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Glaucoma

Basic Information

Glaucoma is a condition in which optic nerves inside the eye are damaged, typically as a result of increased fluid pressure inside the eye. This fluid pressure is called "intraocular pressure" (IOP). Glaucoma can lead to visual field impairment and even blindness. While it used to be common understanding that elevated IOP is the condition itself, recent discoveries show that elevated IOP is simply the largest risk factor for developing the optic nerve damage associated with glaucoma. IOP occurs when the clear liquid in the eye, which is usually secreted into the eye then washed out, does not drain properly. The increasing pressure compacts the optic nerves, and pushes them up against the retina toward the back of the eye. This cuts off blood circulation to the retinal nerves, which can result in both the damage and eventual destruction of the optic nerves. As the optic nerve complex degenerates, the person will experience blind spots and other vision alterations. These changes are typically found to effect the peripheral vision first. Once vision damage occurs, it is permanent. Other factors that can lead to glaucoma when people have normal IOP levels are insufficient blood supply to the eye, autonomic insufficiency, low blood pressure, abnormally low intracranial pressure, autoimmune phenomena, and primary ganglion cell degeneration.

There are several types of glaucoma. The most common form is "open-angle glaucoma". While people with open-angle glaucoma have eyes that function normally, there is typically a problem with the drain of the eye (the trabecular meshwork). As a result of some obstruction at the site of the trabecular meshwork, the ocular fluid cannot filter out of the eye and properly drain, leading to an increase in intraocular pressure. Open-angle glaucoma damages both eyes simultaneously. It is thought that a decreased cell count in the trabecular meshwork due to aging retards the ocular drain from performing its function. Open-angle glaucoma is a chronic disease (progressing slowly or persistently )that currently does not have a cure. In cases of open-angle glaucoma, the build-up of IOP can be extremely slow, so that it may take months for the eye damage to occur and become noticeable.

Another form of glaucoma is "angle-closure glaucoma". This condition can be chronic or acute (appearing suddenly). The source of the problem in cases of angle-closure glaucoma is the eye itself. In this case, the drainage systems are obstructed not at the site of the trabecular meshwork, but between the iris and the cornea. As a person gets older the lens of the eye enlarges. This can cause the angle between the iris and cornea to "close", leading to improper drainage and increased IOP. The onset of acute angle-closure glaucoma is rapid. The sudden increase of IOP can be severe, and optic nerve damage resulting in vision loss can happen in a matter of hours. The acute condition is linked to pupillary dilation and it is thought that the use of drops to dilate the eyes may trigger the sudden onset. Anti-depressants, cold medications, and antihistamines can all cause dilation. Many of these attacks occur in the dark where pupils must dilate to adjust for the decreased light. Conversely, chronic angle-closure glaucoma behaves more like open-angle glaucoma. While like acute angle-closure glaucoma it develops at the obstructed drainage juncture between the iris and the cornea, its development is slow and gradual. As scar tissue from the iris forms slowly over the drain, eventually covering it, the IOP rises and begins to damage the optic nerve system.

Secondary glaucoma can be attributed to an earlier complication, such as a previous injury or disease. In particular, eyes diseases such as "uveitis" and the use of drugs, in particular "corticosteroids", can develop over time into glaucoma.

Childhood glaucoma begins in the early years of a child's development. It is a rare condition. There often are no symptoms in the early stages of this kind of glaucoma, and if left untreated, it can lead to permanent blindness.

Congenital glaucoma is present at birth, or soon after. Unlike childhood glaucoma, there are visible signs when a person has this condition. It is the result of a defective development of the eye and often necessitates surgery. Both childhood and congenital glaucoma are considered hereditary.

The various forms of glaucoma affect different parts of the demographic population. Open-angle glaucoma is the most common form affecting Caucasians and Africans. In fact, it is a leading cause of blindness among African-Americans. Not only are African-Americans 6-8 times more likely to develop open-angle glaucoma than Caucasians, but they also experience a higher incidence of it occurring early on in life. The American Academy of Ophthalmology recommends that African-Americans have regular eye examinations (under 40 years of age, every 3-5 years; over 40, every two years). At the same time, although angle-closure glaucoma is unusual, it seems to be more prevalent among people of Asian and Eskimo ancestry. Congenital glaucoma is twice as likely to affect boys as it is girls. It is estimated that 2% of all people over the age of 40 have chronic glaucoma. Angle-closure glaucoma affects about a half million people in the United States.

Risk factors for the possible development of glaucoma include elevated intraocular pressure, family history, ethnic background, old age (over the age of 40), and previous optic nerve damage.

Symptoms

In most cases of glaucoma, there are either no symptoms or the people do not observe any symptoms until their vision begins to deteriorate. As aforementioned, the optic nerve damage caused by glaucoma initially affects the peripheral vision, which can be difficult to detect. Chronic glaucoma, whether open-angle or angle-closure, typically does not have any early warning signs. Because the deterioration is so gradual, the fact that there are no symptoms can be a problem because by the time a person notices the vision loss the nerve damage may already be permanent. When there are symptoms present, they include:

  • frequent need to change eyeglasses
  • inability to adjust eyes to dark rooms
  • gradual loss of peripheral vision
  • blurred or foggy vision
  • mild, chronic headaches
  • seeing rainbow-colored halos around lights

While the chronic form of glaucoma typically does not have any symptoms, the acute variety does. The problem here is that the onset of acute angle-closure glaucoma can be so rapid that the symptoms often only add irritation rather than give the inflicted person a warning so that the person can prevent complications. The rapid increase of pressure in the eye as a result of acute angle-closure glaucoma can cause any of the following:

  • severe eye and facial pain
  • blurred vision; loss of vision
  • cloudy vision with halos appearing around lights
  • red eye
  • headache; nausea and vomiting
  • dilated pupil

Acute angle-closure glaucoma is an unusual, but severely debilitating, condition and requires immediate medical attention.

