Near, Far, Intermediate Zones

[BuckeyeG]

As an optician, it is becoming more difficult every day to understand the differences between all of the progressives. There is no difficulty in identifying progressives by material, seg height and extras such as transistions. But, add lifestyle dispensing into the equation and it becomes more complex. So, I ask you - what are the top three short-corridor progressives with a wide near? What about the top short corridor with a wide far zone and normal near and inter? Dr. Sheedy's study brought most of this information out but we need a guide that translates this information into usuable data that all opticians could benefit from. We need to know which progressives have the widest zones inorder to really do an adequate job in lifestyle dispensing.

Any help would be appreciated
Thanks

[Fezz]

Welcome to Optiboard!


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

[drk]

Hey, Buckeye.

This is an oddly coincidental thread, as I was here to start something similar.

Instead of linking, I will cut-n-paste a personally saved excerpt of an Optiboard thread, written by a now-unidentified savant poster:

Manufacturer Name Corridor Length Minimum Height
AO/SOLA Compact 13 mm 17 mm
AO/SOLA SOLAMAX 12.4 mm 18 mm
Essilor Varilux Panamic 12.5 mm 18 mm
Essilor
Nikon? Presio? i 13?
13 mm 17 mm
Hoya Summit CD 11 mm 14 mm
Kodak ConciseTM 14 mm 17 mm
Pentax AF mini 14 mm 17 mm
Rodenstock Progressiv® XS 12 mm 16 mm
Seiko Proceed II Short 14 mm 18 mm
Shamir Piccolo 11.5 mm 16 mm
Vision-Ease Outlook 14 mm 18 mm
Younger Image® 13.5 mm 18 mm
Zeiss Gradal Individual 14 mm 18 mm
Zeiss Short i 11 mm 15 mm
The Essilor varilux lens will actually be a min fitting ht of 14mm and a corridor length of 9.5mm. It will be released April 1st and is called Ellipse
Corridor length (sometimes called progression length)--the distance over which the power progression occurs. Since the power typically begins to vary several millimeters below the fitting cross, the corridor length is generally shorter than the minimum fitting height. For general purpose progressives with a min fitting height of 18-22 mm, corridor length would typically be around 14-18 mm.
Regarding intermediate, any truly short corridor lens is going to have a minimal intermediate zone. These lenses are not going to be especially well-suited for intermediate tasks.
The research conducted when developing Varilux Ellipse turned up a couple interesting findings. First, not surprisingly, patients strongly preferred a short progression when wearing a small "B" frame. Secondly, and perhaps more interesting, patients wearing short "B" frames were most sensitive to peripheral restrictions in the distance portion of the lens.
All truly "short" progressions are going to be relatively (relative to general use PAL designs, that is) narrow in the near zone. However, most of the "short" corridor PALs currently available on the market also use the distance periphery to distribute the unwanted cylinder that occurs with a seamless progression of power.
Varilux Ellipse will have 140 degrees of clear distance. This is about 15% more than the closest competitor design, and really seems to improve patient acceptance of the lens. My theory is that this occurs because- in the end- most of us still use our eyewear for distance viewing more than for close tasks.
In my opinion, that is why a lens like Ovation (or any other general use PAL that has a progression short enough to give near function in a small frame) works better than the "short" PALs. Nothing against Shamir Piccolo, but the area of unrestricted distance viewing is only 103 degrees. AO Compact has 109 degrees, and Summit CD has 118 degrees. Compared to most general use PALs, these lenses restrict the area of distance viewing. In a small frame, the result is a very limited distance area.
Of course, there are other considerations as well. For example, AO Compact is an extremely hard design that presents the wearer with a lot of motion in the near periphery. This explains why even general use PALs like Varilux Comfort score higher than AO Compact in wearer tests- even in the areas of near vision (where a design like AO Compact should theoretically excel).
Unfortunately, physics being what they are, you cannot have a generous intermediate while cramming the progression into a tiny area. Therefore, the vast majority of your "short-corridor" offerings are little more than a general type design with a dislocated fitting cross, near verification circle, or both. The ones that are actually short have considerable distortion crammed into the distance periphery- and usually also have poor symmetry between the nasal and temporal periphery of the near zone (causing swim).
Since most "short corridors" are fit to lower add powers, most wearers don't notice they have been fit down into the top of the progression- or that they have compromised the intermediate zone.
Keep in mind that few manufacturers adhere to the same standard of corridor measurement, so if you asked each of them separately for their own figures, they probably wouldn't be very consistent with each other. Some may measure to 85% of the add power (Essilor), some to 95% (SOLA), some to the add power less 0.12 (AO), some to the near circle, some using surface power, some using front vertex power, and so on. Also, the "length of the corridor" is only so meaningful, as I discuss below.
On this point (and many others, I would suspect), we completely agree. The "old" measures of PAL performance (width of zones, softness of design, and more recently corridor length), have been replaced by several considerations which are addressed in modern lenses. Namely, does the design take into account the ametropia and level of presbyopia of the wearer? How symmetrical is the distortion in the lens? How smooth is the peripheral progression in the lens? And so on...
The minimum height you can fit a Varilux Comfort and receive the optimal benefit of the entire reading area is 22mm.
At 18mm, Varilux Comfort provides about 5.5mm of comfortable reading area. So, while an 18mm height isn't optimal, it does permit the design to work as well as- better in most cases, actually- than a lens originally marketed with a shorter fitting height recommendation.
Based on the power progression profile of the design, the Hoya Summit CD probably doesn't perform all that well at 14-15mm. On the other hand, the Rodenstock Life XS is a rather short- if extremely hard- design, so it should work better at lower fitting heights. In fact, wearer studies Essilor has performed comparing the Life XS and Varilux Ellipse show that the Rodenstock product performs pretty well (Varilux Ellipse scored better, but the Rodenstock product wasn't bad).
Progressive lenses must obey certain mathematical principles in order to produce a change in add power with a smooth surface (having smoothly increasing power and magnification). One of the most important of these principles is that the change in surface astigmatism must increase as the rate of change in add power increases. Shorter corridor lengths require more rapid changes in add power and, consequently, more rapid changes in surface astigmatism.
So, progressive lens manufacturers must make certain compromises or trade-offs when using shorter corridors because of the added restrictions imposed by the increasing astigmatism. They must also find an acceptable balance between viewing zone sizes, peripheral blur, swim, and so on. Unfortunately, there is no magic formula here.
You will also find that conventional progressive lenses have a relatively small range of corridor lengths (on the order of only a few millimeters for +2.00 adds), suggesting that manufacturers have found an optimum range of corridor lengths that allows for a good balance of optical performance and utility. Consequently, you have to ask yourself what compromises you might be tolerating by using corridor lengths that are significantly shorter than necessary simply for the sake of unrestrained frame selection.

