The police officer and later Dr. Foreman suffered from primary amoebic menigio-cephelitis. The long name, broken down, simply means swelling and destruction of neural tissue and the meninges (membranes surrounding the brain) as a direct consequence of amoebic infection. The organism in question, Naegleria fowleri, is quite lethal: of the 175 people or so known to have been infected, about 97% have died. Wholesale destruction of neurons in the brain caused by the parasite is the usual cause of death. Symptoms depend on what part of the brain the parasites attack; their usual route of entry is through the nose and along the olfactory nerve, which leads into the basal ganglia, where some of the most vital and delicate structures are found. Unlike some parts of the brain, there is little redundency here. It doesn't take much damage to cause significant problems.
Dr. Cameron: Reliable witness?
House: His name’s “Baby Shoes.” How bad can he be?
Dr. Foreman: What’s Dr. Cameron wearing?
Joe: Dark blue pants, white shirt, black shoes.
Dr. Foreman: Ooh, almost. Except for the pants, shirt, and shoes. You’re blind.