Primary Angle Closure Glaucoma (POAG)

Angle closure glaucoma is an eye condition caused by an anatomical problem that stops fluid from leaving the eye. The fluid pressure builds up, damaging the optic nerve and causing damage to vision.

What is angle closure glaucoma?

Angle closure glaucoma is a specific type of glaucoma, the most serious type of glaucoma. It can be prevented or controlled by treating its underlying cause, a narrowing of the eye's drainage angle, a structure at the junction of the iris and cornea. When this angle narrows, fluid is more difficult to drain from the eye. This causes increased pressure in the eye that can damage optic nerve fibers, leading to vision loss.

More women than men are affected by angle closure glaucoma. It is rare in people younger than 40 years old. In rare cases, angle closure glaucoma can be inherited.

Symptoms of angle closure glaucoma Angle closure glaucoma can cause symptoms, such as sudden blurred vision or halos around lights, and often affects both eyes at the same time. Sometimes symptoms are so mild that people do not notice them. Angle closure glaucoma is often a cause of sudden blindness.

Angle closure glaucoma is treated by lowering the pressure inside the eye with eye drops or medicine. A laser or surgical treatment can also be used. Sometimes cataracts must also be treated.

In some cases, it is possible that angle closure glaucoma does not cause any symptoms at all.

History

he discovery of open angle glaucoma was long delayed due to its slower rate of progression. Dr. J. William Bowman discovered the condition and gave the condition the name glaucoma in the early 19th century. He believed that glaucoma resulted from a build-up of liquid in the eyeball. The name glaucoma is derived from the Greek word for “water pipe” or “water channel.” Medical encyclopedias of the time used more descriptive terms, such as “dark waters” or “ocular dropsy.” However, because the condition is now known to be caused by elevated pressure inside the eye, these terms are no longer used.

Narrow Angle Glaucoma

Angle-closure glaucoma and narrow-angle glaucoma are terms for the same condition. Narrow-angle glaucoma is distinguished by the presence of angle closure. The narrower angle is the lower part of the eye that allows the aqueous humor to pass out of the eye. If this is blocked the pressure in the eye rises and if the condition is not treated, vision is lost.

In some cases of narrow-angle glaucoma, the patient may have a form of angle closure called "episcleral vein". This is caused by large blood vessels growing over the cornea.

Narrow angle glaucoma is distinguished by the presence of angle closure.

If the Angle is Closed, then that could prevent the fluid (intra ocular fluid) flowing out causing increased pressure. But that does not mean there will be glaucoma. There could be other risk factors that would contribute to glaucoma. An example of a risk factor is "axial hypermetropia" (Far Sightedness) which would also cause increased pressure without the "angle" being "closed".

Angle closure glaucoma (ACG) is usually caused by closure of the drainage angle of the eye, but it is possible to have narrow angles and glaucoma (called "primary ACG") without angle closure.

What is narrow angle glaucoma?

Narrow angle glaucoma is caused by a blockage of the drainage of aqueous humor from the anterior chamber into the posterior chamber through the angle of the eye (the structure that contains the iris and trabecular meshwork and is situated between the iris and cornea). As a result, the eye pressure increases (known as intraocular pressure or IOP) and damages the optic nerve. If left untreated, it can lead to permanent vision loss, and in many cases to blindness.

Treatment for narrow angle glaucoma usually requires laser treatment. It is important to detect narrow angle glaucoma as early as possible, as it is usually very difficult to detect the condition in its early stages. There is no known cure for narrow angle glaucoma. The condition is associated with thin corneas and buphthalmos (very large eyes).

What is normal angle width?

Normal angle width varies from 180 degrees to around 140 degrees. Angle width can be seen on a gonioscopy examination.

What is angle closure?

In narrow angle glaucoma, the angle can become closed by the iris blocking it. An exam called gonioscopy can be used to evaluate the angle.

Closure of the angle can be caused by lens material lying over the angle. It can also be caused by congenital conditions such as when the angle is abnormally large, when the iris is congenitally large, or in some cases when the lens is smaller than normal.

If you are referring to angle closure glaucoma, as opposed to open angle glaucoma refer to the last part of the previous sentence.

