The fluid found in the brain and spinal cord is called cerebrospinal fluid, or CSF. Optic nerve swelling occurs when cerebrospinal fluid (CSF) builds up where the optic nerve and central retinal vein travel between the brain and the optic nerve. This swelling or edema in this area puts pressure on the nerve and vessel, preventing blood and fluid from leaving the eye at the normal rate. This causes papilledema. Major causes of swelling that lead to papilledema include: Head trauma, Anemia (lack of sufficient red blood cells or hemoglobin), Cerebrospinal fluid (CSF) buildup in the brain, Brain hemorrhage, Brain inflammation, Inflammation of brain tissue.