Glaucoma

What is Glaucoma?

Glaucoma is a multifactorial disease process of the optic nerve inside of the back portion of the eye. The optic nerve contains nearly 1.5 million nerve fibers and is the size of a thin pencil. The optic nerve transmits the visual information from the retina to the vision center in the back portion of the brain called the occipital lobe. In the simplest terms, glaucoma is the result of the eye pressure inside the eye being higher than the optic nerve can tolerate. This leads to a slow death or damage to the optic nerve fibers. Slowly over time the nerve continually loses nerve fibers leading to blindness.

There are approximately 3 million people in the United States with glaucoma. Nearly half of those people do not know they have glaucoma. Glaucoma is the second leading cause of permanent blindness in people over age 65 only behind macular degeneration in the United States. Worldwide, glaucoma is the second leading cause of blindness behind cataracts.

What Causes Glaucoma?

The ciliary body located behind the iris (colored portion of the eye) slowly produces fluid called the aqueous humor. The aqueous humor supplies nutritional material to the structures inside the eye and keeps the eye formed to its proper structure. The fluid passes through the pupil into the anterior chamber of the eye. The anterior chamber is the fluid filled space between the iris and the cornea (clear portion of the eye in front of the iris).

Inside the anterior chamber at the junction of the iris and the cornea inside the eye is a structure called the trabecular meshwork. On the outside of the eye, it is located underneath the junction of the cornea and sclera (white portion of the eye). The trabecular meshwork looks like cheese cloth and the fluid percolates through the meshwork into a drainage channel called Schlemm’s canal. The aqueous humor passes from Schlemm’s canal into venous canals on the surface of the eye into the blood system. There is a constant production of fluid inside the eye and a constant flow of fluid from the eye. A normal eye pressure is maintained by this system.

In the most common type of glaucoma, the meshwork gradually becomes obstructed with debris which limits the flow of fluid out of the anterior chamber. This obstruction raises the pressure inside the eye. The increased eye pressure causes damage to the optic nerve resulting in blindness over time.

It is believed that the eye pressure inside the eye limits or diminishes the blood flow in the optic nerve and this causes the damage to the nerve. Just like when you blow up a balloon and the balloon becomes tighter with more air, it becomes harder to force more air into the balloon. The eye pressure inside the eye reduces the flow of blood into the eye because of the increased resistance.

As stated at the start, there are many factors that contribute to the development of glaucoma and damage to the eye from glaucoma. Eye pressure is the major factor but there are many others.

Who Develops Glaucoma?

Glaucoma becomes more prevalent after age sixty. Age does have a factor in the development of glaucoma. African-Americans are three times more likely to have glaucoma verses Caucasians in the United States. Hispanics, Latins, American Indians, and Filipino-Americans have much higher rates of glaucoma. Filipino-Americans have a much higher risk of normal pressure glaucoma. African-Americans may have higher rates of glaucoma as there are studies that show they have thinner corneas which can cause errors in measuring the intraocular pressure.

Several genetic factors have been isolated related to the development of glaucoma. Some recent studies have shown that consistent routine exercise may help prevent glaucoma.

Risk Factors for Glaucoma

Symptoms of Glaucoma

For the most common types of glaucoma, there are no symptoms related to glaucoma in the beginning of the disease. This is why glaucoma is called “silent thief of sight” or “thief in the night”. It is not until the glaucoma has advanced that symptoms begin to appear. In the early stages, glaucoma does not blur vision or cause any loss of central vision. Glaucoma slowly steals small portions of the side vision. This is so insidious, that is not noticed or detected. The brain will compensate for the loss of side vision by turning the head more or the eyes more to compensate for the loss of side vision. This all happens subconsciously. Many times, people have lost significant amount of their side vision and are unaware of the loss until they are made aware of it. There can be significant and irreversible vision loss from glaucoma before it is detected.

Types of Glaucoma

There are two basic types or categories of glaucoma which are open angle glaucoma and narrow or angle closure glaucoma. The term angle refers to the angle between the iris and the cornea where they meet inside the eye. Another reference point is where the sclera and the cornea meet on the outside of the eye. If the angle is open enough to allow easy flow of the aqueous humor into the trabecular meshwork, the angle or opening to the meshwork is open. If the iris and the cornea are nearly touching or start to touch, the angle is narrow or closed. The aqueous humor cannot get to the meshwork and drain from the eye. In the United States, open angle glaucoma comprises over 95% of glaucoma and angle closure glaucoma 4 or 5%.

