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Materials for different contact lenses

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Nicholas Yiu        02/05/2007

Materials for different contact lenses

There are three main types of contact lenses. They are hard contact lenses, soft lenses and gas permeable lenses. Contact lenses were invented a century ago. At the beginning, there are only hard contact lenses which are made out of glass, then soft contact lenses were invented and gas permeable lenses have only started the development in the last decade. They are trying new material for gas permeable lenses.

Hard contact lenses

Hard contact lenses nowadays are made of Polymethylmethacrylate (PMMA) which is generally known as Perspex. It is the second stage of hard contact lenses. The advantage of hard contact lenses is that it doesn’t pull moisture from eyes. The hardness of the material cause it to retain shape better which make the vision crisper.

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Soft contact lenses

Soft contact lenses are made of hydroxyethylmethacrylate (HEMA). The structure of the polymer contains OH chains which mean they are 35-80% water. Therefore, they are part way between solid and liquid. The advantage of soft contact lenses is that they are flexible, which make them easier to mould to the contours of the eyes. They allow some oxygen through which is essential for health of eyes. However, soft contact lenses tend to collect deposits and that harbour bacteria. They could dehydrate when it is left in the air, also, they tear easily. This makes them quite expensive and hard to care.

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These disadvantages are overcome by the fact that they have no barrier to gas; this stops the development of some long-term contact lens problems to the eyes. They also resist deposits therefore; they are less likely to harbour bacteria. The do not dehydrate and pull moisture from the eyes. They are hard to scratch or tear because of the structure of the polymers. They are also firmer than soft contact lenses. However, they are not as hard as hard contact lenses. This combines the advantages of soft and hard contact lenses. These properties make it last longer than soft contact lenses. Therefore, in long term, they actually are better for the eyes and they are also more economical than soft contact lenses.

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