Understanding the anatomy and physiology of the eye, the orbit, and the central connections is key to understanding neuro-ophthalmologic emergencies. Anisocoria is an important sign that requires a systematic approach to avoid misdiagnosis of serious conditions, including carotid dissection (miosis) and aneurysmal third nerve palsy (mydriasis). Ptosis may be a sign of either Horner syndrome or third nerve palsy. An explanation should be pursued for diplopia since the differential diagnosis ranges from the trivial to life-threatening causes.