After facial palsy: the eye that blinks when you smile, crocodile tears and long-term lid care

After facial palsy, the eye can narrow when you smile or chew and water when you eat, because nerve fibres that regrow sometimes reach the wrong muscle or gland. The first problem is called synkinesis and the second crocodile tears. Both come from the nerve regrowing, not from a new injury, and both can be treated. The acute stage, when the eye will not close, is in my article on Bell's palsy and the eye. This one is about the months and years afterwards.

Why does my eye narrow or close when I smile after facial palsy?

Because damaged facial nerve fibres can regrow into the wrong muscles, so a signal meant for the mouth also reaches the muscle that closes the eye. This is oculo-oral synkinesis, synkinesis being the medical name for movements that happen together when only one was intended. An international review describes the most common complaint as unintentional eye narrowing or closure during voluntary mouth movements such as smiling, kissing or blowing, or the reverse: the cheek and mouth pulling when you close the eye.

The same review sets out how it happens. Synkinesis needs actual damage to nerve fibres (axons), not just a temporary blockage of conduction, so many people with Bell's palsy never develop it. After damage, each fibre sends out several sprouts that regrow at random into different branches of the nerve, and one fibre can end up supplying two muscles. Other contributors have been proposed, including over-excitable nerve cells in the brainstem, nerve fibres that cross-excite one another, and reorganisation in the brain, but misguided regrowth is the most widely accepted mechanism.

The numbers are worth knowing. After standard corticosteroid treatment of idiopathic palsy, about 70 to 90% recover within 12 months and about 10 to 30% develop synkinesis. The rate is higher, about 40%, when axon injury is proven, and about 6.6% develop moderate to severe synkinesis. It also takes time to declare itself: the review notes that the final pattern is not reached until 12 to 15 months after onset, which is why grading is left until then. EyeWiki adds that hemifacial spasm, involuntary contraction of one side of the face, can also occur as part of the picture after palsy, and the article on hemifacial spasm explains it.

Why does my eye water when I eat, and what are crocodile tears?

Crocodile tears, medically gustatory hyperlacrimation, is watering of the eye while eating, caused by nerve fibres that respond to eating regrowing into the tear-making gland (the lacrimal gland) instead of their original target. The international review describes it as a rare symptom of misdirected reinnervation, reached through a branch called the greater superficial petrosal nerve. It can be shown by a modified Schirmer test, in which a strip of paper measures tear production while the person eats.

Not every watering eye after palsy is this. EyeWiki, the American Academy of Ophthalmology's reference, notes that tearing after facial palsy can come from synkinesis or from inadequate tear drainage, and it lists a sagging lower lid (ectropion) and a weak blink among the findings to check. Watering all day, not only at meals, points away from crocodile tears. The NHS also lists a constantly watering eye among the symptoms that can remain when weakness does not fully recover. The ectropion article and the guide to blocked tear ducts explain the drainage side.

What helps synkinesis: facial retraining or botulinum toxin?

Usually both, in that order. The international review recommends facial training, mainly biofeedback retraining, as first-line treatment, then botulinum toxin, with surgery reserved for individual cases that are not helped enough. The evidence behind each step differs, and it is better to know how firm it is.

For training, a Cochrane review of physical therapy for Bell's palsy included 12 studies and 872 participants and concluded there was no high quality evidence of significant benefit or harm. It found low quality evidence that tailored facial exercises help function, mainly in moderate and chronic cases: one study of 34 participants improved by 20.4 points on a 0 to 100 disability scale, and in a study of 145 people with acute palsy fewer developed synkinesis with exercise (risk ratio 0.24). A 2022 update added seven randomised trials, and the four rated high quality all reported benefit, although differences in design prevented pooling. The international review adds that there is no standard international protocol for facial training.

Botulinum toxin type A works the other way, by weakening the overactive muscles. In a double-blind, placebo-controlled trial of 30 patients, with six more in an open-label pilot, injections suppressed involuntary eyelid closure with smiling, chewing and puckering, and improved scores for quality of life, social interaction and appearance. A systematic review of 34 studies and 1,314 patients found a mean improvement of 11.6 points on the Synkinesis Assessment Questionnaire in the three studies that could be pooled (106 patients). Doses, injection sites and intervals varied so much that no standard protocol could be derived, and its authors conclude treatment is individual. An earlier review found only three randomised studies and described a paucity of data, adding that toxin combined with physical therapy may be particularly helpful.

