Glaucoma
Glaucoma refers to a category of eye disorders often associated with a dangerous buildup of internal eye pressure (intraocular pressure or IOP), which can damage the eye's optic nerve that transmits visual information to the brain.

With untreated or uncontrolled glaucoma, you might eventually notice decreased ability to see at the edges of your vision (peripheral vision). Progressive eye damage could then lead to blindness.

In fact, glaucoma creates at least some vision loss in more than half of the approximately 2.5 million Americans estimated to have the eye disease and is the second leading cause of blindness.

Glaucoma Symptoms
Glaucoma is often called the "silent thief of sight," because most types typically cause no pain and produce no symptoms. For this reason, glaucoma often progresses undetected until the optic nerve already has been irreversibly damaged, with varying degrees of permanent vision loss.

But with acute angle-closure glaucoma, symptoms that occur suddenly can include blurry vision, halos around lights, intense eye pain, nausea and vomiting. If you have these symptoms, make sure you see an eye care practitioner or visit the emergency room immediately so steps can be taken to prevent permanent vision loss.

Diagnosis, Screening and Tests for Glaucoma
During routine eye exams, a tonometer is used to measure your intraocular pressure, or IOP. Your eye typically is numbed with eye drops, and a small probe gently rests against your eye's surface. Other tonometers send a puff of air onto your eye's surface.

An abnormally high IOP reading indicates a problem with the amount of fluid (aqueous humor) in the eye. Either the eye is producing too much fluid, or it's not draining properly. Normally, IOP should be below 21 mmHg (millimeters of mercury) — a unit of measurement based on how much force is exerted within a certain defined area.

If your IOP is higher than 30 mmHg, your risk of glaucoma damage is 40 times greater than someone with an IOP of 15 mmHG or lower.* This is why glaucoma treatments such as eye drops are designed to keep IOP low.

Other methods of monitoring glaucoma involve imaging of the eye's optic nerve and internal structures (scanning laser polarimetry or SLP, optical coherence tomography or OCT, confocal scanning laser ophthalmoscopy, etc.) to establish a baseline and make sure no obvious changes have occurred over a period of time, which might indicate progressive glaucoma damage.

Visual field testing is another way to monitor whether blind spots are developing in your range of vision, resulting from glaucoma damage to the optic nerve. Visual field testing involves staring straight ahead into a machine and clicking a button when you notice a blinking light in your peripheral vision. The visual field test may be repeated at regular intervals so your eye doctor can determine the extent of vision loss.

Instruments such as an ophthalmoscope also may be used to help your eye doctor view internal eye structures, to make sure nothing unusual interferes with the outflow and drainage of eye fluids. Ultrasound biomicroscopy also may be used to evaluate how well fluids flow through related angles of the eye's internal structure. Specialized lenses also may be used (gonioscopy) for better viewing of internal eye structures.

Types of Glaucoma
The two major types of glaucoma are acute angle-closure glaucoma, with angle referring to the configuration of internal eye structures that drain fluids, and chronic or primary open-angle glaucoma (POAG). Other variations include congenital glaucoma, pigmentary glaucoma, and secondary glaucoma.

• Primary open-angle glaucoma (POAG): About half of Americans with chronic glaucoma don't know they have it. Glaucoma gradually reduces your peripheral vision. But by the time you notice it, permanent damage has already occurred.
  
  If your IOP remains high, the destruction can progress until tunnel vision develops, and you will be able to see only objects that are straight ahead.


• Normal-tension glaucoma: Like POAG, normal-tension glaucoma (also termed normal-pressure glaucoma, low-tension glaucoma or low-pressure glaucoma) is an open-angle type of glaucoma that can cause visual field loss due to optic nerve damage. But in normal-tension glaucoma, the eye's IOP remains in the normal range.
  
  Also, pain is unlikely and permanent damage to the eye's optic nerve may not be noticed until symptoms such as tunnel vision occur.
  
  The cause of normal-tension glaucoma is not known. But many doctors believe it is related to poor blood flow to the optic nerve. Normal-tension glaucoma is more common in those who are Japanese, are female and/or have a history of vascular disease.


• Pigmentary glaucoma: This rare form of glaucoma is caused by pigment deposited from the iris that clogs the draining angles, preventing aqueous humor from leaving the eye. Over time, the inflammatory response to the blocked angle damages the drainage system.
  
  You are unlikely to notice any symptoms with pigmentary glaucoma, though some pain and blurry vision may occur after exercise. Pigmentary glaucoma affects mostly white males in their mid-30s to mid-40s.


• Angle-closure glaucoma: Angle-closure or narrow angle glaucoma produces sudden symptoms such as eye pain, headaches, halos around lights, dilated pupils, vision loss, red eyes, nausea and vomiting.
  
  These signs may last for a few hours, then return again for another round. Each attack takes with it part of your field of vision.


• Secondary glaucoma: Symptoms of chronic glaucoma following an eye injury could indicate secondary glaucoma, which also may develop with presence of infection, inflammation, a tumor or an enlarged cataract.


• Congenital glaucoma: This inherited form of glaucoma is present at birth, with 80 percent of cases diagnosed by age one. These children are born with narrow angles or some other defect in the drainage system of the eye.
  
  It's difficult to spot signs of congenital glaucoma, because children are too young to understand what is happening to them. If you notice a cloudy, white, hazy, enlarged or protruding eye in your child, consult your eye doctor. Congenital glaucoma typically occurs more in boys than in girls.

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