Knowing the history of this space-age composite will help you fit your patients with a thin, light and impact-resistant lens material.
Glass or CR-39? For years, those were our lens options. Imagine our excitement when we learned that there was going to be a “new” ophthalmic lens material available. It would be lighter than glass, thinner than CR-39 and impact resistant. Polycarbonate changed our industry in a very positive way. Its influence has spanned the decades.
Safety in eye protection has always been an issue. Shortly after World War II, Gentex was contracted to make flight helmets for the U.S. military. The helmets were to have visors made out of the new optical material that was very rough and impact resistant made from a combination of polymers and carbonate groups. Polycarbonate was even used for astronaut helmet visors and space shuttle windshields.
In the 1960s, polycarbonate was filtered in materials for bullet proofing windows in banks and schools. Omnitech organized a number of former American Optical employees to research and develop optical products using this material. They introduced a nuclear flash-protection system for flight helmets, sunglass lenses and a line of welding filter plates. The polycarbonate material was showing lots of potential and yet was still limited because it was extremely soft in its natural state. The answer came in the 1970s when the Dupont Company developed a hardcoating material that seemed ideal for polycarbonate. The marriage of the two products and diligent research moved polycarbonate from strictly a safety product to an optical-quality product for ophthalmic dress lenses.
Today, Gentex Corp., which became a subsidiary of Essilor International in 1995, serves as a primary source for polycarbonate ranging from finished and semi-finished, single vision, multifocals and progressives lens options.
Polycarbonate is 20% to 30% lighter than 1.50 plastic with a specific gravity of 1.21 compared to Crown glass at 2.54 or CR-39 at 1.32. Polycarbonate, by nature of the material, offers 100% protection from UVA and UVB. In comparison, CR-39 has a UVA transmittance of 10.3, and Crown glass has a transmittance of 84.3 of UVA and 30.5 of UVB.
The most significant benefit of polycarbonate is its impact resistance, up to 12 times that of plastic. The lightweight, UV protection and safety quality of this material make it a perfect option for sports eyewear, kid’s eyewear and sunglasses. Because of its protective qualities, one reason retailers across the country made polycarbonate their material of choice for children’s eyewear was to address liability issues. Kids tend to be rougher on their eyewear. They drop them, toss them and simply play rough with them. The molecular structure of the polycarbonate makes it more flexible for those circumstances.
Also, being among the most impact-resistant lens materials available, polycarbonate is also the choice for safety eyewear. If a polycarbonate lens is hit with force, it will not shatter but instead will flex and remake intact.
Tinting of polycarbonate lenses can be challenging due to the softness of the material, which makes the acceptance of the dye more difficult to control. Also, polycarbonate’s shatter resistance is the same quality that limits its frame options. For example, polycarbonate will expand and shrink when exposed to heat, so drilling holes in a lens for a drill-mount frame heats the material and causes the lens to have a higher tendency to crack or “starburst” at the drill point.
Polycarbonate, which is marketed under several different names, is available across the market in the ophthalmic lens industry. Based on lens shipment reports from The Vision Council, it makes up about half of the market. Retail percentages are higher. It may be marketed under several different names.
The beauty of polycarbonate is that it is available for any lens design-single vision, segmented multifocal, progressive addition lenses and digital designs. The lens is available with a plethora of add-ons from glare-free treatments to variable tints. The price point of polycarbonate material makes it even more appealing. Polycarbonate, it’s the material that your patients will appreciate and that you can feel good about recommending.
Jill Luebbert, CPOT, ABOC, is a certified paraoptometric and optician practicing in northeastern Nebraska.