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Glaucoma

Glaucoma is a disorder associated with pressure in the eye, and is characterized by damage to the optic nerve, with consequent visual loss, initially peripheral, but potentially blinding if relentlessly progressive. Unfortunately, glaucoma is usually a disease in which the patient is entirely asymptomatic (without symptoms) until late in the disease. The disorder we refer to as glaucoma, is not a single disease, but rather a myriad of diseases with one final common insult, injury to the optic nerve.

Glaucoma affects 2 million Americans, and half of those people are unaware they have the disease. Approximately 5 to 10 million Americans have elevated eye pressure, which places them at risk for the development of glaucoma. Eighty thousand Americans are already blind from the disease. African-Americans have a five-fold greater risk of developing glaucoma and, in this population, it is the single most common cause of irreversible blindness.

In recent years, it has been shown that at least one-third of glaucoma patients have eye pressures in the “normal range”, which is 10 to 21mm Hg. This information has challenged traditional thought that glaucoma is a disorder of high eye pressure. There are consequently multiple theories regarding the cause of glaucoma. Suffice it to say that besides eye pressure, perfusion (blood flow) of the optic nerve, mechanical factors in and around the optic nerve itself, and biochemical factors also probably play a role. Most ophthalmologists believe that patients with sustained eye pressures in the high 20’s or above will eventually develop glaucoma but there is no level of pressure at which glaucoma never occurs. This is one of the most difficult concepts for glaucoma patients to understand, i.e., that glaucoma may not only occur but may progress in the face of a “normal pressure.” Glaucoma is much more complex than most patients would like to believe. This very fact is the reason that glaucoma sub-specialist ophthalmologists have an additional one to two years of fellowship training beyond the three to four years of general ophthalmology residency training.

There are many risk factors for glaucoma, and these must be taken into account in the management of patients with suspected or manifest glaucoma. The strongest risk factors include elevated intraocular (eye) pressure, family history of glaucoma, advanced age, and being of African-American descent. Other risk factors include cardiovascular disease (e.g., history of heart attack or stroke), diabetes mellitus (sugar diabetes), myopia (nearsightedness), high blood pressure, and migraine headache.

Glaucoma is not usually diagnosed on the initial exam, and certainly cannot be determined by measuring eye pressure alone, regardless of the pressure. In general, the diagnosis of glaucoma implies optic nerve injury and loss of peripheral vision. Patients with increased eye pressures only, are said to have “ocular hypertension,” or possibly are referred to as “glaucoma suspects”. On the initial evaluation, most ophthalmologists will obtain eye pressure readings and complete a dilated eye exam in which the optic nerve is carefully evaluated. An enlarged depression (called a “cup to disc ratio“) in the optic nerve may be indicative of glaucoma. (The exact description of this and a number of other important variables are disregarded here for the sake of succinctness).

If the ophthalmologist is concerned about the possibility of glaucoma, the patient is scheduled for a visual field test. This is a computer-assisted test that evaluates a patient for subtle peripheral vision deficits. Some patients believe, when they are told they need a peripheral vision test, that their peripheral vision is “fine” because they can see their waving hand off to the side. In reality, this kind of testing is so gross as to be entirely useless except in end-stage glaucoma or certain stroke patients. If peripheral vision deficits are found on the visual field test that are consistent with glaucoma, the patient will be informed and further evaluation scheduled or a treatment plan discussed. Many ophthalmologists recommend two or three baseline pressure readings prior to initiating treatment. This helps the ophthalmologist to gauge the pressure reduction once treatment has begun.

During one of the initial visits, the ophthalmologist will also evaluate the angle of the eye to determine whether it is “open”, “narrow”, or “closed”. The angle of the eye is the primary anatomical site where fluid egress from the eye occurs. This piece of information is used not only to define the two major categories of glaucoma, i.e., open angle glaucoma vs. closed (narrow) angle glaucoma, but is critical to the treatment plan.

For those patients diagnosed with glaucoma, a treatment and follow-up plan will be organized. The goal of glaucoma therapy is to preserve the patient’s present level of vision, i.e., to prevent further peripheral, and sometimes central, vision loss. The treatment plan will vary widely depending on the type of glaucoma diagnosed, the degree to which the glaucoma has progressed, the patient’s underlying risk factors, and many other variables which are beyond the scope of this brief overview. In general, medicine (both topical eye-drops and oral medications), laser procedures, and operative procedures are all utilized in attempt to preserve vision. Patients are followed at variable intervals according to the severity of disease and response to treatment, however, most patients will be evaluated 2 to 4 times a year with pressure measurements, optic nerve evaluations, and visual field testing. In some cases, despite the most meticulous care and aggressive management, patients will continue to lose vision. However, in the majority of cases in which patients present early in the course of their disease and are compliant with the ophthalmologist’s advice, useful vision can be maintained throughout life.

