The optic nerve is the “cable” of 1.2 million neurons that run from your eye to your brain. Your retinal tissue is large made up of these neurons as they spread out over the inner surface of your eye. The retina serves as the “film” of the eye. Any loss of connection to the “film” leads to loss of that part of the “picture”. Therefore if any of these fibers in the optic nerve are damaged, we lose part of the visual field in the areas of the retina that the nerve corresponds to. All of the action of glaucoma occurs at the junction with the eye ball itself. When the “cable” (optic nerve) breaks down at this junction, a patient can lose whole sections of visual field corresponding to that area of the retina. Lowering intraocular pressure in most cases prevents breakdown of the nerve tissue in this area.