Glaucoma is a condition in which the optic nerve is subject to damage--usually, but not always, because of excessive pressure within the eye. If untreated, optic nerve damage results in progressive, permanent vision loss, starting with unnoticeable blind spots at the edge of the field of vision, progressing to tunnel vision, then to blindness.
More than two million people in the United States have glaucoma, 80,000 of whom are legally blind as a result. It is the leading cause of preventable blindness in the United States and the most frequent cause of blindness in African-Americans, who are at about a three-fold higher risk of glaucoma than the rest of the population. The risk of glaucoma increases dramatically with age,but it can strike any age group, even newborn infants and fetuses.
Glaucoma is actually a class of diseases--there are at least twenty differentforms. It is a secondary condition of over 60 widely diverse diseases. It can also result from injury. Most glaucoma is probably inherited. At least tendefective genes causing glaucoma have been identified.
Glaucoma occurs when the aqueous humor (a watery fluid bathing the iris, cornea and lens of the eye) is not removed rapidly enough or when the body produces it too rapidly, causing pressure to build up. The pressure distorts the shape of the optic nerve and destroys it. This causes blind spots in places where the image from the eye is not being transmitted to the brain.
Open-angle glaucoma accounts for over 90% of all cases. It is called "open-angle" because the corner where the aqueous fluid drains is open, allowing drainage. Pressure usually builds slowly. At first, chronic open-angle glaucoma has no noticeable symptoms. The vision loss is too gradual to be noticed and each eye fills in the image where its partner has a blind spot. If not treated, however, vision loss becomes evident, and the condition can be very painful.
In narrow-angle glaucoma, the corner is narrow and may therefore drain slowlyor may be at risk of closing.
A closed-angle glaucoma attack usually occurs suddenly, when the drainage area is blocked. Such an attack is obvious from the beginning. The symptoms areblurred vision, severe pain, sensitivity to light, nausea , and halosaround lights. Normally clear corneas may be hazy. This is an emergency and needs to be treated immediately.
Similarly, congenital glaucoma is evident at birth. Symptoms are bulging eyes, cloudy corneas, excessive tearing, and sensitivity to light.
To diagnose glaucoma, pressure within the eye is measured with an instrumentknown as a tonometer. One type of tonometer involves numbing the eye with aneyedrop and touching it with a small probe. This quick test is a routine partof an eye examination.
Ophthalmoscopes, hand-held instruments with a light source, are used to detect optic nerve damage by looking through the pupil. Visual field tests (perimetry) can detect blind spots before the patient is aware of them.
Pressure within the eye can vary throughout the day, so several visits may beneeded to measure pressure at different times.
When glaucoma is diagnosed, drugs, typically given as eye drops, are usuallytried before surgery. Beta blockers (such as Timoptic), carbonic anhydrase inhibitors (acetazolamide), and alpha-2 agonists (Alphagan) inhibit theproduction of aqueous humor. Miotics (pilocarpine) and prostaglandin analogues (Xalatan) increase the outflow of aqueous humor.
It is important for patients to tell their doctors about any conditions theyhave or medications they are taking. Certain drugs used to treat glaucoma would not be prescribed for patients with pre-existing conditions. All of the drugs mentioned above have side effects, some of which are rare but serious andpotentially life-threatening, so patients should be monitored closely, especially for cardiovascular, pulmonary, and behavioral symptoms.
Attacks of acute closed-angle glaucoma are medical emergencies. Pressure canbe rapidly lowered by acetazolamide, hyperosmotic agents, a topical beta-blocker, and pilocarpine.
Laser surgery or microsurgery to open the drainage canals or make an openingin the iris can also increase the outflow of aqueous humor. These surgeries are usually successful, but the effects often last less than a year. Nevertheless, they are an effective treatment for patients whose pressure is not sufficiently lowered by drugs and for those who can't tolerate the drugs.
Sight lost due to glaucoma cannot be restored.
Vitamin C, vitamin B1 (thiamine), chromium, zinc, and rutin may reduce pressure within the eye. There is evidence that marijuana lowers pressure, but it has serious side effects and contains substances linked to cancer. Although the U.S. Food and Drug Administration and NationalInstitutes of Health currently recommend against treating glaucoma with marijuana, they are supporting research to learn more about it.
Any glaucoma patient using alternative methods to prevent optic nerve damageshould also be under the care of a traditionally trained ophthalmologist or optometrist licensed to treat glaucoma.
About half of the people stricken by glaucoma are not aware of it. Many willbecome blind. On the other hand, the prospects for patients whose glaucoma istreated are excellent.
The best form of prevention is to have regular eye exams . Any personwho is glaucoma-susceptible should read warning labels on over-the-counter medicines and inform their physician of products they are considering taking. Steroids may also raise pressure within the eye, so patients taking them may need to be monitored more frequently.
As more is learned about the genes that cause glaucoma, it will become possible to test DNA and identify potential glaucoma victims, so they can be treated before their pressure becomes elevated.