Polycarbonate - "Tough as Nails"
How strong is a polycarbonate lens? The photo at the right gives some idea. A nail has been hammered through the lens, and it is now anchored in the lens. The lens has not shattered or cracked as might be expected.
Polycarbonate is used in many applications requiring great flexibility and strength, such as "bullet proof" windows and safety lenses. Some of polycarbonate's other properties make it an excellent choice for regular glasses as well.
For maximum impact resistance, polycarbonate is the obvious choice. Polycarbonate lenses are ten times more impact resistant than conventional plastic or glass lenses. While impact resistant does not mean shatterproof, polycarbonate lenses can give an extra level of protection to lens wearers who have active lives or participate in sports. Polycarbonate is the material preferred for children and teenagers, as well as people who work in hazardous manufacturing occupations.
The basic polycarbonate material is quite soft which is why the material can absorb so much impact. When used for eyeglass lenses, polycarbonate always includes a tough, scratch-resistant coating applied to both sides of the lens. This coating provides protection against normal handling scratches.
Developed originally for the aerospace industry, polycarbonate is used in the windows found in airliners and face plates in astronauts' helmets. The helmets used by baseball and football players are also made from polycarbonate.
Polycarbonate lenses are thinner and lighter than conventional plastic or glass lenses. Polycarbonate was the first plastic "high index" lens material. High-index materials are useful because they bend light more - so less material is needed to create a given prescription.
Long-term exposure to ultraviolet light (especially UV-B) is thought to increase the risk of cataracts and damage to the retina. Wearing a pair of sunglasses that absorbs visible light but NOT ultraviolet light is probably more damaging than not wearing sunglasses at all - because sunglasses leave the wearer less conscious of the dose of ultraviolet he is receiving. Polycarbonate lenses have built-in ultraviolet protective properties. Just as sunblock can help prevent the sun from damaging your skin, polycarbonate's built-in UV protection can help prevent damage to your eyes.
The frame makes a difference!
Using a "dress" frame with polycarbonate lenses is fine when your primary goal is to create thinner, more cosmetically appealing lenses.
When your goal is eye protection for sports, remember that the frame is all that anchors the lenses at a safe distance in front of your eyes. A frame that is stylish but not made from durable materials, greatly reduces the safety advantages of polycarbonate. Try to choose a frame that provides greater facial coverage and deeper grooves for holding the lenses in the frame. Frames with thin eyewires (part of frame surrounding lenses) usually have shallower lens grooves. If your lenses are impacted, a frame with thicker eyewires and deeper lens grooves is simply more likely to hold the lenses in place.
Polycarbonate lenses can protect eyes from many hazards in the workplace or at home, but if they are placed in a frame that is not safety rated, they may not provide adequate protection. If glasses are to be used in the workplace, the law requires that certain standards are met; the term safety "glasses" refers to the frame just as much as it does to the lenses.
Always wear appropriate protective eyewear when participating in activities such as baseball, basketball, hockey, lacrosse, football, soccer, paintball and racquet sports.
In addition to being the most shatter resistant material available, polycarbonate is also thinner and lighter than standard plastic, so it improves the appearance of most prescription lenses. Whether used for dress or sports eyewear, polycarbonate has some definite advantages. The next time you visit your eye doctor, be sure to ask if lenses made from polycarbonate would be a good choice for you.
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