Idiopathic Intracranial Hypertension
Michael Wall, M.D.
The University of Iowa
Department of Neurology and
Department of Ophthalmology and Visual Sciences
What is the relationship between optic nerve swelling and visual loss?
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 .
What is the danger of papilledema to vision?
When the optic nerve fibers are under pressure, their microcirculation or blood supply is also under pressure. This results in decreased blood flow to the optic nerve, damage to the nerve and resultant visual loss. Since all the optic nerve fibers are under pressure, a visual field examination is necessary to determine whether visual loss is taking place so that the appropriate treatment can be started.
Can vision loss be reversed?
Fortunately, visual loss can be reversed. However, much depends on how long the visual loss has been present. In some cases, full recovery takes place and in others partial recovery. Most patients with visual loss have some recovery with treatment .
What are the earliest signs of permanent vision loss?
The most common early sign of visual loss is inferior nasal loss found with visual field testing. However, other types of visual loss can occur. What is important is that it is rare for early visual loss to involve the central area of vision. And, early peripheral visual loss is seldom recognized by the patient. This is yet another reason why perimetry is very necessary in the evaluation and management of patients with idiopathic intracranial hypertension.