In this condition, the function of the facial (seventh cranial) nerve is impaired. This nerve supplies the muscles of facial expression, and so there is reduced or absent facial movement on the side of the problem.
The main features in the eye are:
1. Lower eyelid ectropion. The orbicularis muscle tension helps keep the eyelid against the eye, and when this tension goes, the eyelid becomes more floppy and can stand away from the eye.
2. Epiphora, or watering of the eye. This occurs because the opening to the tear duct in the lower eyelid is carried out of position by the ectropion, and also because of loss of the 'lacrimal pump' - the effect that blinking has on the drainage of tears.
3. Incomplete closure of the eye on blinking, and failure of the eye to close during sleep.
4. Exposure keratopathy. The eyelids normally act like windscreen wipers on the surface of eye, and carry tears over the eye in a smoothed - out layer. When the eye loses its blink, it dries out in little patches. It then becomes red and painful, and may become infected.
Treatment can be considered in two categories:
1. If nerve function is likely to be restored, then all that is necessary is protection of the cornea.
This might involve drops, ointment, a bandage contact lens, taping or gel protection of the eye's surface, and could involve temporary closure of the eyelid with surgery or Botox.
2. If nerve function is permanently lost, then definitive surgical procedures are necessary.
A brow lift is used to raise the brow, which has fallen due to paralysis of the frontalis muscle.
Upper lid lowering may need to be carried out; the height of the upper eyelid is the result of a balance between the action of the levator muscle, which lifts the eyelid, and the orbicularis muscle, which closes it. When the orbicularis muscle is paralysed, the levator muscle action is unopposed, and the lid rises. When the eyelid rests in a high position, producing a staring appearance, it can be lowered by lengthening the levator muscle.
When the resting position of the eyelid is OK, but the blink is poor, upper lid gold weights can be implanted to produce a gravity - assisted blink.
Medial or lateral tarsorrhaphy may be necessary to reduce the area of the eye which is exposed to the environment. Often this is enough to address the ectropion, but occasionally a fascial sling is necessary, in which the fascia lata from the thigh is used to build up the lower eyelid.
John Pitts is an oculoplastic surgeon in full-time private practice in London and Barbados following a substantive NHS consultant position. He graduated MB ChB from Glasgow University in 1983 and, in 1987, after working in pathology and neurology, he trained in ophthalmology in Glasgow, Nottingham and London. He has travelled extensively, working in centres of excellence in Los Angeles, New Orleans, Melbourne, Barbados, Brunei and Vancouver. He has undertaken Fellowship training in oculoplastics at Moorfields Eye Hospital.