There are several types of open angle glaucoma which are primary open angle glaucoma (POAG), pigmentary glaucoma, low-pressure or normal-tension glaucoma, pseudoexfoliation glaucoma, secondary glaucoma, neovascular glaucoma, and congenital glaucoma. Ocular hypertension and glaucoma suspect are terms used to describe eyes that have elevated eye pressures but no glaucoma damage or the eyes are at risk of developing glaucoma.

The other major type of glaucoma is narrow angle, acute angle closure glaucoma and chronic angle closure glaucoma.

Primary Open Angle Glaucoma

This is the most common type of glaucoma. The angle is open but the trabecular meshwork is partially closed from a variety of reasons restricting the flow of fluid from the ye. The causes the fluid to build up inside the eye raising the intraocular pressure. The elevated eye pressure damages the optic nerve over time and the eye will begin to lose vision. As stated before, the side vision is slowly lost which can lead to so called “tunnel vision”. Eventually all the sight will be lost if left untreated. The goal of treatment is to lower the eye pressure to a safe level.

Pigmentary Glaucoma

Pigmentary glaucoma is the result of pigment shedding from the pigment layer of the iris. The pigment collects in the trabecular meshwork obstructing the flow of fluid from the eye. Pigmentary glaucoma can occur at a younger age from the mid-30s to the 40s and is more common in males.

Normal Tension Glaucoma or Low-Pressure Glaucoma

Normal tension glaucoma, low-pressure glaucoma, or normal pressure glaucoma is very similar to primary open angle glaucoma except that the optic nerve is being damaged with a normal eye pressure. Normal tension glaucoma occurs more often in people of Japanese descent, female, history of vascular disease, and the elderly. It is believed that the optic nerve is more sensitive to pressure secondary to poor blood flow in the optic nerve. People with this type of glaucoma need to maintain a very low eye pressure.

Pseudoexfoliation Syndrome and Glaucoma (PXF or PEX)

Pseudoexfoliation syndrome is a disease characterized by flakey whitish deposits inside the anterior chamber of the eye. These deposits can obstruct the trabecular meshwork causing glaucoma. Glaucoma occurs in about 50% of people with pseudoexfoliation syndrome. There is poor pupil dilation due to the deposits on the iris. The capsule and zonules of the lens can be weakened by this process which can increase the risk of complications during cataract surgery.

Secondary Glaucoma

Other eye diseases may cause glaucoma secondarily. Inflammation in the eye can cause glaucoma from the inflammatory cells collecting in the trabecular meshwork and blocking the flow of fluid out of the eye. Other secondary causes for glaucoma are tumors, over ripe cataracts, and eye injuries. The use of corticosteroids, prednisone, or cortisone can increase the eye pressure. The increase in eye pressure can occur by taking these orally, nasal spray, applied to the skin, or injections.

Neovascular Glaucoma

Neovascular glaucoma could be listed as a secondary glaucoma but it is different form the other secondary glaucoma diseases. This is the most aggressive and/or severe type of glaucoma and is the most difficult to treat. This type of glaucoma is the result of abnormal and fragile new blood vessel growth into the angle, trabecular meshwork, iris, and retina. The new vessel growth or neovascularization develops secondary to the obstruction or loss of blood flow in the retina causing ischemia. This can be due to a blocked central retinal vein or branch retinal vein that drains the blood from the eye. Blood flow can be altered from central artery occlusion or from severe carotid artery occlusion which results decreased blood flow to the eye.

All these diseases result in ischemia or reduced blood flow in the retina. When the retina loses its blood supply, the retina produces a substance called vascular endothelial growth factor. This stimulates the development of new blood vessels in response to the loss of blood flow or oxygen supply to the cells of the retina. At first, that may sound great. These new blood vessels could bring more blood flow and oxygen to the retina. The problem is that these new blood vessels are thin, fragile, and grow randomly (many times in the wrong places). These vessels can grow into the trabecular meshwork, angle, iris, and retina. They block the flow of fluid from the eye and bleed very easily. These vessels can cause tremendous damage to the eye. The blood vessels can totally obstruct the trabecular meshwork causing severe elevations in the eye pressure.

