A 26-year-old woman presents with short episodes of “greying” of her vision in both eyes. These episodes are painless, last for a few seconds, and typically occur with changes in position. Between episodes, her vision feels normal. She has also experienced daily headaches for the past three months. Her past medical history is significant for a body mass index of 37 kg/m². She has not taken any medications recently. Her past ocular history is significant only for myopia. On examination, her visual acuity is 20/20 in both eyes. She does not have a relative afferent pupillary defect, and she has no dyschromatopsia on formal colour vision testing. The anterior segment examination is within normal limits; there is no evidence of anterior chamber or vitreous cells. Fundus examination revealed bilateral optic disc edema with cotton wool spots and peripapillary hemorrhages. A neurologic examination was normal.

Optic disc edema refers to swelling of the nerve fibre layer at the optic nerve head, and can be caused by a variety of pathologic processes. Papilledema is defined as optic disc swelling secondary to raised intracranial pressure. The differential diagnosis of a swollen optic disc is broad and includes common causes such as papilledema, anterior ischemic optic neuropathy, optic neuritis, and pseudopapilledema. Pseudopapilledema is a broad term that refers to situations where there is an elevated appearance of the optic nerve head without edema of the nerve fibre layer (e.g. optic nerve head drusen). Less common causes of a swollen optic disc include central retinal vein occlusion, neuroretinitis, diabetic papillopathy, uveitis, malignant hypertension, optic perineuritis, intrinsic optic disc tumors, Leber’s hereditary optic neuropathy, and optic nerve infiltration.¹ A thorough history, clinical exam, and ancillary testing can help distinguish between these entities.

The retinal nerve fibres converge at the optic nerve head and travel through the lamina cribosa to form the optic nerve. The lamina cribosa is a circular opening within the posterior sclera that functions as a pressure barrier between the intraocular space and the retrobulbar space. Raised intracranial pressure is transmitted to the optic nerve sheath and results in axoplasmic stasis within the optic nerve. The obstruction of flow of intra-axonal fluids results in edema of the axons and leakage of water, protein and other cellular contents, resulting in an edematous optic nerve head. The axoplasmic stasis and edema can subsequently result in venous obstruction and dilation, nerve fibre ischemia, and vascular telangiectasias.