Below, the reader will find a brief discussion of each of the most common types of glaucoma. A review of laser procedures and glaucoma filtration (surgical) procedures can be found in the library of “Eye Procedures” elsewhere in this site.

Primary Open Angle Glaucoma

Primary open angle glaucoma (POAG) is the most common of all types of glaucoma. The condition is diagnosed in the presence of an open angle, evidence of optic nerve damage, and peripheral vision loss consistent with glaucoma on a visual field test. Patients are usually treated with eye-drop and/or oral medications first, reserving laser and surgical procedures for “maximum medical therapy” failures, i.e., patients who have progression of glaucoma with a medical regimen. However, in many cases, an argument can also be made that laser therapy (argon laser trabeculoplasty) should be used initially, and medications secondarily. If eye-drop medication is chosen as the initial treatment, many ophthalmologists will recommend treatment of just one eye first, utilizing the second eye as a control, or “barometer”, by which to gauge the effect of treatment. It is important for the patient to realize that eye-drop medications administered to only one eye may also lower pressure in the opposite eye due to a systemic effect. This is why baseline pressure measurements, prior to the initiation of treatment, are extremely important in assessing the efficacy of medications.

Patients who have progression of glaucoma despite medical therapy and, perhaps, argon laser trabeculoplasty (ALT, or laser treatment) are usually recommended to have a glaucoma filtration procedure (trabeculectomy). Certain patients who have failed an initial glaucoma filtration procedure may be recommended for implantation of a glaucoma drainage device. These procedures are reviewed in the “Eye Procedures” section of this site.

Angle Closure Glaucoma

Angle closure glaucoma may be subdivided into two basic types for the purposes of this discussion. These are known as primary angle closure glaucoma and acute angle closure glaucoma.

Primary angle closure glaucoma accounts for 10% of glaucoma patients and two-thirds of these present asymptomatically (without symptoms). This condition is characterized by a narrow angle, i.e., the anatomy of the eye is such that aqueous fluid drainage via the trabecular meshwork (the primary fluid egress site) is relatively obstructed. In essence, the iris (colored part of the eye) is in close apposition to the cornea (front clear part of the eye) and physically obstructs the flow of fluid out of the eye. The treatment for this condition is a peripheral iridotomy (laser) or peripheral iridectomy (surgery). The effect of either procedure is the creation of a tiny opening in the iris. This allows aqueous fluid, made in the ciliary body (behind the iris), to flow directly through the iridotomy or iridectomy site, thereby leading to a falling backwards of the iris. This, in turn, clears the obstruction to the trabecular meshwork (drainage area). Treatment with glaucoma medications may be used before, and/or after, either procedure to further control glaucoma. The effect of a laser peripheral iridotomy (PI) is to convert a closed-angle into an open-angle, however, because of significant optic nerve damage, the patient may still require treatment for glaucoma.

Acute angle closure glaucoma is one of the few types of glaucoma that presents with symptoms. Patients may present with blurred vision, colored halos, severe pain, red eye, and nausea or vomiting. On examination, the eye pressure is extraordinarily high, generally 40 to 70 mmHg (normal 10 to 21). The angle is noted to be closed in the affected eye except in cases in which the corneal edema (swelling) is so severe that it cannot be visualized. In this case, the ophthalmologist may examine the fellow eye and note a narrow angle or angle closure. The condition may require medical management to reduce the pressure, thereby allowing the corneal edema to resolve, and then a laser peripheral iridotomy (PI) is completed. If a laser PI cannot be completed due to severe corneal edema, a surgical peripheral iridectomy is completed.

Normal Pressure Glaucoma (Low-Tension Glaucoma)

Normal pressure glaucoma, also known as low-tension glaucoma, occurs in approximately one-third of all patients afflicted with glaucoma. Patients with this condition have essentially the same findings as patients with primary open angle glaucoma (abnormal optic nerve findings and visual field loss), except that they are not demonstrated to have high intraocular pressures. As noted above, it is theorized that hypoperfusion (poor blood flow) of the optic nerve, mechanical factors in and around the nerve, and biochemical factors may play a role in the development of not only this type of glaucoma, but other types as well. The fact that migraines are more common in this form of glaucoma is further evidence to support the vascular (hypoperfusion) theory of normal pressure glaucoma. (Migraine is known to have a vasospastic (transient hypoperfusion) component, which leads to the headache).