The eye can suffer hemorrhaging and the blood can nearly fill the eye in some cases. Many times, medications may have limited effect in lowering the eye pressure. Glaucoma surgeries are difficult with significant bleeding during the surgery and may have limited results.

Congenital Glaucoma

Congenital glaucoma is an inherited form of glaucoma. This type of glaucoma is diagnosed at birth or at a very young age. These children have large protruding eyes, large corneas, cloudy or hazy corneas, painful eyes, and/or watery eyes. It is important to diagnose congenital glaucoma as soon as possible to preserve the vision. There are areas around the world that congenital glaucoma is very common with many children 6 or 7 years of age that are blind from glaucoma. Some famous people have lost their vision from congenital glaucoma such as Ray Charles and Andrea Bocelli.

Ocular Hypertension

Ocular hypertension is actually a pre-glaucoma diagnosis. The eye pressure is higher than normal but there is no glaucoma damage to the optic nerve. All the tests for diagnosing glaucoma are normal. The person needs to be monitored closely and may need to be started on treatment because the eye pressure is deemed to be unsafe for the eye. That determination will be made by the eye doctor and you.

Glaucoma Suspect

This is another category or diagnosis of someone who is at risk of developing glaucoma but has no glaucoma damage to the optic nerve. The eye pressure is normal and the glaucoma tests are normal. But, there is a family history of glaucoma that means they need to be followed closely. There may be asymmetric cupping of the optic nerve which is a risk factor for glaucoma, very large cupping of the optic nerves, and/or some of the glaucoma tests are borderline for glaucoma damage.

Acute Angle Closure Glaucoma

This type of glaucoma is based solely on the size and shape of the eye. People with narrow angles have small eyes. The iris is very close to the cornea and the anterior chamber is very shallow. If the iris happens to block the trabecular meshwork, no fluid can get out of the eye and the eye pressure rockets upward. The eye pressure can get so high that the blood flow into the eye is blocked. This can cause severe damage to the eye and permanent loss of vision. This type of glaucoma does have symptoms. There is severe pain in and around the eye. The pain can be so severe that it causes nausea and vomiting.

Many years ago, people were taken to surgery because the doctor thought the patient had a brain aneurysm because the pupil was dilated and the severe pain. The pupil is dilated to mid-dilated and not reactive to light in acute angle closure glaucoma. Other symptoms are red eyes, cloudy cornea, blurred vision, loss of vision, halos or rings around lights.

This is an eye emergency. The treatment is to make a small opening in the peripheral portion of the iris with a laser. This opening allows the aqueous humor direct access to the trabecular meshwork. The fluid does not have to travel through the pupil and then towards the angle. The opening rapidly lowers the eye pressure. The laser treatment needs to be performed as soon as possible. If not treated soon, the eye will suffer significant vision loss and permanent damage to the structures of the eye due to lack of blood flow and oxygen.

Chronic Angle Closure Glaucoma

This is a less common form of angle closure glaucoma. Chronic angle closure glaucoma occurs when there are multiple mini, small, or partial acute angle closure glaucoma events. The angle slowly closes down over time with these attacks.

Narrow Angles

The goal with acute angle glaucoma is to discover the narrow angles before an attack of angle closure glaucoma occurs. During an eye exam, the eye doctors will see that the angle is narrow and evaluate the degree of the narrow angles. If the angles appear to be so narrow that an attack of angle closure glaucoma is possible, a laser iridotomy can be performed before the attack. This opening is like a safety valve and prevents the attack from beginning. As stated before, the narrow angles are secondary to the size of the eye. Narrow angles can also have a heredity component as well.

JAMES E. CROLEY III, M.D.

Dr. James E. Croley III is a board-certified ophthalmologist and the founder of the Cataract & Refractive Institute of Florida. He graduated magna cum laude from Cumberland College before attending medical school at the University of Miami and completing his residency at the University of Alabama Eye Foundation Hospital. Additionally, he studied at Stanford University where he gained further education in advanced ophthalmology techniques. Dr. Croley is a member of the American Academy of Ophthalmology and the Florida Society of Ophthalmology.