Unexpected things learned with Free-form Progressives

[Barry Santini]

1. Yes, you can place the design on any time of material, index, tint or color that is available in SV form. But...BUT: For the same Rx, not every option will arrive on the expected base curve. Example:Poly progressive Transitions. Rx required a +5.25 Base curve, and and +5.25 was supplied (as "expected"). Companion pair was a CR-39 Polarized. These lenses, in CR 39 SV form, are available almost exclusively 2,4,6, etc. bases. The algorithym for this design specified again a +5.25 Base for these suns, but would not allow a choice of a +6.00 base, but would allow a +4.25 base. So a "marked" +4.25 SV brand was supplied, but it clocked a true curve of +3.87. So, now we have an instance where the lower indice was on the flatter base...not what one would expect.

2. Back-side, higher-plus/higher add progressives will put you where you may not realize you're going.
Example:
Rx:

+5.50 OU. +2.75 Add.

Client was wearing Physio (not 360) 1.67 Transitions. Base curve supplied by Essilor was +7.37.

Identical Rx made with 1.67 transitions in back-side free form: Base curve rec'd was +9.50 (!). (Remember that here you are also restricted to the base curves available in 1.67 Transitions) Why? With the progressive on the back, the base curve choice is determined by using the *total power* (w/add); i.e., +8.25 Diopters!
(Also remember that with conventional progressives, they achieve their add *steepening* on the front side, but only in the progressive area)

What a shock when I got those in. They were going into a rimless (yes, a Colorama). I specified a 0.5mmFE, and the drill points were just fine for the bushings. I did have to manipulate the bridge alittle, though.

Another day, another thing or two learned in the Wild West of free form.

Barry

[Jacqui]

Another day, another thing or two learned in the wild west of free form.

Barry

Yes, and we're going to learn more tidbits as time and lenses pass.

:cheers:

[Fezz]

Barry,

Thanks for blazing the *Free-Form Trail* for us! Keep on trucking, I am still fumbling along behind you.....but I am still trudging on!


:cheers::cheers::cheers::cheers::cheers::cheers:

[Barry Santini]

Update on the +5.50 w/ the 950 base:

FAIL!

(Non- adapt!) Goin' back to Physio +7.37 base curve

Barry

[HarryChiling]

Update on the +5.50 w/ the 950 base:

FAIL!

(Non- adapt!) Goin' back to Physio +7.37 base curve

Barry

That brings up a thought I had a while ago, I bet that if you look at the non-adapt rate of FF vs traditional it would be higher maybe even significantly higher. Follow me on this one you FF lovers, I think most people put their difficult to fit patients in FF products so it lowers the non-adapt rates on the traditionals and offsets them onto the FF products. I would be curious to see a blanket non-adpat rate to see if the wide spread introduction of FFinto the market has made a difference in the number of non-adapts, or is it to soon to look any sort of metrics yet?

[AWTECH]

1. Yes, you can place the design on any time of material, index, tint or color that is available in SV form. But...BUT: For the same Rx, not every option will arrive on the expected base curve. Example:Poly progressive Transitions. Rx required a +5.25 Base curve, and and +5.25 was supplied (as "expected"). Companion pair was a CR-39 Polarized. These lenses, in CR 39 SV form, are available almost exclusively 2,4,6, etc. bases. The algorithym for this design specified again a +5.25 Base for these suns, but would not allow a choice of a +6.00 base, but would allow a +4.25 base. So a "marked" +4.25 SV brand was supplied, but it clocked a true curve of +3.87. So, now we have an instance where the lower indice was on the flatter base...not what one would expect.

2. Back-side, higher-plus/higher add progressives will put you where you may not realize you're going.
Example:
Rx:

+5.50 OU. +2.75 Add.

Client was wearing Physio (not 360) 1.67 Transitions. Base curve supplied by Essilor was +7.37.

Identical Rx made with 1.67 transitions in back-side free form: Base curve rec'd was +9.50 (!). (Remember that here you are also restricted to the base curves available in 1.67 Transitions) Why? With the progressive on the back, the base curve choice is determined by using the *total power* (w/add); i.e., +8.25 Diopters!
(Also remember that with conventional progressives, they achieve their add *steepening* on the front side, but only in the progressive area)

What a shock when I got those in. They were going into a rimless (yes, a Colorama). I specified a 0.5mmFE, and the drill points were just fine for the bushings. I did have to manipulate the bridge alittle, though.

Another day, another thing or two learned in the Wild West of free form.

Barry

FYI: We just produced a +5.75, -0.25 @ 175 with a +2.25 add with a 7 base front curve. This is for a patient who is wearing an ICE-TECH who is currently in an ICE-TECH +5.00, -0.25 with 2.25 add from over one year ago. These were both made using an ICE-TECH custom digitally surfaced lens.

We also made an 8 base wrap around PAL for this patient.

[RT]

I bet that if you look at the non-adapt rate of FF vs traditional it would be higher maybe even significantly higher.

That has not been our experience.

[Robert Martellaro]

2. Back-side, higher-plus/higher add progressives will put you where you may not realize you're going.
Example:
Rx:

+5.50 OU. +2.75 Add.

Client was wearing Physio (not 360) 1.67 Transitions. Base curve supplied by Essilor was +7.37.

