Glaucoma - Causes, Symptoms, Diagnosis, Treatment

Medically Reviewed By: Henry Nwanguma

WHAT IS GLAUCOMA?  

Glaucoma is a disease that damages your eye's optic nerve. It usually occurs when fluid builds up in the front part of your eye. That extra fluid increases the pressure in your eye, damaging the optic nerve. Glaucoma is a leading cause of blindness for people over 60 years old. But blindness from glaucoma can often be prevented with early treatment.

TYPES OF GLAUCOMA 

There are two major types of glaucoma, they include;

• Primary open-angle glaucoma

This type of glaucoma is common. It happens gradually, when the eye does not drain fluid as well as it should (like a clogged drain). As a result, eye pressure builds and starts to damage the optic nerve. This type of glaucoma is painless and cause no vision changes at first.

Some people can have optic nerves that are sensitive to normal eye pressure. This means their risk of getting glaucoma is higher than normal. Regular eye exams are important to find early signs of damage to their optic nerve.

• Angle-closure glaucoma (also called "closed-angle glaucoma" or "narrow-angle glaucoma")

This type of glaucoma happens when someone's iris is very close to the drainage angle in their eye. The iris can end up blocking the drainage angle. You can think of it like a piece of paper sliding over a sink drain. When the drainage angle gets completely blocked, eye pressure rises very quickly. This is called an 'acute attack'. It is a true eye emergency, and you should call your ophthalmologist right away or you might go blind.

Here are the signs of an acute angle-closure glaucoma attack:

• Your vision is suddenly blurry.
• You have severe eye pain.
• You have a headache.
• You feel sick to your stomach (nausea).
• You see rainbow-colored rings or halos around lights.

Many people with angle-closure develop it gradually. This is called 'chronic angle-closure glaucoma'. There are no symptoms at first, so they don't know they have it until the damage is severe or they have an attack.

WHAT ARE THE SYMPTOMS OF GLAUCOMA?

Open-angle glaucoma symptoms 

With open-angle glaucoma, there are no warning signs or obvious symptoms in the early stages. As the disease progresses, blind spots develop in your peripheral (side) vision.

Most people with open-angle glaucoma do not notice any change in their vision until the damage is quite severe. This is why glaucoma is called the "silent thief of sight". Having regular eye exams can help your ophthalmologist find this disease before you lose sight. Your ophthalmologist can tell you how often you should be examined.

Angle-closure glaucoma symptoms 

People at risk for angle-closure glaucoma usually show no symptoms before an attack. Some early symptoms of an attack may include; blurred vision, halos, mild headaches or eye pain. People with these symptoms should be checked by their ophthalmologist as soon as possible. Other symptoms involved; severe pain in the forehead, redness of the eye and vomiting.

Normal tension glaucoma 

People with "normal tension glaucoma" have eye pressure that is within normal ranges, but show signs of glaucoma, such as blind spots in their field of vision and optic nerve damage.

Glaucoma suspects 

Some people have no signs of damage but have higher than normal eye pressure (called ocular hypertension). These patients are considered "glaucoma suspects" and have a higher risk of eventually developing glaucoma. They should be carefully monitored by an ophthalmologist.

CAUSES OF GLAUCOMA

Your eye constantly makes aqueous humor. As new aqueous flows into your eye, the same amount should drain out. The fluid drains out through an area called the drainage angle. This process keeps pressure in the eye (called intraocular pressure or IOP) stable. But if the drainage angle is not working properly, fluid builds up. Pressure inside the eye rises, damaging the optic nerve.

The optic nerve is made of more than a million tiny nerve fibers. It is like an electric cable made up of many small wires. As these nerve fibers die, you will develop blind spots in your vision. You may not notice these blind spots until most of your optic nerve fibers have died. If all of the fibers die, you will become blind.

WHO IS AT RISK FOR GLAUCOMA?

Some people have a higher than normal risk of getting glaucoma. They include;

• People who are over age 40.
• People who have family members with glaucoma.
• People who are of African or Hispanic heritage.
• People who have high eye pressure.
• People who are farsighted or nearsighted.
• People who had an eye injury.
• People who have corneas that are thin in the center.
• People who have thinning of the optic nerve.
• People who have diabetes, migraines, poor blood circulation or other health problems affecting the whole body.

