Glaucoma

Definition

Glaucoma is a group of eye diseases that damage the optic nerve. The optic nerve is the main nerve to the eye (located in the back of the eye) that is responsible for transmitting electrical impulses to the brain. Damage usually occurs as a result of elevated fluid (called aqueous humor) pressure in the eye. This damage results in gradual visual changes and then loss of vision.

Description

The eye is protected by the sclera (the white covering of the eye). At the front of the eye is a clear window (the cornea) that lets light in. The iris is the colored part of the eye which controls the amount of light that can enter the eye by automatically opening and closing the pupil (the opening of the eye). The lens (the portion of the eye lying behind the pupil) focuses light onto the retina (the innermost layer of the eye and the sensitive organ upon where light rays are focused). Nerve fibers and blood vessels in the retina gather together to form the optic nerve which carries images to the brain. The place where the optic nerve leaves the eye is called the optic disc.

The front part of the eye is filled with aqueous humor (fluid) that nourishes the lens, iris and cornea, as well as maintains the shape of the eye. This fluid is continuously produced every hour by ciliary tissues. The fluid circulates from behind the iris through the opening at the center of the pupil and into the spaces between the iris and cornea. Since this fluid is constantly produced, it must be drained. The fluid drains through an area called the drainage angle (located where the iris and cornea meet) to the trabecular meshwork (the valve that regulates pressure within the eye) to a channel (called the canal of Schlemm), and then to a system of small veins outside of the eye, called the drainage canals. When there is a problem in the drainage, the fluid builds up in the eye and presses against the optic nerve (called intraocular pressure or IOP), resulting in glaucoma.

This increased fluid pressure actually pushes the optic nerve back into a "cupped" or concave shape. If the intraocular pressure remains too high for too long, the extra pressure damages parts of the optic nerve. This damage appears as gradual visual changes and then loss of vision. The early visual changes are very slight and do not affect the central vision the center portion of what is seen when looking straight ahead or when reading. Certain parts of the peripheral vision (the top, sides and bottom) are affected first. Glaucoma usually occurs in both eyes, but extra fluid pressure first begins to build up in one eye.

There are many types of glaucoma, but the two most common types are open-angle glaucoma and closed angle (angle-closure) glaucoma.

Open-angle glaucoma, (also called chronic glaucoma) accounts for 90 percent of all glaucoma cases and occurs when the trabecular meshwork becomes blocked and the fluid can't get to the normal drainage canals. This blockage results in fluid build-up and intraocular pressure. The fluid build-up happens gradually.

Closed angle glaucoma, (also called acute glaucoma), accounts for about 9 percent of all glaucoma cases and occurs when the opening between the cornea and iris narrows, such that the fluid cannot get to the trabecular meshwork and normal drainage channels. This narrowing results in fluid build-up and intraocular pressure. The fluid build-up happens very quickly.

Other less common glaucomas include:

• normal tension glaucoma: optic nerve is damaged even though intraocular pressure is consistently within a normal range

• congenital glaucoma: incorrect or incomplete development of the eye's drainage canals during the prenatal period

• childhood glaucoma: open-angle glaucoma in infancy, childhood or adolescence

• secondary glaucoma: occurs as a result of eye injury, inflammation or tumor, or in advanced cases of cataracts or diabetes

Causes and Risk Factors

There are several factors that can put a person "at risk" for developing glaucoma:

• Family history of glaucoma - There is a 20 percent chance of developing glaucoma of a parent had it, and 50 percent chance if a sibling has it.

• Age - If the person is 65 to 79 years of age, there is a 3 percent chance of developing glaucoma. If the person is 80 years of age or older, there is a 14 percent of developing glaucoma.

• Medical conditions, such as morning headaches, diabetes, lupus, Crohn's disease, rheumatoid arthritis, myopia (nearsightedness), and high blood pressure

• Use of topical steroid (prednisone or cortisone) medications

• Race - Blacks are three to four times more likely than Caucasians to develop glaucoma. Asians and Eskimos are more likely to develop glaucoma than Caucasians.

• Abnormally high intraocular pressure

• Previous eye injuries

• Recurrent blurry vision

• Pain around the eyes after watching TV or leaving a dark theater

• Seeing a rainbow - hued halos around lights at night

• Peripheral (side) vision is decreasing

Symptoms

Known as the "sneak thief" of sight, open-angle glaucoma has no early warning signs or symptoms. However, as the disease progresses a person may experience:

• Tiny blind spots appear at the edges of the visual field (peripheral or side vision) that slowly get larger and spread

• Blurred vision

• Appearance of colored halos around lights

• Adjustment problems on entering a dark room

• Repeated difficulties that new eyeglass prescriptions do not help

The symptoms of closed angle glaucoma are:

• Severely blurred vision

• Severe eye and head pain

• Nausea or vomiting

• Appearance of rainbow-colored halos around bright lights

• Rapid loss of vision

Diagnosis

There are four (4) important factors in the diagnosis of glaucoma: intraocular pressure, the condition of the optic nerve, the patient's visual field and the angle where the iris meets the cornea. To detect these factors, the ophthalmologist will do the following diagnostic tests:

• Tonometry - used to measure intraocular pressure. Drops are put in the eyes to numb the eye and then the doctor measures the eye pressure, using an instrument called a tonometer. This instrument measures the inner pressure of the eye by determining how much pressure is necessary to cause a slight indentation on the outer part of the eye.

• Ophthalmoscopy - used to examine the inside of the eye, the optic nerve and the patient's field of vision. Drops are put in the eyes to dilate the pupil and then the doctor uses an instrument called an ophthalmoscope that lights up and magnifies the inside of the eye.

