Haws Syndrome in Cats: Why Both Third Eyelids Are Showing

By Dr Duncan Houston

Seeing a pale membrane suddenly covering part of both of your cat’s eyes can be alarming. It may look as though the eyes are rolling backwards or that your cat is losing their vision.

When both third eyelids appear symmetrically and the eyes are otherwise comfortable and normal, one possible explanation is Haws syndrome, also commonly written as Haw’s syndrome.

True Haws syndrome is usually self-limiting and does not damage the eyes. The important part is confirming that it really is Haws syndrome, because eye pain, Horner syndrome, dehydration and serious neurological disease can also make a cat’s third eyelids visible.

Quick Answer

Haws syndrome causes sudden, usually symmetrical protrusion of both third eyelids in a cat whose eyes are otherwise normal and non-painful. It appears to involve temporary dysfunction of the sympathetic nerves controlling the eyelids and is often, but not always, associated with diarrhoea or another gastrointestinal disturbance.

Most cats recover without specific eye treatment over several weeks. However, a cat with squinting, redness, discharge, cloudy eyes, unequal pupils, severe gastrointestinal illness or other neurological signs needs prompt veterinary assessment rather than being assumed to have Haws syndrome.

What Is Haws Syndrome?

Haws syndrome is a clinical condition characterised by:

• Protrusion of the third eyelid in both eyes

• A mild droop of the upper eyelids, called ptosis, in some cats

• Normal-sized pupils

• No corneal ulcer, conjunctivitis or other obvious eye disease

• Little or no ocular discomfort

• An otherwise healthy appearance in many affected cats

• Possible recent or concurrent diarrhoea

In a 2024 study of 10 cats with acute Haws syndrome, every cat had bilateral third-eyelid protrusion and ptosis. None had the small pupils typically associated with classic Horner syndrome, and no other ocular abnormalities were identified.

Haws syndrome describes a pattern, not simply the observation that a third eyelid is visible. A veterinarian must first exclude other ocular, neurological and systemic causes.

What Is a Cat’s Third Eyelid?

The third eyelid is also called the:

• Nictitating membrane

• Nictitans

• Haw

It normally sits in the inner corner of the eye, close to the nose. It moves across the ocular surface to help distribute tears, remove debris and protect the cornea. It also contains glandular and immune tissue that contributes to ocular-surface health.

A small edge may occasionally be visible when a cat is deeply relaxed. It should not remain prominently extended across the eye while the cat is fully awake and alert.

What Does Haws Syndrome Look Like?

The typical appearance is:

• A pale pink, white, grey or naturally pigmented membrane extending from the inner corner of each eye

• A similar degree of protrusion in both eyes

• Both pupils remaining approximately equal in size

• Clear corneas

• No marked eye redness

• No significant discharge

• No repeated squinting

• No pawing or rubbing at the eyes

• No obvious loss of vision

• Possible mild drooping of both upper eyelids

The amount of protrusion may change during the day. One moment the membrane may cover only the inner quarter of the eye, while later it may extend almost halfway across it.

The third eyelids can partly obstruct your cat’s field of view when significantly elevated, but true Haws syndrome does not directly damage the retina, lens or cornea. Published cases were defined by the absence of other ocular abnormalities.

Is Haws Syndrome Painful?

True Haws syndrome is not expected to cause significant eye pain.

A cat with uncomplicated Haws syndrome should not be:

• Holding the eyes tightly closed

• Repeatedly squinting

• Avoiding light

• Pawing at the face

• Producing thick eye discharge

• Showing marked eye redness

• Reacting painfully when the area around the eye is approached

These signs suggest that another ocular condition may be present.

What matters most here is comfort. A visible third eyelid in a comfortable cat is very different from a visible third eyelid in a cat with a cloudy, red or tightly closed eye.

How Worried Should You Be?

