The eye is a fluid-filled globe about an inch in diameter. To focus light, the eye needs to maintain a smooth round shape. To keep the eye round, the eye is filled with a fluid called the aqueous, much like the tires on your car are filled with air to keep them round. There is a certain pressure in this aqueous fluid just like your car tire has pressure in the air. Under normal circumstances, the pressure in the eye is between 10 and 20. The fluid is created by a special tissue called the ciliary body. It then circulates through the eye and eventually drains out of the eye at the drainage tissue called the trabecular meshwork.
A visual image is formed when light enters the eye and is focused onto the retina by the clear lens. The retina then changes the image into electrical signals that are sent along one million tiny nerve fibers in the optic nerve. These electrical signals arrive in a special area of the brain where the electrical signals are interpreted.
So how do fluid flow and electrical signals relate to glaucoma? Glaucoma is a disease where the optic nerve and the tiny nerve fibers within it degenerate. A damaged nerve leads to decreased vision and even blindness in advanced cases. The most common cause of the nerve damage (glaucoma damage) is an increased eye pressure. The eye pressure increases when the drain inside the eye (trabecular meshwork) gets clogged and the fluid doesn’t flow through it easily. When the pressure increases, this pushes against the nerve and over many months and years causes the nerve to degenerate.