Glaucoma is the name for a group of eye diseases that damage the optic nerve. This nerve carries information from the eye to the brain. Glaucoma is one of the most common causes of legal blindness in the world. At first, people with glaucoma lose side (peripheral) vision. However, if the disease is not treated, vision loss may get worse. Over time, this can lead to total blindness.

The exact cause of the optic nerve damage from glaucoma is not fully understood. An abnormally high pressure in the eye, intraocular pressure, often causes this damage. Nevertheless, some people who have glaucoma have normal eye pressure. Some people get glaucoma after an eye injury or after eye surgery. Some medicines, such as corticosteroids, used to treat other diseases may also contribute to glaucoma.

There are many types of glaucoma, but most types fall into the categories of "open-angle" glaucoma or "angle-closure" glaucoma, which may sometimes occur suddenly and cause eye pain and blurred vision. All types of glaucoma can lead to loss of peripheral vision.

Open-angle glaucoma is the most common form of glaucoma and has no warning signs. The effect of this type is gradual and the change in vision is the only symptom that can be noticed.

Angle-closure glaucoma can cause mild symptoms, such as eye pain, and symptoms like blurred vision disappear in a short time. Longer episodes of blurred vision, pain in the eye or around it, red eyes, nausea and vomiting are severe signs of angle-closure glaucoma that require immediate attention.

Glaucoma can be diagnosed during routine exams with eye doctor. The doctor will ask questions about the symptoms and the family history with a physical exam.

Glaucoma cannot be cured. However, there are measures that can help prevent further damage to the optic nerve and, consequently, prevent vision loss. For example, eye drops, laser treatment and surgery are the most common treatments.

Regular eye exams to check for eye pressure help in recognizing glaucoma in very early stages. If glaucoma is treated early, vision loss can be slowed or prevented.

Glaucoma is a group of diseases that damage the eye’s optic nerve and result in vision loss and blindness. It usually happens when aqueous humor, the fluid that nourishes parts of the eye and give it its shape, builds up in the front part of the eye. Extra fluid increases the pressure in the eye, damaging the optic nerve.  While glaucoma can affect anyone, the risk is much greater for people over 60. Glaucoma is one of the most common causes of blindness in the world. People with glaucoma lose peripheral vision in the beginning, but if the disease is not treated, vision loss may get worse. This can lead to total blindness over time.

Glaucoma is a term that includes five types of diseases that cause damage to the optic nerve. These types are:

1) Primary open-angle glaucoma

This is the most common type of glaucoma. It happens gradually, where the eye does not drain fluid as well as it should. As a result, eye pressure builds and starts to damage the optic nerve. In this type of glaucoma, the optic nerve is damaged bit by bit in a manner that it is painless and causes no vision changes at first.

2) Angle-closure glaucoma         

Also called closed –angle glaucoma or narrow-angle glaucoma, this type is less common and happens when the iris and the lens block movement of fluid between the chambers of the eye. This causes pressure to build up and the iris to press on the drainage system of the eye, so eye pressure rises very quickly. Angle-closure glaucoma may occur suddenly (acute angle-closure glaucoma) or gradually (chronic angle-closure glaucoma). Acute angle glaucoma is a medical emergency.

3) Normal-tension glaucoma

In this type of glaucoma, the optic nerve becomes damaged even though eye pressure is within the normal range. The exact reason for this type is not known. The optic nerve may be sensitive, or may have less blood being supplied to it.

4) Congenital glaucoma

This type is a rare form of glaucoma that some infants have at birth. Some children and young adults can also get this type of the disease.

5) Pigmentary glaucoma

In pigmentary glaucoma, pigment granules from the iris build up in the drainage channel, slowing or blocking fluid exiting the eye.

It is very well known that glaucoma is the result of damage to the optic nerve. The exact cause of this damage, however, is not fully understood. Ophthalmologists believe this damage is usually related to increased pressure in the eye.

Elevated eye pressure is due to a buildup of a fluid  called aqueous humor that flows throughout the eye. This fluid normally drains into the anterior chamber of the eye through the trabecular meshwork at the angle where the iris and cornea meet.

