AN31.1-5 | Orbit — Summary & Reflection

REFLECT

A patient presents with diplopia specifically when descending stairs. You notice he tilts his head to the left. Which nerve palsy would you suspect, and on which side? Trace the pathway of that nerve from its nucleus to the affected muscle.

KEY TAKEAWAYS

Orbit — Key Points

• Extraocular muscles: 4 recti (annulus of Zinn) + 2 obliques. LR6 SO4 rest 3.
• CN III palsy: down and out, complete ptosis, dilated pupil — surgical emergency if new.
• CN IV palsy: head tilt, diplopia on downward gaze, superior oblique affected.
• CN VI palsy: esotropia, diplopia on lateral gaze, lateral rectus paralysed.
• Horner's syndrome: ptosis (partial), miosis, anhidrosis — 3-neuron sympathetic arc interrupted.
• Ophthalmic artery: branch of ICA; central artery of retina occlusion = sudden blindness.
• Superior ophthalmic vein: drains to cavernous sinus (no valves — explains cavernous sinus thrombosis from "danger triangle" infections).
• Lacrimal drainage: puncta → canaliculi → lacrimal sac → nasolacrimal duct → inferior meatus.
• Lacrimal secretion: CN VII → greater petrosal nerve → pterygopalatine ganglion → lacrimal gland.