Soft and rigid gas permeable (RGP) are two main categories of contact lenses. All medical contact lenses demand prescriptions. More detailed classification of contacts is the next:
 1. Soft contacts
This type of lenses is made of supple and soft plastics. The main and very important characteristic of this material is that it passes the oxygen through. Soft lenses are more comfortable to wear and it’s easy to fit them. There is no adaptation period for it’s wearing, unlike gas permeable lenses. Some of the last soft lenses models have silicone-hydrogels in its composition for better oxygen supply.
2. Rigid gas permeable contacts (RGP lenses)
This type of lenses is made of rigid plastic. But this kind of plastic is not that hard as polymethylmethacrylate (material for old hard lenses). Silicon was added to the structure of GPs. It made them less hard and oxygen penetrating. Gas permeable contacts are more economical since they are more long-lasting in usage and deposit resistant. Also GPs provide better vision than soft lenses for people with vision problems.
Unlike the soft lenses (which can be easily torn because of water in its composition), the only way to damage GPs is to step on them. This type of lenses has one serious disadvantage: they are somewhat uncomfortable to wear for the first time and they require couple week adaptation period.
3. Disposable contact lenses
A special program of frequent lenses substitution is designed for the vast majority of people, who wear soft contact lenses. This means that person changes one pair of lenses for another one constantly. A definition “disposable” implies that lenses replacement takes place each day. But, as usual, wearers use disposable lenses for certain prescribed period, which can last from couple of days to one month. After this period the lenses are discarded.
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