Glaucoma: What is Glaucoma? Glaucoma is the leading cause of blindness in the United States, especially for older people. But loss of sight from glaucoma is preventable if you get treatment early enough. Glaucoma is a disease of the optic nerve. The optic nerve carries the images we see to the brain. Many people know that glaucoma has something to do with pressure inside the eye. The higher the pressure inside the eye, the greater the chance of damage to the optic nerve. The optic nerve is like an electric cable containing a huge number of wires. Glaucoma can damage nerve fibers, causing blind spots to develop. Often people don't notice these blind areas until much optic nerve damage has already occurred. If the entire nerve is destroyed, blindness results. Early detection and treatment by your ophthalmologist are the keys to preventing optic nerve damage and blindness from glaucoma. What Causes Glaucoma? Clear liquid, called the aqueous humor, flows in and out of the eye. This liquid is not part of the tears on the outer surface of the eye. You can think of the flow of aqueous fluid as a sink with the faucet turned on all the time. If the "drainpipe" gets clogged, water collects in the sink and pressure builds up. If the drainage area of the eye - called the drainage angle - is blocked, the fluid pressure within the inner eye may increase, which can damage the optic nerve.