 Although soft contacts are more common, gas permeable (GP) contact lenses become more and more popular among lenses wearers. There are also other names for this type of lenses: rigid gas permeable lenses, oxygen permeable lenses, RGPs.
GP contacts are made or rigid plastic, but it’s not old hard contact lenses, which are out of production now. The outdated ones were made of polymethylmethacrylate (PMMA). Almost all contacts were made of this type of plastic before the soft contact lenses were invented. But it had one serious disadvantage: it didn’t allow the oxygen to pass through to the retina. Also they were uncomfortable to wear. If compare GP lenses and soft lenses, GP lenses are smaller in diameter.
GP lenses are newer than soft lenses (they were invented in the second part of the 1970s, and soft lenses were introduced in 1971). Also silicon was added to the composition of GPs. Thanks to this they are more flexible than hard lenses. Silicon is oxygen permeable material, that’s why new GP lenses became safer for eyes. GP contacts pass through even more oxygen than soft lenses thanks to the silicon in its structure (except silicone hydrogel soft lenses).
GPs have many other advantages: they are more wear-resistant and deposit resistant; they supply better vision for wearers. It’s much easier to clean them. They are more economical.
GPs wearers see more clearly than soft lenses wearers thanks to their hardness (it stays in the right form even if a person blinks).
A person can wear GP lenses for many years unless he or she needs new prescription or step on it.
Also they don’t contain water. This means that lipids and protein from eyes won’t make deposits on the lenses.
For many categories of people GP lenses are the best way to correct vision. They are: people with astigmatism, who are not satisfied with the acuity of their vision with soft lenses; people, for whom the quality of their vision is very important.
Also there is great variety of bifocal and multifocal designs of GP lenses, which are appropriate for people with presbyopia (a lot of GP bifocals wearers affirm that the mixture of close and distance acuity is the best).
GP contacts are also good for people with keratoconus and people after refractive surgery.
Some ophthalmologists use GP lenses to perform ortho-k (a procedure for producing of good vision without surgical aggression).
Among large number of advantages a few disadvantages should be named. One of the main faults of GPs is the lack of comfort for wearers. An adaptation period is to pass before you get use to these lenses and feel comfortable. You have to wear them constantly and make breaks for no longer than one week.
Also GPs wearers might feel spectacle blur (after you take off the lenses your vision will be blurry for some period).
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