Glaucoma refers to certain eye diseases that affect the optic nerve and cause vision loss. Most, but not all, of these diseases typically produce elevated pressure inside the eye, called intraocular pressure (IOP). Normal IOP is measured in millimeters of mercury and can range from 10-21 mm Hg. An elevated IOP is the most important risk factor for the development of glaucoma.
Elevated IOP is sometimes called ocular hypertension. If your doctor diagnosesocular hypertension, it does not mean you have glaucoma, but it does mean you are at a higher risk for developing the condition, and you should see anophthalmologist (a medical doctor who specializes in eye care and surgery) frequently. Half of the people with glaucoma are usually unaware of it until a serious loss of vision has occurred.
Many factors are associated with an increased risk of developing glaucoma, some of which are elevated IOP, a family history, ethnic background, and older age.
- The two main types of glaucoma are angle closure and open angle.
- In angle-closure glaucoma, the normal drainage canals within the eye are physically blocked. Angle-closure glaucoma can be acute (sudden) or chronic (long-lasting). In acute angle-closure glaucoma, a sudden increase in IOP occurs because of the buildup of fluid known as aqueous humor. Acute angle-closure glaucoma is considered an emergency because optic nerve damage and vision loss can occur within hours of the onset of the problem. Chronic angle-closure glaucoma may cause vision damage without symptoms.
- In open-angle glaucoma, the drainage system remains open. Open-angle glaucoma also may cause vision damage without symptoms.
- Normal (or low) tension glaucoma is an unusual and poorly understood form of the disease. In this type of glaucoma, the optic nerve is damaged even though the IOP is consistently within a range usually considered normal.
- Childhood glaucoma is rare and starts in infancy, childhood, or adolescence. It is similar to open-angle glaucoma, and few, if any, symptoms are present in the early stage. Blindness can result if it is left untreated. Like most types of glaucoma, this childhood form is thought to be inherited.
- Congenital glaucoma is a type of childhood glaucoma that usually appears soon after birth, although it may be delayed until later in the first year of life. Unlike childhood glaucoma, though, congenital glaucoma often has noticeable signs that may include tearing, light sensitivity, and cloudiness of the cornea. This type of glaucoma is more common in boys and can affect one or both eyes.
- Secondary glaucoma refers to an increased IOP that is a result of a structural problem within the eye. This secondary type may be the result of injury to the eye or other medical conditions. This form of glaucoma is different because treatment is aimed at treating the underlying cause as well as lowering the increased pressure within the eye.
Most people with glaucoma do not notice symptoms until they begin to have significant vision loss. As optic nerve fibers are damaged by glaucoma, small blind spots may begin to develop, usually in the peripheral or side vision. If the entire optic nerve is destroyed, blindness results.
Other symptoms usually are related to sudden increases in IOP, particularly with acute angle-closure glaucoma, and may include blurred vision, halos around lights, severe eye pain, headache, abdominal pain, nausea and vomiting.
Glaucoma risk factors?
Glaucoma is often called "the sneak thief of sight". This is because, as already mentioned, in most cases, the intraocular pressure can build up and destroy sight without causing obvious symptoms.
Thus, awareness and early detection of glaucoma are extremely important because this disease can be successfully treated when diagnosed early. While everyone is at risk for glaucoma, certain people are at a much higher risk and need to be checked more frequently by their eye doctor.
The major risk factors for glaucoma include the following:
- Age over 45 years.
- Family history of glaucoma.
- Black racial ancestry.
- History of elevated intraocular pressure.
- Nearsightedness (high degree of myopia), which is the inability to see distant objects clearly.
- History of injury to the eye.
- Use of cortisone (steroids), either in the eye or systemically (orally or injected).
- Farsightedness (hyperopia), which is seeing distant objects better than close ones (Farsighted people may have narrow drainage angles, which predispose them to acute [sudden] attacks of angle-closure glaucoma).
Glaucoma involves increased pressure within the eye. In the normal eye, a clear fluid called aqueous humor is produced in the rear chamber and flows through the pupil into the front chamber.
Once in the front part of the eye, the fluid drains out of the eye through an area called the canals of Schlemm. Aqueous humor provides structural support, oxygen, and nutrition to tissues within the eye.
- Increased IOP results from either increased production or decreased drainage of aqueous humor. The resulting increase in pressure within the eye may eventually damage the optic nerve. This increase in IOP is by far the most common risk factor for vision loss due to glaucoma, but it is not the only factor involved.
- For many years, it was believed that high IOP was the primary cause of optic nerve damage in glaucoma. Now we know that even people with normal IOP can experience vision loss from glaucoma. On the other hand, some people with high IOP never develop the optic nerve damage of glaucoma. Therefore, other factors may affect the optic nerve even when IOP is within the normal range.
- Elevated IOP is still considered a major risk factor for glaucoma, though, because studies have shown that the higher the IOP is, the more likely the optic nerve will be damaged.
- No one knows why certain ethnic groups, such as African Americans, have higher rates of glaucoma that lead to blindness. Primary open-angle glaucomais the leading cause of blindness among African Americans and Alaska Natives, occurring 6-8 times more often than in whites, often in the earlier stages of life.
