Neuro-Ophthalmology
Core concepts
Understand the afferent and efferent visual pathways. Know the pupil light reflex and the swinging flashlight test for relative afferent pupillary defect (RAPD). Learn the optic neuropathies: ischemic (AION), compressive, toxic/nutritional, and demyelinating (optic neuritis). Understand the classic features of optic neuritis: pain with eye movement, reduced color vision, and a central scotoma, with RAPD. Know the cranial nerve palsies affecting eye movements (III, IV, VI) and their clinical signs: ptosis and a down-and-out eye in CN III palsy, vertical diplopia in CN IV, and horizontal diplopia in CN VI. Understand papilledema and its causes.
Traps
An RAPD indicates an optic nerve or extensive retinal problem, not a simple refractive error. In optic neuritis, the eye may look normal on fundoscopy; the RAPD is the key. Do not miss a CN III palsy with pupil involvement (suggests aneurysm or compression) versus pupil-sparing (often diabetic microvascular). Papilledema is bilateral; unilateral disc swelling is not papilledema.
Rule of thumb
Painful vision loss with a RAPD and normal disc = suspect optic neuritis; painless vision loss with a swollen disc in an older patient = suspect AION. Pupil-involving CN III palsy = urgent imaging.
Worked example
A young woman has unilateral vision loss, pain on eye movement, and a RAPD. The disc is normal. This is optic neuritis; consider MRI for demyelinating disease and refer to neurology.