What is Glaucoma?
Glaucoma is a disease that damages the optic nerves. The damage does not become noticeable until a significant amount of it has occurred. If not treated, glaucoma can lead to severe vision loss or even blindness. Glaucoma is usually (but not always) associated with high intraocular pressure, and begins with a loss of peripheral vision. This loss of vision progresses to eventually include central vision. If the disease is detected early and treated appropriately, it is quite possible to greatly slow the disease and prevent vision loss.
The normal human eye produces a fluid called aqueous humor. This fluid feeds and nourishes the structures in the front of the eye and also helps focus light that enters the eye. As glaucoma progresses, for reasons still not fully understood, an imbalance develops in the production and drainage of aqueous, which increases the eye pressure to unhealthy levels.
The aqueous is produced by cells in the ciliary body. Once produced, the aqueous flows through the pupil into a structure in the front of the eye called the anterior chamber. From here, the aqueous is filtered through a meshwork, which then delivers the fluid to the canal of Schlemm. This canal is a channel in the eye that collects and delivers aqueous humor into the anterior ciliary veins, which then transmit the fluid into the bloodstream. Normally, this process provides the eyes with a fresh supply of aqueous humor at a constant rate. When there is a failure in the eye’s fluid production and drainage system—either due to genetics, injury, or infection—pressure increases, and glaucoma is usually the result.
Forms of Glaucoma
- Normal-tension Glaucoma occurs when there is optic nerve damage and loss of vision, which can happen even if intraocular pressure is within a normal range
- Angle-Closure Glaucoma: Increased intraocular pressure due to fluid not being able to exit the eye due to a blockage of the meshwork inside the eye. This can cause blurry vision, haloes around lights, pain, headaches, nausea, red eyes, and vision loss. According to the NEI, “This is a medical emergency. If your doctor is unavailable, go to the nearest hospital or clinic. Without treatment to improve the flow of fluid, the eye can become blind in as few as one or two days.”
- Secondary Glaucoma can be caused by diseases like iritis or uveitis. It can also occur after eye surgery, or possibly as a result of medical conditions like diabetes.
- Congenital Glaucoma is present at birth due to birth defects that hinder the flow of fluid out of the eye and make the eyes cloudy and sensitive to light.
- Open-Angle Glaucoma: This is the most common type of glaucoma. It occurs when fluid production and drainage becomes abnormal, causing intraocular pressure to increase, damaging the optic nerves and eventually leading to vision loss. Usually peripheral vision is damaged first, causing tunnel vision and eventually leading to blindness if not properly treated and monitored.
Warning signs are different for each form of glaucoma. In almost all cases, glaucoma is usually not noticeable until significant damage has been done to the optic nerves and some degree of vision loss develops. Let’s go over each type of glaucoma and its symptoms:
Open-Angle Glaucoma Symptoms include:
- Vision loss
- Gradual loss of peripheral vision
Angle-Closure Glaucoma Symptoms include:
- Symptoms appear and disappear in early stages, but steadily worsen
- Decreased vision
- Cloudy vision
- Sudden, severe pain, usually in one eye
- Eye feels swollen
- Red eyes
- Halos around lights
- Nausea and vomiting
Congenital Glaucoma Symptoms include:
- Symptoms become noticeable when child is a few months old
- Cloudiness in front of the eye, usually on the iris (the colored part of the eye)
- Red eye
- Photophobia (sensitivity to light)
- One or both eyes become enlarged
Secondary Glaucoma Symptoms include:
- Vision loss
- Could be mild or severe depending on which type it is (open-angle or angle-closure glaucoma)
Normal-Tension Glaucoma Symptoms include:
- No symptoms present until late stages of disease
- Vision loss
What Causes Glaucoma?