Risk level	What it may look like	What to do
Lower immediate risk	Both third eyelids are equally visible, pupils look equal, eyes remain open and clear, and the cat is bright and eating	Arrange a routine veterinary examination, particularly if the change persists beyond 24 hours
Moderate concern	Bilateral protrusion with diarrhoea, vomiting, reduced appetite, weight loss or signs lasting more than several days	Book a veterinary examination within the next one to three days
High concern	One eye is affected more than the other, or there is squinting, redness, discharge, cloudiness, an abnormal pupil or significant lethargy	Seek same-day veterinary care
Critical	Sudden blindness, severe eye trauma, a bulging eye, collapse, seizures, difficulty swallowing, urinary retention or profound weakness	Go to an emergency veterinary hospital immediately

Haws syndrome itself is usually low risk. The danger comes from incorrectly labelling a painful eye, neurological disease or severe systemic illness as Haws syndrome.

What Causes Haws Syndrome?

The exact cause remains uncertain.

The strongest current evidence suggests that Haws syndrome involves temporary dysfunction of the sympathetic nerve supply responsible for maintaining normal upper-eyelid and third-eyelid position.

In the 2024 case series, topical adrenergic medication temporarily returned the eyelids to their normal position in every cat. This response supported the conclusion that Haws syndrome is a sympathetic neuropathy.

What triggers that neuropathy is less clear.

Why Is Haws Syndrome Associated With Diarrhoea?

Haws syndrome has long been associated with:

• Acute diarrhoea

• Soft stools

• Gastrointestinal parasites

• Infectious enteritis

• Gastrointestinal inflammation

• Changes in the intestinal microbiome

The proposed connection involves the gut-brain axis, the two-way communication network linking the gastrointestinal tract, immune system and nervous system.

One theory is that intestinal infection or microbiome disruption temporarily alters autonomic nerve function, allowing both third eyelids to protrude. This remains a plausible hypothesis rather than a proven mechanism.

Diarrhoea is not present in every affected cat. In the 2024 study, only four of 10 cats had diarrhoea, while the remaining cats were otherwise systemically healthy.

Are Parasites Responsible?

Parasites may be involved in some cases, but they do not explain every case of Haws syndrome.

In the 2024 study:

• Four of nine tested cats had a positive Giardia test

• Four of 10 cats had diarrhoea

• Some cats had Haws syndrome without gastrointestinal signs

• The study was too small to establish Giardia as the cause

A separate 2026 case series found Giardia-positive faecal tests in four of five cats with Haws syndrome. Again, this association does not prove that Giardia caused the eye signs, particularly because Haws syndrome often resolves spontaneously.

A faecal test is therefore reasonable when diarrhoea is present, particularly in:

• Kittens

• Recently adopted cats

• Cats from shelters or multi-cat homes

• Cats with outdoor access

• Cats with recurring gastrointestinal signs

• Cats with incomplete parasite prevention

It is more useful to identify and treat the actual gastrointestinal problem than to assume that every affected cat simply needs a random worming product.

Could a Virus Cause Haws Syndrome?

A gastrointestinal virus has also been proposed as a possible trigger.

A 1990 study compared 50 cats with protruding third eyelids and diarrhoea with cats that had diarrhoea alone and healthy controls. A novel torovirus-like agent was isolated from 11 cats, including seven cats with both third-eyelid protrusion and diarrhoea.

This historical finding supported the possibility of an infectious gastrointestinal trigger, but it did not establish one universal viral cause.

More recent research suggests that several different gastrointestinal pathogens or changes in the intestinal microbiome may be capable of triggering a similar neurological response.

Is Haws Syndrome Contagious?

The third-eyelid protrusion itself is not known to spread directly between cats.

However, the gastrointestinal condition triggering it may be transmissible.

In the 2024 study, a newly adopted kitten developed Haws syndrome and diarrhoea. The three resident cats in the same household developed Haws syndrome within four to 11 days. This cluster raised suspicion that an infectious gastrointestinal trigger may have spread through the household.

