Neuro-Ophthalmology
Core concepts
Master the afferent and efferent pathways. Know how to localize visual field defects: optic nerve (central scotoma), chiasm (bitemporal hemianopia), optic tract (homonymous hemianopia), and occipital lobe (homonymous hemianopia with macular sparing). Understand optic neuritis (pain with eye movement, relative afferent pupillary defect, decreased color vision) and its association with multiple sclerosis. Know papilledema (bilateral disc swelling from raised intracranial pressure, preserved acuity early) versus papillitis (unilateral, acuity loss). Master pupil abnormalities: Horner syndrome (ptosis, miosis, anhidrosis), Adie tonic pupil, and Argyll Robertson pupil. Know cranial nerve palsies: third nerve palsy with pupil involvement suggests compression (aneurysm), while pupil sparing suggests ischemia.
Traps
Questions test that a relative afferent pupillary defect indicates optic nerve disease, not cataract. Another trap: distinguishing papilledema from pseudopapilledema (drusen). Also know that a third nerve palsy with a dilated pupil is a neurosurgical emergency until proven otherwise.
Worked example / rule of thumb
A patient has sudden diplopia, ptosis, and a dilated pupil. That is a compressive third nerve palsy, possibly from a posterior communicating artery aneurysm. Obtain urgent imaging. Rule of thumb: pupil-involving third nerve palsy equals urgent imaging; pupil-sparing suggests microvascular ischemia.