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Spectacle Lens Materials: Which Choice is Right For You? 
by Kira Connally June 10, 2005

The Materials-Lightweight Lenses Defined

Glass-Glass lenses are rapidly becoming outdated. Glass spectacle lenses are significantly thicker and heavier than plastic lenses. Though glass lenses are heat-tempered to further harden them before they are cut to fit your frame, they offer no safety protection. They are difficult to manufacture and replace, causing them to be more expensive than plastic.

Glass lenses also frequently break during the cutting process, which can lengthen the time you’ll have to wait for your glasses to be completed. Glass lenses may be fashion-tinted or treated to darken in the sun while remaining clear indoors. The only benefit to glass lenses is their superior scratch-resistance.

CR-39 Plastic-This is the standard plastic lens available in today’s optical shops. CR-39, commonly referred to as plain old plastic, is a much lighter lens material than glass and is very cost-effective. These lenses are suitable for most prescriptions and can be coated to provide scratch resistance, ultra-violet protection and anti-glare qualities. CR-39 lenses are also available in fashion tints, sunglasses, or treated to darken outdoors. CR-39 lenses are not suitable for safety purposes, children, or people with severely compromised vision.

Polycarbonate-Polycarbonate lenses are a popular choice for a variety of needs. These lenses are thirty percent thinner and lighter than CR-39 and have the added benefit of impact-resistance. All safety lenses certified by OSHA for use in the workplace are made of polycarbonate. These lenses are recommended for athletes, children and those with severely compromised vision to protect their eyes from injury.

Polycarbonate lenses, because of their thinner and lighter qualities, are a good choice for people with moderate to high prescriptions. Anyone with more than three diopters (+3.00 or -3.00 written on the prescription) of visual correction will notice the improvement in comfort over glass or CR-39 lenses.

Lenses made of polycarbonate offer better scratch-resistance than CR-39 and come with built-in ultra-violet protection. They can be tinted for comfort, made into polarized sunglasses, treated to darken outdoors or to reduce glare.

Polycarbonate lenses are not the thinnest lenses available, and they can cause visual distortion at the edges in high prescriptions or those lenses including astigmatism. Even with these drawbacks, these are the best lenses for safety glasses, children, or those who want more protection for their eyes in case of an accident. Many insurance companies and optical retailers discount polycarbonate lenses for children’s spectacles.



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