Normal pressure glaucoma is often treated with eye-drop medications in attempt to further reduce pressure and stabilize the visual field. At this time, there appears to be more evidence to support the use of the eye-drop medication brimonidine than any other medicine in the treatment of normal pressure glaucoma. Some ophthalmologists also recommend argon laser trabeculoplasty (ALT) since this procedure may avoid the risks and expense of medications.

Pigmentary Glaucoma (Pigment Dispersion Syndrome)

Pigmentary glaucoma is a form of glaucoma that usually presents in young males, 20 to 50 years old. Other risk factors include moderate myopia (nearsightedness) and African-American ancestry. Many of these patients present to the ophthalmologist relating episodes of blurry vision, and sometimes eye pain, after exercise. The underlying cause is dispersion of pigment in the eye as a result of the posterior aspect of the iris rubbing against the zonules (microscopic fibers which hold the natural lens in place). This is known as iris-zonular touch. In fact, all patients with pigmentary glaucoma will necessarily have pigmentary dispersion syndrome prior to the onset of glaucoma (i.e., actual optic nerve damage and peripheral vision loss).

The mechanism of glaucoma development in this syndrome is the deposition of pigment from the iris into the trabecular meshwork (primary site of fluid egress), essentially “plugging” the microscopic spaces through which fluid escapes. On exam, the ophthalmologist makes the diagnosis of pigmentary glaucoma by first noting transillumination defects (windows) in the iris indicative of pigment loss. Many patients will also have pigment on the posterior (back) side of the cornea and heavy pigment deposited in the trabecular meshwork.

Though the “best” method of treatment still remains somewhat controversial amongst ophthalmologists, many forms of treatment have clear benefit, and treatment should not be delayed. Methods of treatment that have been commonly utilized include the use of miotics, laser peripheral iridotomy (PI), and argon laser trabeculoplasty (ALT). Miotics are topically applied (eye-drop) medications that constrict the pupil, thereby minimizing iris-zonular touch. A laser PI has been argued to release the pressure differential between the anterior and posterior chambers, thereby allowing the iris to bow forward away from the zonules. This procedure may, therefore, have the most benefit in terms of prevention of glaucoma. It may not be as valuable once the glaucoma is well-established (i.e., most of the pigment has rubbed off of the iris). ALT has been shown to have a very clear benefit in terms of pressure control in these patients. This procedure, therefore, may be more appropriate once the condition is well-established.

Pseudoexfoliative Glaucoma

Pseudoexfoliative glaucoma, which follows pseudoexfoliation syndrome, is a type of glaucoma thought to be caused by the deposition of “pseudoexfoliative material” into the trabecular meshwork eventually resulting in “plugging” of the microscopic canals, with consequent pressure rise. The origin of this pseudoexfoliative material is thought to be the capsule, which surrounds the natural lens of the eye. Pseudoexfoliation syndrome is diagnosed by the ophthalmologist primarily by the identification of the characteristic “fluffy material” on the border of the pupillary margin and on the natural lens capsule.

Treatment of this condition is quite similar to that of primary open angle glaucoma, however, this condition has been shown to respond better to argon laser trabeculoplasty (ALT) than any other variety of glaucoma.

It is important to note that pseudoexfoliation syndrome (or pseudoexfoliative glaucoma) may place the patient at higher risk for complications at the time of cataract surgery, due to weakened zonules, which hold the natural lens in place. Furthermore, the condition is often associated with poorly dilating pupils, making diagnosis prior to cataract surgery difficult or impossible.

Angle Recession Glaucoma

Angle recession glaucoma is a type of glaucoma that follows an often remote incident of rather severe blunt-trauma to the eye, usually with intraocular hemorrhage (hyphema). The angle recession itself represents severe damage to the aqueous fluid outflow pathway for the eye. It is believed that tears in the intraocular result in a scarred, non-functional outflow pathway, thereby leading to the pressure rise.

Medical treatment is often minimally effective though cycloplegic (dilating) as well as miotic (pupil-constricting) agents may both be effective. ALT (laser) is rarely effective and, therefore, if the glaucoma is relentlessly progresses despite medical management, a surgical filtration procedure will most likely be recommended.

Neovascular Glaucoma

Neovascular glaucoma is a form of glaucoma that most commonly is associated with proliferative diabetic retinopathy (PDR) and central retinal vein occlusion (CRVO). Other causative factors include carotid occlusive disease (carotid artery plaques resulting in significant lumen narrowing or occlusion), central retinal artery occlusion (CRAO), temporal arteritis, and many other conditions which result in ischemia (reduced blood flow) of the retina or ciliary body.