See an ophthalmologist about your risk for getting glaucoma. People with more than one of these risk factors have an even higher risk of glaucoma.

GLAUCOMA DIAGNOSIS 

The only sure way to diagnose glaucoma is with a complete eye exam. A glaucoma screening that only checks eye pressure is not enough to find glaucoma.

During a glaucoma exam, your ophthalmologist will:

• Measure your eye pressure.
• Inspect your eye's drainage angle.
• Examine your optic nerve for damage.
• Test your peripheral (side) vision.
• Take a picture or computer measurement of your optic nerve.
• Measure the thickness of your cornea.

  
DIAGNOSTIC TOOLS PHYSICIANS USE TO DIAGNOSE GLAUCOMA

Your eye doctor has a variety of diagnostic tools which aid in determining whether or not you have glaucoma - even before you have any symptoms. Let us explore these tools and what they do.


The Tonometer

The tonometer measures the pressure in your eye. Your doctor places a numbing eye drop in your eye. Then you sit at a slit-lamp, resting your chin and forehead on a support that keeps your head steady. The lamp, which lets your doctor see a magnified view of your eye, is moved forward until the tonometer, a plastic prism, barely touches the cornea to measure your IOP. The test is quick, easy and painless.   

The Pachymeter 

The pachymeter measures central corneal thickness (CCT). Like the tonometer, your doctor will first anesthetize your eyes. Then a small probe will be placed perpendicular to the central cornea.

CCT is an important measure and helps your doctor interpret your IOP levels. Some people with thin central corneal thickness will have pressures that are actually higher than when measured by tonometry. Likewise, those with thick CCT will have a true IOP that is lower than that measured. Measuring your central corneal thickness is also important since recent studies have found that thin CCT is a strong predictor of developing glaucoma in patients with high IOP.

Visual Field Test

Visual field is an important measure of the extent of damage to your optic nerve from elevated IOP. In glaucoma, it is the peripheral (side) vision that is most commonly affected first. Testing your visual field lets your doctor know if peripheral vision is being lost. There are several methods of examination available to your doctor; visual field testing has advanced significantly in recent years.

In computerized visual field testing, you will be asked to place your chin on a stand which appears before a concave computerized screen. Whenever you see a flash of light appear, you press a buzzer. At the end of this test, your doctor will receive a printout of your field of vision. New software has been developed to help your doctor analyze these tests as well as monitor progression of visual field loss over successive tests.

Ophthalmoscopy 

Using an instrument called an ophthalmoscope, your eye doctor can look directly through the pupil at the optic nerve. Its color and appearance can indicate whether or not damage from glaucoma is present and how extensive it is. This technique remains the most important in diagnosing and monitoring glaucoma.

Imaging Technology

A number of new and highly sophisticated image analysis systems are now available to evaluate the optic nerve and retinal nerve fiber layer, the areas of the eye damaged by glaucoma. These devices include; scanning laser tomography (e.g. HRT3), laser polarimetry (e.g. GDX), and ocular coherence tomography (e.g. older time-domain OCT or newer spectral-domain OCT). These instruments can help your doctor by giving a quantitative measure of the anatomical structures in the eye. Photographs of the optic nerve can also be useful to follow the progression of damage over time. Large databases have been established to compare an individual's anatomic structures to those of other patients in the same age group. This software and technology are developing rapidly and show great promise. However, they have not yet evolved to replace ophthalmoscopy, where the doctor looks directly at the optic nerve.

Gonioscopy 

Your doctor may perform a gonioscopy to closely examine the trabecular meshwork and the angle where fluid drains out of the eye. After dilating and numbing the eye with anesthetic drops, the doctor places a special type of hand-held contact lens, with mirrors inside, on the eye. The mirrors enable the doctor to view the interior of the eye from different directions. In this procedure, the doctor can determine whether the angle is open or narrow. Individuals with narrow angles have an increased risk for a sudden closure of the angle, which can cause an acute glaucoma attack. Gonioscopy can also determine if anything, such as abnormal blood vessels or excessive pigment, might be blocking the drainage of the aqueous humor out of the eye. 

