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

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Glaucoma is an eye disease in which pressure increases in the eye due to clogged or blocked passages. Fluid that normally drains through these passages begins to build up, and the increased pressure can damage the optic nerve. Open-angle glaucoma tends to develop without warning--often painlessly and with no symptoms. Because of this, it can cause damage and blindness more quickly when untreated. Risk factors for developing glaucoma include people over the age of 40; those who have a family history of glaucoma; those who are very nearsighted; diabetics; and African-Americans.

Additional keywords and misspellings:
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A form of glaucoma in which the pressure of the eye becomes elevated due to the inability of the aqueous fluid to drain properly; specifically, because the iris prevents the fluid from reaching the anterior chamber drainage tissue (trabecular meshwork). The drainage tissue functions normally but the iris blocks the passage of the fluid.

Gonioscopy is a test performed on patients who either have or are suspected to have glaucoma. A special mirrored contact lens is used to allow the doctor to examine the eye’s drainage system.

Another name for corpus nigra.