When fluid is overproduced or the drainage system does not work properly, the fluid cannot flow out at its normal rate and pressure builds up.

In open-angle glaucoma, blockage of the flow happens at the trabecular meshwork. While in angle-closure glaucoma, narrowing of the angle of drainage leads to an inefficient drainage system which causes pressure to build up.

Glaucoma tends to run in families. Scientists have identified genes related to high eye pressure and optic nerve damage. However, some people who have glaucoma have normal eye pressure, or get glaucoma after an eye injury or after eye surgery. Medicines used to treat other diseases, such as corticosteroids, may also cause glaucoma.

Because the most common form of glaucoma has no warning signs, and the effect is so gradual, the patient may not notice a change in vision until the condition is at an advanced stage. Being aware of the risk factors that increase the chance of developing glaucoma helps in detecting the disease early on and prevent vision loss. The following are risk factors for glaucoma:

1) Intraocular pressure: High internal eye pressure is often linked with open-angle glaucoma.

2) Age: The risk of glaucoma increases rapidly after age 40, and becomes even higher after age 60.

3) Race: Blacks are more likely to have glaucoma than whites are.

4) Family history: Glaucoma tends to run in families. The most common type of glaucoma, primary open-angle glaucoma, is more common in people with a family history of glaucoma.

5) Some medical conditions: Diabetes, heart disease, high blood pressure and sickle cell anemia all increase the risk of developing glaucoma.

6) Eye conditions: Certain eye conditions, such as nearsightedness or farsightedness, increase the chance of glaucoma.

7) Injury: Eye injury or certain types of eye surgery may increase the risk of glaucoma.

8) Early estrogen deficiency: Estrogen deficiency caused, for example, after removal of both ovaries before age 43.

9) Corticosteroid medications: Using corticosteroids, especially in the form of eye drops, for a long time may lead to glaucoma.

10) Gender: Older women are more likely than older men to develop Closed-angle glaucoma.

11) History of glaucoma: People who had prior loss of vision in one eye due to glaucoma are at an increased risk of future damage in the other eye.

12) Infections during pregnancy: Children whose mothers contracted an infection during pregnancy are at an increased risk for congenital glaucoma. Mothers who had certain viral infections, such as rubella, are more likely to have a child with the condition.

In the front of the eye there is a space called the anterior chamber through which fluid leaves at the open-angle where the cornea and iris meet. When the fluid reaches the angle, it flows through trabecular meshwork, and leaves the eye. However, when the drainage system does not work properly, the fluid cannot flow out at its normal rate and pressure builds up.

Eye pressure plays a role in damaging the delicate nerve fibers of the optic nerve, which carries images from the retina, the specialized light sensing tissue, to the brain so we can see. When a significant number of nerve fibers are damaged, blind spots develop in the field of vision. Once nerve damage and visual loss occur, it is permanent and can't be recovered. If the entire nerve is destroyed, blindness results. The exact pathophysiology of glaucoma is not fully understood.

The signs and symptoms of glaucoma vary depending on the type and stage of the condition as the following:  

The common types of glaucoma, open-angle, angle-closure and congenital glaucoma have completely different symptoms:

Open-angle glaucoma

Most people who develop open-angle glaucoma do not experience any noticeable symptoms at first. The symptoms are likely to be:

1) Gradual loss of peripheral vision, usually in both eyes.

2) Tunnel vision, characterized by loss of peripheral vision with the retention of central vision, in the advanced stages.

Acute angle-closure glaucoma

Acute angle-closure glaucoma develops rapidly and is considered a medical emergency. Symptoms of this type include:

1) Severe headache

2) Eye pain

3) Nausea and vomiting

4) Blurred vision

5) Halos around lights

6) Eye redness

Chronic Angle-Closure Glaucoma

This type is similar to open-angle glaucoma in which it progresses slowly, and can damage the optic nerve without symptoms.

Congenital glaucoma

Congenital glaucoma, otherwise known as childhood glaucoma, causes the following symptoms:

1) Watery eyes and sensitivity to light.

2) An eye or eyes that look cloudy; this is a sign that the clear front surface of the eye has been damaged.