When more than one cat develops diarrhoea or third-eyelid protrusion:

• Use separate food and water bowls where practical

• Clean litter trays frequently

• Remove faeces promptly

• Wash hands after cleaning litter

• Avoid sharing contaminated bedding

• Ask your veterinarian whether faecal testing is appropriate

• Monitor every cat’s appetite, weight and stool quality

Do not assume the eyes themselves are infectious. The potential concern is the underlying gastrointestinal agent.

Which Cats Are Most Commonly Affected?

Published reports commonly involve kittens and young adult cats.

The 10 cats in the 2024 study ranged from two to 36 months old, with an average age of approximately 18 months.

However, this does not mean an older cat cannot develop the condition.

Age should influence suspicion, not replace examination. A senior cat with newly visible third eyelids, weight loss and reduced appetite deserves a broader medical investigation rather than an automatic Haws diagnosis.

What Else Can Cause Both Third Eyelids to Show?

Several conditions can imitate Haws syndrome.

Horner Syndrome

Horner syndrome develops when the sympathetic nerve pathway to an eye is disrupted.

Typical signs include:

• A smaller pupil, called miosis

• Drooping of the upper eyelid

• The eyeball sitting slightly deeper within the socket

• Protrusion of the third eyelid

Horner syndrome is most commonly unilateral, although bilateral disease is possible. Causes may include middle-ear disease, trauma, neck or chest lesions, surgery and other neurological disorders.

The most useful visible distinction is the pupil:

• Haws syndrome: pupils generally remain normal and equal

• Horner syndrome: the affected pupil is usually abnormally small

A subtle pupil difference can be difficult to assess at home, particularly under uneven lighting.

Painful Eye Disease

Eye pain can cause the globe to retract slightly, allowing the third eyelid to move across the cornea.

Possible causes include:

• Corneal ulceration

• Foreign material

• Uveitis

• Glaucoma

• Eye trauma

• Severe conjunctivitis

• Eyelid disease

Painful corneal disease and uveitis may also produce an abnormally small pupil, redness, tearing, cloudiness or squinting.

Eye pain is not consistent with uncomplicated Haws syndrome.

Feline Dysautonomia

Feline dysautonomia, also called Key-Gaskell syndrome, is a rare but serious neurological disorder affecting the autonomic nervous system.

It can cause bilateral third-eyelid protrusion, but affected cats usually have other abnormalities such as:

• Dilated pupils with poor light responses

• Reduced tear production

• Dry nose or mouth

• Difficulty swallowing

• Regurgitation

• Vomiting

• Constipation

• Intestinal dilation

• Urinary retention

• Slow heart rate

• Reduced appetite

• Severe lethargy

The prognosis can be poor in severely affected cats, making it critically important not to confuse dysautonomia with benign Haws syndrome.

A cat with protruding third eyelids and large unresponsive pupils, difficulty swallowing, constipation or urinary problems needs urgent neurological and medical assessment.

Dehydration, Weight Loss or Systemic Illness

When a cat becomes dehydrated, loses substantial body fat or becomes systemically unwell, the eyes may sit slightly deeper within the sockets. This can make the third eyelids more visible.

Clues include:

• Dry or tacky gums

• Reduced skin elasticity

• Weight loss

• Reduced appetite

• Vomiting or diarrhoea

• Weakness

• A sunken facial appearance

In these cats, the third eyelids are a sign of the wider illness rather than Haws syndrome itself.

A Mass Behind or Around the Eye

A mass, abscess, inflammation or other lesion within the orbit can alter the position of the eyeball and third eyelid.

This is more concerning when:

• Only one eye is affected

• The eye protrudes or sits abnormally

• The mouth is painful to open

• Facial swelling is present

• One-sided nasal discharge develops

• The third eyelid looks thickened or contains a lump

• The condition progressively worsens

Imaging such as ultrasound, CT or MRI may be required when orbital or neurological disease is suspected.

