A young woman's eye pain on movement + blurred vision — optic neuritis; MRI checks for MS. Optic neuritis (demyelination — painful eye movements, vision loss, color desaturation, RAPD — relative afferent pupillary defect): IV methylprednisolone hastens recovery; MRI brain — white-matter lesions predict MS (disease-modifying therapy). Papilledema (raised ICP — bilateral disc swelling, headache, vomiting, transient obscurations: tumor, hydrocephalus — neuroimaging urgently; vs papillitis — unilateral, painful). Field defects — chiasmal (bitemporal hemianopia — pituitary), optic tract (homonymous — stroke). The painful eye movement is the clue — movement pain means nerve inflammation.