[drk]

I have two conventional short corridors I work with and a cheating method.

Ellipse:
As discussed above, it seems Essilor designed the Ellipse to be clear in the distance but very short. The corridor is about 9 mm (taller than a 7x28 TF seg, for comparison) and with a paltry 5 mm near zone height, you can get away with 14 mm of near/intermediate zone (mentally compare to a 14x35 CRT TF). Of course, the gestalt will be one of the visual system getting about 2/3 of the full add power, IMO*


* This is my own "gestalt", and is not "official". I will say it helps when fitting aspheric CLs, FWIW:
Average power of corridor on a +2.00 add = +1.00
Power in near zone = +2.00
Weighted average:
(9mm/14mm) X (+1.00 D ) + (5mm/14mm) X (+2.00 D) =
(+0.64 D) + (+0.71 D) = +1.35 D
+1.35 D/ +2.00 D x 100% = 67%


So, fitting the Ellipse at 14 to 16 is nice from a distance vision perspective, and decent at near. Intermediate vision is really problematic with this lens, though, as can be expected. Something's gotta give. I envision it as a FT28, and think it's better for distance-oriented wearers.

But, who isn't working on a computer eight hours a day, anymore? We have many white-collar fully presbyopic women in my practice that want to look good and see "good" at work. Not everyone wants a second pair of NVF lenses to go with their shorty-PALs, although that's my recommendation.

Piccolo:
What about the Piccolo? From my experience, the above excerpt, and "the Sheedy", it has maximized intermediate and near zone widths (at least, since it can't maximize height with 16 mm to work with) at the expense of distance zone peripheral astigmatism, and some degree of hardness in the near zone periphery. (I envision it as an hourglass design, not unlike a NVF lens with the distance zone enlarged downward, compressing the intermediate and near vertically.) I think this lens design works best for intermediate and near-oriented wearers.

