When eye safety is a concern, polycarbonate lenses usually are the best choice for your eyeglasses, sunglasses and sports eyewear. Polycarbonate lenses are thinner and lighter than regular plastic lenses. They also offer 100 percent protection from the sun’s harmful UV light and are up to 10 times more impact-resistant than plastic or glass lenses. This combination of lightweight comfort, UV protection and impact resistance also makes polycarbonate lenses an excellent choice for children’s glasses and safety glasses. Polycarbonate was developed in the 1970s for aerospace applications, and is currently used for the helmet visors of astronauts and for space shuttle windshields. Eyeglass lenses made of polycarbonate were introduced in the early 1980s in response to a demand for lightweight, impact-resistant lenses. Since then, polycarbonate lenses have become the standard for safety glasses, sports goggles and children’s eyewear. Because they are less likely to fracture than regular plastic lenses, polycarbonate lenses also are a good choice for rimless eyewear designs where the lenses are attached to the frame components with drill mountings.
How Polycarbonate Lenses Are Made
Most other plastic lenses are made from a cast molding process, where a liquid plastic material is baked for long periods in lens forms, solidifying the liquid plastic to create a lens. But polycarbonate is a thermoplastic that starts as a solid material in the form of small pellets. In a lens manufacturing process called injection molding, the pellets are heated until they melt. The liquid polycarbonate is then rapidly injected into lens molds, compressed under high pressure and cooled to form a finished lens product in a matter of minutes.
In this test, a BB was shot at three different lenses worn by a mannequin. The first lens, made of polycarbonate, didn’t break into pieces because it had more “give.” The second lens (plastic) and third lens (glass) were completely shattered. Never try this test at home because of risk of serious injury. (Images: Vision Consultants Inc. and Gentex Optics)
UV and Scratch Protection
Similar to the way sunblock prevents the sun’s UV rays from damaging your skin, eyeglass lenses should shield your eyes from harmful solar radiation. Polycarbonate lenses block 100 percent of the sun’s harmful UV radiation. This built-in protection is provided by the lens material itself. So there’s no need to purchase special UV-blocking lens coatings.
Part of the reason polycarbonate is such an impact-resistant lens material is because it’s a relatively “soft” material, meaning it is able to absorb energy without fracturing. This flexibility also means polycarbonate lenses need a scratch-resistant coating to prevent surface scratches. Today’s modern scratch-resistant coatings can make the surface of polycarbonate lenses nearly as hard as glass. Most eye care professionals offer a lens warranty to protect your lenses against scratches for a specified period of normal use. Ask your optician for details.
More About Impact Resistance
Regular glass and plastic eyeglass lens materials can shatter upon violent contact in the same way that car safety glass does, which can cause serious injuries to your eyes and face. But polycarbonate lenses are safer for eyeglasses than traditional lens materials because they aren’t brittle. They usually won’t break if they are struck by fast-moving objects such as balls, racquets or BBs. Studies have compared what happens with a polycarbonate lens versus a traditional plastic lens when an object traveling at high speed meets the materials. Using film that is slowed down and viewed frame by frame, one investigation showed that a fast-moving ball coming into contact with a plastic lens broke the lens and impacted the eye. In contrast, the same ball traveling at the same rate of speed impacted the polycarbonate lens and flexed the lens but did not break it.
(Caution: Do not test polycarbonate lenses by firing BBs or hurling objects at them while someone is wearing them! Polycarbonate lenses are highly impact resistant, but that doesn’t guarantee they are shatterproof.)
Proper Frames for Polycarbonate Lenses
But when it comes to eye safety, lenses are only part of the solution. For the best eye protection at work and during sports, be sure you invest in high-quality safety frames or frames designed specifically for sport eyeglasses. Regular eyeglass frames are not rated for use as safety glasses and typically don’t provide the type of eye protection needed for sports. Therefore, playing sports while wearing an eyeglass frame that is not rated for sports eyewear is dangerous and defeats the purpose of wearing polycarbonate lenses for safety. Polycarbonate is recommended for all types of children’s frames because kids tend to be rough at play even when they are not taking part in an organized sport.