Third nerve palsy

 A patient with left third nerve palsy
A patient with a left aberrant third nerve regeneration.
Note left upper lid elevation on downgaze.

Third nerve palsy has been mentioned in ptosis (refer to ptosis section for questions). Here we will look at the features 
of ocular motility in third nerve palsy.

In complete third nerve palsy, the patient will have complete ptosis. The eye appears as down and out when the lid 
is elevated. In isolated third nerve palsy, the functions of the fourth and sixth nerves can be demonstrated by normal 
intortion and abduction respectively. Note: intortion can be seen by getting the patient to look down. If this is not 
obvious you may want to examine the patient on the slit-lamp and observe movement of a landmark such as a superior 
conjunctival blood vessel for intact intortion.

Aberrant regeneration of the third nerve is seen only in compressive lesion and never in medical cause of third nerve 
palsy. The physical signs are the results of misdirection of the third nerve fibres. The commonest ones being :

a. Lid-gaze dyskinesis: the most common one being upper lid elevation on down-gaze (see picture above). 
    Less commonly there is lid elevation on adduction
b. Pupil-gaze dyskinesis: the pupil constricts on down-gaze or adduction.

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