What Is Glaucoma?
Glaucoma, often called ?the silent thief of sight,? is a disorder in which nerve fibers in the eye are damaged. This damage to the eye can lead to permanent vision loss. Nearly 1 million Americans are receiving treatment for glaucoma. Another 1 million Americans have glaucoma but do not yet realize it. It is extremely important to discover and treat glaucoma early because of the risk of blindness if untreated. In the United States, glaucoma is the second-leading cause of permanent blindness among Caucasians and the leading cause of blindness among African Americans.
What Causes Glaucoma?
The most common cause of glaucoma is increased pressure within the eye. This increased pressure is caused by clogged channels that prevent the normal fluid within the eye from draining out. Over many years, the increased pressure within the eye compresses nerves at the back of the eye. The compression on the nerve slowly destroys it. First, the outer fibers of the nerve are destroyed, causing loss of peripheral vision. If nerve destruction continues, tunnel vision develops, followed by blindness. As the disease advances, damage to the eye and loss of vision occur at a faster rate.
What Are the Symptoms of Glaucoma?
Unfortunately, glaucoma has no symptoms. The first sign of glaucoma typically is the loss of peripheral vision. By the time the loss of peripheral vision is noticed, permanent nerve damage and vision loss have occurred.
Who Is at Risk for Developing Glaucoma?
Glaucoma can occur at any age, but the prevalence increases with age. It is more common in African Americans, who also suffer from more severe cases of glaucoma. Glaucoma also tends to run in families. Certain medical conditions also increase the risk of glaucoma, including diabetes mellitus, extreme near-sightedness, migraine headaches, high blood pressure, long-term steroid use, and previous eye injury.
When to See the Doctor
Regular eye examinations are the best means for early diagnosis and preservation of sight. Damage to the optic nerve is often visible on examination before loss of vision is noticeable. The American Academy of Ophthalmology makes the following recommendations:
During an eye examination, the optometrist will look for the presence of optic nerve damage and loss of peripheral vision. He or she can also measure the pressure within the eye using a simple and painless test that blows a quick burst of air into the eye. Pressure greater than 21 mm Hg represents a risk for developing glaucoma, but not everyone with a pressure greater than 21 mm Hg will develop glaucoma.
How Is Glaucoma Treated?
Currently, there is no cure for glaucoma. Treatment is aimed at preventing further vision loss by reducing pressure within the eye, and can involve medications or surgery. Most medications currently available are instilled into the eye.
Beta blockers, including timolol, betaxolol, levo-bunolol, carteolol, and metipranolol, are the most commonly prescribed medications to treat glaucoma. These medications lower the pressure inside the eye by preventing production of fluid within the eye. A small amount of the medication is absorbed into the bloodstream, which can cause adverse effects in other parts of the body, including slower heart rate, lower blood pressure, vomiting, and difficulty breathing. Beta blockers should be used cautiously in individuals with asthma, emphysema, or heart disease. Diabetics should understand that beta blockers often hide the symptoms of hypoglycemia.
Before the introduction of beta blockers, miotics or cholinergic agonists were widely prescribed for glaucoma. The most common miotic agent is pilocarpine, which decreases pressure within the eye by increasing the outflow of fluid. The major disadvantage of pilo-carpine therapy is the need to administer it into the eye several times a day. Newer formulations, such as gels and wafers, allow for less frequent administration. The use of pilocarpine can cause decreased vision, particularly in poorly lighted areas or while driving at night. Other side effects associated with pilocarpine include teary eyes, eye pain, and allergic reactions. Demecarium, isoflurophate, and echothiophate are long-acting miotics, but their use is limited due to a greater potential for serious side effects, including retinal detachment and cataracts.
Epinephrine and similar medications are called sym-pathomimetics or adrenergic agonists. These agents lower pressure within the eye by increasing the flow of fluid from the eye and decreasing the rate of fluid production. Epinephrine is rarely prescribed for glaucoma anymore because of a high incidence of side effects, including burning in the eyes, allergic reactions, anxiety, headaches, palpitations, increased blood pressure, and abnormal heart rhythms. Dipivefrin, another sympath-omimetic, is converted to epinephrine within the eye. Although dipivefrin does not cause increased blood pressure and abnormal heart rhythms as often as epinephrine, it does cause burning in the eye. Epinephrine and dipivefrin should not be used in persons with high blood pressure or heart disease. Apraclonidine and brimonidine cause fewer side effects than epinephrine and dipivefrin. The side effects most commonly associated with these two agents are dry mouth, changes in taste, and red eyes.
Carbonic Anhydrase Inhibitors
Carbonic anhydrase inhibitors, including dorzol-amide and brinzolamide, reduce the production of fluid in the eye. They are usually prescribed when other medications are not effective. Common side effects include fatigue, decreased appetite, burning in the eyes, and tingling in the fingers and toes. Although carbonic anhy-drase inhibitor tablets are available, their use is limited by their side effects.
Prostaglandins, including latanoprost, represent the newest class of glaucoma treatments. They decrease pressure in the eye by increasing the outflow of fluid. The advantages to latanoprost are its once-daily administration and limited side effects. Common side effects are itching, burning, and redness in the eye, and muscle pain. It also causes a permanent darkening of eye color to brown in individuals with blue or green eyes, as well as thickening and lengthening of eyelashes.
Laser surgery is becoming a popular treatment for glaucoma. The more common type of laser surgery takes only a few minutes to perform and allows the patient to remain awake. During the procedure, the doctor makes multiple laser cuts that allow the fluid to drain out of the eye. This surgery usually is not effective in individuals younger than 40 years of age.
Glaucoma remains a serious disease with no cure. Regular eye examinations are the best way to prevent vision loss. Although there is no cure, medications are available to prevent progression of the disease.