Optic Neuritis: The Daily PANCE Blueprint

The answer is B. Optic neuritis

Subacute monocular vision loss with pain on eye movement, red desaturation, and a relative afferent pupillary defect in a young woman is optic neuritis — demyelinating inflammation of the optic nerve. The classic teaching phrase captures the exam finding perfectly: “the patient sees nothing and the doctor sees nothing” — two-thirds are retrobulbar, so the disc looks completely normal even though vision is badly impaired. The APD is the objective sign that the lesion is in the nerve rather than the media or retina. Now the traps, and they are all about how the other causes of vision loss feel: acute angle-closure glaucoma is a painful red eye with a hazy cornea, a fixed mid-dilated pupil, halos, nausea, and a rock-hard globe; central retinal artery occlusion is painless, sudden, and complete, with a pale retina and a “cherry-red spot”; papilledema is bilateral disc swelling from raised intracranial pressure and typically spares acuity early, giving transient obscurations rather than steady loss; and amaurosis fugax is painless, transient — a “curtain” lasting minutes — and points to carotid embolism. Management is MRI of the brain and orbits with gadolinium, both to support the diagnosis and to look for demyelinating lesions, because optic neuritis is frequently the first presentation of multiple sclerosis. Treat significant vision loss with IV methylprednisolone, which speeds recovery; most patients recover well over weeks. Oral prednisone alone is contraindicated — it raises the rate of recurrence.