The effect wears off. The international review advises intervals of not less than four months, and notes that people who no longer want injections every four to six months are the ones who typically ask about surgery, which is irreversible and should not be done before synkinesis has reached its final state.

Can botulinum toxin into the tear gland stop crocodile tears?

It can reduce them, according to small studies, and the international review calls it the off-label therapy of choice, with symptom-free periods of at least six months. Off-label means the medicine is used for a purpose outside its licensed indications. The toxin is injected into the lacrimal gland, which lessens the reflex tearing at meals.

The studies are small and uncontrolled, so these figures are signals, not proof. In four patients given an average of 20 units, tearing during taste stimulation fell, the effect began within 24 to 48 hours and lasted 4 to 5 months, and one person had a mild increase in existing upper lid ptosis. In six patients given 5 units into the gland through the conjunctiva, the Schirmer reading fell from 27.8 mm to 11.6 mm (P=0.002), and two had mild, temporary ptosis. A third series of two patients with crocodile tears found stimulated tearing approaching the unaffected side at 1 and 24 weeks. Because an eye that blinks poorly depends on its tears, the decision belongs with an eye doctor who knows the lid position.

What happens to the eyelids and brow years after facial palsy?

When the nerve does not fully recover, the muscles that hold the lids and brow in place stay weak, so the lower lid can sag away from the eye, the brow can drop, and the upper lid can fail to close fully. EyeWiki lists paralytic ectropion (a lower lid turning outward from laxity), paralytic brow ptosis and lagophthalmos, the medical name for an eye that does not close fully, among the later problems. A drooping brow is a different mechanism from a drooping lid, as the brow and eyelid ptosis article explains.

Procedures are named here so you can recognise them, and which one suits an eye is decided on examination. EyeWiki lists:

• an upper lid gold or platinum weight, typically 1.0 to 1.8 g, covered in the article on lid weights;
• a lateral tarsal strip, which tightens the lower lid at the outer corner, with a spacer graft in more severe cases, or a fascia lata sling;
• a tarsorrhaphy, partly joining the upper and lower lids, for temporary or permanent corneal protection;
• surgical correction of paralytic brow ptosis, and botulinum toxin to improve brow position;
• conjunctivodacryocystorhinostomy with a Jones tube, for tearing from a weak tear pump.

Timing matters. EyeWiki says surgery to protect the cornea is considered when there is limited likelihood of functional improvement in the nerve. Synkinesis adds a trap: the international review warns that overactivity around the eye can falsely suggest the upper lid is working well, advises re-evaluation if a weight was never placed, and notes that lid loading can improve blinking and so lessen the synkinesis effect.

Who looks after what, and when is it urgent?

Several specialties share facial palsy care, and the eye is one part of it. The international review lists ear, nose and throat (head and neck) surgeons, oral and maxillofacial surgeons, plastic and reconstructive surgeons, neurosurgeons, neurologists and facial therapists in speech or physiotherapy. The questions about the eye itself, namely lid position, the cornea, the blink and tearing, are the ones an ophthalmologist examines, and an oculoplastic surgeon is the ophthalmologist who works on the lids, tear system and the socket around the eye. The NHS advises returning to a GP if Bell's palsy is not improving after 3 weeks, and says symptoms should get better within 6 months, though it can take longer.

See an eye doctor promptly for a painful, red or light-sensitive eye, a gritty feeling that does not settle, or any drop in vision. EyeWiki lists redness, burning and a foreign body sensation among the effects of an eye that does not close, and the NHS notes that if you cannot close your eye you may need treatment to prevent damage to your vision. A sudden new droop on one side of the face is different: the NHS says it can be a stroke and to call 999.

Dr Catherine Chow begins consulting at Eagle Eye Centre Malaysia, Petaling Jaya, from early 2027. Until then, a person whose eye waters, narrows, will not close or hurts after facial palsy should be seen by an ophthalmologist. For the closing problem, see the article on lagophthalmos, the eyelids section, and my hub article on why eyes look tired.