Prolapse of the Third-Eyelid Gland

A prolapsed third-eyelid gland, commonly called cherry eye, looks different from Haws syndrome.

Cherry eye usually appears as a rounded, fleshy pink or red mass at the inner corner of the eye. Haws syndrome causes the entire flat third-eyelid membrane to extend across both eyes.

Third-eyelid gland prolapse is much less common in cats than in dogs and may require surgical repositioning. It should not be confused with bilateral neurological protrusion.

Conjunctivitis

Conjunctivitis can make the third eyelid swollen or more visible.

Unlike uncomplicated Haws syndrome, conjunctivitis commonly causes:

• Redness

• Watery or sticky discharge

• Swelling

• Frequent blinking

• Squinting

• Sneezing or nasal discharge in infectious cases

A cat with discharge and inflamed eye tissue should not be diagnosed with Haws syndrome based on the third eyelids alone.

Haws Syndrome vs Horner Syndrome vs Dysautonomia

Feature	Haws syndrome	Horner syndrome	Feline dysautonomia
Third eyelids	Both usually protrude	Usually one, occasionally both	Commonly both
Pupils	Usually normal and equal	Affected pupil usually small	Pupils often large and poorly responsive
Eye pain	Not expected	Not usually painful itself	Not usually primary eye pain
Upper eyelids	Mild bilateral ptosis may occur	Ptosis on the affected side	May appear drooped
Other signs	Possible diarrhoea	Ear, neck, chest or neurological abnormalities may be present	Dry eyes, swallowing problems, gut and bladder dysfunction, bradycardia
General prognosis	Usually excellent	Depends on the cause	Guarded in severely affected cats

These patterns help organise the differential diagnosis, but they do not replace an ophthalmic and neurological examination.

How Do Vets Diagnose Haws Syndrome?

There is no single laboratory test that definitively confirms Haws syndrome.

Diagnosis requires:

1. Recognising the characteristic bilateral pattern

2. Confirming that the pupils and eyes are otherwise normal

3. Looking for evidence of sympathetic nerve dysfunction

4. Excluding painful eye disease, Horner syndrome and dysautonomia

5. Investigating gastrointestinal illness when present

The Physical Examination

Your veterinarian may assess:

• Hydration

• Body weight and condition

• Temperature

• Heart rate

• Abdominal comfort

• Intestinal sounds

• Stool quality

• Ability to swallow

• Bladder size

• Ear canals

• Neurological function

• Recent parasite-prevention history

This wider examination is important because third-eyelid protrusion can reflect systemic disease rather than a primary eye problem.

The Eye Examination

A feline ophthalmic examination may include:

• Assessment of vision

• Pupil size and light responses

• Evaluation of eyelid position

• Examination of the cornea and conjunctiva

• Tear-production testing

• Intraocular-pressure measurement

• Fluorescein staining for corneal ulcers

• Examination behind the third eyelid

• Assessment of eye position and movement

These tests help confirm that the cat does not have an ulcer, uveitis, glaucoma, tear-film disease or another ocular explanation. A complete feline eye examination commonly includes neuro-ophthalmic assessment, tear testing, tonometry and fluorescein staining.

The Phenylephrine Challenge

A veterinarian may apply a low-concentration phenylephrine solution to one or both eyes.

Phenylephrine stimulates adrenergic receptors. In cats with Haws syndrome, the third eyelid and drooping upper eyelid may temporarily return to their normal position.

In the 2024 study, every affected cat had temporary resolution of the signs within 20 minutes after topical phenylephrine or a related adrenergic medication was applied.

In the 2026 case series, the ocular signs also resolved temporarily following 1% phenylephrine, supporting the presence of sympathetic neuropathy.

Does a positive phenylephrine test prove Haws syndrome?

No.

The test supports a sympathetic nerve abnormality, but the overall pattern still matters.

