area of the progressive if a flatter curve is used)

[Fezz]

Thanks.

[hyperoptic]

Yes... There is some rhetoric out now that for a lens to be "truly" free-form it must include wearer measured and customized face-form, panto, and tilt. I am just trying to crush that rhetoric.

As well, your points on plus power I have noted in other forums but is seldom discussed, there are limits to FF advantage on higher plus powers.

Honestly I think the word Freeform is used by many lens designers and it is used without consistency, the best thing to do is ignore the buzz words and find out which lenses do what you want for your patients, we all have our own idea of what is best. I want to also say that if the designs are properly used in plus patients the results are stupendous (I am a plus 7.25 and my VA is vastly superior to my conventional lenses, the difference is I made them on a 8.50 base not a 7.)

[sharpstick777]

Why?

Another way, If we use Vogels Rule to determine optimal base curve, the base curve rate in Plus Powers rises fairly quickly. Free-form gives us tremendous ability to fix that (Free-form is still great for plus powers, but not to an infinite point) only to the point where the backside curve starts getting flat. With the add on the back, it gets flat faster than on the add on the front. We can't have a convex lens on the back-side even with Free-form. Free-form works great up to a +4.00 total power (spherical plus add), but after that the advantages decrease with each increase in plus power. Good, but just not as good.

We see the same thing in minus, the front can only get so flat but its usually so high of an RX that its rarer, and then we could go bi-concave if we wanted to.

[sharpstick777]

Honestly I think the word Freeform is used by many lens designers and it is used without consistency, the best thing to do is ignore the buzz words and find out which lenses do what you want for your patients, we all have our own idea of what is best. I want to also say that if the designs are properly used in plus patients the results are stupendous (I am a plus 7.25 and my VA is vastly superior to my conventional lenses, the difference is I made them on a 8.50 base not a 7.)

You will gain a lot of advantages with plus powers and FF, but if we could ideally move some of the add to the front, and steepen your backside curve a little, we would gain a little more VA in theory. The only lens that does this now is the Zeiss Individual (German version only) I believe.

The definition of Free-form has morphed since 1997 when Zeiss first used it to describe a modified and customized atoric cyl curve. Now with more lens choices we have the option of great to mediocre free-form. Its nice problem to have though.

[Fezz]

Thanks!

[hyperoptic]

Another way, If we use Vogels Rule to determine optimal base curve, the base curve rate in Plus Powers rises fairly quickly. Free-form gives us tremendous ability to fix that (Free-form is still great for plus powers, but not to an infinite point) only to the point where the backside curve starts getting flat. With the add on the back, it gets flat faster than on the add on the front. We can't have a convex lens on the back-side even with Free-form. Free-form works great up to a +4.00 total power (spherical plus add), but after that the advantages decrease with each increase in plus power. Good, but just not as good.

We see the same thing in minus, the front can only get so flat but its usually so high of an RX that its rarer, and then we could go bi-concave if we wanted to.

Speaking from personal experience I will stick with digital compensated lenses because if the proper Base curve is chosen it is certainly better than a conventional alternative, but the key is proper base curve selection which often times makes to much cosmetic compramise.

[AustinEyewear]

Check out this chart of digitally surfaced lenses. It describes the front and back surface of each to help give you an idea of what is truly freeform.

thelensguru.com/digitalChart.php

I was just looking at your chart yesterday, which is exactly what brought me to the Optiboard (and all over the net) in an attempt to get clarification and lo-and-behold, this thread, and your post! Is Essilor really producing a Free Form, Digitally Surfaced Backside Progressive?

Essilor doesn't have a true freeform yet, so consider Shamir AutoII, Hoya ID, Zeiss Individual, and Kodak Unique.

What is Essilor up to here? I'm unclear, are they true free forms?

http://dualoptix.com/varilux.html

http://www.luzerneoptical.com/pdf/va...-portfolio.pdf (good for seeing where Dualoptix is applied)

http://www.luzerneoptical.com/top-wh...e-2.html?sl=EN (video says digitally surfaced)

http://www.totallyoptical.com/Media/ScriptTabs/FreeForm_Chart_May2011.pdf

[Judy Canty]

Digitally surfaced and free form are NOT the same thing.

[AustinEyewear]

Digitally surfaced and free form are NOT the same thing.

Ah, but true free form lenses are digitally surfaced on a CNC machine! Do you happen know the answer to my question above?