This is the insertion point of the optic nerve into the back of the eye. The optic nerve is a large nerve that connects the eyeball to the brain. This nerve inserts on the back of the eyeball and looks like a tube or pipe piercing the back of the eye. We can see the nerve insertion inside the eye during a dilated retina exam. Because we are viewing the nerve straight on it looks like a circle or a “disk” sitting in the middle of the retina. Examination of the disk is useful for monitoring many problems. For example, with glaucoma high ocular pressure slowly kills off the individual nerve fibers that fill the optic nerve. This creates a hollowed out area or “cup” that can be seen in the middle of the optic disk. This is called glaucomatous cupping and we follow the “cupping to disk ratio” over time to monitor for glaucoma damage. With pseudotumor cerebri, the pressure inside the skull (intracranial pressure) is high. This causes headaches and potentially neurologic problems if left untreated. The intracranial pressure is hard to measure, however, short of performing a spinal tap. However, this pressure can sometimes be seen at the optic disk because the fluid pressure can flow down the optic nerve and appear as optic disk swelling inside the eye.