Contact lenses were once made of a Rigid Gas Permeable plastic (RGP) and before that, it was a plexiglass material called polymethyl methacrylate (PMMA). These lenses would last much longer than the disposable type of contacts we have today, although RGP and PMMA lenses are still available. In most cases, these lenses last anywhere from a month to a year.
RGP and PMMA contacts require a regular daily care regimen. This involves removing the contacts each night and storing them in a solution after being cleaned. Instead of throwing the contacts out, wearers use the same lenses for an extended period of time that is determined by the expiry date of the lenses.
Although it is possible to wear your contacts past their replacement date, it is not recommended. Doing so can cause irritation or infections.
The one major difference between the two lenses is that RGP contacts allow oxygen to penetrate through to the eye, while PMMA contacts do not. Because of this and the fact that these lenses are so durable, bad habits with respect to the daily maintenance routine can lead to eye health issues.
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