The veterinarian must interpret the response alongside:

• Whether one or both eyes are affected

• Pupil size

• Presence of ptosis

• Eye pain

• Neurological findings

• Ear disease

• Gastrointestinal signs

• General health

Phenylephrine testing should be performed and interpreted by a veterinarian. Human redness-relief eye drops should not be used as a home diagnostic experiment.

Does Your Cat Need Blood Tests?

Blood tests are not mandatory for every bright young cat with a classic presentation.

They become more useful when the cat has:

• Reduced appetite

• Vomiting

• Weight loss

• Fever

• Lethargy

• Dehydration

• Abnormal pupils

• Slow heart rate

• Difficulty swallowing

• Urinary or bowel abnormalities

• Persistent or recurring signs

• Senior age

• Another chronic medical condition

Testing may include a complete blood count, serum biochemistry, electrolytes and tests directed at the suspected underlying disease.

Does Your Cat Need a Faecal Test?

A faecal test is particularly reasonable when there is:

• Current or recent diarrhoea

• Recurrent soft stool

• Recent adoption

• Shelter or cattery exposure

• Outdoor access

• A multi-cat household outbreak

• Incomplete parasite prevention

• Weight loss

• Vomiting

• Giardia risk

Depending on the history, testing may involve faecal flotation, Giardia antigen testing, direct examination or a gastrointestinal PCR panel.

A single negative test does not exclude every gastrointestinal pathogen. Repeat or alternative testing may occasionally be needed.

How Is Haws Syndrome Treated?

True Haws syndrome usually does not require direct treatment of the eyes.

Management focuses on:

• Confirming that the diagnosis is correct

• Monitoring the cat’s comfort and vision

• Identifying gastrointestinal disease

• Correcting dehydration

• Treating confirmed parasites or infection

• Maintaining adequate nutrition

• Allowing the sympathetic nerve dysfunction to resolve

Treating Diarrhoea or Gastrointestinal Disease

Treatment depends on the cause and may include:

• Rehydration

• A complete, highly digestible gastrointestinal diet

• Targeted parasite treatment

• Treatment of confirmed infection

• Probiotics in selected cases

• Anti-nausea medication

• Additional investigation for persistent diarrhoea

Avoid repeated empirical medication without a diagnosis, particularly when gastrointestinal signs are severe or recurring.

A 2026 case series described five cats managed with a prebiotic-enriched gastrointestinal diet. Eye signs resolved within 11 to 39 days, and gastrointestinal signs improved in some cats. However, the study involved only five cats, had no untreated control group and evaluated a condition that commonly resolves by itself, so it does not prove that the diet caused the recovery.

The practical takeaway is that treating genuine gastrointestinal disease is sensible. A particular diet should not be marketed as a proven cure for Haws syndrome on the basis of this small study.

Are Eye Drops Needed?

Usually not.

Adrenergic drops such as phenylephrine can temporarily retract the third eyelids, but they do not necessarily shorten the duration of the syndrome.

They may occasionally be considered when:

• The membranes are significantly obstructing vision

• A veterinarian needs to support the diagnosis

• The cat’s safety or function is affected

Routine long-term use is rarely necessary.

Do not use:

• Human redness-relief drops

• Leftover antibiotic drops

• Steroid-containing eye medication

• Another animal’s prescription

• Herbal eye products

• Contact-lens solution

The eyes should first be examined to confirm that the corneas are healthy.

How Long Does Haws Syndrome Last?

Recovery is usually gradual.

In the 2024 study:

• Nine of 10 cats recovered

• Resolution took 12 to 95 days

• The average was approximately 38 days

• Three of the nine recovered cats experienced recurrence approximately five to six months later

In the 2026 five-cat series, ocular signs resolved within 11 to 39 days.

A practical expectation is:

• Some improvement may appear within one to three weeks

• Many cases resolve within four to eight weeks

• A smaller number may take two to three months

• Recurrence is possible

The third eyelids may retract unevenly or vary from day to day during recovery.

