Sunday, January 15, 2006

glaucoma

Glaucoma is an ocular disease characterized by an increase in intraocular pressure, excavation and degeneration of the optic disk, and nerve fiber bundle damage producing defects in the visual field. The rate of aqueous production by the ciliary body and the resistance to the outflow of aqueous humor at the angle of the anterior chamber determines the height of the intraocular pressure. Clinically this pressure is estimated by tonometry; an instrument designed to check the pressure. A definite diagnosis of glaucoma cannot be made unless the increased intraocular pressure has produced damage to the optic nerve. The chances for developing glaucoma increase as a person ages. Three out of every 100 people over age 65 have the disease, an estimated 722,000. Glaucoma is one of the leading causes of blindness for people over age 65, accounting for almost 20% of known cases. Women run a higher risk of developing glaucoma than men do. Although glaucoma cannot be prevented, the resultant blindness can be prevented through early detection and appropriate medical treatment. The primary glaucomas are generally bilateral (both-eye) diseases, which are in part genetically determined. The term "secondary glaucoma" refers to pressure rises caused by some known ocular disease and is usually unilateral.
Glaucoma may be classified into angle-closure glaucomas, open-angle glaucoma and a mixed group in which both angle-closure and trabecular mechanisms may be contributory. Angle-closure glaucoma occurs typically in hyperopic (farsighted) eyes, which have shallow anterior chambers. The resulting forward displacement of the peripheral iris covering the trabecular meshwork (filter controlling aqueous flow) with dilation of the pupil can lead to closure of the angle. Tension elevation tends to occur abruptly, causing typical symptoms of halos, hazy vision, and ocular pain. Laser iridotomy (hole made with laser in iris for better aqueous flow) usually bypasses the pupillary block and normalizes the outward flow of fluids if the trabecular meshwork is not damaged. Secondary angle-closure glaucoma may be caused by a swollen lens, posterior synechiae (adhesion of iris to front of lens) to the lens, or lens subluxation. Each entity is treated according to its underlying cause. With open-angle glaucoma, the most common type, the iris is not in contact with the trabecular meshwork; the sieve that allows aqueous to drain outside the eye. The reduced outflow of fluid is caused by an increase in the resistance in the trabecular meshwork and other portions of the outflow passages to the venous system. Symptoms are usually negligible until extensive ocular damage has occurred. The treatment of open-angle glaucoma is mainly medical. Topical eye drops are first used, then oral medication can be added if necessary. Laser treatment of the trabecular meshwork may help lower the pressure. Surgery is indicated if the intraocular pressure is persistently high or if there is progression of optic disk or visual field changes. Secondary open-angle glaucoma may be caused by trauma, inflammation, and tumors.
Newell, F. W., Ophthalmology Principles and Concepts, 6th ed. St. Louis: C. V. Mosby, Co., 1986.

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