Facial nerve has a lot of functions in the face, the most important of which is controlling the facial muscles. Injury of the facial nerve causes paralysis of these muscles. The facial muscles can be divided to several groups according to the function of each muscle. Some of them are controlling eye movements, others are controlling the lips movements (The most important of which is smiling) and other muscles have a role in forehead movements.
Generally speaking, the facial movements depend on the existence of an intact facial nerve and well functioning facial muscles. In case any of them are injured, the facial movements will be affected either partially or completely according to the degree and site of injury.
Manifestations of facial paralysis:
The eye:
Facial paralysis leads to inability to close the eyelids. This leaves the eye unprotected and exposed for a long duration which leads to eye dryness and recurrent attacks of inflammations. Several attacks of inflammations and infections will eventually affects the vision which may be lost completely.
The upper and lower lips:
Facial paralysis leads to loss of movements of the upper, lower lips and the mouth. Deviation of the mouth to the unaffected side is evident and inability to smile is severely distressing.