When Should Your Cat Be Rechecked?

Arrange an earlier recheck if:

• The protrusion becomes one-sided

• The pupils become unequal

• The cat begins squinting

• Redness or discharge develops

• The cornea becomes cloudy

• Appetite falls

• Vomiting or diarrhoea worsens

• Weight loss develops

• Your cat becomes lethargic

• New neurological signs appear

Even when the diagnosis appears secure, reassessment is sensible if there is no improvement within approximately two to four weeks.

Persistence beyond six to eight weeks does not automatically mean something dangerous is present, because documented cases have lasted longer. It does mean the original diagnosis and any underlying gastrointestinal problem should be reviewed.

When Is Third-Eyelid Protrusion an Emergency?

Haws syndrome itself is not usually an emergency.

Go to an emergency veterinary hospital immediately if your cat has:

• A bulging or ruptured eye

• Severe eye trauma

• Chemical exposure

• Sudden apparent blindness

• A blue, white or severely cloudy eye

• An abnormally large, fixed pupil

• Collapse

• Seizures

• Severe weakness

• Difficulty swallowing

• Repeated regurgitation

• A greatly enlarged bladder or inability to urinate

• Open-mouth breathing

• Rapid deterioration

Seek same-day veterinary care if:

• One eye is affected

• The eye is held shut

• There is marked redness

• Discharge is thick or rapidly accumulating

• The pupil looks different from the other eye

• The cat repeatedly paws at the eye

• Significant vomiting or diarrhoea is present

• The cat has stopped eating

• A kitten is becoming dehydrated or lethargic

The absence of eye pain is one of the features that makes Haws syndrome relatively reassuring. Once pain appears, the situation has changed.

What Should You Do Right Now?

1. Confirm whether both eyes are affected

Take a clear photograph facing your cat directly.

Compare:

• How far each third eyelid extends

• Pupil size

• Upper-eyelid position

• Corneal clarity

• Eye redness

A strongly one-sided change is less consistent with Haws syndrome.

2. Watch for eye pain

Look for:

• Squinting

• Repeated blinking

• Light avoidance

• Pawing

• Face rubbing

• Reluctance to have the head touched

Eye pain warrants prompt examination.

3. Check your cat’s general health

Monitor:

• Appetite

• Water intake

• Energy

• Body weight

• Vomiting

• Stool consistency

• Urination

• Ability to swallow

• Grooming

Haws syndrome should not be used to explain away a cat that is clearly unwell.

4. Photograph the eyes daily

Take photographs in similar lighting and from the same angle.

This will help you judge whether the membranes are:

• Retracting

• Becoming more prominent

• Changing asymmetrically

• Remaining completely unchanged

5. Save a fresh stool sample

When diarrhoea is present, collect a fresh sample in a clean sealed container and ask the clinic how it should be stored before the appointment.

6. Maintain litter hygiene

In a multi-cat household:

• Remove faeces promptly

• Wash litter trays regularly

• Avoid overcrowding

• Provide enough litter trays

• Clean shared surfaces

• Wash hands after handling faeces

This is particularly important when an infectious gastrointestinal trigger is possible.

7. Do not apply eye drops

Do not attempt a home phenylephrine challenge or use human redness-relief medication.

8. Arrange a veterinary examination

A persistent third eyelid deserves assessment even when Haws syndrome looks likely. The objective is not to turn a benign problem into a medical drama. It is to make sure a medical drama is not wearing a benign problem’s costume.

Common Mistakes Owners Make

Assuming any visible third eyelid means Haws syndrome

Haws syndrome has a specific bilateral, non-painful pattern. One-sided protrusion or an abnormal pupil changes the differential list.

Ignoring squinting because both eyes are affected

Pain is not expected with uncomplicated Haws syndrome. Bilateral eye disease can still be painful.