The cause of glaucoma depends on which type is present. As of 2011, the cause of open-angle glaucoma is still unknown, but experts know that all cases show a gradual increase in eye pressure. Open-angle glaucoma is usually genetic, and affects people of African descent more than any other race. Angle-closure glaucoma is caused by a sudden blockage that prevents the drainage of aqueous humor. This type of glaucoma is very different from the open-angle form, and is considered an emergency. Pain is often felt as the pressure increases.
During the human gestation period, if the fluid outflow channels in the eye develop abnormally, congenital glaucoma is the result. This type of glaucoma is usually hereditary, and symptoms are usually present at birth but may not become noticeable for a few months. Secondary glaucoma usually develops after another eye disease or systemic disease develops. Occasionally, drugs such as corticosteroids may cause secondary glaucoma. Like open-angle glaucoma, normal-tension glaucoma is not well understood, but experts believe it is caused by damage to fragile optic nerves, which can happen even if pressure inside the eye is normal. Some experts believe a reduction in blood flow to the optic nerve can also cause normal-tension glaucoma.
Most forms of glaucoma are detected in a similar fashion, using identical tests. During your initial visit, your eye doctor will ask you questions about your symptoms, family and personal medical history, diet, and lifestyle. Your eye doctor will dilate your pupils by administering eye drops. The purpose of the drops is to allow the doctor to see through the pupil and into the eye during the examination. Although a tonometer (a test for checking intraocular pressure, i.e., pressure inside the eye) is an important and common tool used during a glaucoma screening, it is not enough for a correct diagnosis because eye pressure often changes. Additional tests used to diagnose glaucoma include:
Visual acuity test: this test determines how well you can read letters at a distance (usually fourteen to twenty feet away). It uses the Snellen chart, which consists of several rows of letters that get smaller towards the bottom of the chart. The top letter is usually a big E.
Pupillary reflex response: this is similar to a reflex test done on the knee. The eye doctor stimulates the pupil with light and evaluates its response.
Slit lamp examination: this test examines most parts of the eyes, including the cornea, lens, anterior chamber, and iris. The slit lamp is a special microscope that can help identify glaucoma.
Gonioscopy: this test measures the drainage angle of your eye by using a special contact lens.
Retinal examination: this test checks the retina for damage. It is best performed while the eyes are dilated.
Visual field test: this test helps an eye doctor test for peripheral vision loss, which is a sign of glaucoma.
Nerve fiber analyzer: this is a highly sensitive and accurate instrument that examines the fibers of the optic nerve for damage.
Optic nerve imaging: photographs are taken of the inside of your eye to check for abnormalities or damage. These photos are used later for reference and comparison.
The goal of treatment is to reduce the pressure inside the eye. The most conventional treatments for glaucoma are medication or surgery, or a combination of both. The medications can either decrease the amount of fluid produced or help the eye drain fluid more easily. Glaucoma medication may interfere with other medications, so it is a good idea to consult with your doctor and let him or her know about any medications you are taking.
There are several different types of glaucoma medication, so your doctor may want to try another one if it conflicts with medication you are currently taking or causes unwanted side effects (see chart below). For most people, medication is enough to control glaucoma. For others, surgery is the better option.
Laser trabeculoplasty is one surgical option for decreasing pressure in the eyes. The ophthalmologist sends a laser beam into the trabecular meshwork, where fluid drainage occurs. This improves drainage and lowers pressure. Argon Laser Trabeculoplasty (ALT), damages the surrounding tissue in the meshwork, and another session is usually necessary within a few years. Sometimes medication must also be taken. With Selective Laser Trabeculoplasty (SLT), a specially designed laser emits a low-energy laser light that targets only melanin-containing cells in the trabecular meshwork. The laser is heated only enough to affect the opening of the meshwork, so adjacent areas are not damaged. This allows for repeat treatments as needed.
