What comprises the optic nerve?
It is made up of about 1 million small individual thread-like nerve fibers that come from the retina. The fibers bend about 90 degrees as they leave the retina and enter the front of the optic nerve (known as the optic nerve head). Normally, there is a small crater-like depression seen at the front of the optic nerve head. This depression is known as the cup. Its diameter is smaller than the diameter of the optic nerve. In the old days, when a doctor looked at the nerve with a monocular magnification device, the nerve head looked like a cup on a saucer (or disc). This started a whole group of optic nerve descriptors (cup to disc ratio, cupping, cupped, etc.). How is optic nerve damage detected? The normal cup to disc ratio (the diameter of the cup divided by the diameter of the whole nerve head or disc) is about 1/3 or 0.3. There is some normal variation here, with some people having almost no cup (thus having 1/10 or 0.1), and others having 4/5ths or 0.8 as a cup to disc ratio. If som
