Glaucoma is a disease of the optic nerve that gradually steals sight without warning. In the early stages of glaucoma, there may be no symptoms. It is estimated that half of the people affected by glaucoma may not know they have it.

Vision loss is caused by damage to the optic nerve, the conduit that carries images from the eye to the brain. There is no cure for glaucoma—yet. However, medication or surgery can slow or prevent further vision loss. The appropriate treatment depends upon the type of glaucoma among other factors. Early detection is vital to stopping the progress of the disease.

It was once thought that high pressure within the eye, also known as intraocular pressure or IOP, is the main cause of this optic nerve damage. Although IOP is clearly a risk factor, we now know that other factors must also be involved because even people with “normal” levels of pressure can experience vision loss from glaucoma.

The eye receives its nourishment from a clear fluid that circulates inside the eye. This fluid must be constantly returned to the blood stream through the eye's drainage canal, called the trabecular meshwork. High eye pressure is a result of inadequate drainage of the clear fluid from the eye. Inadequate drainage takes place when the drain of the eye is internally clogged (open angle glaucoma) or when the drain of the eye is physically blocked by the iris (narrow angle glaucoma).