HOW OFTEN SHOULD SOMEONE BE SCREENED FOR GLAUCOMA? 

The following are the American Academy of Ophthalmology's recommended intervals for eye exams:

• Age 20 to 29: Individuals of African descent or with a family history of glaucoma should have an eye examination every three to five years. Others should have an eye exam at least once during this period.
• Age 30 to 39: Individuals of African descent or with a family history of glaucoma should have an eye examination every two to four years. Others should have an eye exam at least twice during this period. 
• Age 40 to 64: Individuals should have an eye examination every two to four years.
• Age 65 or older: Individuals should have an eye examination every one to two years. 

These routine eye screening and examinations are important since glaucoma usually causes no symptoms (asymptomatic) in its early stages. Once damage to the optic nerve has occurred, it can not be reversed. Thus, in order to preserve vision, glaucoma must be diagnose early and followed regularly. Patients with glaucoma need to be aware that it is a lifelong disease. Compliance with scheduled visits to the eye doctor and with prescribed medication regimens offers the best chance for maintaining vision.

GLAUCOMA TREATMENT 

Glaucoma damage is permanent - it cannot be reversed. But medicine and surgery help to stop further damage. To treat glaucoma, your ophthalmologist may use one or more of the following treatments.

1. MEDICATION

Glaucoma is usually controlled with eyedrop medicine. Used everyday, these eyedrops lower eye pressure. Some do this by reducing the amount of aqueous fluid the eye makes. Others reduce pressure by helping fluid flow better through the drainage angle.

Glaucoma medications can help you keep your vision, but they may also produce side effects. Some eye drops may cause:

• A stinging or itching sensation.
• Red eyes or red skin around the eyes.
• Changes in your pulse and heartbeat.
• Changes in your energy level.
• Changes in breathing (especially if you have asthma or breathing problems).
• Dry mouth.
• Blurred vision.
• Eyelash growth.
• Changes in your eye color, the skin around your eyes or eyelid appearance. 

All medications can have side effects. Some drugs can cause problems when taken with other medications. It is important to give your doctor a list of every medicine you take regularly. Be sure to talk with your ophthalmologist if you think you may have side effects from glaucoma medicines.

2. LASER SURGERY 

There are two main types of laser surgery to treat glaucoma. They help aqueous drain from the eye. These procedures are usually done in the ophthalmologist's office or an outpatient surgery center.

• Trabeculoplasty

This surgery is for people who have open-angle glaucoma. The eye surgeon uses a laser to make the drainage angle work better. That way 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

Some glaucoma surgery is done in an operating room. It creates a new drainage channel for the aqueous humor to leave the eye.

• Trabeculectomy

This is where your eye surgeon creates a tiny flap in the sclera (white of your eye). He or she will also create a bubble (like a pocket) in the conjunctiva called a filtration bleb. It is usually hidden under the upper eyelid and cannot be seen. Aqueous humor will be able to drain out of the eye through the flap and into the bleb. In the bleb, the fluid is absorbed by tissue around your eye, lowering eye pressure.

• Glaucoma drainage devices

Your ophthalmologist may implant a tiny drainage tube in your eye. It sends the fluid to a collection area (called a reservoir). Your eye surgeon creates this reservoir beneath the conjunctiva (the thin membrane that covers the inside of your eyelids and white part of your eye). The fluid is then absorbed into nearby blood vessels.


YOUR ROLE IN GLAUCOMA TREATMENT 

Treating glaucoma successfully is a team work between you and your doctor. Your ophthalmologist will prescribe your glaucoma treatment. It is up to you to follow your doctor's instructions and use your eye drops.

Once you are taking medications for glaucoma, your ophthalmologist will want to see you regularly. You can expect to visit your ophthalmologist about every 3-4 months. However, this can vary depending on your treatment needs.

If you have any questions about your eyes or your treatment, talk to your ophthalmologist.

WHAT EYEDROPS TREAT GLAUCOMA?

