Rigid Gas Permeable Lenses

Rigid gas permeable lenses (RGP lenses) are also made of plastic. Unlike the plastic that makes a soft contact lens, the rigid gas permeable lens transmits oxygen without absorbing water. Instead, RGP lenses have microscopic holes in them that allow the oxygen to filter through. For this reason, RGP lenses are classified by their oxygen permeability instead of their water content. Most RGP lenses are now made of three main materials: acrylate, silicone and fluorine.

RGP lenses are sometimes called “hard” lenses, but they aren’t like the “hard” lenses of decades ago that were made mostly of acrylate. Those lenses are no longer prescribed because not enough oxygen could get through this type of material. Lens manufacturers added silicone to increase oxygen permeability over the years and eventually added flourine to help keep the lenses moist while still retaining their shape. This shape-retaining property allows for them to be used as treatment for the correction of eye issues such as keratoconus (when the cornea is misshapen).

Some contact lens wearers who crave a better visual experience through their contact lenses also like the visual acuity that comes from wearing a contact lens that is firmer and stays put on the eye.