What are Rigid Gas Permeable Contact Lenses?
The first contact lenses were made from the acrylic (plastic) known as polymethyl methacrylate (PMMA) or Plexiglas.
Back then the science of plastics was on the move as acrylic polymers were manipulated by crosslinking carbon chains with various elements like fluorine and silicone improving the amount of gases, oxygen being most important, getting through the lenses. In other words gas permeability was enhanced, and because the lenses material could now breathe so could the cornea. PMMA although having excellent optical qualities, does not breathe at all.
Since PMMA lenses were known as hard contact lenses what should the new breathable lenses be called? They’ve come to be known as rigid gas permeable lenses or RGPs, and to distinguish “soft contact lenses” from the two types of hard material, PMMA and RGP, the latter group has come to be known as “firm lenses.”
Since hard lenses are made from PMMA, now you are asking, “Just what is the material that RGPs are made of?” Right?
Although rarely used PMMA remains a constant, but the variations of RGP materials are boundless. The original material was cellulose acetate butyrate or CAB. Since then RGPs are made from such things as paflufocon, telefocon, flusilfocon, migafocon, and the list is endless. PMMA is a singular material. RGPs are a class of materials in a constant state of change.
Photo credit: Nieuw~commonswiki – contact lenses Confortissimo, Wikimedia Commons