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Lens materials

Plastic lenses, first introduced in the 1960s, seemed to have many advantages over glass lenses.

health and fitness Updated: Aug 06, 2003 19:10 IST
PTI

For 600 years the traditional lens material has been glass. Today we have a range of materials to choose from:

Glass

Plastic

Poly carbonates

High Index plastics

Glass: The earliest documented use of spectacles has been in the 13th century in Italy. Since then to the mid-twentieth century glass has been the material from which lenses have been made. The properties that make glass a good material for making lenses are:

It has excellent optical qualities

It is scratch resistant

The disadvantages of using glass for spectacles are:

It is heavy

It shatters easily

It gives the soda bottle look and is not preferred for aesthetic reasons.

Plastic: Conventional plastic lenses, first introduced in the 1960s, seemed to have many advantages over glass lenses. But their usefulness has been challenged by the arrival of (polyurethane) high index plastic.

Advantages of the traditional plastic lenses are:

They are lighter than glass

They do not shatter like glass

The disadvantages, however, are:

They are as thick as glass lenses

They are not scratch resistant

(To be continued)

(Source: Webhealthcentre.com)