Glaucoma is a condition in which the nerve cells which transmit information from the eye to the brain become damaged. This prevents visual information from getting from the retina in the eye to the brain. Glaucoma is often associated with a build-up of pressure in the eye. The eye is filled with fluid which is constantly being replaced. If excessive amounts of fluid are produced, or if it cannot drain away properly, the pressure inside the eye can increase. In some forms of glaucoma, the pressure inside the eye can become extremely high, but in other forms the pressure may remain normal.