Glaucoma

Cataracts | Diabetic Retinopathy | Glaucoma | Macular Degeneration

What is Glaucoma?
A part of the eye called the ciliary body produces a fluid called aqueous humor. This fluid flows through the pupil and into the anterior chamber (the space directly behind the cornea) where it nourishes the lens, iris and cornea. It then drains through a series of tiny holes that line the iris called the trabecular meshwork and back into the blood stream. With glaucoma, this drainage system is faulty, and the aqueous humor does not drain properly. This causes an increase in the intraocular pressure (IOP), which damages and can eventually destroy the nerve fibers that transmit the signals to your brain. This process is gradual and has no symptoms until most of the vision has been destroyed.

Types of Glaucoma

There are two main forms of glaucoma. Open angle and Narrow angle. Other types of glaucoma include Closed angle and Neovascualr glaucoma.

Open Angle Glaucoma

In this condition, the angle formed by the back of the cornea and the iris (drainage angle) is normal and is not blocking the trabecular meshwork. But for reasons not fully understood, the drainage system does not work properly. Fluid produced cannot drain off fast enough causing the pressure within the eye to rise. This increased pressure is what damages the optic nerve. This is the most common form of glaucoma.

Narrow Angle Glaucoma / Closed Angle Glaucoma

With narrow angle glaucoma, the drainage angle formed by the back of the cornea and the iris is to narrow. This blocks the trabecular meshwork and prevents it from draining the fluid from inside the eye.

In closed angle glaucoma (sometimes referred to as a glaucoma attack), the angle formed by the back of the cornea and the iris narrows suddenly, completely blocking the trabecular meshwork. This causes a rapid rise in the intraocular pressure. This conditions usually affects one eye at a time. Patients with this condition complain of headaches or pain around the eye, blurred vision, halos or rainbows around lights, even nausea and vomiting. This is a very serious condition and must be treated immediately to prevent loss of vision.

Neovascular Glaucoma

This condition usually affects patients with diabetic retinopathy. With neovascular glaucoma, abnormal blood vessels grow within the drainage angle. These abnormal vessels block the trabecular meshwork, preventing fluid from draining from the eye raising the intraocular pressure.

Diagnosis of Glaucoma

A common misconception among patients is that there is a single test to determine glaucoma. Truth of the matter is that your doctor has to look at a combination of things to determine if you have glaucoma.

Taking Your Medical History

Glaucoma is often hereditary, so during an eye exam a complete medical history, including past family history will be taken. Your doctor will also want to know about other medical conditions that could affect the pressure in your eye such as diabetes and hypertension.

Measurement of Your Eye Pressure

After numbing your eye with a few anesthetic drops, the doctor or technician uses a device called tonometer to measure the pressure inside your eye. This device gently presses on your eye to determine the intraocular pressure.

Sometimes patients can have high pressures but show no other signs of glaucoma. These people all called Glaucoma Suspects and are followed closely to see if they develop any other signs of glaucoma.

The doctor may also take a measurement of your corneal thickness. It has been discovered that patient's who have thicker than normal corneas may register false high intraocular pressures. This may be an important factor in making a diagnosis.

Examination of the Optic Nerve

Using a device called a slit lamp (a microscope), the doctor can examine your optic nerves for signs of glaucoma. Optic nerves damaged by glaucoma show enlargement or "cupping". The doctor also looks for changes in the blood vessels that might show signs glaucoma. Sometimes, retinal photographs are taken. These photographs don't serve any immediate diagnostic purpose. Rather they are used during future eye exams. Your doctor can compare your optic nerve to past visits to see if any changes have occurred in your condition. You may have them repeated from time to time. Sometimes, patients may have abnormal looking optic nerves but show no other signs of glaucoma. These people are called Glaucoma Suspects and are followed closely to see if they develop any other signs of glaucoma.

Examination of the Drainage Angle

To examine your drainage angle the doctor performs gonioscopy. To do this, the doctor numbs your eye with a few anesthetic drops, the places a special lens on your eye. This lens has a mirror in it which allows the doctor to examine the drainage angle to see whether it is open or closed.

Visual Field Testing

If your eye shows signs of glaucoma, your doctor may order a special test called a visual field. This test measures your peripheral or side vision. In glaucoma, nerve fibers that carry the impulses to the brain are damaged and/or destroyed. The ones that are affected first are the ones that control side vision. During this test you sit at a bowl shaped object with one eye patched looking straight ahead. When you see a dot of light you press a button. A printout is generated from this information which show your field of vision. Dark areas on the printout show reduced side (peripheral) vision.

Treatment of Glaucoma

If diagnosed with glaucoma there are many forms of treatment available. For open angle glaucoma, the most common form of glaucoma, your doctor may prescribe medication. This may be in the form of eye drops or oral medications. These medications essentially work to do one of two things. Either they slow production of fluid (aqueous humor) or they increase drainage.

If patients don't respond to medications and the intraocular pressure remains elevated. The doctor may then recommend a procedure called a trabeculoplasty. Using a laser, the doctor treats the trabecular meshwork so fluid can drain more freely. If patients have narrow or closed angle glaucoma, they may have a procedure called an iridotomy. Using a laser, the doctor makes tiny opening in your iris, allowing fluid to drain.

Patients not responding to medication and/or laser may have to undergo surgery. The doctor may suggest a surgical procedure called a trabeculectomy. During this procedure, a new drain is made in your eye, bypassing the clogged drainage system. A flap is made in the eye, with a tiny hole made underneath. Fluid drains through this hole and out of the eye. In another form of surgery, an Ahmed Valve with a shunt is placed inside the eye. This shunt carries fluid out of the eye maintaining the pressure.

Self Help for Glaucoma

Routine Eye Exams

One of the major risk factors for glaucoma is age. People over the age of 35 should have routine eye exams every two years. It is recommended that people over the age of 50 have them yearly. People who are of African-American heritage are more at risk to developing open angle glaucoma. People of Asian heritage are more at risk to developing closed or narrow angle glaucoma. If diagnosed with a form of glaucoma be sure to keep all of your appointments so your doctor can monitor your condition.

Take Your Medication

If diagnosed with glaucoma and taking medication(s) for it, it is very important that you do so exactly as directed by your doctor. Even after your pressure is under good control, stopping your medications will cause the pressure to rise again damaging your optic nerve further. If you forget your medication, take it as soon as you remember, don't wait for your next scheduled time. Never stop you medication, unless directed to do so by your doctor. Let your other doctors know you have glaucoma and are taking medication for it. This can help prevent drug interactions.

For additional information on Glaucoma, click on the links below:

StLukesEye | Glaucoma Research Foundation | National Eye Institute - Facts

Cataracts | Diabetic Retinopathy | Glaucoma | Macular Degeneration