Primary Open Angle Glaucoma (OAG)
This is the most common form of glaucoma, affecting about three million Americans. It happens when the eye's drainage canals become clogged over time. A clear fluid, called aqueous humor, fills the front of the eye (anterior chamber) and provides nourishment to the tissues. The aqueous also provides pressure to help maintain the shape of the eye.

If open angle glaucoma is not diagnosed and treated, it can cause a gradual loss of vision (see simulation at left). This type of glaucoma develops slowly and sometimes without noticeable sight loss for many years. It usually responds well to medication, especially if caught early and treated.

Open Angle Glaucoma progresses slowly.
There is no associated pain or other
noticeable symptoms until much of the
outside area of the field of vision is lost.



Click on image for a larger version.





Click on image for a larger version.


Due to glaucoma, the inner eye pressure (also called intraocular pressure or IOP) rises because the correct amount of aqueous humor fluid can't drain out of the eye.

 

Angle Closure Glaucoma
This type of glaucoma is also known as acute glaucoma or narrow angle glaucoma. It is much more rare and is very different from open angle glaucoma in that the eye pressure usually goes up very fast. This happens when the drainage canals get blocked or covered over. With angle closure glaucoma, the iris and cornea is not as wide and open as it should be. The outer edge of the iris bunches up over the drainage canals, when the pupil enlarges too much or too quickly. This can happen when entering a dark room.

Treatment of angle closure glaucoma usually involves surgery to remove a small portion of the outer edge of the iris. This helps unblock the drainage canals so that the extra fluid can drain. Usually surgery is successful and long lasting. However, you should still receive regular check-ups.

Symptoms of angle closure glaucoma may include headaches, eye pain, nausea, rainbows around lights at night, and very blurred vision.

Secondary Glaucoma
Glaucoma can occur as the result of an eye injury, inflammation, tumor, or in advanced cases of cataract or diabetes. It can also be caused by certain drugs such as steroids. This form of glaucoma may be mild or severe. The type of treatment will depend on whether it is open angle or angle closure glaucoma.

Normal Tension Glaucoma (NTG)
Normal tension glaucoma is also known as low tension glaucoma or normal pressure glaucoma. In this type of glaucoma, the optic nerve is damaged even though intraocular pressure (IOP) is not very high. Doctors do not know why some people's optic nerves are damaged even though they have what is considered to be "normal" (between 12-22 mm Hg) pressure levels.

Those at higher risk for this form of glaucoma are people with a family history of normal tension glaucoma, people of Japanese ancestry, and people with a history of systemic heart disease, such as irregular heart rhythm. Normal tension glaucoma is usually detected after an examination of the optic nerve.

Currently, most doctors treat normal tension glaucoma by keeping normal eye pressures as low as possible with medicines, laser surgery, or filtering surgery.

Low Pressure or Low Tension Glaucoma (LTG)
Approximately 30% of patients who show signs of damage to the optic nerve do not have pressures over 21mm. These patients are referred to as having Low Tension Glaucoma - LTG. The presumption is that they have nerves that are much more sensitive than average and can undergo damage at lower than normal pressures. Therefore, patients' pressures have to be lowered to even lower levels to prevent damage from progressing.

Pigmentary Glaucoma
This is a form of secondary open angle glaucoma. It occurs when the pigment granules in the back of the iris (the colored part of the eye) break into the clear fluid produced inside the eye. These tiny pigment granules flow toward the drainage canals in the eye and slowly clog them, causing eye pressure to rise. Treatment usually includes medications or surgery.
   
 
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