Expansion
Eye movements, pupils, lids and diplopia together
Expansion
The test: with the head still, follow a target through an H pattern, then convergence, then the pupils. Ask about diplopia at each position and in which direction the images separate furthest.
Muscle supply, by the rhyme LR6 SO4, all the rest are 3:
- VI (abducens): lateral rectus, so abduction
- IV (trochlear): superior oblique, so depression in adduction and intorsion
- III (oculomotor): all the rest, plus levator palpebrae superioris and the parasympathetic supply to the sphincter pupillae and ciliary muscle
The palsies
| Nerve | Eye position | Diplopia | Other |
|---|---|---|---|
| III | Down and out | Worse looking up and in | Ptosis, dilated pupil if surgical |
| IV | Slight elevation, extorsion | Vertical, worse looking down and in, so on stairs | Head tilt away from the lesion |
| VI | Adducted, cannot abduct | Horizontal, worse on looking to that side |
The critical distinction in third nerve palsy
- Surgical (compressive): the parasympathetic fibres run on the outside of the nerve, so they are compressed first. The pupil is dilated and unreactive, and there is often pain. Causes are posterior communicating artery aneurysm, uncal herniation and tumour. It is an emergency
- Medical (ischaemic): the vasa vasorum supply the core, so the pupil is spared. Causes are diabetes, hypertension and giant cell arteritis
Internuclear ophthalmoplegia, from a medial longitudinal fasciculus lesion, gives failure of adduction with nystagmus in the abducting eye, and in a young patient suggests multiple sclerosis.