Glaucoma - March 2, 2010 Newsletter

Glaucoma

EHE Newsletter, Volume 10, Number 9
March 2, 2010

Glaucoma

According to the National Eye Institute (NEI), glaucoma affects approximately four million Americans, nearly half of whom are unaware that they have the disease. Between 9 and 12 percent of all cases of blindness in the U.S. (affecting approximately 120 thousand Americans) are caused by glaucoma. Glaucoma has no warning signs and can cause permanent vision loss if left untreated. The key to preserving vision is the timely diagnosis and treatment of glaucoma through regular and complete eye examinations.

As the population of older adults in the U.S. continues to grow, the number of people experiencing vision loss will also increase. Additionally, as the number of Americans with diabetes continues to increase, the number of cases of major eye diseases (including glaucoma) is expected to increase. There are currently more than 23 million Americans who have diabetes. The Centers for Disease Control and Prevention (CDC) project that that number will more than double to 48 million by the year 2050. Adults with diabetes are nearly twice as likely to develop glaucoma as other adults, and the longer that a person has diabetes, the more likely he or she is to develop glaucoma.

What is Glaucoma?

Glaucoma refers to a group of eye diseases that have one feature in common: progressive damage to the optic nerve caused by increased pressure within the eyeball. The optic nerve is a bundle of more than one million nerve fibers that connect the retina to the brain. The pressure comes from a clear fluid called the "aqueous humor" which helps to maintain normal eye pressure and provides nutrients to the cornea and lens. This fluid is produced constantly. It circulates in front of the eye and drains through a spongy tissue called the "trabecular meshwork." There is normally a balance between the amount of fluid produced and the amount that leaves the eye. In individuals with glaucoma, however, the fluid does not drain properly and pressure builds up within the eye, damaging the optic nerve. As this deterioration of the optic nerve continues, vision worsens and, eventually, total blindness can result.

According to the CDC, the two major types of glaucoma are open–angle glaucoma and closed–angle glaucoma.

Open–angle glaucoma is the most common form of glaucoma in the U.S. It is a chronic condition in which the pressure within the eye slowly rises and the cornea adapts without swelling. With this type of glaucoma, the structures in the eye appear to be normal but fluid does not drain properly because of tissue changes in and along the drainage passage. It is painless and progresses slowly over a long period of time without noticeable vision loss until the disease is very advanced. This type of glaucoma has no early warning signs and can go undetected for years.

Closed–angle glaucoma occurs when the normal drainage passage in the eye is narrowed and eventually becomes blocked. It is much less common than open–angle glaucoma and can be either chronic or acute. "Chronic" closed–angle glaucoma progresses slowly and can result in optic nerve damage without symptoms showing until vision is lost. Individuals with "acute" closed–angle glaucoma experience a sudden increase in eye pressure that is painful. Symptoms can include severe eye pain, headaches, nausea, redness of the eye, blurred vision and the sight of "halos" around lights at night. If these symptoms occur, treatment must immediately be sought from an eye care professional or hospital emergency room. Vision loss can progress quickly. Without treatment, blindness can result in one or two days.

Risk Factors

Anyone can develop glaucoma — it affects individuals of all ages and races. Certain factors, however, can increase an individual’s risk for developing glaucoma. These risk factors include:

