Grant,

I have a list of all direct-to-surface lens designs available in the US.  The
only lenses that don't use metal/glass molds for the front surface is the Hoya
lens, although Zeiss does switch the free-form surface from back to front in
higher powers (using traditional generators for the back). To be sure, it's
debatable whether Hoya's approach offers any optical advantages, it probably
avoids paying royalties to Seiko since they have the patent on free-form back
surface PAL designs.  

Most use free-form technology (computer numerical controlled (CNC) generator fed
with thousands of data points which define the surface) to generate a back
surface that contains the PAL and power. Definity does put .75 of the add on a
front molded surface though, and the Physio 360 uses a front PAL (molded) using
free-form for the back surface, again probably to avoid a fee to Seiko.

So, one might ask why put the PAL on the back if you have to pay Seiko a
royalty? Probably because they don't have to stock and manufacture at least ten
add powers in addition to seven or eight base curves for each add power.  

It's probably all in the marketing. For instance, the Liberty is marketed in
Europe as a budget general purpose PAL, in the US it's recommended as an ideal
design for switching segmented wearers to PALs.

Regards,

Robert Martellaro
~~~~~~~~~~~~~~~~~~
Optician/Owner
Roberts Optical
Wauwatosa Wi.
~~~~~~~~~~~~~~~~~~
"Science is a way of trying not to fool yourself."
- Richard Feynman

The Ipseo was never moulded. It was laser generated front and back
from day 1. That was the reason to test head/eye movement so as to
vary the reading band accordingly.

You americans are very funny then if you get a generated physio as
they are  diamond cut on the rear surface everywhere else to account
for the aberrations of a given prescription. You can't get that from a
generator, thus nullifying any benefit of the lens.

grant

Grant,

Sorry, I lost track of this thread, probably the holidays.

In the U.S., and this may not be true in Europe, Asia, and Australia, the Physio
is a traditional PAL with the progressivity molded on the front, using standard
generators to grind the Rx on the back. The Physio 360 has the same front design
but is direct surfaced on the back with free-form generators. The Ipseo started
out as a double sided direct surfaced lens but is now done on one surface only,
but I don't know which surface has the progressive.

Regards,

Robert Martellaro
~~~~~~~~~~~~~~~~~~
Optician/Owner
Roberts Optical
Wauwatosa Wi.
~~~~~~~~~~~~~~~~~~
"Science is a way of trying not to fool yourself."
- Richard Feynman

Robert, the 360 is freeform on both surfaces, the Physio on the back
only. The MF is purely front surface on both, but the aberration
profile is better controlled over both surfaces on the 360.

grant

Correction- the progressive is molded on the front surface and uses free-form
technology to create the back surface.

Robert

The 360 uses free-form technology, surfacing the add power on the back of the
lens instead molded on the front surface. You won't see too much difference in
the designs unless you need a high add (above +2.00) or are very astigmatic
(above +2.50).


Robert Martellaro
~~~~~~~~~~~~~~~~~~
Optician/Owner
Roberts Optical
Wauwatosa, Wi.
~~~~~~~~~~~~~~~~~~
"Science is a way of trying not to fool yourself."
 - Richard Feynman

Could someone please explain the difference between the Physio and
Physio360.  I've been to
 Varilux.Com, but they are far from clear on the target market of
either product.

 I know the following question has been asked and answered in many
posts, but I am getting ready to
 make a purchase and just want to be sure (the retailers tell me the
opposite of what I read here)...

 For a light prescription using a Varilux lens and a regular metal
frame, I am better off getting
 a standard plastic lens as opposed to a polycarb lens...  is that
generally correct?

 
 Thanks

  Tom