Glaucoma is a term applied to a group of eye diseases that cause a characteristic and recognizable deterioration of the optic nerve. The optic nerve carries visual information from the eye to the brain. When the optic nerve is damaged or injured, the transmission of visual information and, hence, the visual image is impaired. Fortunately, we can usually detect glaucomatous optic nerve damage before there is noticeable visual loss by examining the back of the eye. Sometimes, damage to the nerve can be observed before there is a change in vision by specialized tests of vision.

Figure 1: Nerve fibers are seen to fan out
onto the retina from the optic nerve
head early defects seen at the arrows