Pete Hanlin said:
Seems to me the fact that different patients prefer different designs is self-illustrative that there are indeed differences in each design.
Panamic and Ovation come from the same "generation" of PALs. Which is to say that they both feature individual designs for each base curve/add power combination. Each design was developed by seperate teams, however.
Panamic is a revolutionary design for Essilor. Panamic incorporates something called Global Design Management(TM). What this means is that Panamic was
not designed to have a "wider" channel. In fact, Panamic wasn't designed to have a channel at all. Instead of working towards a wide channel with optimal properties, Panamic is designed around balancing the entire lens.
In Panamic, levels of unwanted astigmatism are equally balanced on either side of the intermediate. While you can create a "wider" intermediate than Panamic's, the result is more unwanted astigmatism on one side of the intermediate or the other. Therefore, binocular vision is compromised. Also, the wearer will notice greater amounts of "swim" at intermediate and near.
What does all this mean for wearers? When properly fit, Panamic provides wider zones of
binocular vision. Even though the design does not appear particularly wide on a contour plot, the effect experienced by the wearer should be one of more comfortable vision. Unfortunately, this also means Panamic is less forgiving if fit to improper parameters.
Most PALs have "sweet spots," Panamic has no such specific area of vision that is better than other areas in the lens. Again, the idea is to provide the eyes with similar images to each other. However, if the lens is fit either off measurement or off power, the eyes do not benefit from the design- and furthermore- do not have the reference points inherent to traditional PAL designs.
Comfort, on the other hand, was a design that combined a relatively short corridor (Comfort actually reaches 85-90% of its total add power just 12.4mm below the fitting cross) with a very soft design. Comfort is very forgiving and works relatively well even when misfit.
Natural is very similar to Comfort, and Ovation is similar to Panamic. All of these designs feature near point insets that increase as add power increases and progression lengths that vary depending upon the ametropia of the patient.
There will be situations where a patient is going to be more comfortable in a Comfort or Natural than in a Panamic or Ovation. Field reports have indicated that it can be difficult to convert a Comfort wearer into another design.
I hope this at least partially answers some of your question regarding the differences in Essilor PAL designs. Yes, to some degree PAL designs will be similar. However, throw them all in a bag, and you
can tell the difference (first of all, you just look at the identification marks on the lenses, and...). Just kidding, Varilux has conducted wearer tests over the years involving 1,000s of patients through the process of designing new PALs, and the results of each new test provide new information on what PAL wearers experience and require.
You should see some of the design innovations that are waiting just around the corner! There will be some truly exciting stuff in the coming two or three years!
Bookmarks