(RGP), or just Gas Permeable (GP) lenses are sometimes mistaken for old-fashioned lenses. The old hard contact lenses that people know are rarely used today.
RGP lenses are more pliable, more comfortable, and they allow oxygen to the cornea. Gas permeable lenses also allow more oxygen to the cornea than traditional soft contact lenses.
The biggest disadvantage of RGP lenses is that patients need to get used to them. They are not immediately comfortable like soft lenses. RGP lenses can take several days for patients to adapt to them. They need to be worn regularly to achieve optimal comfort. They are smaller in size, so they can dislodge from the eye more easily than soft lenses.