Glaucoma

Introduction

The purpose of this page is to acquaint the reader with the medical condition called glaucoma. We will discuss what glaucoma is, how it is diagnosed, treated and how blindness can be prevented. Special types of glaucoma will be addressed as well as possible future developments with regard to treatment.  Feel free after reading below to view a video http://www.aao.org/eye-health/diseases/what-is-glaucoma.

Definition

Glaucoma is the name given to a group of disorders in which the eye pressure is too great for the health of the optic nerve. Other less well-documented effects may also play a role in glaucoma. The optic nerve is the part of the eye that send signals to the brain allowing us to see. If left untreated, optic nerve damage will occur that may lead to slow painless loss of side vision. Once vision is lost from glaucoma, it cannot be recovered. It is estimated that at least two million Americans have glaucoma and that one half of these people are unaware that they have it. Glaucoma is a leading cause of irreversible blindness in the United States, but fortunately, with early diagnosis and treatment, blindness is not inevitable.

Risk Factors

Anyone may develop glaucoma at some point in their life. However, there are certain groups who are at increased risk for the disease. Glaucoma is estimated to affect close to one percent of the American population. African-Americans are 5-6 times more likely than whites to develop glaucoma. In addition, glaucoma in African-Americans tends to be more difficult to treat. As a result, African-Americans are much more likely to go blind from their disease than their white counterparts. The reasons for this discrepancy remains unclear.

In some forms of glaucoma a genetic predisposition has been found. Therefore, glaucoma may run in families. If you have a blood relative with glaucoma, then you are at increased risk. Others at increased risk for glaucoma are those with diabetes, hypertension, near-sightedness (myopia), those with previous eye injuries and patients who take steroid medication chronically. Glaucoma can affect children but this condition is rare. Glaucoma usually begins after age forty.

Diagnosis

Glaucoma causes no symptoms early in the disease. Therefore, the only way glaucoma can be diagnosed at this stage is with an eye examination. Remember, once vision is lost, it cannot be recovered. Early diagnosis is imperative to preserve vision. To diagnose glaucoma, an ophthalmologist will first check the eye pressure. Second, the area of the eye where fluid drains out is inspected. This will determine what type of glaucoma may be present. Next, the optic nerves will be examined. The normal optic nerve has a orange-pink color. In glaucoma, the center of the optic nerve becomes excavated as it loses nerve fibers. This leaves it with a pale “cupped out” center.

e11 Glaucoma

The above photographs show normal (left) and glaucomatous (right) optic nerve heads

If glaucoma is suspected, the ophthalmologist will then perform a test of the side vision called a peripheral visual field. Glaucoma usually affects the side vision first, and that is why most patients are unaware of their condition until the late stages.

Once glaucoma is diagnosed, treatment can be instituted.

TREATMENT

In order to preserve vision, it is important to institute treatment once glaucoma is diagnosed. The initial treatment for most patients with chronic open-angle glaucoma is in the form of eye drops. If patients are unresponsive to medications or develop side effects, then laser surgery can be performed. If laser surgery is ineffective and the glaucoma continues to progress, then glaucoma filtration surgery may be performed. These treatments will be discussed in further detail below.

Medication

Medications have been used to treat chronic open angle glaucoma since the 1870s. Until recently, however, our choices for therapy where quite limited. In the past ten years, several new classes of medications have been developed with the goal of improving effectiveness and safety. The medical therapy must be tailored to the individual patient and must take into consideration their effectiveness, convenience, cost and side-effect profile. The following is a list of the most commonly used medications for glaucoma.