Beta-adrenergic antagonists act against, or block, adrenaline-like substances. These drops work in the treatment of glaucoma by reducing the production of the aqueous humor. For years, they were the gold standard (to which other agents are compared) for treating glaucoma. A few of these medications are timolol (Timoptic), levobunolol (Betagan), carteolol (Ocupress), and metipranolol (Optipranolol). 

Used once or twice daily, these drops are very effective but have side effects. However, side effects, such as the worsening of asthma or emphysema, bradycardia (slow heart rate), low blood pressure, fatigue and impotence. Betaxotol (Betoptic) is a beta-adrenergic antagonist that is more selective in working just on the eye and, therefore, carries less risk of heart (cardiac) or lung (pulmonary) side effects than other drops of this type.

Prostaglandin analogs are similar in chemical structure to the body's prostaglandins. Prostaglandins are hormone-like substances that involved in a wide range of functions throughout the body. These drops work in glaucoma by increasing the outflow (drainage) of fluid from the eye.

The prostaglandin analogs have replaced beta-blockers as the most commonly prescribed drops for glaucoma. They can be used just once a day. This class of medication has fewer systematic (involving the rest of the body) side effects than beta-blockers, but can change the color of the iris as well as thicken and darken the eyelashes. In addition, some atrophy of the fat around the eye may occur. These drops are also more likely to cause redness of the eyes than some other classes of eye drops. In some patient, they may also cause inflammation inside the eye. Examples of these medications include; latanoprost (Xalatan), travoprost (Travatan), bimatoprost (Lumigan), and tafluprost (Zioptan). 

Adrenergic agonists are a type of drops that act like adrenaline. They work in glaucoma by both reducing the production of fluid by the eye and increasing its outflow (drainage). The most popular adrenergic agonist is brimonidine (Alphagan). However, there is at least a 12% risk of significant local (eye) allergic reactions. Other members of this class of drops include; epinephrine, dipivefrin (Propine), and apraclonidine (Lopidine).

Carbonic anhydrase inhibitors work in glaucoma by reducing the production of fluid in the eye. Eyedrop forms of this type of medication include dorzolamide (Trusopt) and brinzolamide (Azopt). They are used two or three times daily. Carbonic anhydrase inhibitors may also be rarely taken as pills (systemically) to remove fluid from the body, including the eye. Oral forms of these medications used for glaucoma involved; acetazolamide (Diamox) and methazolamide (Neptazane). Their use in this condition, however, is limited due to their systemic (throughout the body) side effects, including reduction of body potassium, kidney stones, numbness or tingling sensations in the lips, arms, and legs, fatigue, and nausea.

Parasympathomimetic agents, which are also called miotics because they narrow (constrict) the pupils, act by opposing adrenalin-like substances. They work in glaucoma by increasing the aqueous outflow from the eye.

The parasympathomimetics were used for many years to treat glaucoma, but because of the development of beta-blockers and prostaglandins, they are now used infrequently because they need to be used three to four times a day and produce side effects in the eye. These side effects include a small pupil, blurred vision, an aching brow, and an increased risk of retinal detachment. Currently, pilocarpine is used primarily to keep the pupil small in patients with a particular iris configuration (plateau iris) or in patients with a narrow angle prior to laser iridotomy.

Osmotic agents are an additional class of medications used to treat sudden (acute) forms of glaucoma where the eye pressure remains extremely high despite other treatments. These medications include isosorbide (Ismotic, given by mouth) and mannitol (Osmitrol), given through the veins. These medications must be used cautiously as they have significant side effects, including nausea, fluid accumulation, in the heart and/or lungs (congestive heart failure and/or pulmonary edema), bleeding in the brain, and kidney problems. Their use is prohibited in patients with uncontrolled diabetes, heart, kidney, or liver problems.

Ophthalmologists often prescribe an eyedrop containing more than one class of drug to patients who require more than one type of drug for control of their glaucoma. This simplifies the taking of drops by the patient. Examples of these include the combination of timolol and dorzolamide in the same drop (Cosopt), the combination of timolol and brimonidine in the same drop (Combigan), and the combination of brinzolamide and brimonidine in the same drop (Simbrinza). Combination drops that include both beta-adrenergic antagonists and prostaglandin analogs are available in Europe and Japan but have not been approved by the United States Food and Drug Administration (FDA) for use in the US.   

