Third nerve palsy
'Down and out' of the left globe in complete third nerve palsy.
The patient may have complete third nerve palsy with the classical signs or partial palsy with aberrant regeneration.
a. Features of complete third nerve palsy.
The patient has a complete ptosis. The eye under the lid is depressed and abducted (down and out). The pupil is dilated and unreactive to light or accommodation. The fourth nerve and sixth nerve function are intact as
evidenced by the normal intortion and abduction respectively.
Note: intortion can be seen by getting the abducted eye to look down.
- tell the examiner you would like to examine the head for craniotomy scar (operation for berry aneurysm)
- neurological examination of the limbs for contralateral hemiparesis (Weber's syndrome), contralateral coarse involuntary tremor (Benedikt's syndrome) or cerebellar ataxia (Norhnagel's syndrome)
b. Features of partial third nerve palsy:
The affected eye has a partial ptosis. Pupil of the affected side may be larger or the same size as the opposite pupil. Elevation, adduction and depression of the affected side are limited. But abduction and intortion are normal.
- Check for aberrant regeneration especially there is a dilated ipsilateral pupil (suggestive of a compressive lesion)
- This may be one or a combination of the following:
- adduction on attempted upgaze
- constriction of pupil on lateral gaze
- elevation of the upper lid on down gaze
1. Why is the pupil affected in compressive third nerve palsy but not if the cause is infarction?