Defining Generations of PAL design...

[Pete Hanlin]

Just wrapping up some info for a new course on PAL characteristics, and I'm trying to generally define the "generations" of PAL design.

What I plan to use so far is as follows:
First Generation
symetrical design
R/L acheived by rotating the lens

Second Generation
asymetric design
defined R/L lenses

Third Generation
multi designs
design changes as bc/add changes

I'm sure there are more generations than these (which is one reason I'm posting here :) ). Also, I'm sure y'all can give me examples of each generation (e.g., I'm a little young to remember symetric designs- I would imagine the VIP is a good example of what I'd call a second generation lens).

Also, would the current array of "new" PALs truly qualify as a fourth (or fifth or sixth, depending on how may y'all can add to my list) generation? If so, what is the primary difference between these "as worn" "retina forward" and so on designs and those previous? It seems to me that the last real advance in PAL design was multi-designing the lens for different bcs and adds. The "new" lenses just seem to have finally taken into account that goal should be to acheive an Rx that is accurate to the wearer- not the lensometer!

Thanks for your input! This particular forum is always a good resource for information such as this (read "I am trying to finish this up and I really need y'alls help quick)!

Pete

[chip anderson]

Sorry I can't be of help to you on this, but has anyone defined what "retina forward" is yet?

Chip

[Darryl Meister]

Hi Pete,

I would probably differentiate between designs that change by add power (i.e., multi-design) and designs that change by both base curve and add power (e.g., SOLA's Design by Prescription). Multi-design lenses have been around for many years and represent what one might call a "Third Generation" lens design. However, designs that change by both base curve and add power represent a significant departure from this conventional design philosophy, and should probably be grouped into a "Fourth" or even "Fifth Generation" category. This category should also included lenses that have been designed with as-worn optimization or complex atoric surfaces, as well.

Also, I would say that many "Second Generation" lenses include the use of more asphericity in the distance portion to smooth out the lens design. (Most "First Generation" lenses were relatively spherical designs.) Keep in mind though, that the use of these "Generation" classifications are often relative -- and very much depend upon the individual manufacturer and how its lens designs have evolved over the years. Furthermore, even the newest progressive lens design from a given manufacturer may not necessarily incorporate the most advanced design strategies.

Best regards,
Darryl

[Laurie]

Examples of 5 generations...

Hi Pete (and Darryl!!) (good to see you back, Darryl!)

I would echo that we are up to 5th generation PALs...

To use one line: (Essilor, for example)...

1st: Varilux (Dr. Brooks talks about this in the original "blue book") ...it has a spherical distance portion with an aspheric bottom portion.

2nd: Varilux II (Aspheric throughout the entire front surface, not just the bottom)

3rd: Varilux Infinity (softer design)

4th: Varilux Comfort (softer design and shorter intermediate), considering more prescription stages.

5th: Varilux Panamic (maximizing horzontal symmetry) for maximum side to side vision without "swim".

Maybe other people could add to this thread outlining the generations of other lines?

Hope this helps,

Laurie