RIGID GAS PERMEABLE (RGP) LENSES

                Shortly after the introduction of hydrogel 
                lenses, rigid gas permeable (RGP) lens 
                materials were developed.  The oxygen 
                permeability was achieved by adding 
                silicone to PMMA.  The increased oxygen 
                permeability significantly decreased the 
                corneal edema.

                Adding the silicone decreased the surface       
                wettability, that is the tear film would not  
                always form on the lens causing vision 
                problems, deposit formation of the lenses, 
                and decreased comfort.  Other compounds 
                were added to minimize these problems 
                including methylacrylic acid, HEMA and 
                fluorine.

Today the vast majority of rigid lenses fitted are gas permeable due to the advantages with respect to corneal health.