Cheating Method:
I am also considering a "third option", and will be applying it immediately. "Back in the day", before I started experimenting with short-corridor designs, I fit Panamic all day long on everyone. I fit it as low as 16 with regularity. I was quite pleased to be successful with it. Why do I think it worked?

I think a lot of latest generation conventional progressives have gone "high and wide", as they say. I think the Physio is that way, and the GT2 is that way. They also seem to be otherwise quite balanced, and manage peripheral astigmatism quite well.

So, I think these designs can be utilized this way with good effect:
Fit the GT2 or Physio down as low as 15. Bump the add +0.25 at the 16mm fitting height level, and +0.50 at the 15mm fitting height level. It will increase peripheral astigmatism, but "so what?". I think we will be essentially dispensing lenses that are about a 12 mm corridor with a 3-4 mm near zone (mostly a corridor!). I think what we're doing here is creating a third concept to the above: a short corridor lens with a lot of distance, intermediate but little near. But I think the "gestalt" will be wearable to a lot of distance and computer-oriented people.

Really, Martellaro should post on this, as he is very knowledgeable on this stuff.

[Happylady]

DKR, what do you think of the Definity Short? It's supposed to have a better intermediate area and can be fit at 15. I like the Ellipise for it's great distance and decent near but so many of my progressive wears want a decent intermediate. I don't worry about it if the add is under a +2.00 but it becomes important with higher adds.

I have a pair of Definity Short lense fit 17 high and they seem pretty good but I do notice that I can't raise my head at all without running into the intermediate area. I can read with them but since my distance is a -2.25 and my near is a +2.25 I often take them off if I am just reading.

What has been people's experience with this lens?

[chrome surfer]

I fit a staff member with the compact ultra and she is loves them much better than any other short pal and has become one of my favs have not had any problems with it at all. I have not used the definity short.

[TradeoffH8er]

I am a progressive lens designer and am familiar with Sheedy's articles describing an objective rating system for PALs. I know that the constraints he defines to determine zone width/area are 0.25 D sphere error and 0.50 D cylinder error. I could not discern for myself whether the 0.25 D sphere error refers to mean sphere or maximum sphere measurement. Mean sphere would make more sense to me off hand. Does anyone else know?

Thanks:hammer::cheers:

[bhess25]

Hey, Buckeye.

This is an oddly coincidental thread, as I was here to start something similar.

Instead of linking, I will cut-n-paste a personally saved excerpt of an Optiboard thread, written by a now-unidentified savant poster:

