ask the labs
Photochromics Panorama
by Karlen McLean, ABOC, NCLC
METHODICAL MATERIALS
Q Are there any issues with processing today's photochromic lenses?
A Few, if any, processing issues exist today with fabricating photochromics. The leading photochromic technology utilizes imbibing or a transbonding method to impregnate lenses with a proprietary process. With this method, the photochromic layer becomes part of the lens substrate, and is isolated from virtually any fabrication processes a lab uses.
Another method of incorporating adjustable tint into a lens is through in-mass technology. The concentration of photochromics with this process can at times make high-plus lenses darker in the middle and high-minus lenses darker at the edges.
—Jeff Szymanski, sales manager,
Toledo Optical, Toledo, Ohio
EQUIPMENT EXCELLENCE
Q Are there equipment tips that apply specifically to working with photochromic lenses?
A There are few variations on processing photochromics, with the standard materials caveats. It's important to create and support a stable reduction method that's a set routine.
Machine maintenance is at the top of this list. It's important to keep finishing wheels sharp, since grinding is different with various materials, and a sharp wheel makes the process more accurate and less prone to failure.
Again, a standardized system is the key. Keep equipment in as close to new working order as possible, and parts as sharp as new. Yes, it's expensive to replace wheels, but consider the alternative: production breakdown and product spoilage. Which is more costly in the long run? Upkeep is the most important factor in processing any lens, including photochromic lenses.
—John Barry, corporate production manager, Soderberg Ophthalmic Services, Inc., St. Paul, Minn.
| photochromic processing |
|---|
| Q Do you have any hints for processing photochromic lenses? A Processing photochromic lenses doesn't create any unusual problems for us. We've found that plastic photochromic material does require some extra attention because it is softer than CR39. We've solved the challenges associated with this material by using surface saver tape on the front of the lenses, and a 1.5 to 2mm extra grind off is required. We want no less than 2.0mm center thickness because the material is so soft that it will flex more when surfacing and edging, and most important, when inserting into both zyl and metal frames. Processing poly, 1.60, or 1.67 material is not any different for a photochromic than a clear lens. The only photochromic dispensing concerns we've run into are cost and the lenses getting too dark in the winter months. —Chuck Flood, owner, Enterprise Optical, Madison Heights, Mich. |
If you have a question you'd like to have answered in Ask the Labs, send it to Karlen McLean. Email: karlen.mclean@wolterskluwer.com. Fax: 215-367-2155. An archive of past Ask the Labs columns can be found on the Eyecare Business website at www.eyecarebusiness.com.
![]({"src":"/media/zjpdmce0/82008.jpg","focalPoint":null,"crops":[{"alias":"thumbnail","width":1110,"height":700,"coordinates":null}]})