Polycarbonate Lenses: Tough as Nails

Polycarbonate lenses are thinner and lighter than traditional plastic eyeglass lenses. They also offer 100 percent ultraviolet (UV) protection and are up to 10 times more impact-resistant than regular plastic lenses.

This combination of lightweight comfort, UV protection and impact resistance makes polycarbonate lenses an excellent choice for children's glasses, sports eyewear 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 are also a good choice for rimless eyewear designs where the lenses are attached to the frame components with drill mountings.

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.

While polycarbonate is widely used in eyeglass lenses, another lightweight material known as Trivex now represents a significant rival.

In 2001, PPG Industries introduced Trivex as a new, impact-resistant material for eyeglass lenses. This urethane-based monomer (component from which plastics are made) is cast-molded in a manner similar to how regular plastic lenses are created. This gives Trivex lenses the advantage of crisper optics than injection-molded polycarbonate lenses, according to PPG.

Like polycarbonate lenses, eyeglass lenses made of Trivex are lighter, thinner and much more impact-resistant than regular plastic lenses. Ask your professional optician to show you samples of polycarbonate and Trivex lenses so you can decide which lens material is the best choice for your needs and budget.

Similar to the way sunblock prevents the sun's rays from damaging your skin, UV protection in eyeglass lenses shields your eyes from harmful solar radiation.

Both polycarbonate and Trivex lenses block 100 percent of the sun's UV rays. This built-in protection is provided by the lens material itself. So there's no need to purchase special UV-blocking lens coatings.

Polycarbonate lenses are actually constructed out of material that is identical to what is called "bulletproof glass." But while polycarbonate is extremely impact-resistant, it's a relatively soft material. This "softness" gives polycarbonate lenses their ability to absorb energy without breaking.

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 to protect against scratches. And most eyecare professionals offer a lens warranty to protect your lenses against scratches for a specified period of normal use. (Ask your optician for details.)

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 won't usually break if they come into contact with fast-moving objects such as balls, racquets or BBs.

Because polycarbonate lenses hold up better under impact, they are recommended in children's glasses, sports goggles and safety eyewear

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.)
 

Polycarbonate's impact resistant nature could tempt you to forgo purchasing a proper sports frame to instead wear a regular "dress" eyeglass frame to play basketball, racquetball and so forth.

The danger in not using a sports frame is that, while the polycarbonate lenses provide eye protection, a regular eyeglass frame is not capable of holding up to the impact of a ball or racquet.

Therefore, playing sports while wearing polycarbonate lenses in an eyeglass frame that is not rated for sports eyewear is dangerous and defeats the purpose of using polycarbonate lenses for safety.

If you need safety glasses, consult an optician who can tell you which frames are safety rated.

Polycarbonate is always 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.