Bad eye

This is an eye suffering from papilledema. There are blind spots, swelling and a blurred disc. Papilledema is the swelling of optic nerve.
The anatomy of the Optic Nerve makes it a sensitive marker for problems inside the brain. This nerve is a thick cord that connects the back of each eyeball and it's retina to the brain. In its short span between the brain and the eye, the Optic Nerve's whole surface is bathed by Cerebral Spinal Fluid (CSF). Although this fluid protects the nerve from sudden movement, even slight increases in the pressure of this fluid (from swelling of the brain) can affect the Optic Nerve, because it can compress the nerve around it's whole circumference in a "choking" manner. It is when this nerve is exposed to high pressure, or when it develops inflammation of its own that it can bulge into the back wall of the eyeball resulting in Papilledema.