Manufacturer Name Corridor Length Minimum Height
AO/SOLA Compact 13 mm 17 mm
AO/SOLA SOLAMAX 12.4 mm 18 mm
Essilor Varilux Panamic 12.5 mm 18 mm
Essilor
Nikon? Presio? i 13?
13 mm 17 mm
Hoya Summit CD 11 mm 14 mm
Kodak ConciseTM 14 mm 17 mm
Pentax AF mini 14 mm 17 mm
Rodenstock Progressiv® XS 12 mm 16 mm
Seiko Proceed II Short 14 mm 18 mm
Shamir Piccolo 11.5 mm 16 mm
Vision-Ease Outlook 14 mm 18 mm
Younger Image® 13.5 mm 18 mm
Zeiss Gradal Individual 14 mm 18 mm
Zeiss Short i 11 mm 15 mm
The Essilor varilux lens will actually be a min fitting ht of 14mm and a corridor length of 9.5mm. It will be released April 1st and is called Ellipse
Corridor length (sometimes called progression length)--the distance over which the power progression occurs. Since the power typically begins to vary several millimeters below the fitting cross, the corridor length is generally shorter than the minimum fitting height. For general purpose progressives with a min fitting height of 18-22 mm, corridor length would typically be around 14-18 mm.
Regarding intermediate, any truly short corridor lens is going to have a minimal intermediate zone. These lenses are not going to be especially well-suited for intermediate tasks.
The research conducted when developing Varilux Ellipse turned up a couple interesting findings. First, not surprisingly, patients strongly preferred a short progression when wearing a small "B" frame. Secondly, and perhaps more interesting, patients wearing short "B" frames were most sensitive to peripheral restrictions in the distance portion of the lens.
All truly "short" progressions are going to be relatively (relative to general use PAL designs, that is) narrow in the near zone. However, most of the "short" corridor PALs currently available on the market also use the distance periphery to distribute the unwanted cylinder that occurs with a seamless progression of power.
Varilux Ellipse will have 140 degrees of clear distance. This is about 15% more than the closest competitor design, and really seems to improve patient acceptance of the lens. My theory is that this occurs because- in the end- most of us still use our eyewear for distance viewing more than for close tasks.
In my opinion, that is why a lens like Ovation (or any other general use PAL that has a progression short enough to give near function in a small frame) works better than the "short" PALs. Nothing against Shamir Piccolo, but the area of unrestricted distance viewing is only 103 degrees. AO Compact has 109 degrees, and Summit CD has 118 degrees. Compared to most general use PALs, these lenses restrict the area of distance viewing. In a small frame, the result is a very limited distance area.
Of course, there are other considerations as well. For example, AO Compact is an extremely hard design that presents the wearer with a lot of motion in the near periphery. This explains why even general use PALs like Varilux Comfort score higher than AO Compact in wearer tests- even in the areas of near vision (where a design like AO Compact should theoretically excel).
Unfortunately, physics being what they are, you cannot have a generous intermediate while cramming the progression into a tiny area. Therefore, the vast majority of your "short-corridor" offerings are little more than a general type design with a dislocated fitting cross, near verification circle, or both. The ones that are actually short have considerable distortion crammed into the distance periphery- and usually also have poor symmetry between the nasal and temporal periphery of the near zone (causing swim).
Since most "short corridors" are fit to lower add powers, most wearers don't notice they have been fit down into the top of the progression- or that they have compromised the intermediate zone.
Keep in mind that few manufacturers adhere to the same standard of corridor measurement, so if you asked each of them separately for their own figures, they probably wouldn't be very consistent with each other. Some may measure to 85% of the add power (Essilor), some to 95% (SOLA), some to the add power less 0.12 (AO), some to the near circle, some using surface power, some using front vertex power, and so on. Also, the "length of the corridor" is only so meaningful, as I discuss below.
On this point (and many others, I would suspect), we completely agree. The "old" measures of PAL performance (width of zones, softness of design, and more recently corridor length), have been replaced by several considerations which are addressed in modern lenses. Namely, does the design take into account the ametropia and level of presbyopia of the wearer? How symmetrical is the distortion in the lens? How smooth is the peripheral progression in the lens? And so on...
The minimum height you can fit a Varilux Comfort and receive the optimal benefit of the entire reading area is 22mm.
At 18mm, Varilux Comfort provides about 5.5mm of comfortable reading area. So, while an 18mm height isn't optimal, it does permit the design to work as well as- better in most cases, actually- than a lens originally marketed with a shorter fitting height recommendation.
Based on the power progression profile of the design, the Hoya Summit CD probably doesn't perform all that well at 14-15mm. On the other hand, the Rodenstock Life XS is a rather short- if extremely hard- design, so it should work better at lower fitting heights. In fact, wearer studies Essilor has performed comparing the Life XS and Varilux Ellipse show that the Rodenstock product performs pretty well (Varilux Ellipse scored better, but the Rodenstock product wasn't bad).
Progressive lenses must obey certain mathematical principles in order to produce a change in add power with a smooth surface (having smoothly increasing power and magnification). One of the most important of these principles is that the change in surface astigmatism must increase as the rate of change in add power increases. Shorter corridor lengths require more rapid changes in add power and, consequently, more rapid changes in surface astigmatism.
So, progressive lens manufacturers must make certain compromises or trade-offs when using shorter corridors because of the added restrictions imposed by the increasing astigmatism. They must also find an acceptable balance between viewing zone sizes, peripheral blur, swim, and so on. Unfortunately, there is no magic formula here.
You will also find that conventional progressive lenses have a relatively small range of corridor lengths (on the order of only a few millimeters for +2.00 adds), suggesting that manufacturers have found an optimum range of corridor lengths that allows for a good balance of optical performance and utility. Consequently, you have to ask yourself what compromises you might be tolerating by using corridor lengths that are significantly shorter than necessary simply for the sake of unrestrained frame selection.

A.D.D. sucks!!...back to the top!!

[Raanan Bavli]

If this needed any proof, jsut read drk's post. He's obviously very knowledgeable, but just think about comparing two or more designs based on a good description such as in his post.... Wouldn't it be nice to have something like this?

[bhess25]

If this needed any proof, jsut read drk's post. He's obviously very knowledgeable, but just think about comparing two or more designs based on a good description such as in his post.... Wouldn't it be nice to have something like this?

anyone know what lens that is on the bottom right?

