Facial palsy is paralysis of part of the face caused by non-functioning of the facial nerve that controls the muscles, especially around the eye and to the mouth. The facial nerve is also called the seventh cranial nerve.
It has a complex course from the brain stem to reach the muscles governing facial expression. It controls the muscles that lift the eyebrows, the muscles that close the eyelids, the muscles of the cheek and around the mouth.
Facial palsy can be congenital — present at birth or shortly after — or acquired, possibly following a viral illness or through no obvious cause. Under these circumstances, it is referred to as Bell’s palsy. Sometimes a tumour can compress and damage the nerve. Other causes include serious infections and skull fracture.
Facial paralysis usually affects half the face, which flattens and loses forehead wrinkles and horizontal lines. Other symptoms include a droopy eyebrow, difficulty closing the eye, an inability to whistle and the corner of the mouth being pulled down.
The effects on the eyes are particularly significant. The lower eyelid can sag and turn outward (ectropion), resulting in a watering eye, inability to close the eye and exposure or drying of the cornea. The eye can become red, vision can blur and sight is occasionally affected by ulceration and scarring (exposure keratopathy).
Rarely, patients may suffer a lack of sensation on the surface of the eye (cornea), so that they cannot feel dryness, foreign bodies or injuries to the surface of the eye. This puts them at risk of developing a corneal ulcer and suffering severe damage to their sight.
Crocodile tears are another rare consequence of facial nerve paralysis. They occur when the damaged nerve tries to grow back along its old pathway but goes instead to the tear (lacrimal) gland and to the muscles of the jaw. This results in embarrassing tears when the patients chews.
Other consequences of a nerve regrowing in the wrong direction include closing of the eyelid and muscle spasms in the eyelid, cheek and around the mouth.
