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Lenses are
made from several different materials. There are a great many lens formulas
and coatings with different performance characteristics.
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Glass-
Original material used for glasses, these lenses are made mainly of sand
(silicon dioxide) plus various element (such as titanium dioxide for
thinness). Glass lenses are long-lasting and naturally scratch-resistant.
They are heavy and breakable but can be treated for shock resistance.
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Standard
Plastic- Developed in the 1960's, plastic lenses are made of hard resin
that is light and impact resistant. It is thick and easily scratched
unless treated with a protective coating.
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Mid-index
Plastic- First used in the early 1990's, higher index refraction means
this material reduces lens thickness without compromising optical
performance. It is recommended for light to moderate prescriptions. A
protective treatment can reduce scratches.
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High-index
Plastic- The third wave of plastic materials provides an even higher index
of refraction. It is ideal for those with moderate to severe correction
needs because higher power prescriptions can be made lighter and thinner.
A protective treatment can reduce scratches.
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Polycarbonate- The newest lens material is an acrylic-like resin that is
used for airplane windshields. It is the thinnest, lightest and most
impact-resistance of all lens materials, and comes with a
scratch-resistant coating. Polycarbonates are also inherently good at
filtering UV rays.
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