Glaucoma is a disease that damages the eye's optic nerve. The optic nerve is connected to the retina — a layer of light-sensitive tissue lining the back of the eye — and is made up of many nerve fibers, like an electric cable is made up of many wires. It is the optic nerve that sends signals from the retina to the brain, where these signals are interpreted as the images one sees.
In the healthy eye, a clear fluid called Aqueous Humor circulates inside the front portion of the eye. To maintain a constant healthy eye pressure, the eye continually produces a small amount of aqueous while an equal amount of this fluid flows out of the eye. In one with Glaucoma, the aqueous does not flow out of the eye properly. Fluid pressure in the eye builds up and, over time, causes damage to the optic nerve fibers.
Glaucoma can cause blindness if it is left untreated. Only about half of the estimated three million Americans who have Glaucoma are even aware that they have the condition. When Glaucoma develops, there are often few early symptoms and the disease progresses slowly. In this way, glaucoma can steal sight very gradually. Fortunately, early detection and treatment (with eyedrops, Glaucoma Surgery or both) can help preserve vision.
The most common form of Glaucoma is called Primary Open-Angle Glaucoma. It occurs when the trabecular meshwork of the eye gradually becomes less efficient at draining fluid. As this happens, eye pressure, called Intraocular Pressure (IOP), rises. Raised eye pressure leads to damage of the optic nerve. Damage to the optic nerve can occur at different eye pressures among different patients. Eye care providers establish a target eye pressure that he or she predicts will protect the optic nerve from further damage. Different patients have different target pressures.
Typically, Open-Angle Glaucoma has no symptoms in its early stages and vision remains normal. As the optic nerve becomes more damaged, blank spots begin to appear in the field of vision. Most patients usually won't notice these blank spots in their day-to-day activities until the optic nerve is significantly damaged and these spots become large. If all the optic nerve fibers die, blindness results.
Half of patients with Glaucoma do not have high eye pressure when first examined. Many individuals will only occasionally have high eye pressures on repeat testing; thus, a single eye pressure test misses many with Glaucoma. In addition to routine eye pressure testing, it is essential that the optic nerve be examined by an eye doctor for proper diagnosis.