SYMPTOM

Third eyelid showing across the eye

Owners notice a pale pink or pigmented membrane creeping in from the inner corner of one or both eyes, sometimes covering a significant portion of the eye's surface, occasionally alongside squinting, discharge, or a generally withdrawn demeanour.

Idiopathic (haws syndrome)

In many cases, both third eyelids elevate without any identifiable eye disease, a pattern seen mostly in young cats (aged 2 months to 3 years in one published series of 10 cats). Diarrhoea was present in 4 of those 10 cats, and the others were otherwise well.

Gastrointestinal Disturbance

Diarrhoea or other gut upset has a recognised association with bilateral third eyelid elevation. Giardia has been found in the faeces of some affected cats, but a causal role has not been shown. This is thought to relate to altered autonomic nervous system signalling rather than any problem within the eye itself.

Ocular Surface Disease

Conjunctivitis, corneal ulceration, or other surface irritation of the eye can cause reflexive protrusion of the third eyelid as a protective response. This is typically confined to the affected eye and often accompanied by discharge or squinting. A deep or melting corneal ulcer can soften the cornea rapidly and may perforate it, and its depth cannot be judged by looking at the eye at home.

Intraocular Inflammation

Inflammation within the eye itself, such as uveitis, can trigger pain-related elevation of the third eyelid. This usually appears alongside a smaller pupil, redness, squinting or cloudiness of the eye. Uveitis can lead to glaucoma or blindness, and in cats it is often linked to wider illness such as feline infectious peritonitis or lymphoma.

Horner's Syndrome

Disruption of the sympathetic nerve supply to the eye, which can arise from middle ear disease, trauma, or a lesion along the nerve pathway, produces third eyelid elevation confined to one eye. This is typically alongside a smaller pupil and a slightly sunken appearance.

Systemic Illness or Dehydration

Reduced fat and fluid volume behind the eye, associated with dehydration or significant weight loss from chronic systemic disease, can cause the eye to sit slightly further back in the socket. This allows the third eyelid to passively rise.

Why timing matters

Early observation

Third eyelids that rise in both eyes and settle over several weeks, especially alongside a short bout of loose stool, fit the self-limiting idiopathic bilateral form. In one published series of 10 cats, signs settled in nine of them in an average of about five weeks (range 12 to 95 days), and came back months later in three. An early presentation confined to both eyes equally, without pain or discharge, generally carries a different context to one affecting a single eye from the outset.

Later presentation

Protrusion that persists beyond about three months, or that is confined to one eye throughout, points away from the typical idiopathic pattern and towards a more localised or ongoing underlying process. The longer a one-sided presentation continues without change, the more it supports a discrete, identifiable cause rather than a generalised, self-resolving one.

Whether the sign affects one eye or both, and whether it is static, intermittent, or gradually worsening, helps separate the generally self-resolving bilateral pattern from a one-sided neurological or ocular process that may need its own characterisation. A shift from bilateral to unilateral, or the appearance of discharge or squinting partway through, would suggest the picture is evolving rather than settling.

Conditions commonly associated

Horner's Syndrome

Disruption of the sympathetic nerve supply to the eye produces one-sided third eyelid elevation, typically alongside a smaller pupil on the affected side.

Conjunctivitis

Inflammation of the ocular surface commonly triggers reflexive third eyelid protrusion, usually confined to the affected eye.

Corneal Ulcers

Pain from a corneal defect can cause protective elevation of the third eyelid over the affected eye, often with squinting or discharge.

The page on this condition is being checked again and is offline for now.

Uveitis

Inflammation within the eye can produce pain-related third eyelid elevation alongside changes in pupil size or eye clarity.

Gastroenteritis in Cats

Gastrointestinal upset has a recognised association with bilateral third eyelid elevation, thought to relate to autonomic nervous system changes.

Feline Herpesvirus (FHV-1)

This common cause of feline conjunctivitis can produce ocular surface irritation and secondary third eyelid protrusion.

Giardiasis

In one published series of cats with bilateral third eyelid elevation, Giardia was found in the faeces of 4 of 9 cats tested, though a causal role has not been shown.

Entropion

Entropion can lead to a prominent third eyelid when the inward-rolling eyelid causes pain and irritation to the cornea, prompting the eye to mount a protective response. The third eyelid may appear alongside squinting, tearing, or visible inflammation as the eye reacts to the ongoing friction.

Glaucoma

Glaucoma may produce a visible third eyelid as a consequence of the pain and pressure inside the eye, which can trigger a protective reflex. This can appear alongside other signs such as a dilated pupil, cloudiness of the cornea, redness, or a visibly enlarged eye.

Otitis Media

Infection of the middle ear can damage the sympathetic nerve supply to the eye that runs close to it, producing Horner's syndrome with a raised third eyelid and a smaller pupil on that side.

When to explore further

Third eyelid protrusion affecting only one eye, particularly alongside a smaller pupil or a slightly sunken appearance on that side, points towards Horner's syndrome, or towards uveitis, which also narrows the pupil and raises the third eyelid, rather than a gastrointestinal cause. Telling the two apart needs an eye examination.

Protrusion accompanied by visible discomfort, discharge, redness, or holding the eye partially closed suggests surface or intraocular involvement rather than the idiopathic bilateral pattern. A corneal ulcer, uveitis or glaucoma can cost sight, and ulcer depth or the pressure inside the eye cannot be judged at home, so this picture does not suit a wait-and-see approach.

Bilateral protrusion in a young cat that is otherwise bright and eating, with or without diarrhoea, fits a recognised pattern that usually resolves over several weeks. Reduced appetite, vomiting, lethargy or dilated pupils are not part of that pattern and point towards systemic illness or dehydration instead.

Protrusion appearing gradually alongside weight loss or reduced water intake in an older cat may reflect a systemic or dehydration-related contribution rather than a primary eye problem.

A sudden appearance following any head trauma or recent ear disease is a scenario where the timing adds useful context, given the association between middle ear pathology and one-sided third eyelid elevation.

A photograph taken directly from the front of the face in even lighting, showing both eyes together, is one of the most useful pieces of documentation, as it allows comparison of pupil size and symmetry between the two sides. Noting whether one eye or both are affected, how long the protrusion has persisted, and any accompanying stool changes, discharge, or appetite shift adds further context. For the painless pattern affecting both eyes, repeating the photograph every few days can help establish whether it is stable, resolving, or progressing. A photograph cannot show the depth of an ulcer or the pressure inside the eye, so it does not stand in for an examination when one eye is squinting, red or cloudy.

Last reviewed: 10 October 2026 · Dr Alastair Greenway MRCVS