Several new classes of glaucoma drops are currently under development or awaiting FDA approval. These include nitrous oxide donating medication combined with prostaglandins (Latanoprostene), rho-kinase inhibitors (Rhopressa), and A-1 receptor selective adenosine mimetics (Trabodenoson). Although marijuana use has been shown to reduce intraocular pressure; eyedrops are available that accomplish the same purpose and with greater efficacy and less systemic risk.

HOW SHOULD I USE MY GLAUCOMA EYEDROPS? 

If eyedrops have been prescribed for treating your glaucoma, you need to use them properly, as instructed by your eye care professional. Proper use of your glaucoma medication can improve the medicine's effectiveness and reduce your risk of side effects.

To properly apply your eyedrops, follow these steps:

• Wash your hands.
• Hold the bottle upside down.
• Tilt your head back.
• Hold the bottle in one hand and place it as close as possible to the eye.
• With the other hand, pull down your lower eyelid. This forms a pocket.
• Place the prescribed number of drops into the lower eyelid pocket. If you are using more than one eyedrop, be sure to wait at least 5 minutes before applying the second eyedrop. 
• Close your eye or pres the lower lid lightly with your finger for at least 1 minute. Either of these steps keep the drops in the eye and help prevent the drops from draining into the tear duct, which can increase your risk of side effects. 

IS IT POSSIBLE TO PREVENT GLAUCOMA? 

Primary open-angle glaucoma cannot be prevented, given our current state of knowledge. However, the optic nerve damage and visual loss resulting from glaucoma can be prevented by earlier diagnosis, effective treatment, and compliance with treatment.

Secondary types of glaucoma can be prevented by avoidance of trauma to the eye and prompt treatment of eye inflammation and other diseases of the eye or body that may cause secondary forms of glaucoma.

Most cases of visual loss from angle-closure glaucoma can be prevented by the appropriate use of laser iridotomy in eyes at risk for the development of acute or chronic angle-closure glaucoma.

REFERENCES 

• The AGIS Investigators. "The Advanced Glaucoma Intervention Study (AGIS): Comparison of treatment outcomes within race: 10-year results." Ophthalmology 111.4 (2004): 651-664.
• Epstein, D. L., et al. "A long-term clinical trial of timolol therapy versus no treatment in the management of glaucoma suspects." Ophthalmology 96.10 (1989): 1460-1467.
• Gedde, S. J., et al. "Treatment outcomes in the Tube Versus Trabeculectomy (TVT) Study after five years of follow-up." American Journal Ophthalmology 153.5 (2012): 789-803.e2. Gordon, M. O., et al. "The Ocular Hypertension Treatment Study: Baseline factors that predict the onset of primary open-angle glaucoma." Archives of Ophthalmology 120.6 (2002): 714-720.
• Heijl A, et al. "Reduction of intraocular pressure and glaucoma progression: results from the Early Manifest Glaucoma Trial." Archives of  Ophthalmology 120.10 (2002): 1268-1279.
• Kass, M. A., et al. "The Ocular Hypertension Treatment Study: A randomized trial determines that topical ocular hypertensive medication delays or prevents the onset of primary open-angle glaucoma." Archives of Ophthalmology 120.6 (2002): 701-713.
• Katz, L. J., et al. "Selective laser trabeculoplasty versus medical therapy as initial treatment of glaucoma: a prospective, randomized trial." Journal of Glaucoma 21.7 (2012): 460-468.
• Krupin, T., et al. "Low-Pressure Glaucoma Study Group. A randomized trial of brimonidine versus timolol in preserving visual function: results from the Low-Pressure Glaucoma Treatment Study." American Journal of Ophthalmology 151.4 (2011) 671-681.
• Lichter, P. R., et al "CIGTS Study Group. Interim clinical outcomes in the Collaborative Initial Glaucoma Treatment Study comparing initial treatment randomized to medications or surgery." Ophthalmology 108.11 (2001): 1943-1953.
• Musch, D. C., et al. "CIGTS Study Group. Intraocular pressure control and long-term visual field loss in the Collaborative Initial Glaucoma Treatment Study." Ophthalmology 118.9 (2011): 1766-1773.