3) Eyes that look larger than normal because the eyeballs have become enlarged as a result of high pressure.

4) babies with congenital glaucoma may rub their eyes, squint, or keep their eyes closed much of the time.

Early detection of glaucoma is important for controlling the condition and preventing blindness. The only sure way to diagnose glaucoma is with taking a medical history and a complete physical exam. The following tests are used to diagnose glaucoma:

1) Eye structure: 

The ophthalmologist may check the structures of the eye through the following tests:

• Ophthalmoscopy: The doctor examines the interior of the eye by looking through the pupil with a special instrument. This test can help detect damage to the optic nerve caused by glaucoma.
• Gonioscopy: The doctor uses this instrument to view the front part of the eye called the anterior chamber to determine if the iris is closer than normal to the back of the cornea. This test can help diagnose closed-angle glaucoma.

• Optic coherence tomography: This method uses light beams to make detailed images of the inside of the eye. This test can find eye problems such as age-related macular degeneration or glaucoma. During the test, light beams are focused onto the back of the eye. The test can help find retina or optic nerve problems. Before this test, the pupils may need to be widened or dilated using drops. Optic coherence tomography takes about 10 to 20 minutes.

2) Eye pressure:

Measuring internal eye pressure, also called intraocular pressure is done through a test called tonometry. Tonometry methods include:

• Applanation tonometry: This type of tonometry uses a small probe to gently flatten part of the cornea to measure eye pressure and a microscope called a slit lamp to look at the eye. The pressure in your eye is measured by how much force is needed to flatten your cornea. This type of tonometry is very accurate and is often used to measure pressure after a simple screening test such as air-puff tonometry that discovers increased internal eye pressure.
• Electronic indentation tonometry: Electronic tonometry is being used more often to check for increased eye pressure. Although it is very accurate, electronic tonometry results can be different from applanation tonometry.
• Noncontact tonometry (pneumotonometry): Noncontact or air-puff tonometry does not touch your eye but uses a puff of air to flatten your cornea. This type of tonometry is not the best way to measure internal eye pressure. However, it is often used as a simple way to check for high eye pressure and is the easiest way to test children. This type of tonometry does not use numbing eye drops.

3) Vision tests:

Vision tests check many different functions of the eye. They are usually done along with exams and tests that check the health of the eye. Here are some common tests that check for blurred or low vision:

• Visual Field Test: This test measures the entire area seen by the forward-looking eye to document straight-ahead (central) and side (peripheral) vision. It is also known as a perimetry test that measures  the dimmest light seen at each area tested. A perimetry test can help find certain patterns of vision loss. This may mean a certain type of eye disease is present. It is very useful in finding early changes in vision caused by nerve damage from glaucoma. Regular perimetry tests can be used to see if treatment for glaucoma is preventing further vision loss.
• Visual Acuity Test: This test measures sight at various distances. While seated 20 feet, about 6 meters, from an eye chart, the patient reads standardized visual charts with an eye with and without corrective lenses while the other is covered. Then, the patient repeats the test with the other eye.

4) Cornea thickness:

Tests such as ultrasound pachymetry measure the thickness of the cornea. Cornea thickness, along with intraocular pressure, helps determine the risk for glaucoma.

Glaucoma damage is permanent; treatment cannot restore eyesight that has already been lost. However, when glaucoma is recognized early, vision loss can be slowed or prevented.

Medication:

There are two types of medication used in the treatment of glaucoma:

• Eye drops

Glaucoma treatment often starts with eye drops. These can help decrease eye pressure by improving how fluid drains from the eye or by decreasing the amount of fluid the eye can make.

Prescription eye drop medications include:

• Prostaglandins: These increase the outflow of the aqueous humor in the eye and reduce pressure.
• Beta-blockers: These reduce the production of aqueous humor in the eye, thereby lowering the internal pressure.
• Alpha-adrenergic agonists: This medication both reduces aqueous humor production and increases its outflow.

• Carbonic anhydrase inhibitors: Rarely used for glaucoma, these drugs may reduce the production of aqueous humor in the eye.
• Miotic or cholinergic agents: These increase the outflow of aqueous humor from the eye. 