Congenital glaucoma can have the following symptoms:

  • tearing
  • over sensitivity to light
  • redness of the eye
  • corneal haziness
  • an enlarged cornea

Diagnosis/Treatment

Because many forms of glaucoma are asymptomatic, it is very important to have regular eye examinations in order to detect and prevent optic nerve damage. In some cases when a person has acute glaucoma, a series of diagnostic tests is unnecessary. In such an instance, a doctor can immediately detect the presence of glaucoma if the pupil is non-reactive (it doesn't adjust to differing frequencies of light) or if the eye feels hard to the touch. In most cases, however, a routine diagnostic examination includes:

  • History evaluation: the doctor will ask you questions about both your personal and your family's medical history.
  • Tonometry: using tonometry, the doctor can measure intraocular pressure. In most cases the eye is anesthetized and a pressure-sensitive plastic prism used to gauge IOP is gently placed on the cornea.
  • Perimetry: this tests the visual field. The visual field is the area outside the eye that can be viewed when the eye looks straight ahead. This is the most accurate test when it comes to measuring optic nerve damage. In this test, a person sits in front of a computer screen and is asked to push a button whenever they see a light flash on the screen. By observing how often a person fails to respond to a lightflash, a doctor can measure the extent of the ocular damage.
  • Ophthalmoscopy: use of drops to dilate the pupil so that the doctor can examine the optic nerve. The color and appearance of the nerve can indicate the condition of the nerve.
  • Gonioscopy: situating a mirrored lens on the cornea in order to view the drainage angle directly. With this test, narrow angles or even angle-closure can be observed.

The American Academy of Ophthalmology suggests that you have an examination every 3-5 years if you are over the age of 39, and every 1-2 years if you are over the age of 50; have a family history of glaucoma; are of African ancestry; have had a serious eye injury in the past; are taking steroid medication.

While glaucoma typically cannot be prevented, if it is detected early enough, its development can be slowed. As damaged optic nerves cannot be repaired, the loss of vision is permanent. That is why treatment focuses on preventing continued vision impairment rather than regaining lost vision. A major part of treatment consists of reducing and regulating intraocular pressure so that any blockages in the drainage system of the eye or of the trabecular mesh can be removed. Controlling IOP is done with medications or surgery, depending on what form of glaucoma the person has.

In most cases of chronic angle-closure glaucoma and open-angle glaucoma, medications can effectively reduce intraocular pressure. These medications can be administered orally, intravenously, or topically as eyedrops. Beta-adrenergic blocking agents in drop-form can slow down the rate at which ocular fluid flows into the eye. Beta-blockers include Timolol, Betagen, and OptiPranolol. Epinephrine drops are effective at decreasing IOP by increasing the rate of fluid flowing out of the eye, and pilocarpine drops are sometimes used to open the ocular drain as well. The problem with these medications, particularly when used as eyedrops, is that they often have irritating side-effects on the eyes or the body-system itself. This can be even more frustrating to a person with a form of glaucoma that does not have any abrasive symptoms. These people cannot understand why they should take an aggravating medication to cure a unnoticeable health condition. These patients must be made to understand the utter importance of taking the medication in order to prevent further visual deterioration. In most cases where there are side-effects, the effects are irritating but not intolerable. There are instances, however, when the side-effects are so intolerable that laser or operative surgery are required in order to control the intraocular pressure.

Similarly, doctors will usually try to treat cases of acute angle-closure glaucoma with eyedrop medications. In some emergency situations, an iridotomy may be necessary. An iridotomy is a type of surgery that creates a drainage hole in the iris so that the pressure can be lessened. It can be performed using laser surgery without making an incision in the eye. An iridotomy is also the type of surgery someone with chronic angle-closure glaucoma would have if they could not tolerate IOP-regulating medications.

For people who have open-angle glaucoma and cannot tolerate the side-effects of IOP-regulating medications, there is a form of surgery called Argon Laser Trabeculoplasty. It takes up to twenty minutes, is painless, and is performed on an outpatient basis. In this surgery, a beam of concentrated heat is focused on the trabecular meshwork. The exposure to heat makes certain parts of the trabecular meshwork shrink, so that other areas will stretch open and allow fluids to pass.

Besides laser surgery, operative surgery is also possible. In the procedure called a trabeculectomy, the surgeon removes a small segment of the trabecular meshwork. This allows the ocular fluid to drain, and as this happens the pressure in the eye decreases. While the procedure itself is safe, about a third of all patients who undergo a trabeculectomy incur cataracts within five years of the operation. Patients who have this kind of surgery usually do not need to use medications anymore.

If left untreated, acute glaucoma can cause permanent vision loss. Conversely, quick treatment can prevent further vision loss. At the same time, untreated chronic glaucoma can result in blindness within 20-25 years. Early treatment is a major part of preventing further vision loss, and can have very successful results.