glaucoma Glaucoma Open-angle glaucoma needlessly blinds over 80,000 Americans each year.  It causes another 900,000 to lose some vision. Glaucomas are a group of diseases sharing some features, commonly including intraocular pressure, damaged optic nerves, and loss of peripheral vision.  Early detection can contain two glaucomas: chronic (also called common) and acute. Primary open-angle glaucoma affects mostly adults over age 35. This is the most prevalent form and is the "sneak thief" disease without noticeable symptoms. By the time it's detected, it has started doing damage. The uncommon primary angle-closure glaucoma may seem the opposite of common glaucoma, erupting in a sudden, violent attack.  It's also possible to get both common and acute ("combined-mechanism") together. The unusual low-pressure glaucoma is another type. Regular eye examinations can help protect against the onset of open-angle and closed-angle glaucomas. Glaucoma Basics The cornea is the clear outer covering of the eye. Separating it from the iris (the colored part) is the anterior chamber, a space filled and inflated by aqueous humor. This fluid, unrelated to the tears which bathe the outside surface of the cornea, originates in the ciliary body just behind the iris. It circulates in the anterior chamber, nourishing the eye's delicate tissue and keeping it from collapsing, at a pressure usually measuring between 10 and 20 millimeters of mercury.  To maintain balance, the aqueous humor drains through a porous tissue in the angle in front of the iris where it meets the cornea called the trabecular meshwork. If the aqueous humor cannot drain properly, either because the drainage canals become clogged (as in chronic glaucoma) or because the iris is pushing against the cornea (as in angle-closure glaucoma), it backs up, exerting pressure on the gel in the vitreous cavity at the center of the eye. Eventually the building pressure affects the delicate optic nerve in the rear.  Since the optic nerve transmits visual images to the brain, damage to parts of it therefore reduces vision. Pressure of over 21 millimeters may prompt concern, while pressure over 24 mm can indicate glaucoma level, but not always.  These measures are not absolute.  Some individuals tolerate higher pressures than others. Half the people with undiagnosed glaucoma have pressures below 22 mm, while others with higher pressures never develop the disease, with optic nerve damage causing the loss of vision.  Low-pressure glaucoma can be particularly elusive. Tonometry Tonometry is the measurement of eye pressure. Tonometry is affected by many factors, even by the time of day.  Usually intraocular pressure measures highest in the morning. Tonometry measures the force necessary to indent the eye.  One method is to anesthetize the eye, then press a tonometer onto it.  Another is to measure the force needed for a puff of air to indent the cornea. While widespread eye-puff testing at public health fairs can detect pressure levels, a more thorough examination calls for an ophthalmoscopic test enabling eye doctors to see into your eye to examine the optic nerve for damage or a high ratio of its central cup to the surrounding disc. They must also consider personal traits into account in evaluating your risk of this disease. We have a lot of additional information you can find on the navigation panel on glaucoma and treatment.