    • B blockers (timolol maleate, betaxolol, carteolol, optipranolol)
action:
decrease production of eye fluid (aqueous humor)
most common side effects:
shortness of breath, slowing of heart rate, fatigue, depression, burning, stinging, allergy
    • Miotics (pilocarpine, carbachol, echothiophate iodide)
action:
increase aqueous outflow
most common side effects:
headache, dim vision, burning, stinging, allergy
    • Carbonic Anhydrase Inhibitors (dorzolamide, brinzolamide)
      (acetazolamide, methazolamide – oral agents)
action:
decrease production of aqueous
most common side effects:
burning, stinging, bitter taste, allergy. Oral agents have also been associated with kidney stones and more serious side effects
    • Alpha-Agonists (apraclonidine, brimonidine)
action:
decrease production of eye fluid (aqueous humor) brimonidine also improves aqueous outflow
most common side effects:
dry mouth, red eye, burning, stinging, headache, blurry vision, foreign-body sensation, fatigue, allergy
    • Prostaglandins (latanoprost)
action:
enhances drainage of aqueous from the eye
most common side effects:
blurred vision, burning, stinging, red eye, foreign body sensation, itching, increased iris pigmentation, may promote intraocular inflammation.

Laser

Glaucoma laser surgery (trabeculoplasty) can be an effective means of lowering eye pressure in patients with chronic open-angle glaucoma. The laser beam is actually a light which is applied to the drainage site of the eye causing an alteration which improves the outflow of aqueous from the eye. The procedure takes only five to ten minutes and is virtually painless. The main side effect is a temporary rise in eye pressure which may occur shortly after the procedure. Medications are now given which greatly decrease the chance of a spike in eye pressure. It may take up to six weeks for the full effect of the laser to become evident.

Laser trabeculoplasty is effective in up to 80% of patients with chronic open-angle glaucoma, but the effect may be temporary. At five years, in approximately one half of patients, the effect of the laser treatment will be lost and the eye pressure may rise.

Laser iridotomy is another procedure (see section on angle-closure) which is effective for patients with chronic or acute closure of the eye drain.

Surgery

Glaucoma filtration surgery (trabeculectomy) is indicated in patients who do not respond to medical and/or laser therapy. If the eye pressure is judged to be too high for the health of the optic nerve, surgery may be indicated.

Trabeculectomy involves surgically creating a “trap door” on the white of the eye (sclera) which acts as a filter to lower eye pressure. This procedure is performed in an operating room.

This procedure is a very effective way of stabilizing the eye pressure and the effect may be life-long. If successful, the eye drops can often be discontinued.

SPECIAL CONSIDERATIONS

Low-tension glaucoma

We think of glaucoma as a disease which involves high eye pressure but as we learn more about this condition, we are beginning to understand that other factors are involved. There is a group of patients who develop characteristic optic nerve damage and visual field loss despite having a “normal” eye pressure. These patients tend to have a higher incidence of vascular medical conditions such as migraine headaches and Raynaud’s phenomenon. Raynaud’s phenomenon is a condition in which patients experience excessive constriction of the peripheral blood vessels in response to exposure to cold temperature. Other conditions which affect the flow of blood to the optic nerve may also lead to low-tension glaucoma. Recently, investigators have demonstrated in the laboratory that retinal cells may be injured by the toxic effect of certain body chemicals. This may also play a role in optic nerve damage.

Low tension glaucoma can be difficult to diagnose and treat. Our current medications which attempt to lower eye pressure are inadequate to prevent progressive damage in some patients. Newer therapies aimed at protecting the optic nerve rather than just lowering eye pressure are being studied.

Congenital glaucoma

Most people are over 40 when they develop glaucoma but occasionally it can begin earlier. A few babies are born with glaucoma or develop it early in life. There is usually no family history of congenital glaucoma but the gene for this disorder can be inherited. Unlike adults in whom there are no symptoms initially, babies are usually diagnosed early. Because until approximately age three babies eyes are very elastic, they will enlarge when then eye pressure rises. Babies will have tearing and they will be uncomfortable.

Congenital glaucoma is a surgical disease. Medication and laser are ineffective because there is an anatomic disturbance in the drain of the eye. Surgery involves mechanically opening the drain of the eye. Sometimes artificial drains are required. Fortunately, congenital glaucoma is rare and with prompt diagnosis surgery can be very effective.