The position of the iris relative to the angle is also thought to be a factor in glaucoma. In other words, even if the angle is open, a high degree of iris bowing into the angle is thought to lead to damage of the trabecular meshwork. This is similar to the damage that is produced when the iris is moved into the angle in narrow angle glaucoma. For more information refer to Iris Asymmetry Glaucoma itself produces the angle to narrow slightly and this can be a risk factor for the future development of angle closure glaucoma.

With angle closure the iris is too close to the trabecular meshwork. The normal drainage angle allows aqueous humor to enter the Schlemm's canal and exit out the trabecular meshwork and into the canal of Schlemm.

What Causes POAG?

The exact cause of glaucoma is not known, but risk factors include family history, age, race, and certain medical conditions.

Primary open-angle glaucoma, the most common form of glaucoma, is usually associated with abnormally high pressure in the eye. This pressure is due to increased resistance to the flow of aqueous humor from the eye.

Aqueous humor is a clear fluid that fills the anterior segment of the eye and flows out through the trabecular meshwork and the Schlemm's canal. Normally, the amount of aqueous humor produced daily by the ciliary body is equal to the amount that flows out of the eye, but in glaucoma, there is a decrease in outflow of aqueous humor and an increase in its production, causing increased pressure inside the eye. This increase in pressure may cause damage to the optic nerve and can lead to permanent vision loss. Normal pressure glaucoma occurs in some individuals with POAG in whom the pressure in the eye is not abnormally high.

Primary angle-closure glaucoma occurs when the drainage angle of the eye becomes blocked by iris, causing decreased outflow of aqueous humor and increased pressure. This form of glaucoma usually affects people over age 40. Risk factors for PACG include the following eye conditions:

  • Pseudoexfoliation
  • myopia
  • hyperopia

Generally, PACG begins as an asymptomatic disease that slowly increases in severity and may even occur in both eyes in a short period of time.

Primary angle closure glaucoma is a potentially blinding eye disease in which a sudden and severe increase in intraocular pressure leads to severe damage to the optic nerve. Glaucoma damage is irreversible and progresses until the point of total vision loss. Primary angle closure glaucoma can be both acute and chronic. The more common chronic condition is generally asymptomatic. This form of glaucoma develops slowly over many years, and, if left untreated, it will eventually lead to blindness.

A sudden, painful episode is characteristic of the acute form of PACGand should be treated quickly to prevent permanent vision loss.

There are three major risk factors for PACG:

  • Ethnicity: People of Asian descent, particularly people from India, are at high risk for primary angle closure glaucoma. People of Hispanic origin and African-Americans are also at increased risk for primary angle closure glaucoma.

  • Gender: Women of Asian descent have been shown to have a much higher than average risk of developing this type of glaucoma. Specifically, a 2001 study showed that one in every nine women of Chinese descent over the age of 40 will develop primary angle closure glaucoma, comparedwith one in every 60 men.

  • Age: The risk of PACG increases with age. People over age 40 are at greater risk than younger individuals.

Acute angle closure glaucoma

In acute angle closure glaucoma, the patient suffers from acute angle closure due to pupillary block, trabecular meshwork block, or lens subluxation. The iris blocks the trabecular meshwork, causing an increase in the intraocular pressure and a sharp pain and halos around lights. If left untreated, irreversible damage occurs to the optic nerve, leading to blindness.

The effect of a foreign body depends on the type of material, the position of the object in the anterior chamber, and the extent of the damage to the trabecular meshwork. Small objects such as cotton swabs, cotton balls, cotton fibers, and metal wire, which do not occlude the iridocorneal angle and do not cause chronic inflammation, generally cause a transient increase in intraocular pressure. The pressure is usually transient and returns to normal within a few days, and the patient has no permanent damage. Cotton-wool "and/or" swabs should never be used in patients with acute angle-closure glaucoma or acute iridocyclitis.

Blepharitis

A chronic inflammatory condition of the eyelids.

Contact Lens-Induced

Glaucoma Many people wear contact lenses and some of them have glaucoma. The Glaucoma Wiki defines contact lens-induced glaucoma as follows: Contact lens-induced glaucoma is a special type of open-angle glaucoma that is associated with long-term contact lens wear. Contact lens-induced glaucoma usually occurs after many years of contact lens wear, and is believed to occur when the pressure of a contact lens presses against the cornea, which blocks the drainage angle.