Trabeculectomy is another surgical option for decreasing eye pressure in the long term. The procedure requires the surgeon to create a drainage channel on the surface of the eye. A microscopic hole is made in the eye’s wall, which allows a small amount of fluid to constantly drain through it. The hole is constructed so it doesn’t create a leak, and the patient is not aware of its presence. Sometimes, depending on the type and severity of the glaucoma, a surgeon will place a shunt on the site of the trabeculectomy.
Endoscopic CycloPhotocoagulation (ECP) is another way to help alleviate eye pressure if medication and laser trabeculoplasty are not effective. Unlike laser trabeculoplasty, ECP uses lasers to target the ciliary body that produces fluid. This causes less fluid to be produced and in effect lowers pressure.
Again, most glaucoma can be controlled with medication. The chart below shows the various drugs prescribed to treat glaucoma. If you have questions, please consult with your eye care professional.
|Type||Drug||Side Effects||How They Work|
|Beta blockers||BetaxololCarteololLevobetaxalolMetipranololTimolol||Lightheadedness; cold fingers and toes; shortness of breath; slow heartbeat; depression; hallucinations; hair loss; sexual dysfunction; vivid dreams; fatigue; insomnia;||Given as eye drops, beta blockers decrease the production of aqueous humor|
|Prostaglandin-like compounds||BimatoprostLatanoprostTravoprostUnoprostone||Increased eye and skin pigmentation; elongated and thickened eyelashes; muscle, joint, and back pain; skin rash; red eyes||Given as eye drops, prostaglandin-like compounds increase the aqueous humor outflow|
|Alpha-agonists||ApraclonidineBrimonidineDipivefrinEpinephrine||Dry nose and mouth; fatigue; headaches; blood pressure changes; abnormal heart beat; red eyes||Given as eye drops, alpha-agonists decrease aqueous humor production and increase the aqueous humor outflow|
|Carbonic anhydrase inhibitors||AcetazolamideBrinzolamideDorzolamideMethazolamide||Weight loss; low blood counts; kidney stones; fatigue; depression; loss of appetite; impotence; metallic or bitter taste in mouth; diarrhea||Brinzolamide and dorzolamide are given as eye drops; others are given by mouth; all decrease aqueous humor production|
|Cholinergic agents||CarbacholDemecariumEchothiophatePhysostigminePilocarpine||Demecarium, echothiophate, and physostigmine are more potent and more likely to cause cataracts and systemic side effects than the others||Physostigmine is given as ointment; the rest are given as eye drops; all increase aqueous humor outflow and may widen the angle of the eye|
Angle-closure glaucoma is considered a medical emergency for which treatment must not be delayed. Blindness is known to occur within days of the onset of symptoms. Drops, pills, or medicines delivered via IV are used to lower the eye pressure. At some point an iridotomy must be performed. During this procedure, a laser is used to open a channel in the iris to relieve pressure and prevent another attack.
Treatment for congenital glaucoma involves surgery to open the outflow channels of the angle.
Since there is no cure for glaucoma, treatment is directed at minimizing the damage it causes, or at least slowing the progressive damage to the optic nerves. The importance of routine check-ups can’t be overstated, because glaucoma is unnoticeable at first. This is especially true if you have a family history of glaucoma or other risk factors.
Risk Factors for Glaucoma
Risk factors for glaucoma include race, certain medical disorders, and family medical history. Glaucoma is more common in African American, Asian, and Hispanic patients, especially in the elderly. Diabetics or people who have had eye surgery are also more likely to have glaucoma. A family history of glaucoma increases the risk by 6 percent. Women of Caucasian descent have shallower anterior chambers than men, increasing their risk by 20 to 40 percent Additional risk factors may include:
- Prolonged steroid use
- Abnormal fetal growth and development
- Previous medical condition that restricts blood flow to the eye, such as in diabetic retinopathy and uveitis
- History of hypertension
- Thinner central corneal thickness
- Nearsightedness or farsightedness, depending on the type of glaucoma
- Low blood pressure
If any of these factors relate to you, then you should definitely go for more frequent eye exams.
