Why do the optic nerves swell with increased intracranial pressure?
Idiopathic intracranial hypertension is a disorder of increased in the fluid filled spaces around the brain pressure of unknown cause. The increased pressure takes place in the subarachnoid space, a space between the brain / spinal cord complex and its coverings called the meninges (Figure 1, 2). When a spinal tap is done, the needle is placed in the subarachnoid space to measure the pressure. Well, the eye is an outgrowth of the brain and with this outgrowth, the subarachnoid space continues right up to the optic nerve head (optic disc, papilla) in the back of the eyeball. When the pressure increases in this space, fibers in the optic nerve are compressed. This makes it harder for the neurons to transport their proteins and organelles so there is a decrease or slow down in flow in optic nerve fibers. This buildup is seen as swelling or edema of the optic nerve head or papilla, hence the term papilledema. A more extensive discussion can be found here .