Cataracts and Glaucoma

Glaucoma is a potentially devastating eye disease that may lead to permanent visual loss if not treated. Since glaucoma and cataracts tend to occur with advancing age, there are many people who have both. One eye drop called pilocarpine makes the pupil small, allowing less light to enter the eye. This side effect, in combination with a cataract can seriously impair vision. It is important to identify people who have cataracts and glaucoma because the treatment options can lead to improved sight.

Surgery is indicated for cataracts when they are significantly interfering with one’s daily life. Glaucoma surgery is necessary when eye pressure cannot be controlled medically or with laser. High eye pressure may lead to permanent visual loss from destruction of the optic nerve. If both of these conditions exist simultaneously, surgery for cataracts and glaucoma can be safely performed at the same time.

Today, cataracts and glaucoma can be effectively treated surgically to both restore vision by removing the cataract and to preserve vision by lowering eye pressure.

Acute angle-closure

Most patients with glaucoma have anatomically open angles. The drainage apparatus of the eye (trabecular meshwork) is located in an angle of the eye formed by the iris and the cornea. In about 5% of patients there is a narrowing of this angle which may occur slowly over time. These people are at risk for a sudden complete closure of the angle which will prohibit the exit of fluid from the eye. This will result in a rapid rise in eye pressure causing pain, redness, blurred vision, halos around lights, nausea and vomiting.

e2 Glaucoma

Schematic representation of open angle
e3 Glaucoma

Schematic representation of closed angle

Acute angle-closure can quickly lead to visual loss if not treated. The treatment involves eye drops as well as oral and possibly intravenous medications. The laser is also used to create a hole in the iris (iridotomy) which can relieve the attack. Sometimes glaucoma filtration surgery is required.

e14 Glaucoma

Photograph of laser iridotomy

It is recommended that some people with very narrow angles undergo a prophylactic (preventative) laser iridotomy to prevent acute angle-closure.

Pseudoexfoliation glaucoma

Pseudoexfoliation is the build up of flaky white material within the eye. It has also been found in other parts of the body but its origin remains unclear. This material may clog the drain of the eye (trabecular meshwork) leading to impaired outflow of aqueous humor. This results in increased eye pressure which may ultimately cause optic nerve damage and glaucoma.

Pseudoexfoliation glaucoma is a common type found in those of Scandinavian origin. One eye may be affected more severely than the other. This type of glaucoma is treated the same as primary open-angle glaucoma. Pseudoexfoliation glaucoma responds well to laser therapy.

PREVENTING BLINDNESS

Fortunately, with early diagnosis and treatment, few people will go blind from glaucoma. Because glaucoma has no symptoms early on, a complete eye examination is the only way to detect it. It is very disheartening to see a patient who has gone blind from a treatable disease. Therefore, it is important to make routine visits to an ophthalmologist.

Glaucoma can strike anyone, but those at increased risk are people:
  • of African ancestry
  • with a family history of glaucoma
  • with diabetes
  • with hypertension
  • who use steroids chronically
  • who have had serious eye injury

THE FUTURE

Neuroprotection

At the present time, our main focus of treatment for glaucoma involves lowering the eye pressure. However, we know that some patients continue to suffer visual loss despite seemingly well-controlled eye pressure. This occurrence has stimulated the search for other factors that may play a role in the pathogenesis of glaucoma. Two important thrusts of research involve the role of circulatory factors and that of certain chemicals (neurotransmitters) within the eye. Retinal cells may be directly or indirectly damaged through mechanisms unrelated to eye pressure.

Agents which may protect the optic nerve from damage are now being tested but effective treatments are years away. One medication that shows some promise as a neuroprotective drug is brimonidine. Clinical trials to test these laboratory findings are beginning.

Genetics

Because glaucoma tends to run in families, a genetic basis for the disease is certain. Other environmental factors may also play a role. The chromosomal abnormality for juvenile glaucoma has been found. Finding the offending gene in open-angle glaucoma is a more difficult challenge but there are presently several suspects.

It is important to understand the genetic basis for diseases like glaucoma. First, it may lead to screening tests for those at risk. Second, it may lead to newer therapies that target offending genes and control the process from its origin rather than from the secondary effects such as high eye pressure or the build up of toxic substances.