Ask the Labs
By Joseph L. Bruneni

POLY THICKNESS FOR KIDS

Q In discussing lens thickness for children's eyewear, we use standard 1.5mm thickness polycarbonate. Our doctor has decided that a minimum of 1.8mm to 2.0mm would be safer. Are there legal ramifications to using standard thickness poly? The cost difference between stock 1.5mm polycarbonate and surfaced lenses is substantial.

A The Polycarbonate Council advises not using super thin (1.0mm CT) poly for children even though at 1.0mm center thickness, the lenses far surpass FDA minimum impact requirements. The usual recommendation is standard thickness poly for children since poly and Trivex are the safest materials currently available. If the doctor or dispenser feels better (or safer) using thicker lenses for active youngsters, 2mm poly would add protection. Using 3mm thick poly lenses serves little purpose and adds cosmetic and weight disadvantages. The new proposed ANSI Z87 standard is expected to permit industrial prescription safety eyewear to be 2mm thick in poly and the new Trivex. When labs surface poly to 2mm thick, it does add cost, but there may be a bright note in the future. If and when the proposed Z87 standard allowing 2mm industrial safety lenses is finally approved, manufacturers are expected to produce 2mm poly stock lenses for industrial use. That should reduce cost for 2mm lenses.

--Polycarbonate Lens Council

UPDATE ON TRIVEX LENSES

Q I am writing about the Ask the Lab item entitled Myth or Reality in April's Eyecare Business. The Trivex material (Phoenix) lenses cannot be surfaced to a 1.0 CT. They can only be ground to a 1.3 CT. We have had several accounts request a 1.0 and I have always just been told that we cannot go less than 1.3 center thickness.

--Natalie

A Hoya's scratch coated Phoenix Trivex lenses can routinely be surfaced to 1.0mm centers. When Phoenix lenses are AR-coated, it's prudent to leave the material slightly thicker (1.3mm) as a safety precaution. Our laboratories never know whether customers will later have lenses with 1.0mm centers AR-coated. For safety reasons, we prefer to err on the side of caution and not process thinner than 1.3mm. Hoya is a conservative company and believes this precaution protects our customers and their patients.

--Bill Norwood, Exec. V.P., Hoya Vision Care Headquarters

Editor's note: Younger Optics also produces lenses made of Trivex, which they call Trilogy. Younger's printed literature states that Trilogy lenses can be processed to 1.0mm center or edge thickness and still maintain excellent optics. Individual laboratories sometimes establish their own minimum thickness for various types of lens materials.

NO MORE GLASS BASHING

A Eyecare Business' recent article "Testing for Toughness" stated, "Following the new FDA regulation, however, glass lenses had to be no less than 2.2mm thick at their thinnest point." That only tells half the story and could lead to the impression glass lenses are dangerous and there is still a minimum thickness standard. There is NO minimum thickness requirement for glass dress lenses (except "carryover legislation" in California). The minimum CT for glass safety lenses is 3.2mm. Early FDA rulings (1971) did not recognize chem tempering. FDA's concern was that heat-tempered lenses varied in impact tests. FDA regulations never specified a minimum thickness. New FDA rulings require that all glass lenses pass the "drop ball test." Glass lenses are 100 percent tested for impact resistance, unlike other lenses that are untested or tested in sample quantities. The 2.0mm minimum thickness was required in ANSI Z80.1-1972, recommended in ANSI Z80.1-1979 and dropped from ANSI Z80.1-1987.

--John Miller, X-Cel Optical

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.