Light rays enter the clear cornea and then pass through the pupil and the lens. These light rays are focused onto the retina, a light-sensitive tissue lining the back of the eye. The optic nerve is connected to the retina, and is made up of many nerve fibers. Signals from the retina are sent through the optic nerve to the brain.
Glaucoma can damage optic nerve cells. Once enough nerve cells are destroyed, “blind spots” begin to form in the field of vision. These “blind spots” usually develop first in the peripheral field of vision (the outer sides of the field of vision). In the later stages of glaucoma, these “blind spots” affect central vision. This vision loss is irreversible because once the nerve cells are dead they cannot be restored.