Although nerve damage and visual loss from glaucoma cannot usually be reversed, glaucoma is a disease that can generally be controlled. That is, treatment can make the intraocular pressure normal and, therefore, prevent or retard further nerve damage and visual loss. Treatment may involve the use of eyedrops, pills (rarely), laser ,or surgery.
In the United States, eyedrops are usually used first in treating most types of open-angle glaucoma. In contrast, in Europe, laser or surgery is sometimes the first choice of treatment. One or more types of eyedrops may have to be taken up to several times a day to lower intraocular pressure.
These drops work either by reducing the production of the aqueous fluid (shutting the faucet) or by increasing the drainage of the fluid out of the eye. Each type of therapy has its benefits and potential complications.
Glaucoma medications (eyedrops)
Beta-adrenergic antagonists act against, or block, adrenalin-like substances. These drops work in the treatment of glaucoma by reducing the production of the aqueous humor. For years, they have been the gold standard (to which other agents are compared) for treating glaucoma. These medications include timolol (Timoptic), levobunolol (Betagan), carteolol (Ocupress), and metipranolol (Optipranolol).
Used once or twice daily, these drops are very effective. However, side effects, such as the worsening of asthma or emphysema,bradycardia (slow heart rate), low blood pressure, fatigue, and impotence prohibit their use in some patients. Betaxolol(Betoptic) is a beta-adrenergic antagonist that is more selective in working just on the eye and, therefore, carries less risk of heart (cardiac) or lung (pulmonary) side effects than other drops of this type.
Prostaglandin analogs are similar in chemical structure to the body's prostaglandins. Prostaglandins are hormone-like substances that are involved in a wide range of functions throughout the body. These drops work in glaucoma by increasing the outflow (drainage) of fluid from the eye.
The prostaglandin analogs have replaced timolol as the most commonly prescribed drops for glaucoma. They can be used just once a day. This class of medications has fewer systemic (involving the rest of the body) side effects than timolol, but can change the color of the iris as well as thicken and darken the eyelashes.
These drops are also more likely to cause redness of the eyes than some other classes of eyedrops. In some patients, they may also cause inflammation inside the eye. These medications includelatanoprost (Xalatan), travoprost (Travatan), and bimatoprost (Lumigan).
Adrenergic agonists are a type of drops that act like adrenalin. They work in glaucoma by both reducing the production of fluid by the eye and increasing its outflow (drainage). The most popular adrenergic agonist isbrimonidine (Alphagan). However, there is at least a 12% risk of significant local (eye) allergic reactions. Other members of this class of drops includeepinephrine, dipivefrin (Propine) and apraclonidine (Iopidine).
Carbonic anhydrase inhibitors work in glaucoma by reducing the production of fluid in the eye. Eyedrop forms of this type of medication include dorzolamide (Trusopt) and brinzolamide (Azopt). They are used two or three times daily. Carbonic anhydrase inhibitors may also be used as pills (systemically) to remove fluid from the body, including the eye. Oral forms of these medications used for glaucoma include acetazolamide (Diamox) andmethazolamide (Neptazane).
Their use in this condition, however, is limited due to their systemic (throughout the body) side effects, including reduction of body potassium, kidney stones, numbness or tingling sensations in the arms and legs, fatigue, and nausea.
Parasympathomimetic agents, which are also called miotics because they narrow (constrict) the pupils, act by opposing adrenalin-like substances. They work in glaucoma by increasing the aqueous outflow from the eye. These drops include pilocarpine (Salagen), demecarium(Humorsol), echothiophate (Phospholine Iodide), and isoflurophate(Floropryl).
The parasympathomimetics had been used for many years to treat glaucoma, but they are currently out of favor because they need to be used three to four times a day and produce side effects in the eye. These side effects include a small pupil, blurred vision, an aching brow, and an increased risk of retinal detachment.
Currently, pilocarpine is the only one of these medications being used for glaucoma. It is used primarily to keep the pupil small in patients with a particular iris configuration (plateau iris) or in patients with a narrow angle prior to laser iridotomy. (See the section above on angle-closure glaucoma).
Osmotic agents are an additional class of medications used to treat sudden (acute) forms of glaucoma where the eye pressure remains extremely high despite other treatments. These medications include isosorbide (Ismotic, given by mouth) and mannitol (Osmitrol, given through the veins).
These medications must be used cautiously as they have significant side effects, including nausea, fluid accumulation in the heart and/or lungs (congestive heart failure and/or pulmonary edema), bleeding in the brain, and kidney problems. Their use is prohibited in patients with uncontrolled diabetes, heart, kidney, or liver problems.
Ophthalmologists often prescribe an eyedrop containing more than one class of drug to patients who require more than one type of drug for control of their glaucoma. This simplifies the taking of drops by the patient. The most common example of this is the combination of timolol and dorzolamidein the same drop (Cosopt).
Several new classes of glaucoma drops are currently under development or awaiting FDA approval. Although marijuana use has been shown to reduce intraocular pressure, eyedrops are available which accomplish the same purpose with greater efficacy and less systemic risk.