Gas Permeable contact lenses are rigid lenses that allow oxygen to pass through them. Most brands today have an oxygen permeable between 60 to 90%. Also, they "wet" much better than the first generation gas permeable so they are much more comfortable.
These lenses are used when the patient has astigmatism that cannot be corrected with a toric soft lens. Also, if the cornea is irregular, these lenses allow sharper vision.
The main disadvantage of this type of lens is that it takes a longer period of time for the patient to adapt to wearing the lenses.
(contributed by H. Frank Storey, OD)