Excessive pressure on the angle reduces the outflow of fluid, and increases the pressure within the eye.

Diagnosis and Treatment of Glaucoma

Glaucoma is a chronic disease that is often asymptomatic until significant damage has already occurred. Therefore, people who have a family history of glaucoma, a personal history of glaucoma, an abnormally large optic nerve head, or who are middle-aged, should be examined by an ophthalmologist.

Closed angle glaucoma

Closed angle glaucoma is a type of glaucoma where the angle of the eye between the iris and the cornea is more closed (between the iris and cornea) and the drainage of the fluid is compromised (drainage through the trabecular meshwork). A few people will naturally have a more closed angle between the iris and the cornea in both eyes (congenital), others will develop closed angle glaucoma when the iris will get stuck on the cornea (acquired). It will depend on which situation the person is in. Usually it is the onset of glaucoma. Due to the damage done to the optic nerve it can cause blindness, or at least blind spots in the field of vision. When the closed angle glaucoma develops rapidly it is called Acute angle closure glaucoma. When the closed angle glaucoma develops slower it is called Subacute angle closure glaucoma. When closed angle glaucoma (CAG) is a common type of glaucoma, occurring primarily in women and Asians. This type of glaucoma is often first detected in middle age or later, and by the time it is diagnosed, the optic nerve damage is already advanced. CAG is a progressive eye condition caused by chronic blockage of aqueous humor drainage and elevated eye pressure (intraocular pressure (IOP)). This blockage results in increased pressure within the eye, which damages the optic nerve. The optic nerve is the nerve that transmits visual information from the eye to the brain. In its most advanced stage, CAG is usually associated with severe vision loss.

To understand how closed angle glaucoma develops, it is first important to understand the anatomy of the eye and its drainage system. In brief, the eye contains a clear fluid called aqueous humor, which nourishes the tissues of the eye. Aqueous humor is continually produced within the eye, and is drained away through a system of tiny, one-way drainage canals.

The iris, a ring of tissue at the front of the eye, separates the aqueous humor-filled anterior chamber from the drainage system. The drainage system comprises three canal tubules, and the canal of Schlemm at the optic disc.

The three canal tubules collectively drain the aqueous humor from the anterior chamber. One canal tubule, which is positioned just behind the iris, enters into the anterior chamber at a place called the point of Huschenbarch. The other canal tubules drain out of the eye before entering into the anterior chamber.

In closed-angle glaucoma, the point of Huschenbarch is often blocked by a blood clot that prevents the aqueous humor from draining. This buildup of fluid results in elevated IOP (see the Glaucoma Symptoms & Diagnosis page for more information).

Glaucoma tests for POAG

Glaucoma is a condition where the fluid inside the eye is not draining well and the pressure builds up. This is known as intraocular pressure. Glaucoma damages the optic nerve which connects the eye to the brain and is how you perceive visual images. This damage cannot be reversed once you start losing vision. So it's important to detect glaucoma early and get treatment.

The most common form of glaucoma is called primary open angle glaucoma. If you have this type of glaucoma there is usually no pain and there are usually no symptoms so it is not diagnosed until your vision is permanently lost. This type of glaucoma is more common in people over 60 years old.

If you do have glaucoma, you may not notice until damage has occurred. If you do have glaucoma there are two types of treatment, one to control glaucoma and one to treat glaucoma.

If you have glaucoma

On the exam, your doctor will look for areas of thinning of the nerve fiber layer, or optic disc, using special magnifying lenses. If you have early glaucoma, he or she may not see any thinning at all. A normal optic disc looks like the bottom half of a spoon. If you have glaucoma, the optic disc will look smaller.

If you have a few optic discs showing signs of early glaucoma and the rest of your eye exam is normal, your doctor may order tests to find out if glaucoma is present. The tests will use an instrument called a tonometer todetermine the pressure of the fluid inside your eye, or aqueous humor.

If glaucoma is present, your doctor may order further tests. This can include an optic disc stereophotography, in which a picture of the optic disc is taken. This is usually done with your unconscious. Hemay also do a visual field test. This tests the sensitivity of the retina. A headset is used and a laser is shone into your eye while you concentrate on it. A sheet of white paper, with small holes on it, is used to determine how much of your field of view can be seen.

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