Glaucoma is a term applied to a group of eye diseases that cause a characteristic deterioration of the optic nerve. The optic nerve carries visual information from the eye to the brain, much like the cable from a computer screen to the computer. In the brain, it is assembled into a visual image that we recognize as sight.

The eye is largely hollow and is inflated with fluid. The inflation pressure is most commonly in the range of 10 to 22mm Hg. Glaucoma is most often associated with higher than normal pressure in the eye, but can be seen in patients with pressure in the normal range. The damage to the optic nerve usually occurs gradually and unnoticeably. The peripheral vision is lost first, but with progression loss of central vision and blindness can occur. The disorder we refer to as glaucoma, is not a single disease, but rather a myriad of diseases with one final common result, 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.
  
 
Who Gets Glaucoma?
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 are elevated intraocular pressure and family history of glaucoma. The older you get the more likely you are to develop glaucoma. Other risk factors include:

  • Diabetes
  • Myopia (nearsightedness)
  • High blood pressure
  • Cardiovascular disease
  • Migraine headaches
  • Topical or systemic steroid use
  • African-American or Asian-American descent
Possible symptoms of glaucoma include:
  • Recurrent blurry vision
  • Haloes around lights at night
  • Decreased peripheral (side) vision
  • Pain around your eyes after watching TV

  
 

What Causes Glaucoma?

Clear liquid, called the aqueous humor, flows in and out of the eye. This liquid is not part of the tears on the outer surface of the eye. The flow of aqueous fluid would be similar to having a sink with the faucet turned on all the time. If the "drainpipe" gets clogged, water collects and pressure builds up. If the drainage area of the eye is blocked, the fluid pressure within the inner eye may increase, which can damage the optic nerve. The aqueous fluid is produced by the ciliary body and passes through the pupil and out of the eye through the trabecular meshwork. Most commonly elevated intraocular pressure is caused by clogging of the trabecular meshwork.

However, we have learned that glaucoma is not just related to the eye pressure. The exact cause is not known for certain. There are multiple theories regarding the cause of glaucoma. Suffice to say, besides eye pressure, perfusion (blood flow) of the optic nerve, mechanical factors in and around the optic nerve itself, and biochemical factors probably play a role. Glaucoma is much more complex than most patients would like to believe.
 
 

How is Glaucoma Diagnosed?

Glaucoma is diagnosed when progressive damage to the optic nerve is observed. Therefore, glaucoma usually cannot be diagnosed on an initial exam, and certainly cannot be determined by measuring eye pressure alone, regardless of the pressure. Patients with increased eye pressures only, are said to have ocular hypertension or possibly are referred to as "glaucoma suspects." The diagnosis of glaucoma usually requires signs of optic nerve injury. This is detected by observation of the appearance of the optic nerve and testing of the peripheral vision.

In the normal state, the optic nerve head looks much like a doughnut, with the outer ring consisting of the nerve tissue. The hole (called the optic cup) is the space which remains after the nerve fibers turn to fan out into the retina. In glaucoma, the nerve fibers are damaged and erode away, leaving a larger cup (or hole of the doughnut). Especially when the degree of enlargement is different between the two eyes, the physician can diagnose early glaucoma from this appearance alone.

  
 




Visual Field Testing
The peripheral vision is tested using a computerized device. Lights are flashed on and off and you indicate when you see them. Subtle abnormalities can be detected.

What Are The Most Common Types of Glaucoma?
There are two major types of glaucoma, open angle and closed angle.

Primary Open-Angle Glaucoma
Primary Open Angle Glaucoma (POAG) is the most common type of glaucoma.

Over 90% of adult glaucoma patients have this type. It occurs when the drainage angle of the eye becomes less efficient or "clogged" and pressure within the eye gradually increases. In open-angle glaucoma, the angle where the iris meets the cornea is as wide and open as it should be but it malfunctions.

It is characterized by elevated intraocular pressure (IOP), cupping and atrophy of the optic nerve head, and typical visual field defects. There are no obvious ocular abnormalities. Both eyes tend to be involved at the same time and to a similar degree. The prevalence of POAG in the Western world has been estimated to be about 0.5% and the incidence increases with age. Most cases are first detected after age 40.

 

  





Angle Closure Glaucoma
Angle closure glaucoma may be subdivided into two basic types: 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 space between the iris and the cornea (narrow angle) Fluid drainage via the trabecular meshwork is impaired.

The treatment for this condition is creation of a small hole in the peripheral iris that allows aqueous fluid, made in the ciliary body , to flow directly through the hole in the iris to the trabecular meshwork.

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).

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. The reason for the optic nerve damage is not clear, but it may be related to poor blood flow to the optic nerve, mechanical factors in and around the nerve, and/or biochemical factors.
  
 

Pigmentary Glaucoma (Pigament 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 anterior chamber. The zonules holding the natural lens rub against the back of the iris, releasing some the iris pigment into the aqueous. The pigment can be seen sticking to the back of the cornea, and clogs the drainage apparatus (trabecular meshwork).

Pseudoexfoliative Glaucoma

Pseudoexfoliative glaucoma is thought to be caused by the deposition of "pseudoexfoliative material" into the drainage apparatus (trabecular meshwork), eventually clogging its microscopic canals. The origin of this pseudoexfoliative material is thought to be the capsule surrounding the natural lens of the eye. In a small percentage of otherwise normal eyes the outside of the capsule peels and sheds this material into the aqueous. Pseudoexfoliation syndrome is diagnosed by the ophthalmologist primarily by the identification of the abnormal material on the border of the pupil 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.

How is Glaucoma Treated?

In almost all cases damage to the ocular nerve can be stopped or prevented by lowering the eye pressure. This is usually achieved with eye drops. These medications decrease eye pressure by either slowing the production of aqueous fluid within the eye or by improving its flow out of the eye. The drops must be taken one to four times daily. The effect of the medicine is short-lived, so you must use them on a regular schedule every day.

Laser surgery may be effective for different types of glaucoma. The laser is usually used in one of two ways:

  1. In open-angle glaucoma, the drain itself is treated. The laser is used to open the drain (trabeculoplasty) to help fluid flow out of the eye.
  2. In angle-closure glaucoma, the laser creates a hole in the iris (iridotomy) to enable aqueous fluid to reach the drain.

Operative surgery may sometimes be needed to control glaucoma. This surgery is performed using miniature instruments to create a new drainage channel for the aqueous fluid to leave the eye. The new channel helps to lower the pressure. There are a variety of techniques, the most common being trabeculoplasty.

For More Information:
www.glaucomaassociates.com

  
 
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Copyright © 2009 Robert C. Arffa, M.D., 1370 Washington Pike, Bridgeville, PA 15017