ASK THE LABS
By Joseph L. Bruneni

WRONG ANSWER OR WRONG TERMINOLOGY?

Q In your Ask the Labs column you answered a question about progressive lenses with laser markings on the lenses. You stated that you "doubt that progressive lenses without laser markings are still made by anyone." In fact, the entire American Optical progressive lens series is made without laser markings. They are etched, while still in the mold, during fabrication. The etchings are generally far less distinct than laser markings, and I, personally, have never known the markings to cause any visual disturbance.

--David Schurgin, O.D., F.A.A.O.

A Questioning inaccurate information in "Ask the Lab" is a valid concern. However, in this case, the fault wasn't in the answer but in the terminology used. The most common term used by optical people for the location marks found on progressive lenses is "laser markings" even though they are not produced by laser.

Producers of most progressives today create these marks with an engraving in the concave glass mold used to produce the front surface. Marks in the master molds are engraved or acid-etched. The process is not exclusive to American Optical lenses. Our answer was correct, but we should have used the term "engravings" rather than "laser markings."

NOT JUST FOR BLOWING NOSES

Q I am a project leader with Consumer Reports magazine and am currently conducting tests of facial tissues. Many consumers use tissues to clean their eyeglasses. Among the brands of tissues we're testing are several that contain lotion. The labels of these brands say specifically that they should not be used to clean eyeglasses. We assumed that this is because the lotion would cause smudges. Someone in a discussion group indicated that the lotion may react with the coating on lenses, in particular the polycarbonate type. Is this true?

A Other than smudges, we don't believe the lotion has any effect on hard and AR coatings. If they did, we would already have trouble because of the lenses/coatings coming in contact with facial lotions, sweat, and all different kinds of make-up lotions. That's why our company is so stringent about the Grisiron Tape Test: it doesn't only indicate the durability of the coating but also the chemical resistance.

--Sabine Rentschar, Carl Zeiss Company

WHICH WAY IS UP?

Q Which way are the molecules in Polaroid sunglasses aligned? I have two sources that seem to conflict about which way the polyvinyl alcohol molecules in the dichroic film are arranged.

--Gary Kenyon, R.O., Faculty, Opticianry Program, Georgian College, Barrie Ontario, Canada

A This has always been a challenge to explain because most people think of light as a beam much like a piece of string. This is not exactly correct, as I understand light and polarization. When we manufacture polarized lenses, we place the film so that the stretch lines are horizontal in the lens when mounted in the frame for the patient. If one views light as a plane of oscillating frequency, not a straight line, then the only planes that will pass through the filter are those that are horizontal when they reach the polarizer. Those planes of light that are perpendicular to the "Venetian blinds" that we call a polarizer are for the most part blocked, depending upon the absorption of the color of dye used in the polarizer. The darker the polarizer, the less transmission.

--Jim Lemmons, Specialty Lens Corporation, Salt Lake City

If you have a question you'd like to have answered in Ask the Labs, send it to Joseph L. Bruneni. Fax: 310-533-8165. Phone: 310-533-4975. E-mail: joe@bruneni.com.  Or mail questions to: Vision Consultants, 2908 Oregon Court, #I-2, Torrance, CA 90503. An archive of past Ask the Labs columns can be found on the Eyecare Business Website at www.eyecarebiz.com.