If the intraocular pressures are not within normal range or if the optic nerve looks unusual, the doctor may do a perimetry or a gonioscopy:

• Perimetry - a special test that produces a map of the complete field of vision.

• Gonioscopy - a test to check whether the angle where the iris meets the cornea is open or closed.

Treatment

There is no cure for glaucoma, but it can be controlled. Ophthalmologists use medication and surgery to prevent further vision loss. These treatment methods are used to bring the intraocular pressure under control.

Medication

Nearly all glaucoma can be treated successfully with topical medications (applied directly to the eyes, such as eye drops or eye ointments) or oral medications (taken by mouth). There are six medications available to treat glaucoma:

1. Miotics are eye drops that help open the drainage canals and increase the flow of aqueous humor out of the eye. This type of medication includes pilocarpine (Isopto Carpine, Pilocar, Pilopine), carbachol and echothiophate.

2. Epinephrine compounds are eye drops that lower the intraocular pressure by increasing the rate of aqueous humor flow out of the eye. This type of medication includes dipivefrin (Propine) and Epifrin.

3. Beta-blockers (available as eye drops or pills) help decrease the rate at which the aqueous humor flows into the eye. This type of medication includes topical timolol (Timoptic), levobunolol (Betagan), betaxolol (Betaoptic-S), Iopidine and Ocupress. Additionally, this type of medication can also be taken orally. Oral medications include propranolol, timolol, atenolol and nadolol.

4. Carbonic anhydrase inhibitors (available as pills or eye drops) help reduce aqueous humor flow into the eye. This type of medication includes oral acetazolamide (Diamox), methazolamide (Neptazane) and chlorpropamide (Daranide), as well as topical dorzolamide (Trusopt).

5. Alpha adrenergic agonists are topical medications used to reduce the aqueous humor production and increase aqueous humor outflow. This type of medication includes apraclonidine (Iopidine) and brimonidine (Alphagan).

6. Prostaglandin analogues are topical medications that help lower intraocular pressure by increasing uveoscleral outflow (outflow through the soft tissues of the front of the eye [iris and ciliary body]). This type of medication includes latanoprost (Xalatan).

Surgery

Surgery is the primary treatment method for acute and congenital glaucoma, because it is generally the only way the blocked or incorrectly formed drainage canals can be opened. In cases of open-angle glaucoma, surgery is considered only when the maximum dosage of medications does not control the intraocular pressures or when a patient cannot tolerate the medications needed to control eye pressures. Surgery is usually scheduled for only one eye at a time, as a safety measure, and also because one eye will often need surgery before the other.

There are two (2) ways of doing surgery now: laser surgery or operative surgery.

Laser Surgery

Laser treatment is a technique that is used in cases of acute and chronic glaucoma. A laser is a tiny, powerful beam of light that can make a small burn or opening in tissue, depending on the strength of the light beam. There are different types of lasers used in eye surgery for various purposes. These include argon, krypton, neodymium-YAG, diode and excimer lasers. The most commonly used laser procedures are Laser Peripheral Iridotomy and Argon Laser Trabeculoplasty.

• Laser Peripheral Iridotomy (LPI) is a procedure most commonly used in patients with angle-closure glaucoma. A laser peripheral Iridotomy creates a hole in the iris, allowing the iris to fall back away from the outflow channel so the fluid can drain out of the eye.

• Argon Laser Trabeculoplasty (ALT) is a procedure used for patients with open angle glaucoma. In this technique, the laser beam is aimed toward the drainage channels of the eye in an attempt to open the channels, thus allowing the drainage system to work better.

Operative Surgery

Operative surgery is a technique that is successful in cases of acute, chronic, congenital and secondary glaucoma. There are four (4) types of operative surgeries available for the treatment of glaucoma - filtering surgery (trabeculectomy), glaucoma implants, combined cataract/glaucoma surgery and cyclodestruction.

• Trabeculectomy involves removing part of the trabecular meshwork of the eye to allow the aqueous humor in the eye to bypass blocked drainage canals and flow safely away from the eyes.

• Glaucoma implants involve inserting an artificial drainage tube into the eye to act as a new drain. This procedure may be recommended because of abnormal eye anatomy or if there is a history of previous eye surgery which makes it impossible for the surgeon to build a new drain from the tissue already present.

• Combined cataract/glaucoma surgery involves the dual removal of the cataract (hazy or cloudy lens of the eye) and trabeculectomy. Cataract surgery involves making a small incision directly into the eye, removing the damaged lens and replacing the damaged lens with a plastic one. This procedure may be recommended if cataracts are present.

• Cyclodestruction involves partial destruction of the ciliary body to decrease the amount of aqueous humor produced in the eye. This procedure may be recommended for eyes which have failed trabeculectomy or those so badly damaged that prognosis for retention of vision is grim.

Prevention

While glaucoma cannot be prevented, the earlier it is diagnosed the better. Recommendations for early detection include:

Have a test every two four years if:

• between the ages of 40 and 65

Have a test every one to two years if:

• 65 years of age or older

• family history of glaucoma

• Black or Asian ancestry

• diabetes or a chronic inflammatory disease

• previous serious eye injury

• taking steroids

Questions to Ask Your Doctor

What tests will be performed?

Will you explain how each test is performed and what it will tell?

What type of glaucoma is it and how severe is it?

Will you be prescribing a medication to treat the glaucoma?

What are the side effects?

What does the medication do to relieve the glaucoma or to stop further deterioration?

Will surgery be performed to relieve the glaucoma?

If so will you recommend laser treatment or microsurgery? What are the risks?

Will any of the symptoms go away after treatment?

Can certain medications cause glaucoma or make the condition worse?

Are there any signs or symptoms that require immediate medical attention?