CausesBy Mayo Clinic staff
For reasons that doctors don't fully understand, increased pressure within the eye (intraocular pressure) is usually, but not always, associated with the optic nerve damage that characterizes glaucoma. This pressure is due to a buildup of a fluid (aqueous humor) that flows in and out of your eye.
This fluid normally exits your eye through a drainage system at the angle where the iris and the cornea meet. When the drainage system doesn't work properly, the fluid can't filter out of the eye at its normal rate, and pressure builds within your eye.
Primary open-angle glaucoma
In primary open-angle glaucoma, the drainage angle formed by the cornea and the iris remains open, but the drainage channels (trabecular meshwork) in the angle are partially blocked, causing the fluid to drain out of the eye too slowly. This causes fluid to back up in your eye, and pressure gradually increases within your eye.
Damage to the optic nerve doesn't cause symptoms or pain, and it happens so slowly that you may lose an extensive amount of vision before you're even aware of a problem. The exact cause of primary open-angle glaucoma remains unknown.
Angle-closure glaucoma, also called closed-angle glaucoma, occurs when the iris bulges forward to narrow or block the drainage angle formed by the cornea and the iris. As a result, fluid can't adequately flow through and exit your eye, and your eye pressure may increase abruptly. Angle-closure glaucoma usually occurs suddenly (acute angle-closure glaucoma), but it can also occur gradually (chronic angle-closure glaucoma).
Some people with an abnormally narrow drainage angle may be at risk of developing angle-closure glaucoma.
If you have a narrow drainage angle, sudden dilation of your pupils may trigger acute angle-closure glaucoma.
In normal-tension glaucoma, your optic nerve becomes damaged. However, your eye pressure remains within the normal range. Doctors don't understand why this occurs. You may have a sensitive optic nerve, or you may have less blood being supplied to your optic nerve. This lack of blood supply could be caused by atherosclerosis — an accumulation of fatty deposits (plaques) in the arteries — or another condition limiting your blood circulation.
Some infants or children may be diagnosed with glaucoma. Rarely, some children may be born with glaucoma (congenital glaucoma), develop glaucoma in the first few years of life (infantile glaucoma) or develop glaucoma after age 4 or 5 (juvenile glaucoma). Children usually won't have any symptoms. However, they have optic nerve damage, which may be caused by angle blockages or malformations (primary infantile glaucoma), or it could develop as the result of other conditions (secondary glaucoma).
In pigmentary glaucoma, pigment granules from your iris build up in the drainage channels (trabecular meshwork), slowing or blocking fluid exiting your eye. Physical activities, such as jogging, sometimes stir up the pigment granules, depositing them on the trabecular meshwork and causing intermittent pressure elevations.
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