Glaucoma

How the Eye Sees

To understand how glaucoma affects your eyes, it is important to understand how your eye sees. Light rays enter the eye through the clear cornea, then through the pupil and the lens. These light rays are focused on to the retina, a light-sensitive tissue lining the back of the eye. The optic nerve is connected to the retina and is made up of many nerve fibers. Signals from the retina are sent through the optic nerve to the brain, where they are interpreted as the images we see. In the healthy eye, a clear liquid, called aqueous humor, circulates inside the front portion of the eye. To maintain a constant, healthy eye pressure, your eye continually produces a small amount of aqueous humor and an equal amount of this fluid flows out of the eye through a microscopic drain (called the trabecular meshwork) in the drainage angle.

Open-Angle

In the healthy eye, a clear liquid, called “aqueous humor”, circulates inside the front portion of the eye. To maintain a constant, healthy eye pressure, your eye continually produces a small amount of aqueous humor and an equal amount of this fluid flows out of the eye through a microscopic drain (called the trabecular meshwork) in the drainage angle. If you have glaucoma, the aqueous humor does not flow through the drainage angle properly. Fluid pressure in the eye increases, and this extra force presses on the optic nerve in the back of the eye, causing damage to the nerve fibers.

Closed-Angle

In the healthy eye, a clear liquid, called “aqueous humor”, circulates inside the front portion of the eye. To maintain a constant, healthy eye pressure, your eye continually produces a small amount of aqueous humor and an equal amount of this fluid flows out of the eye through a microscopic drain (called the trabecular meshwork) in the drainage angle. A less common form of glaucoma, called “closed-angle glaucoma”, occurs when the drainage angle of the eye becomes blocked. The iris, the colored part of the eye, may close off the drainage angle. People of Asian descent, and those who are far-sighted, tend to be more at risk for developing this form of glaucoma.

Nerve Fibers

A normal optic nerve is made up of more than one million tiny nerve fibers. With glaucoma, as the optic nerve is damaged, it loses nerve fibers. As a result, the appearance of the optic nerve changes. We refer to this as “cupping”. As the cupping increases, blind spots begin to develop in your field of vision. Ophthalmologists use a technique called a visual field test to look for these blind spots. The results of this test show us if, and where, blind spots are appearing in your field of vision—spots that you may not even notice.

Visual Field

In the early stages of glaucoma, the visual field remains normal. As the optic nerve experiences further damage, blind spots begin to appear. These blind spots typically go undetected in your day-to-day activities, until your optic nerve is significantly damaged and the blind spots become large. If all the optic nerve fibers die, blindness results.

ALT SLT

Two types of laser procedures, called Argon Laser Trabeculoplasty (known as ALT), and Selective Laser Trabeculoplasty (or SLT) are used for patients with open-angle glaucoma. These laser surgeries are used to treat the drainage system of the eye, known as the trabecular meshwork. Treating this area of the eye’s natural drainage system is designed to improve the flow of fluid out of the eye, helping to lower the pressure.

Iridotomy

Laser iridotomy is a type of laser surgery for people who have, or who may develop, narrow-angle glaucoma. A laser is used to make a small hole in the iris, the colored part of the eye. This hole should restore normal flow of fluid within the eye, and reduce the eye pressure.

Trabeculectomy

The most common draining operation is called a trabeculectomy. The surgery is performed in an operating room, on an outpatient basis. This procedure allows your ophthalmologist to create a new drainage channel for the eye. The trabeculectomy allows fluid from the eye to flow into a filtering area called a “bleb”. The bleb is mostly hidden under the eyelid. When successful, this procedure will lower the pressure in your eye, minimizing the risk of vision loss from glaucoma.

Setons

If your eye is at high risk for scarring, and your eye pressure needs to be lowered to preserve your vision, your ophthalmologist may recommend placing a tiny drainage tube in your eye called a seton. This procedure is performed in the operating room, as an outpatient. The drainage tube creates a new channel for fluid to flow from the eye to a filtering area called a bleb. A tiny plate, placed on the eye, helps the bleb form and remain open. The tube is covered with a patch, and is typically not seen or felt. Once successful, seton surgery will decrease the pressure in your eye, minimizing the risk of vision loss from glaucoma.

Eyedrops

Always wash your hands before putting in your eyedrops. Remove the cap to the eyedrop medication, and do not touch the dropper tip. Tilt your head back slightly. With one hand, pull your lower eyelid away from the eye to form a pocket. You can do this by pulling the lower lid down with your index finger. With your other hand, hold the dropper tip directly over this eyelid pocket. Look up, and let the eyedrop fall into the pocket without touching the bottle to your eye or eyelid (to prevent contamination of the bottle.) Close your eyes, and do not blink, and apply pressure to the point where the lids meet the nose. Hold for two to three minutes, or as long as your ophthalmologist prescribes. Before opening your eyes—and this is very important—wipe unabsorbed drops of tears from the closed lids with a tissue. Then, open your eyes.