Eye movement and associated palsies

All muscles innervated by CN 3 (occulomotor) with the exception of. 

SO= CN 4 (trochlear)

LR = CN6  (Abducens)

Therefore:

3rd nerve palsy à eye looks down and out. *

4th nerve palsy à Pt will have diplopia which is maximal when looking downwards and inwards (action of SO).

6th nerve palsy à Most common isolated palsy. Eye deviated medially and diplopia maximal on lateral gaze.

* Third nerve also carries parasympathetic fibres around the outside. Therefore damage causes a fixed dilated pupil. A third nerve palsy with pupillary sparing is often termed a medical third palsy and often has an ischaemic or diabetic aetiology. Surgical third nerve palsies include tumours or PCA aneurysms.