Safety in eye protection has always been an issue. Shortly after World War II, Gentex was contacted 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 resistance made from a combination of polymers and carbonate groups. Polycarbonate was even used for astronaut helmet visors and space shuttle windshields.
While the primary benefits of eyewear is to enable us to see well, when lenses are made of impact-resistant materials, they can also protect the wearer. Face it, kids like to have fun. They run, they play, they throw things, and sometimes that fun gets out of hand. With impact-resistant eyewear, at least we've made it our responsibility to protect their eyes when things do become dangerous. The same is true for adults who lead active lifestyles, participate in sports or whose jobs require them to have protective eyewear.
The most common impact-resistant prescription lens material are Trivex and Polycarbonate. While the two material possess similar attributes, they are produced in two completely different processing methods. Polycarbonate is created from a thermoplastic, and when it's produced, it starts off in a pellet form that is injected into a lens mold. In these molds, the pellets are heated and compressed until they bond and melt, becoming one solid material. This injection-molded process is what makes the lens super soft yet still extremely durable upon impact. Trivex on the other hand, boasts incredible impart resistance similar to polycarbonate yet has one distinctive advantage when processed. Instead of beginning as a formed thermoplastic pellet, Trivex is a urethane-based monomer that is poured slowly into mold, which allows for sharper optics when compared to polycarbonate. Compared to other materials such as glass, CR-39 and other plastics, polycarbonate and Trivex are made softer. When an object hits glass, or CR-39, there is a higher risk that the lens will shatter and harm the wearer.
Another benefit of using an impact-resistant lenses is that they feature inherent, built-in UV-400 protection. Regardless of the lens material, reflections are always present with optical lenses, and a proper anti-reflective coating will always provide a greater benefit to achieving clearer optics. Lenses are available in a plethora of add-ons from glare-free treatments to variable tints. Choosing the right lens material can be a confusing decision. Consult with your optician to determine what customization will work best for you and your family.
Information gathered from, "What makes lenses impact resistant?" by Frank Gimbel, ABOC-AC and "Polymers + Carbonates" by Jill J Luebbert, CPOT, ABOC in Vision Care magazine.