Identical Rx made with 1.67 transitions in back-side free form: Base curve rec'd was +9.50 (!). (Remember that here you are also restricted to the base curves available in 1.67 Transitions) Why? With the progressive on the back, the base curve choice is determined by using the *total power* (w/add); i.e., +8.25 Diopters!
(Also remember that with conventional progressives, they achieve their add *steepening* on the front side, but only in the progressive area)

Barry

Here's Rodenstock's take on this problem.

http://www.freepatentsonline.com/7210779.html

Single-progressive spectacle lenses and also double-progressive spectacle lenses are known from the prior art. For example, U.S. Pat. No. 6,089,713 (=DE 197 01 312) describes a spectacle lens having a spherical front side and multifocal rear side, and also a method for producing it. Published German patent application no. DE 33 31 757 A1 describes a progressive spectacle lens having a convex aspheric front surface and concave aspheric inside or rear surface.

However, it has been found in the case of spectacle lenses having progressive rear surfaces that in the stronger addition area the spherical front surfaces must be fashioned with more of a curve than the front surfaces in the distance area of lenses having progressive front surfaces. This is felt to be disadvantageous by the spectacle wearer both for optical and for cosmetic reasons. The reason for this resides in the geometry of the lenses: if, for example, a lens is designed with a distance area effect of +5 dpt, in the case of progressive front surfaces use is made, for example, of a front surface with a surface dioptric power of +7 dpt which rises in the near area to approximately +10 dpt if the lens is to have an addition of 3 dpt. The spherical rear surface then has a surface dioptric power of approximately −2 dpt, resulting in an effect of approximately +5 dpt in the distance area.

If, in the case of progressive rear surfaces, a spherical front surface is to be selected which is as flat as the distance area of the lens with a progressive front surface (that is to say 7 dpt), the rear surface would need to have a surface dioptric power of −2 dpt in the distance area. With progressive rear surfaces, the mean curvature needs to decrease from the distance area to the near area and not, however, to increase such as would happen with progressive front surfaces. Thus, the surface dioptric power must rise from −2 dpt by 3 dpt to +1 dpt, in order to effect an addition of 3 dpt. This form of surface configuration is termed reversal of curvature. The surface is no longer only concave, as is the case with conventional products, but has an S-shaped course in a vertical section.

However, rear surfaces with reversal of curvature exhibit specific wearing properties which can lead to problems for the spectacle wearer. One problem is the relative nearness of the rear surface to the eye when such lenses are countersunk in conventional mounts. Since the eyelashes then strike against the lens, this frequently leads to irritation. A further problem is the more frequently occurring reflections which have a disturbing effect and reduce the contrast during seeing.

In order to avoid these effects, it is possible to increase only the curvature of the front surface in the case of lenses with a progressive rear surface, but this entails lenses which are thicker and unattractive cosmetically. Again, this raises the intrinsic magnification of the lenses, the result of which is to intensify the so-called “cow-eye effect”.

Rodenstock's Impression Hyperop can be had with RXs up to +13.00. The Zeiss Gradal Individual (not the newer Zeiss Individual) goes up to +10.00, with I believe the Add on the front surface, with this surface free-form generated, and the back surfaced with regular toric generators.

[optical24/7]

That brings up a thought I had a while ago, I bet that if you look at the non-adapt rate of FF vs traditional it would be higher maybe even significantly higher. Follow me on this one you FF lovers, I think most people put their difficult to fit patients in FF products so it lowers the non-adapt rates on the traditionals and offsets them onto the FF products. I would be curious to see a blanket non-adpat rate to see if the wide spread introduction of FFinto the market has made a difference in the number of non-adapts, or is it to soon to look any sort of metrics yet?

I don't think so Harry. At least in my experience, the vast majority of non-adapts, though few they are, are all almost exclusively new to PAL's. The folks most willing to try a FF are previous wearers of PAL's that have a complaint with their previous pair. Now then, what I'd like info on is the people put in FF's: do they find the value in what they got? Was it only marginally better than their last traditional PAL? Would they shell out the bucks again when their Rx changes?

[Fezz]

Now then, what I'd like info on is the people put in FF's: do they find the value in what they got? Was it only marginally better than their last traditional PAL? Would they shell out the bucks again when their Rx changes?

Great idea! I wonder the very same thing! Maybe we could get the *Free-Form Drum Banging Companies* to get on that! {In a non-biased way of course}


:cheers::cheers:;):cheers::cheers::D

[HarryChiling]

That has not been our experience.

Good to know, I know some office that use it faithfully and then some that use it for their difficult to fit patients (our office), and then some that don't use them at all (bet you thought I was in this category ;)).

I don't think so Harry. At least in my experience, the vast majority of non-adapts, though few they are, are all almost exclusively new to PAL's. The folks most willing to try a FF are previous wearers of PAL's that have a complaint with their previous pair. Now then, what I'd like info on is the people put in FF's: do they find the value in what they got? Was it only marginally better than their last traditional PAL? Would they shell out the bucks again when their Rx changes?

Thanks for the info, I would love to see a study done on the value as well. Luckily the price is coming down to a point where the value can be justified.

[jefe]

In my experience, buyer's remorse can be a factor affecting the non-adapt rate for free-form PALs. There are occasions when a patient with no rx change or a minimal one concludes the difference in price is not worth it when they compare their old glasses with their new ones.

I almost always present at least three PAL options. If I feel resistance from the patient, it's often best to back off. There are, of course, times when I must make a single recommendation, but if someone seems content with what they're wearing, I don't necessarily try to push them to a stratospheric price-point when they're used to a tropospheric one.