Expansion
Down and out, lid's dropping, pupil's blown
Mnemonic
“Down and out, droopy and dilated”:
- Down and out eye, from unopposed lateral rectus (VI) and superior oblique (IV)
- Droopy, a complete ptosis from loss of levator palpebrae superioris
- Dilated pupil, if the parasympathetic fibres are involved
The pupil is the whole diagnosis. The parasympathetic fibres run on the outside of the nerve, so:
- Pupil involved (dilated) means compression: a posterior communicating artery aneurysm, uncal herniation or tumour. This is a surgical emergency
- Pupil spared means ischaemia of the core through the vasa vasorum: diabetes, hypertension, giant cell arteritis
“Compression from the outside in, ischaemia from the inside out.”
Expansion
- Down and out eye position - unopposed lateral rectus and superior oblique
- Ptosis - loss of levator palpebrae superioris
- Dilated unreactive pupil - loss of parasympathetic fibres to the sphincter pupillae