Inside the eye are two fluid-filled chambers. Intraocular fluid, or eye fluid, is responsible for maintaining the correct amount of pressure inside the eye, which keeps the shape of the eye intact. This fluid is clear and watery in the front, or anterior, chamber of the eye. The back or posterior larger chamber, is filled with a thick, jelly-like fluid, which is referred to as the vitreous humor.

The clear and watery eye fluid in the anterior chamber is called the aqueous humor, which is continually being formed and absorbed as it flows through the eye. This fluid is formed near the lens, flows to the front chamber of the eye, and then drains into the venous system through a tiny drainage duct.

Glaucoma, which is a common cause of blindness, is a disease that affects the drainage of the aqueous humor, causing pressure to build within the eye. There are many types and causes of glaucoma. Often, glaucoma occurs when either a sponge-like meshwork that filters eye fluid becomes compacted and prevents fluid from entering the duct or when the iris of the eye covers the canal opening.

In either case, the accumulation of fluid within the eye creates pressure that pushes on the back of the eye and damages the optic nerve. This nerve is responsible for transmitting the images to the brain. Over time, the increased pressure can result in blind spots and even total blindness. Appropriate therapy can halt or slow disease progression but cannot restore lost vision.