Friday, July 4, 2008

Transitions bifocals

Q: I had a patient come in today asking for transitions lenses. He wanted the distance to be photochromic, but the seg he wanted to remain clear.

I was curious as to if such a lens was possible with what little I know of the technology, and if it was, does it exist?

A1: The patient probablly had a glass Photo gray ST 28, probably wants same again, but doesn't know the difference between transitions and photo gray. Glass photo gray ST 28's have clear segs.

As to transitions made this way, I don't think there are any available, but since transtions is a dip, lens could be masked in segment area before dipping.

By: chip anderson

A2: segs on glass lenses are not photochromic, not very appealing, cosmeticly. The seg is a different RI from the rest of the lens that was cast from silver halide laden molten glass. This seg "button" is attached and becomes part of the glass lens in a very interesting process. If you ever have a chance to see glass lenses, especially segmented products being produced at a factory, it is worth seeing.

It is still hard for me to understand why anyone would want that type of look....clear or dark segs and all, with all the great PALS out there, why would anyone want a seg line! I just hit 50 and have had to wear glasses for about 3 years now. The folks I grew up with all hit that age where their arms became to short. I am happy to say only one person among my peers bought bifocals....but his next pair will be a PAL, now that he knows that they exist. His ECP never presented the option to him. Beat that.

I do want to clear up one misconception in the prior posting.

Transitions are not produced by dip coating. Transitions Lenses are produced by placing the photochromic package into the front surface of the lens (imbibition technology) or by bonding a photochromic layer (Transbonding) on Trivex, Polycarbonate and 1.67 Hi Index lens materials.

Both Transitions Lens processes are patent protected.
Thus leaving the dip coating (photochromics disolved in a liquid carrier, lens dipped in the solution, allowed to dry then heated to permenantly place the pc chemicals on the surface of the lens) along with cast in place (photochromic package mixed with monomer (just like glass pc process) and cast in desired lens mold design) as the other options to make a lens photochromic.

By : Jim Schafer

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