The mechanism of neovascular glaucoma is the development of neovascularization (new, abnormal vessels) in the angle of the eye causing obstruction to fluid egress via the trabecular meshwork (primary outflow pathway of the eye). When the retina is ischemic, it is theorized that an “angiogenesis factor“, acting as a local hormone, is released from the ischemic tissue and this results in the development of neovascularization. Neovascularization (new vessel growth) occurs primarily in the following locations: optic nerve, retina, iris, and angle of the eye. Ablation of the ischemic tissue via pan-retinal laser photocoagulation (PRP), therefore, is believed to minimize the angiogenesis factor production, and the neovascular tissue consequently regresses. Medical management, including the use of topical eye-drop medications and steroids, is usually used until the PRP takes effect (vessels regress). Laser ablation of the vessels in the angle of the eye is only occasionally effective and may be used as a temporary measure to help keep the angle open.

For those patients in whom laser photocoagulation (PRP) is not effective, glaucoma filtration surgery, implantation of a glaucoma drainage device (tube shunt), or cyclocryotherapy (freezing therapy of the ciliary body, which produces aqueous fluid) may all be effective. Laser cyclophotocoagulation, which entails use of a laser to destroy part of the ciliary body, may also be used.

The prevention of neovascular glaucoma is extraordinarily important since treatment is difficult and the prognosis is generally poor. Prophylaxis includes the use of PRP laser for patients with both proliferative diabetic retinopathy (PDR) and central retinal vein occlusion (CRVO) in which extensive ischemia (reduced blood flow) is present. Unfortunately, it is not always possible to determine which patients with these underlying conditions will develop neovascular glaucoma, even with the most meticulous care.

Congenital Glaucoma

Congenital glaucoma indicates glaucoma that is present at or near birth. Infantile glaucoma is present within the first 3 years of life and juvenile glaucoma occurs after 3 years of age. Males are affected more often (65%) than females and 70% of cases are bilateral (both eyes affected). If the eye pressure is elevated prior to 3 years of age the eye enlarges (buphthalmos) and rupture of a deep corneal membrane (Descemet’s) may occur with consequent tearing, light sensitivity, clouding of the cornea (front clear part of the eye), and squeezing shut of the eyes in bright light. The condition may be associated with many systemic anomalies including neurofibromatosis, congenital rubella, Lowe’s syndrome, Sturge-Weber syndrome, homocystinuria, Marfan’s syndrome, and Weill-Marchesani syndrome. Ocular anomalies that may be associated with congenital glaucoma include Axenfeld’s, Rieger’s, and Peter’s anomalies, aniridia (congenital absence of the iris), persistent hyperplastic primary vitreous (PHPV), nanophthalmos (small eye), and microcornea (small cornea).

If the condition is suspected by an ophthalmologist, an exam under general anesthesia, to accurately measure the eye pressure, examine the angle of the eye (primary anatomical site of fluid egress), and to evaluate the optic nerve, may be required to determine the presence or absence of glaucoma. If glaucoma is diagnosed, the most common initial procedure is goniotomy. If this procedure fails initially, it is often repeated, and if the pressure remains high, trabeculotomy and/or trabeculectomy (filtration procedure) may be utilized next. Usually, the implantation of a glaucoma drainage device (tube shunt) or cycloablation (a destructive procedure of the ciliary body, which produces aqueous fluid) is reserved for patients who have failed other surgical procedures.

Steroid Induced Glaucoma

Steroid induced glaucoma is defined as an increase in eye pressure of equal to or greater than 15 mmHg with topically (eye-drop) applied steroids. The condition may also occur with systemically administered steroids (e.g. prednisone). Approximately 5% of the general population is considered to be "steroid responders", i.e., may develop steroid induced glaucoma when steroids are administered. However, 95% of patients with primary open angle glaucoma (POAG) fall into the category of steroid responders. In most cases, development of increased eye pressure takes one to two weeks after initiation of steroids. However, in some cases, the increase in eye pressure may occur as soon as a few hours or as long as months to years following the administration of steroids.

Treatment of the condition requires discontinuance of corticosteroid, if possible. The eye pressure usually returns to normal in a few days or weeks. However, if necessary, patients may be treated medically, in the same fashion as an open-angle glaucoma patient (see primary open angle glaucoma above).

Glaucomatocyclitic Crisis (Posner-Schlossman Syndrome)

Glaucomatocyclitic Crisis is a condition characterized by recurrent attacks of acute eye pressure elevation, usually ranging between 40 to 60 mmHg, with minimal inflammation in the eye. Most cases are unilateral, but the condition may be bilateral. The cause of the condition is unknown but release of mediators of inflammation (prostaglandins) is implicated in this disorder. The primary mode of treatment is topical (eye-drop) corticosteroids, which control the inflammation, perhaps with other glaucoma agents as well. Some patients may develop chronic open angle glaucoma after repeated bouts of the condition.

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