Using human redness-relief drops

These products are not appropriate home diagnostic tools and may cause local or systemic adverse effects.

Treating the eyes while ignoring the gut

The eye signs often need no direct treatment, while diarrhoea, dehydration or parasites may require investigation.

Assuming all cases are caused by worms

Giardia and other gastrointestinal agents have been associated with Haws syndrome, but the cause remains unproven and not every cat tests positive.

Waiting indefinitely because Haws is “harmless”

A secure diagnosis can be monitored. An unexamined cat with persistent third-eyelid protrusion should not simply be watched for several months.

Confusing Haws syndrome with dysautonomia

Large unresponsive pupils, dry eyes, swallowing difficulty, constipation and urinary retention are not typical Haws signs. They require urgent investigation.

Can Haws Syndrome Be Prevented?

There is no proven way to prevent Haws syndrome itself because its exact cause remains unknown.

Reasonable measures that may reduce associated gastrointestinal disease include:

• Maintaining an appropriate parasite-prevention programme

• Performing faecal testing when diarrhoea is persistent

• Introducing diet changes gradually

• Feeding a complete, balanced feline diet

• Preventing access to spoiled food

• Cleaning litter trays regularly

• Reducing overcrowding

• Quarantining newly adopted cats when appropriate

• Investigating recurring diarrhoea

• Maintaining good hydration during gastrointestinal illness

These steps support general gastrointestinal health but cannot guarantee that Haws syndrome will not occur.

Will Your Cat Be Okay?

The prognosis for true Haws syndrome is excellent.

Most affected cats:

• Remain comfortable

• Retain normal ocular function

• Recover without permanent eye damage

• Need little or no direct eye treatment

• Return to normal over several weeks

The appearance can be far more dramatic than the disease itself.

What matters is confirming the characteristic pattern:

• Both eyes are involved

• The pupils remain normal

• There is no eye pain

• The corneas are clear

• No serious neurological signs are present

• Any gastrointestinal illness is being addressed

Once those boxes are genuinely ticked, monitoring is usually reasonable.

Frequently Asked Questions

Is Haws syndrome painful for cats?

No. True Haws syndrome should not cause significant eye pain. Squinting, pawing, redness, discharge or a cloudy cornea suggests another eye condition.

How long does Haws syndrome take to resolve?

Many cats recover within four to eight weeks, although published cases have resolved in as little as 11 to 12 days or persisted for approximately three months.

Can Giardia cause Haws syndrome?

Giardia has been found in several cats with Haws syndrome, but current studies are too small to prove that it is the direct cause. Faecal testing is reasonable when diarrhoea or relevant exposure is present.

Is Haws syndrome contagious between cats?

The eye condition itself is not known to be directly contagious. However, a gastrointestinal infection capable of triggering the syndrome may spread between cats, particularly in a multi-cat household.

Can I use phenylephrine eye drops at home?

No. Phenylephrine may be used by a veterinarian as a supportive diagnostic test or temporary treatment, but human eye drops should not be used without veterinary direction.

Final Thoughts

Haws syndrome is one of those conditions that looks considerably worse than it usually is.

The typical cat has both third eyelids protruding symmetrically, normal pupils, clear comfortable eyes and few other signs apart from possible diarrhoea. In that setting, the condition usually resolves gradually without direct eye treatment.

The real clinical skill is not recognising the membrane. It is recognising when the pattern does not fit.

One-sided protrusion, squinting, redness, discharge, an abnormal pupil, cloudy cornea or significant systemic illness should move Haws syndrome down the list and prompt faster investigation.

If the eyes are comfortable, the pupils are equal and your cat remains bright, this is usually less urgent. It still deserves an initial veterinary assessment so that a benign diagnosis is earned rather than guessed.

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If you are unsure whether your cat’s visible third eyelids fit Haws syndrome or indicate a more urgent eye or neurological condition, ASK A VET™ can help you assess the pattern and decide what to do next.