ask the labs
Trivex Troubleshooting
Karlen McLean, ABOC, NCLC
A good number of ECPs agree that Trivex is a great material for high-impact resistance, durability, and edge-to-edge visual acuity, making it ideal for sports and kids eyewear—and really, for anyone. But many ECPs have questions regarding Trivex best practices.
Here are key ECP questions, along with lab experts’ answers.
TRIVEX DESIGN
Q Are all Trivex-branded lenses now available in aspheric design? Are there choices in non-aspheric and aspheric lens design with Trivex, and do I have to designate which I prefer when ordering?
A I'll start out by saying Trivex material, whether aspheric or non-aspheric, is very beneficial for a patient's vision.
Most manufacturers have Trivex lenses available in both aspheric and non-aspheric designs. For example, single vision is available in aspheric more often than D-28s.
When a doctor or optician orders single-vision Trivex, it's best to specify if he or she wants aspheric or non-aspheric. This helps the lab process the order efficiently, and also saves time.
—Joe Kasyan, president, Donaldson Optical Company, Pittsburgh
TRIVEX CENTER THICKNESS
Q What is the generally recommended center thickness to which Trivex can be ground? Can that number differ depending on the manufacturer or lab?
A Manufacturers recommend a 1.4 center thickness for the surfacing of Trivex for AR-coated Rx work to help prevent flexing of the lens while washing and during the actual lens-coating process. For standard dress eyewear, the recommended center thickness is 1.2.
Best practices call for following the manufacturer's recommended thicknesses. Labs may grind Trivex to a 1.1 or 1.0 center depending on the lab's success grinding to these centers.
—Eddie Purmann, director of lab operations, Reliable Optics, Brooklyn, N.Y.
If you have a question you'd like to have answered in Ask the Labs, send it to Karlen McLean, via email at Karlen.McLean@WoltersKluwer.com. An archive of past Ask the Labs columns can be found on the Eyecare Business website at www.eyecarebusiness.com.
Trivex: Lighter, Not Thinner |
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Q I've heard that Trivex is the lightest-weight lens material, but I've also heard that it can be thicker than poly. What gives? A The specific gravity of a lens material determines its weight. The lower the specific gravity the lighter the lens. Polycarbonate specific gravity is 1.20; Trivex is 1.11. For comparison, the specific gravity of standard plastic is 1.32. Thickness can be determined by the index of refraction if all parameters are equal. The lower the index, the thicker the lens. Trivex, with an index of refraction of 1.53, is thicker than poly, which has a 1.59 index of refraction. Poly is thicker than 1.60; 1.60 is thicker than 1.66, and so on. So, in conclusion, Trivex is lighter, but poly is thinner. —Joe Jowanowitch, lab manager, Homer Optical, Silver Spring, Md. |