Ask The Labs
By Joseph L. Bruneni

COUNTING BEADS WITH DIDYMIUM LENSES

Q We have a patient who makes glass beads and needs to update her glasses into a bifocal using didymium. Do you know where we could obtain these lenses?

--Cindy Gaw

A I presume that she is glass blowing or kiln heating, where didymium lenses absorb sodium flair. If she's merely working with unheated or unfired glass beads, no special eyewear is needed. Didymium SF D28 and single vision lenses are available from X-Cel Optical. We also have finished safety thickness (3.2mm) Plano 6 base didymium lenses.

--John Miller, vice president,
X-Cel Optical Company

PROBLEM IN KANSAS

Q What should we recommend to remove what appears to be a thin layer of hard water deposits, maybe calcium carbonate, from a patient's polycarbonate eyeglasses?

A Hard water deposits are difficult to remove from any material. Soaking eyewear in warm water with a few drops of non-detergent dish soap for about 15 minutes, followed by a warm water rinse and drying with a soft clean cloth, will usually remove most of the deposits. With years of build-up, it may be impossible to remove it all. Do not use harsh chemicals, as they may also remove the scratch resistant coating.

--Denny DeCourcy, Vision-Ease Lens

DEEP FREEZING PHOTOCHROMICS

Q My fellow opticians advise our patients to put their photo-chromic glasses in the freezer, telling them that the lenses will perform better. They believe that, since photochromic lenses are influenced by temperature, this makes them turn darker and perform faster. Is this factual?

--Tim, LensCrafters

A There is no truth in this old wives tale! Some photochromics will appear darker, or even too dark, in cold temperatures due to slower opening and closing of the photo-chromic molecules, but storing your lenses in the freezer will not enhance performance or life span. Unless you want to live in your freezer, you'll just get condensation on your lenses when you remove them and put them on!

--Jim Schafer, manager, technical sales, Transitions Optical, Inc.

REALITY or MYTH?

Q I read about the myths regarding Abbe values on the Poly Council's Website. They claim that low Abbe values only come into concern with lenses over 7.00D to 8.00D. Why are lenses less than 7.00D not concerned about Abbe? As an optician, I have noticed chromatic breakdown on poly with lower corrections.

A Many wearers are not sensitive to Abbe-type complaints regarding color fringes towards the edge of the lens. Poly is ideal for minus lenses because of its relatively high index, 1.59, and because it can be surfaced to 1.0 centers. AR coatings are always recommended for high index lenses, no matter which material is selected. AR also often eliminates Abbe-type complaints.

A second option for strong corrections could be the new Trivex material that is now available in lenses produced by Younger and Hoya. This material has a relatively high Abbe and can be surfaced to 1.0 centers, making it ideal for high minus. For another option, we saw some high minus lenses made with Optima's 1.66 with a minus front surface. Again, AR coating would be recommended.

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.