What is glaucoma?

Glaucoma has been described as the "sneak thief" of sight because of its slow, insidious and often painless nature. Glaucoma is a disease caused by increased intraocular pressure (IOP) resulting either from a malformation or malfunction of the eye's drainage structures. The human eye has pressure just like your blood, and when this intraocular pressure increases to dangerous levels, it damages the optic nerve. If left untreated, an elevated IOP causes irreversible damage to the optic nerve and retinal fibers responsible for peripheral vision. This optic nerve damage can then result in a progressive, permanent loss of this peripheral vision. However, early detection and treatment can slow, or even halt the progression of the disease.

Glaucoma affects an estimated 2.9 million Americans, with 115,000 blind due to the condition. Outside of the United States, glaucoma ranks as one of the leading causes of blindness. Even if people with glaucoma do not become blind, vision can be severely impaired.

Early detection, through regular and thorough eye exams, is the key to protecting your vision from damage caused by glaucoma. It is important to have your eyes examined regularly. Your eyes should be tested prior to age 40 every one to two years and after the age of forty every year. Anyone with high risk factors, should be tested every year after the age 35.

What controls pressure in the eye?     

Behind the iris (the colored part of the eye) there exists a layer of cells that produces a watery fluid, called aqueous. The fluid passes through a hole in the middle of the iris (called the pupil) to leave the eye through tiny drainage channels called the trabecular meshwork. This meshwork is in the angle between the front of the eye (the cornea) and the iris and returns the aqueous fluid to the blood stream. Normally the fluid produced is balanced by the fluid draining out, but if it cannot escape, or too much is produced, then your eye pressure will rise. The pressure in the eye has nothing to do with the pressure in the body.

Diagram 1:  A typical flow of the aqueous humor in the human eye is from posterior to anterior

Diagram 2:  When that pressure becomes too high it can damage the optic nerve in the posterior portion of the eye

Risk Factors for Glaucoma

While everyone is at risk for glaucoma certain groups are more at risks than others. Those individuals that have diabetes, hypertension, high myopia (nearsigtedness) or a central corneal thickness less than 0.5 mm (500 microns) are more at risk than the general population. A complete health history at Graf Optical will screen for these risk factors and others below:

Ethnic groups at risk for glaucoma

Certain ethnic groups are more at risk than others for different types of glaucoma.

African-Americans

Glaucoma, especially primary open angle glaucoma, is the leading cause of blindness among African-Americans. The National Eye Institute of Health considers African Americans over the age of 40 at risk for glaucoma. Among African Americans, studies show that glaucoma is:

• Five times more likely to occur in African Americans than in Caucasians.
• About four times more likely to cause blindness in African Americans than in Caucasians.
• Fifteen times more likely to cause blindness in African Americans between the ages of 45-64 than in Caucasians of the same age group.

Thus, glaucoma often occurs earlier in life in African-Americans-on average, about 10 years earlier than in other ethnic populations. Further information is available by viewing either the Baltimore Eye Survey  or the Barbados Eye Study

Hispanics in Older Age Groups

Hispanics, particularly those above the age of 60 are more at risk than the general population. Recent studies indicate that the risk for Hispanic populations is greater than those of predominantly European ancestry. In Hispanic Americans the risk of having glaucoma can approach 20% in persons over 75 years of age.

Asians

Narrow angle glaucoma accounts for less than 10% of all diagnosed cases of glaucoma. People of Asian descent appear to be at some risk for angle closure glaucoma. Otherwise there is no known increased risk in Asian populations. Japanese may be more prone to normal tension glaucoma than the general population. Normal tension glaucoma (NTG), also known as low tension or normal pressure glaucoma, is a form of glaucoma in which damage occurs to the optic nerve without eye pressure exceeding the normal range. Relatively speaking, a "normal" pressure range is between 11-21 mm Hg.

People Over 60

Age alone is considered a risk factor for glaucoma. Studies show that the risk of glaucoma increases by six times if you are over the age of 60. In a major study, less than 1% of people age 60 to 64 had chronic open-angle glaucoma. Among people 10 years older, the prevalence more than doubled to 1.3%, and among those 80 to 84, it more than doubled again to 3%.

Family Members with Glaucoma

The most common type of glaucoma, primary open angle glaucoma, is hereditary. If members of your immediate family have glaucoma, you are at a much higher risk than the rest of the population. Family history increases risk of glaucoma five to nine times. The siblings of persons diagnosed with glaucoma have over a 9-fold increased risk of having glaucoma when compared to siblings of persons without glaucoma. Thus, if you have a close relative who has chronic glaucoma then you should have an eye test at regular intervals. You should advise other members of your family to do the same.

Eye Injury

Have you ever taken a hard trauma to the eye? If, "yes" you should have your eyes evaluated for glaucoma. Hard injuries that "bruise" the eye (called blunt trauma) or injuries that penetrate the eye can damage the eye's drainage system, leading to traumatic glaucoma. Traumatic injuries to the eye are considered a "secondary" open angle glaucoma as the glaucoma is "secondary" to the injury. This type of glaucoma can occur immediately after the injury or years later. The most common causes of secondary glaucoma include automobile injuries such as airbag deployments, sports-related injuries such as receiving a baseball to the eye, and punches or elbows to the eye.

