Now, I want to continue our history lesson that we discussed earlier. You now know that the introduction of the first lens made entirely of PMMA plastic or what we refer to as hard lenses was in 1948, however one of the main concerns was the exchange of oxygen to allow the cornea to breathe. So, in 1978 the introduction of a rigid gas permeable contact lens or more commonly referred to as RGP or GP lenses, made its debut. In 1986, overnight wear of GP contact lenses became available and a new material introduction of fluorosilicone acrylate came about in 1987. 

Refinements continue to be made to help improve comfort. In today's inventory of RGP lenses come from a variety of at least 48 different contact lens materials. If you've ever seen an RGP lens, you know that it's smaller typically from a soft contact lens and you may wonder how does that thing stay on the eye? Well with adequate moisture on the surface of the cornea it creates surface tension, so that the lens may adhere properly. The back surface is contoured to exactly fit the curvature of the cornea and any fluid, if there is any, between the lens and the cornea fills out any irregularities to change the curvature of the front of the lens and defines the refractive power.