Normal adult lumbar CSF pressure is 6–18 cmH2O. A patient with idiopathic intracranial hypertension (IIH) has a CSF pressure of 30 cmH2O. Which of the following correctly explains how elevated ICP manifests as papilledema?

• A Elevated ICP increases aqueous humor production in the eye, causing optic disc swelling
• B Elevated CSF pressure is transmitted along the optic nerve sheath into the periorbital space, obstructing axoplasmic flow at the optic disc and causing disc edema ✓
• C High ICP compresses the ophthalmic artery, reducing retinal blood supply and causing ischemic disc swelling
• D Elevated ICP directly distorts the cribriform plate, pushing the optic nerve anteriorly to create papilledema

Explanation

The subarachnoid space of the optic nerve sheath is continuous with the intracranial subarachnoid space; elevated ICP is transmitted directly along this sheath. The increased pressure around the optic nerve at the lamina cribrosa obstructs orthograde axoplasmic transport (carrying mitochondria, proteins from RGC soma to axon terminals). Stasis of axoplasm causes axonal swelling at the optic disc (papilledema). This is why papilledema is bilateral (both optic sheaths are involved) and why optic nerve sheath fenestration relieves papilledema without affecting ICP.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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Written and medically reviewed by the StethoPrep medical team.