Lens material is a triple jump in technology

March 15, 2006

For strength, light weight, and visual clarity, many eye-care professionals are turning to Trivex, a completely new category of lens material.

Made by Pittsburgh-based PPG Industries Inc., the lens material has a chemistry that enables it to deliver three key qualities in a single lens. This triple jump in technology is not only an advancement over CR-39 material but also a major competitor for polycarbonate, making it an excellent choice for all eyewear, particularly for rimless, three-piece mountings.

Because the lens material delivers its unique trifecta of superior optics and impact resistance in an ultra-lightweight lens, eye-care professionals and their customers no longer need to sacrifice one lens attribute for another. That makes the lens material well suited for children, sports activities, and overall lens performance.

Originally developed as visual armor for the military, the lens material monomer is sold to lens manufacturers for copolymerization and casting for lens production. Its inherent chemical properties allow lenses made from Trivex material to be virtually stress-free.

Although the lens material is a thermosetting plastic (thermoset), it also has thermoplastic characteristics. In thermoplastics, the molecular chains are independent of each other and can flow freely so the material can be re-formed. But in thermoset materials, cross-links are created during polymerization, resulting in a complex, interconnected, and permanent network. Thermosets cannot be melted and reshaped.

Visual clarity, excellent optics

The lens material has an index of refraction at 1.53 and its specific gravity is 1.1, making it the lightest of any prescription lens material available today. There is also 100% UV protection from 315 nm to 394 nm. Because its tensile strength makes it resistant to cracking around the drill holes, lenses made with Trivex material are ideal for drill mountings. An Abbe value of between 43 and 45 makes the lens material optically superior. Polycarbonate has an Abbe value of 29.

Named after optical pioneer Dr. Ernst Karl Abbe, Abbe value is a numerical value indicating the amount of chromatic aberration that occurs when light is bent through the lens. The higher the Abbe value, the lower the amount of chromatic aberration. According to one German study, patients are more likely to perceive color blur in Abbe values less than 40.

Making an impact

Trivex material qualifies for the new high impact requirement created under the American National Standards Institute (ANSI) standard number Z 87.1-2003. Under ANSI Z 87.1-2003, two new impact resistance classifications were established: basic impact and high impact.

In general, impact-resistant glass does not even take 0.1 ft-lb. CR-39 monomer takes 0.3 ft-lb. Polycarbonate and lenses made from Trivex are comparable at about 16 ft-lb., depending on the lens design.