[TradeoffH8er]

anyone know what lens that is on the bottom right?

Yeah, it's the lens with a great-looking cylinder map but a god awful (average) sphere map. Or it's the lens that doesn't achieve the same add as the other ones. I hate tradeoffs!!!!

[bhess25]

Yeah, it's the lens with a great-looking cylinder map but a god awful (average) sphere map. Or it's the lens that doesn't achieve the same add as the other ones. I hate tradeoffs!!!!

it looks like the perfect PAL...at least one i would use in nearly all situations!! (i know theres more to it than a map without any numbers...but from what im seeing..thats a nice lens)

[Happylady]

anyone know what lens that is on the bottom right?

Yes, it looks really good. I would love to know what all of them are!

[Raanan Bavli]

Due to the interest, I went to my files and found this specific one. It's actually a mold made by a small company and being sold in China and eslsewhere in the far east. I attach here the power and cylinder maps, and also the corridor cross sction. The red line in the graph describes the cylinder along the corridor, and as you can see it has a peak of 0.25D at one point. This is not unusual, and considrered as a production-related issue. On the other hand (and someone here did mention trade-off) there's a design-related problem - the peaks of the cylinder map are ~4D. This is far beyond the usual ratio of 1 (or less) between peak cylinder and addition.

[Laurie]

Hi Raanan,

Thanks for posting the graphics.

Is it possible to post more? The Sheedy report is a great resource, and the graphics you posted help to visualize the whole picture.

You mentioned the 1:1 ratio of excessive cylinder/Add power...I believe this is is one of the most important things to look at in design. Do you know how much below 1:1 we can mathematically acheive? And, do you agree that keeping the excessive cylinder/distortion below the 180 is crucial, even if the design becomes harder in the lower peripheri (zone 4)?


: )

Laurie

[Raanan Bavli]

Hi Laurie,

Attached are images of a Pananmic lens. This is an actual lens measured by me, rather than a theoretical map presented by the manufacturer.
As you can see, the Add is 2.31 and -14mm cross section shows about this value for the peaks of the cylinder (ratio ~1). I don't know how low it's possible to obtain, but the (by far) lowest I've seen so far is the Definity. It was 0.65!!! When evaluating the amount of distortions, I believe it's also important to take into account how far these are from the corridor. I'm not an optometrist and this may be the reason for not understanding the meaning of "180" and "zone 4".

[Robert Martellaro]

As an optician, it is becoming more difficult every day to understand the differences between all of the progressives. There is no difficulty in identifying progressives by material, seg height and extras such as transistions. But, add lifestyle dispensing into the equation and it becomes more complex. So, I ask you - what are the top three short-corridor progressives with a wide near?

The short answer is- they're all about the same at near.

What about the top short corridor with a wide far zone and normal near and inter?

Wide far, normal near, and normal intermediate? Pick any two.

Dr. Sheedy's study brought most of this information out but we need a guide that translates this information into useable data that all opticians could benefit from. We need to know which progressives have the widest zones inorder to really do an adequate job in lifestyle dispensing.

I'm a fairly seasoned PAL wearer, and the only time I've noticed the horizontal width of the viewing zones is on distance gaze, although hyperopes might see the difference in near width between the GT and XS. However, I notice a huge difference in the vertical field at near between different corridor lengths; specifically, how quickly the design gets into some and/or all of the reading power.

I would start by getting the fundamentals right; ie, accurate positioning of the fitting cross, lenses as close to the eyes as possible, choosing lens designs that have insets optimized for PD and power, and the use of fully aspheric PALs to minimize magnification. This will result in an optimum field of vision combined with reduced aberrations. Then choose designs that are biased towards near, far, or balanced vision, matching the design to your client's visual needs. IMO the intermediate will take care of itself if the lens is well positioned.

In general, avid readers get the short corridors, others will prefer the moderate to long corridors. However, avid readers might not like the compromise in the distance vision with the short corridor, and might choose a longer design and use separate glasses for near tasks. As you can see, there are numerous combinations possible, and to have any chance of getting it right the first time requires a thorough and detailed interview with your client. Don't forget to select a frame that will accommodate the lens design, doing so after you've decided what type of lens or lenses will be required.

The above assumes ADD powers above +1.50, especially the +2.25 and +2.50 powers. The lens design is not too critical when the ADD is +1.50 or lower, although it's best to stay with soft designs that have reasonably good distance vision, especially if they are first time PAL wearers.