The optic nerve is located in the back of the eye. It is also called the second cranial nerve or cranial nerve II. It is the second of several pairs of cranial nerves. Although the optic nerve is part of the eye, it is considered to be in the central nervous system. The job of the optic nerve is to transfer visual information from the retina to the vision centers of the brain via electrical impulses. The optic nerve is made of ganglionic cells or nerve cells. It consists of over one million nerve fibers. Our blind spot is caused by the absence of specialized photosensitive cells, or photoreceptors, in the part of the retina where the optic nerve exits the eye. Glaucoma is the most common illness affecting the optic nerve. Glaucoma is caused when high intraocular pressure, or high pressure, is in the fluid in the eye (vitreous fluid). This high pressure compresses the optic nerve and causes cells to die, and is referred to as atrophy of the optic nerve.