ask the labs
Q&A
by Karlen McLean, ABOC, NCLC

ABSORBING ANSWER

Q: Is there a standard for the percentage of absorption for tints? How do you measure tint absorption?

A: There is no standard for tint absorption to my knowledge. The rule for tint density is usually in steps of one, two, and three. The lightest, one, blocks about 30 percent of light and transmits around 70 percent. Medium, two, blocks about 50 percent of light and transmits around 50 percent. The darkest, three, blocks about 80 percent and transmits around 20. Ultraviolet and visible light can be measured by a spectrophotometer, which is available from several optical suppliers.

— Daryl Squicciarini, vice president, 1-800-OptiSource, Port Jefferson Station, N.Y.

EDGY QUESTION

Q: Recently, a patient came into our shop with the Rx: OD +1.25 sphere; OS +1.00 sphere; add +1.75. After around two weeks, she called complaining of blinding glare at night. We brought her in for a recheck on the Rx and it remained the same. Although the lenses are AR treated, I'm wondering if the polished edge could be causing her glare problem. Is there an edge treatment you recommend, or should we suggest another type of lens for the nighttime?

A: You're right on track. The polished edge on an AR lens can cause reflections that could annoy the patient. The choices are to forgo the edge polish or to add one of the industry edge treatments available such as Camouflage, which matches the color of the lens edge to the frame. Edge treatments are an affordable, effective way to create a high-fashion look and to help eliminate glare caused by lens edges.

— Dale Parmenteri, vice president, Balester Optical Company, Wilkes-Barre, Pa.

STOPPING TRAFFIC

Q: Do polarized lenses inhibit traffic signal recognition if walking or bicycling?

A: Traffic signal recognition while wearing sunglasses would not be affected unless the specific tint used had a specific recognition reaction. The recognition problem would be the tint, not the polarization, unless there's a specific reaction due to the polarization.

— Steve Rosenberg, president, Kaenon Polarized

Filling in FREEFORM

ATo expand on the answer in "Free Thinker" from the March Ask the Lab, freeform surfacing can be done on either the front or backside of a lens blank. There are currently freeform PALs available in both forms. Not all freeform PALs have the actual progressive lens surface generated via freeform surfacing. Some use a semi-finished progressive front surface combined with an optimized freeform back surface that may be aspheric, atoric, or a surface of a greater complexity. Freeform surfacing can be used to create other lenses as well, including complex single-vision lens designs.

— Darryl Meister, technical marketing manager, Carl Zeiss Vision

If you have a question you'd like to have answered in Ask the Labs, send it to Karlen McLean. E-mail: mcleank@lwwvisioncare.com. Fax: 215-643-1705. An archive of past Ask the Labs columns can be found on the Eyecare Business Website at www.eyecarebusiness.com.