  • Elevated internal eye pressure (intraocular pressure): If an individual’s intraocular pressure is higher than normal, he or she is at an increased risk of developing glaucoma. Not everyone with elevated intraocular pressure, however, will develop the disease.
  • Age: Individuals over age 60 are at increased risk. For African–Americans, the risk increase begins after age 40.
  • Race: African–Americans are six–to–eight times more likely to develop glaucoma than Caucasians, and are much more likely to experience permanent blindness as a result. In fact, African–Americans between the ages of 45 and 64 are 15 times more likely to go blind from glaucoma than Caucasians from the same age group. Mexican–Americans and Asian–Americans also face increased risks.
  • Family history of glaucoma: Having a family history of glaucoma increases the risk of developing glaucoma. A form of juvenile open–angle glaucoma has been clearly linked to genetic abnormalities.
  • Medical conditions: Some studies indicate that diabetes may increase the risk of developing glaucoma, as does high blood pressure and heart disease.
  • Other eye conditions: Severe trauma, such as being hit in the eye, can result in immediate increased eye pressure and future increases in pressure due to internal damage. Injury can also dislocate the lens, closing the drainage angle and increasing pressure within the eye. Certain types of eye surgery may also trigger secondary glaucoma.
  • Nearsightedness: Being nearsighted increases the risk of developing glaucoma.
  • Prolonged corticosteroid use: Using corticosteroids for prolonged periods of time appears to put some individuals at risk of developing glaucoma. This is especially true with corticosteroid eye drops.

According to the CDC, despite the magnitude of the population at risk for vision loss as well as the grave consequences of vision loss and blindness, many individuals do not take advantage of available early detection services, timely treatments and interventions to promote eye health. Only one–half of the estimated 61 million adults in the U.S. who are classified as "high risk" for serious vision loss have visited an eye doctor in the past 12 months.

Detecting Glaucoma

Early detection through regular and complete eye exams is the key to protecting one’s vision from damage or vision loss caused by glaucoma. The U.S. Preventive Services Task Force found insufficient evidence to recommend for or against screening adults for glaucoma. The American Academy of Ophthalmology (AAO), however, recommends that adults with no signs or risk factors for eye disease undergo baseline eye disease screenings beginning at age 40 — the time when early signs of diseases and changes in vision may start to occur. The AAO strongly supports glaucoma screening with the following specific recommendations:

  • Everyone over age 65, and African–Americans over 40 years old, should have periodic eye exams every other year that include tests for glaucoma
  • African–Americans ages 20 to 39 should have eye examinations every 3 to 5 years
  • Other people at higher risk (people with diabetes, a history of eye injuries or a family history of glaucoma, as well as those taking corticosteroid medications) should have eye examinations every year after age 35
  • People with known glaucoma should have frequent examinations to check peripheral vision and eye pressure. After such examinations, the ophthalmologist will assess current treatment and make necessary adjustments

Regular glaucoma check–ups include two routine eye tests:

  • Tonometry: This test is used to determine the intraocular pressure (IOP) of the aqueous humor inside the eye. Typically, drops are used to numb the eye and a special device is used to measure the pressure within the eye.
  • Ophthalmoscopy: This test is used to examine the inside of the eye, especially the optic nerve. To check for damage in the optic nerve, the doctor first uses eye drops to dilate the pupils and then, in a darkened room, magnifies the eye using an ophthalmoscope (an instrument with a small light on the end). This helps the doctor look at the shape and color of the optic nerve.

If the pressure in the eye is not within the normal range, or if the optic nerve looks unusual, one or two special glaucoma tests will be performed:

  • Perimetry: This is also called a "visual field test." In most people with glaucoma, the first areas to become noticeably impaired are the peripheral visual fields. Perimetry tests are used to check peripheral vision. During this test, the individual is asked to look straight ahead and then indicate when a moving light passes his or her peripheral vision.
  • Gonioscopy: This is a painless eye test that checks if the angle where the iris meets the cornea is open or closed, thereby showing if either open–angle or closed–angle glaucoma is present.

Intraocular eye pressure is important in determining the risk of glaucoma. Recent studies show that corneal thickness is an important factor in accurately diagnosing eye pressure. A pachymetry test is a simple, quick and painless test that is used to measure the thickness of the cornea. With this measurement, an eye care professional can better understand an individual’s intraocular eye pressure reading and develop a treatment plan that is right for his or her condition.

Glaucoma cannot be cured, but it can be controlled. The key to preserving vision is the timely diagnosis and treatment of glaucoma through regular and complete eye examinations.

MEDICAL DISCLAIMER: The information is not intended to constitute medical advice and is not a substitute for consultation with a physician or other health care provider. Individuals with specific complaints should seek immediate consultation from their personal physicians.