• Oral medications

If eye drops alone do not decrease eye pressure to the desired level, the doctor may also prescribe an oral medication, usually a carbonic anhydrase inhibitor that reduce fluid production in the eye.

2) Laser surgery

Laser surgery is the most frequently used procedure to treat glaucoma. It normally lowers eye pressure, but the length of time that pressure remains low depends on many factors, including, age of the patient, type of glaucoma and other medical conditions that may be present. Laser surgery includes two main types:

• Trabeculoplasty: This surgery is for people who have open-angle glaucoma. The eye surgeon uses a laser to make the drainage angle work better, so that fluid flows out properly and eye pressure is reduced.
• Iridotomy: This is for people who have angle-closure glaucoma. The ophthalmologist uses a laser to create a tiny hole in the iris. This hole helps fluid flow to the drainage angle.

3) Operating room surgery

Surgical procedures are often used for glaucoma when other treatments have failed. Surgery includes two main types:

• Trabeculectomy: The surgeon creates an opening in the white of the eye and removes part of the trabecular meshwork, which is then partially covered by a flap of tissue taken from the white part of the eye. Aqueous humor will be able to drain out of the eye through the flap and form a bleb or blister under the upper eyelid. In the bleb, the fluid is absorbed by tissue around the eye, lowering eye pressure.
• Glaucoma drainage devices: In this procedure, the eye surgeon inserts a small tube in the eye. It sends the fluid to a collection area, or reservoir, beneath the conjunctiva. The fluid is then absorbed into nearby blood vessels.
• Electrocautery: Your doctor may suggest a minimally invasive procedure to improve fluid flow by removing tissue from the trabecular meshwork using a small electrocautery device.
• Peripheral Iridectomy: Eye doctors use this procedure for angle-closure glaucoma. The doctor removes a small section of the peripheral iris by incision, which allows fluid to drain more easily from the eye.

• Goniotomy: Goniotomy is used almost exclusively for infants with congenital glaucoma. In this procedure, the doctor inserts a tiny blade through the cornea to cut the trabecular meshwork. This procedure allows the eye fluid to flow normally out of the eye.

The complications of glaucoma largely depend on the type of glaucoma the patient has. However, it often results in some degree of permanent vision loss, and it may affect the ability to do certain tasks, such as driving.

The effects of glaucoma are so gradual that you may not notice a change in vision until the condition is at an advanced stage. As vision loss due to glaucoma cannot be recovered, it is important to have regular eye exams that include measurements of eye pressure.

Most risk factors for glaucoma, such as age, race, and family history, are beyond control. However, there are a few steps that can help detect it early, limit vision loss or slow its progress:

• Getting regular eye care: Regular comprehensive eye exams can help detect glaucoma in its early stages before irreversible damage occurs. As a general rule, people should have a comprehensive eye exam every 4 years beginning at age 40, and every two years from age 65.
• Knowing family history: Glaucoma tends to run in families, so people with a family history of glaucoma may need more frequent screening.
• Exercising: Regular, moderate exercise may help prevent glaucoma by reducing eye pressure.
• Taking prescribed eye drops regularly: Glaucoma eye drops can significantly reduce the risk that high eye pressure will progress to glaucoma. To be effective, eye drops prescribed by the doctor need to be used regularly even if no symptoms appear.
• Wearing eye protection: Serious eye injuries can lead to glaucoma. It is imperative to wear eye protection when using power tools or doing any activities that may harm your eyes.

Glaucoma is a group of diseases that can damage the eye’s optic nerve and result in vision loss and blindness. However, with early treatment, the eye can be protected against serious vision loss.

A study published in the Canadian Journal of Ophthalmology reported that glaucoma is the second leading cause of blindness globally. The highest prevalence of open-angle glaucoma occurs in Africans, and the highest prevalence of angle-closure glaucoma occurs in the Inuit. There is an estimated 60 million people globally with glaucomatous optic neuropathy and an estimated 8.4 million people who are blind as the result of glaucoma. These numbers are set to increase to 80 million and 11.2 million by 2020