<prompt> Rigid gas permeable lens are made of-PlymethymethacrylateHydroxymethylmethacrylateCo polymer of PMMA, Silicon containing monomer cellulose acetyl butyrateCellulose acetae Butyrate  <response>: 1. Hard lenses: Made of pokymethylmethacrylate PMMA 2. Rigid gas permeable RGP lenses: Copolymer of PMMA, silicon containing vinyl monomer cellulose acetate butyrate CAB are used to manufacture RGP lenses. 3. Soft lenses: These are made up of hydroxymethymethacrylate HEMA 