The most common form of glaucoma is primary open angle glaucoma (POAG), which results in high fluid pressure in the eye, called intraocular pressure, due to a build-up of aqueous humor at the cornea-iris angle. However, there are several specific forms of POAG and other forms of glaucoma that also damage the optic nerve and can result in blindness. Glaucoma is the leading cause of blindness in African-Americans in the United States and becomes more prevalent with age.
Normal Tension Glaucoma
Also called low tension glaucoma, this form of the disease can be due to aberrant aqueous humor drainage from the eye, and thus considered POAG, but without an increase in the intraocular pressure. Tonometry measures a normal or low intraocular pressure in these patients. Further decreasing the pressure in the eye does slow the disease in some, though it also progresses with no effect of the treatment in others. Some believe that this form of the disease may account for one-third of all POAG cases. Poor blood flow to the optic nerve has been implicated in this form of the disease.
Angle Closure Glaucoma
This form of the disease is characterized by an inability of the fluid in the eye to reach the angle between the cornea and iris, where it normally drains. This is in contrast to POAG in which the angle is not blocked, but the drainage is obscured. Angle closure glaucoma results in a sudden increase in intraocular pressure (also called acute glaucoma), causing pain and nausea, redness of the eye, and blurry vision. Within one to two days, the eye can become blind. Immediate medical treatment is necessary and may include laser surgery to remove the blockage.
Congenital Glaucoma
Approximately 1 out of every 10,000 children are born with a defect that affects fluid drainage in the eye. The glaucoma becomes evident in infants as light sensitivity, cloudy looking eyes, and excessive tearing. Surgery is done as soon as safely possible after diagnosis to ensure healthy vision into their adult lives. It is estimated that 10 percent of primary congenital glaucomas are present at birth, and another 80 percent are diagnosed in the first year of life. If left untreated, childhood glaucoma leads to permanent blindness.
Secondary Glaucomas
Secondary disease develops as a result of another disorder or disease (as opposed to primary disease, which occurs in the absence of other disease). Optic nerve damage may occur as a result of eye surgery or trauma to the eye, as well as cataracts, certain tumors, inflammation around the eye, and neovascular glaucoma caused by diabetes.
The drainage meshwork can also be blocked by pigment from the iris. Myopic eyes (nearsighted) are at an increased risk of the pigment layer rubbing on the lens, sometimes resulting in a flaking of the pigment, which then clogs the trabecular meshwork.
For more information on types of glaucoma, visit The Glaucoma Foundation and National Eye Institute websites.
Alicia Mae Prater - Alicia received her doctorate in Experimental Pathology in 2007. She has been a freelance writer and scientific editor since 2008.
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