Preventing glaucoma is important if you want to enjoy good vision all your life. The best prevention tool is an annual eye examination. Everyone (especially people over the age of 45) should get an eye exam every two years if no risk factors are present, or every year if they are at higher risk. Any change in your vision is also a good reason to visit the eye doctor.
Complications of Glaucoma
Glaucoma is known as the “silent thief of sight.” Complications can be avoided with early detection, but glaucoma typically does not show symptoms until it reaches its later stages. With angle-closure glaucoma, complications such as blindness can be prevented with quick and successful treatment. Complications of glaucoma may include:
- Blindness, or some significant degree of vision loss
- Irreversible optic nerve damage
- Continued pain from pressure
- Treatment may not be able to control the disease in some people
Facts about Glaucoma
Below are some interesting facts about glaucoma that every person should know, whether or not they are at risk. According to the Glaucoma Research Foundation:
- Everyone is at risk for glaucoma.
- There is no cure yet for glaucoma.
- Glaucoma is a leading cause of blindness and the leading cause among African Americans.
- Glaucoma is six to eight times more common in African Americans than Caucasians.
- Symptoms rarely appear until the late stages of the disease.
- Approximately 4 million Americans have glaucoma, but only half of them are aware they have it.
- Approximately 70 million people have glaucoma worldwide.
- Glaucoma accounts for 9 to 12 percent of all cases of blindness in the US.
- About 2 percent of the population ages 40–50 and 8 percent of people over the age of 70 have increased eye pressure.
- Open-angle glaucoma (the most common type) accounts for 19 percent of cases of blindness among African Americans, and 6 percent in Caucasians.
Talking to Your Eye Doctor
Here are some questions to ask your eye care professional about glaucoma:
- Which type of glaucoma do I have?
- Which treatment options will help control the disease?
- If treatment is not working, how long should I wait before contacting you?
- Which new symptoms should I watch for?
- How likely is it that my family members will have glaucoma?
- What is my prognosis?
- What can I do at home to help control the disease?
- What are the chances treatment will not work and I will go blind?
There is much glaucoma research being conducted around the world. Most studies are focused on learning more about the causes of the disease and improving diagnostic testing and treatment methods. An article published in Gleams in May of 2011 talks about a new study that examines how and why glaucoma causes retinal ganglion cells to degenerate, with primary focus on the diverse cellular players and molecular pathways and how they contribute to the onset and progression of the disease. The group Catalyst for a Cure says that they have been observing a loss of connectivity of the cells, both at the level of inputs with the retina and outputs to the brain. Their findings have led them to conclude that early changes to the retinal ganglion cells may contribute significantly to loss of vision in glaucoma. These findings are prompting researchers to come up with new strategies for slowing or halting the disease.
Another study focuses on improving existing drugs. Research is being conducted on several drugs such as travoprost and tafluprost and their relation to commercial drugs. Therapeutic drugs for glaucoma such as the calcium channel-blocker lomerizine and the topical calcium-blocker flunarizine are also being investigated. The goal is to improve the trend of local tolerance by using less toxic preservatives or eliminating preservatives altogether. Improving existing drugs will help slow the progress of glaucoma in some patients.
- M. Beers, MD “The Merck Manual of Medical Information” 2nd home edition (Pocket Books, 2003) 1308
- M. Beers, MD “The Merck Manual of Medical Information” 2nd home edition (Pocket Books, 2003) 1306- 1309
- Glaucoma Research Foundation, April 5, 2011, Glaucoma Facts and Stats http://www.glaucoma.org/glaucoma/glaucoma-facts-and-stats.php
- H. Griffith, MD “Complete Guide to Symptoms, Illness, & Surgery” (The Berkeley Publishing Group, 2006) 336-337
- F.J. Munoz-Negrete, Arch Soc Esp Oftalmol, New Developments in Glaucoma Medical Treatment, Oct. 2009; 84(10): 491-500