Diagnostic Testing for Glaucoma at Graf Family Eye Care and Glaucoma

Four Common Tests for Glaucoma

Regular glaucoma check-ups include two routine eye tests: tonometry and a fundus evaluation of the optic nerve.

Tonometry

The tonometry test measures the inner pressure of the eye. Usually drops are used to numb the eye. Then the doctor or technician will use a device known as a tonometer probe to measure the eye's pressure. The "puff of air test" known as non contact tonometry is typical not used to track pressure over a long term basis because of its variability.

Fundus evaluation of the optic nerve

After being dilated the eye doctor examines the inside of the eye (especially the optic nerve) with the slit lamp microscope and a lens. This helps the doctor look at the shape and color of the optic nerve. If the pressure in the eye is not in the normal range, or if the optic nerve looks suspicious, then three special glaucoma tests will be done. These tests are called visual field testing, gonioscopy, and pachymetry.

Visual Field Testing

The most basic and rudimentary way to check peripheral vision in an eye exam is known as finger counting.  In this test the patient covers one eye, and the eye doctor asks the patient, "How many fingers do you see and when do they come into your vision." 

The "gold standard" for visual field testing is using a perimeter to allow the patient to map out their peripheral vision.  During the visual field test (also kown as perimetry testing)t, you will be asked to look straight ahead and then indicate when a moving light passes your peripheral (or side) vision. This helps draw a "map" of your vision. 

Graf Optical Family Eye Care and Glaucoma strongly recommends that all patients choose the option of having the Zeiss Humphrey Matrix performed as the gold standard of checking peripheral vision.

A sample visual field defect of a patient with glaucoma is presented below.  "Nasal steps" and "arcuate visual field loss" or common visual field loss in patients with glaucoma.  Notice that the areas that are shaded in darkly are areas where the patient is no longer able to see.  Most glaucoma defects progress quite slowly and can take years to become repeatable on perimetry testing.  As the glaucoma visual field progresses the entire hemi-field (entire half field) can become affected.

Gonioscopy

Gonioscopy is a pain free eye test that checks if the angle where the iris meets the cornea is open or closed, showing if either open angle or closed angle glaucoma is present.

Pachymetry— How ultrasounds of the cornea are used in glaucoma evaluations

A pachymeter is a simple, quick, painless ultrasound test to measure the thickness of your cornea. With this measurement, our eye doctors can better understand your intraocular pressure reading, and develop a treatment plan that is right for your condition. The procedure takes only about a minute to measure both eyes.

A pachymeter is now used in glaucoma treatment decisions as a result of the 2002 Ocular Hypertension Study (OHTS). A critical discovery was made regarding corneal thickness and its role in intraocular eye pressure and glaucoma development. In this study it was determined that patients with thin corneas (less than 555 microns) show artificially low IOP readings.. This is a dangerous sign because if your actual pressure reading is higher than the tonometer reveals, you may be at risk for developing glaucoma and your doctor may not know it. Thus, without pachymeter testing in today's glaucoma evaluation there is a danger of misreading the eye pressure. On the other hand a thicker corneal thickness reading may mean less reason to worry about glaucoma.

The GDx nerve fiber analyzer

Graf Optical now uses the state of the art GDX nerve fiber analyzer for the advanced detection of glaucoma. The GDX uses scanning laser polarimetry (GDx) to measure the thickness of the optic nerve fiber layer on the retinal surface just before the fibers pass over the optic nerve margin to form the optic nerve.

Glaucoma Treatment

The best way to prevent vision loss from glaucoma is early diagnosis and treatment. At Graf Optical, Family Eye Care and Glaucoma those diagnosed with glaucoma are seen at least every year for a complete examination, including an intraocular ((IOP) pressure check. People at high risk for glaucoma due to high intraocular pressures, family history, ethnic background, age or optic nerve appearance may need more frequent visits to Graf Optical Family Eye Care and Glaucoma.

A test called the Zeiss Humprhey Visual Field may be performed on glaucoma suspects to detect peripheral vision loss. It involves looking straight ahead into a machine and clicking a button when you notice a blinking light in your peripheral vision. The visual field test may be repeated at regular intervals for a Graf Optical eye doctor to determine the extent of vision loss.

Glaucoma treatment (for any form) entails increasing the fluid drainage, decreasing aqueous humor production, or a combination of the two. Most patients with glaucoma require only medication to control the eye pressure. Sometimes, several medications that complement each other are necessary to reduce the pressure adequately.

Generally the first stage of glaucoma treatment is a prostaglandin analog eyedrops, which will increase drainage of fluid in the eye. There are other pressure-lowering drops besides prostaglandin analogs that are known as alpha-2 agonists and beta blockers. Beta blockers may not be used in people with heart conditions, because they can affect heart or lung function. For this reason beta blockers are used as a second line of treatment. Patients should discuss these issues with both the family physician and the Graf Optical eye care practitioner. These treatments will not restore any vision already lost to glaucoma

Most cases of glaucoma can be controlled with a single drug or drug combinations, but some patients may require or select surgery. Should patients need glaucoma filtering surgery after medications fail to lower pressure, the patients are then sent to Awad Eye Care and the eye surgeon Dr. Omar Awad .