Lagophthalmos: when the eyelids do not close fully

Most people close their eyes without ever thinking about it, hundreds of times an hour, and never notice the work it does. Lagophthalmos is the medical name for what happens when that closure stops being complete: the eyelids meet, but a gap remains, and the eye underneath is left partly open when it should not be. I see this from several different directions in clinic, as one strand of the wider range of eyelid problems that change how the eyes look and function, and this page is the overview I wish every patient had before their first appointment, because the causes are different but the eye's problem is always the same one.

What is lagophthalmos, and why does it happen?

Lagophthalmos means an eyelid that cannot close fully over the eye, whether the person is awake and trying to blink or asleep and not trying at all. The word comes from Greek for hare's eye, because hares were once thought to sleep with their eyes open. Closing an eyelid needs two things working together: a muscle strong enough to pull it shut, the orbicularis oculi, and a lid margin and surrounding tissue loose enough to actually meet its partner. When either fails, whatever the underlying reason, the result looks the same from the outside, a visible gap at the lid margin, even though the causes behind it are quite different medically.

What actually causes an eyelid not to close?

The commonest cause I see is a weak facial nerve, which controls the orbicularis oculi directly. Bell's palsy is the most familiar example, a sudden one-sided facial weakness that I cover in detail, including the eye protection routine that matters from day one, in a separate article on Bell's palsy and the eye. Other causes of facial nerve weakness, from surgery near the ear to a tumour pressing on the nerve, produce the same eyelid problem by the same mechanism.

A different mechanism sits behind thyroid eye disease. Here the eyelid muscles themselves are not weak; the lid is pulled upward by retraction, or the eye is pushed forward by swollen tissue behind it, so the lid simply cannot travel far enough to cover an eye that has moved. I set out that mechanism, and what it means for the cornea specifically, in a dedicated article on thyroid eye disease and eyes that will not close. A third group follows eyelid surgery, when a lid is tightened, shortened or has skin removed more than the tissue can comfortably allow, leaving it unable to reach as far as it used to. Scarring from an old injury, a burn, or a skin condition can pull the lid margin away from the eye in the same way, a pattern called cicatricial lagophthalmos, which overlaps in places with the outward-turning lower lid I cover separately as ectropion, since a lid that has drifted away from the eye contributes to the same exposure problem. Then there is a gentler, extremely common version that has nothing wrong with the nerve or the lid at all: some people simply do not close their eyelids completely during sleep, a pattern called nocturnal lagophthalmos, present in a meaningful minority of otherwise healthy adults and usually harmless precisely because sleep, unlike illness or surgery, tends to be short enough and the tear film resilient enough to cope.

Why does an eyelid gap matter so much for the eye underneath?

Every blink does two jobs at once: it spreads a fresh layer of tears across the cornea, the clear window at the front of the eye, and it protects that surface from the drying effect of the air. Take blinking away, even partially, and the cornea starts to dry, particularly along its lower third where evaporation is fastest. Mild exposure feels like grittiness or a mild ache, often worst on waking if the gap is mainly at night. Left unaddressed, dryness can progress to fine punctate erosions of the surface layer, then to a true epithelial defect, a patch where the surface cells are simply gone, and an open defect is vulnerable to infection and, in severe or neglected cases, to scarring that can affect vision permanently. This whole process is called exposure keratopathy, and it is the reason a seemingly cosmetic complaint, an eye that does not quite shut, is something I take seriously rather than something to watch and wait on indefinitely.

Most people also carry a natural safeguard without knowing it: Bell's phenomenon, a reflex that rolls the eyeball upward and out of view as the lid begins to close, tucking the cornea behind the upper lid even when the gap does not fully shut. Where this reflex is strong, a modest lagophthalmos may cause surprisingly little trouble. Where it is weak or absent, the same millimetre of gap carries real risk, which is one reason I never judge severity from the size of the gap alone.

What does an oculoplastic surgeon actually check?

An assessment for lagophthalmos is not one measurement but several, looked at together. I ask the patient to close their eyes gently, as if falling asleep, and again to squeeze them shut, because the gap on a gentle attempt is usually the one that matters overnight. I check how far the eyeball rolls up with that reflex, whether the orbicularis is weak, retracted, or scarred, and whether the lower lid sits snugly against the eye or has started to sag away from it, since a lax lower lid worsens any degree of upper lid lagophthalmos. On the eye itself, I look at the tear film and examine the corneal surface with a dye that stains any dry or damaged patch, which tells me far more about actual risk than the width of the gap does. Where the cause is not obvious, working out whether the nerve, the thyroid, scarring, or previous surgery is responsible changes the whole management plan, which is why this is an assessment worth having rather than a problem to self-diagnose from a mirror.

How is the eye protected while the underlying cause is addressed?

Whatever the cause, the first-line protection is broadly the same, and it needs doing consistently rather than cleverly. Preservative-free artificial tears through the day keep the surface wet between blinks, and a noticeably thicker lubricating ointment at bedtime holds that protection over the many hours of sleep when nobody is managing it consciously. Taping the eyelid gently closed at night, or using a moisture chamber that seals a humid pocket of air over the eye, adds meaningful protection for the same reason: sleep is usually the highest-risk period, because the gap is present for hours with no blink to interrupt it and the room air is still. This lubrication routine is a holding strategy rather than a fix for whatever caused the gap in the first place, and how long it needs to continue depends entirely on that underlying cause, whether that means waiting for a facial nerve to recover, controlling thyroid eye disease activity, or accepting that a scar will need its own treatment. A dry, gritty eye that persists even after the underlying cause has settled is worth its own conversation, which I address in a separate article on dry eye after eyelid surgery.

What can surgery do when lubrication is not enough?

Some cases need more than drops and tape, generally when exposure is severe, the cornea already shows damage on examination, or the underlying cause is not expected to resolve on its own. An oculoplastic surgeon may consider a small weight, usually gold or platinum, implanted discreetly in the upper lid so that gravity assists closure with each blink attempt, an option most often used for facial nerve palsy. Tightening or repositioning procedures can help where the lower lid has become lax or where scarring is pulling the margin away from the eye. A temporary tarsorrhaphy, in which a portion of the upper and lower lid margins is stitched together, narrows the area the tear film has to protect and can usually be reversed once the underlying problem improves. None of these options is offered as a first step, and each carries its own limits; which one, if any, makes sense depends on the cause, the severity of exposure, and how the cornea has already responded to simpler measures, which is why this is discussed individually rather than presented as a standard menu. My eyelid conditions page sets out how each of these lid problems is assessed.

When does this need urgent attention rather than a routine appointment?

Sudden weakness on one side of the face is a medical emergency until proven otherwise, because it can be the first sign of a stroke rather than Bell's palsy, and it needs emergency assessment straight away rather than a wait-and-see approach at home. Separately, if an eye that is not closing properly becomes increasingly painful, red, or sensitive to light, or if vision changes at all, that eye needs same-day review, since these can be signs that exposure has already progressed to a genuine corneal problem rather than simple dryness. Between those two emergencies sit the more ordinary but still worthwhile reasons to be seen, a lid that has never closed properly since an old operation, a facial weakness that has not improved as expected, or eyes that feel gritty every single morning. None of these needs to wait for a crisis, and early assessment is usually what keeps this a manageable, well-protected problem rather than one that has already reached the cornea.