Haws syndrome is a condition in cats where the third eyelids (the translucent membranes in the inner corners of the eyes) rise up and partially cover both eyes at the same time. It looks alarming, but it’s typically a benign, self-limiting condition that resolves on its own within a few weeks. It’s most common in young cats and is generally linked to mild gastrointestinal illness.
What the Third Eyelid Does
Cats have a third eyelid, also called the nictitating membrane, tucked in the inner corner of each eye. It normally stays retracted and barely visible, sliding across the eye only briefly to spread tears and clear debris. The position of this membrane is controlled by the nervous system, specifically the sympathetic nerves that keep it pulled back out of sight.
In Haws syndrome, something disrupts the nerve signals that hold the third eyelid in its normal position. This causes both membranes to slide upward and become prominently visible, sometimes covering a third or more of the eye’s surface. The disruption appears to involve a partial deficit in the sympathetic nerve pathway, but it’s mild enough that no other neurological signs develop.
What Causes It
The exact mechanism isn’t fully understood, but Haws syndrome is strongly associated with gastrointestinal problems. Many affected cats have recently had a bout of diarrhea or mild intestinal upset, sometimes caused by intestinal parasites, viral infections, or dietary changes. The GI illness often comes first, and the third eyelid elevation follows days later, which can confuse owners who don’t connect the two.
In some cases, no obvious GI symptoms are present at all, and the cause remains unknown. The condition can also appear in clusters among cats in the same household or geographic area, suggesting an infectious trigger like a viral illness that affects the gut and, indirectly, the nerves controlling the third eyelid.
What It Looks Like
The hallmark of Haws syndrome is both third eyelids rising at the same time. Your cat’s eyes may look partially hooded by a pinkish or whitish film creeping up from the inner corners. The eyes themselves are normal underneath: no redness, no discharge, no squinting, and no change in pupil size. Your cat can still see, though the raised membranes may partially obstruct their field of vision.
Cats with Haws syndrome are otherwise healthy and behave normally. They eat, play, and interact as usual. If your cat also has a droopy upper eyelid, a noticeably smaller pupil, or a sunken-looking eye on one side, that points toward a different condition called Horner syndrome, which involves a more significant nerve problem and needs its own workup.
How It’s Diagnosed
Your vet will start with a physical and eye exam to rule out other causes of third eyelid elevation, such as eye pain, masses behind the eye, or neurological disease. The key distinguishing feature of Haws syndrome is that it’s bilateral (both eyes), the cat is otherwise neurologically normal, and there are no signs like eyelid drooping, unequal pupils, or sunken eyes.
A simple confirmatory test involves placing a drop of phenylephrine (a type of stimulating eye drop) in both eyes. If the third eyelids return to their normal position within about 20 minutes, Haws syndrome is confirmed. This response shows that the nerve pathway is intact but underactive, and a little stimulation is all it takes to reset it.
Your vet may also check a stool sample for parasites and do basic bloodwork to look for any underlying illness driving the nerve disruption.
How Haws Syndrome Differs From Horner Syndrome
These two conditions are easy to confuse because both involve a visible third eyelid. But they’re quite different. Horner syndrome typically affects only one side and comes with a cluster of signs: a constricted pupil, a drooping upper eyelid, and an eye that appears sunken into the socket. It indicates a more significant disruption somewhere along the sympathetic nerve chain and often requires imaging or further testing to find the cause.
Haws syndrome, by contrast, affects both eyes symmetrically and produces no other neurological signs. The pupils stay normal, the eyelids function normally, and the eyes sit in their sockets as they should. It’s this clean, isolated presentation that makes it recognizable.
Treatment and Recovery
Haws syndrome typically resolves on its own without specific treatment. Most cats recover within two to six weeks as the underlying trigger (usually mild GI illness) clears and normal nerve function returns. If intestinal parasites are found, deworming treatment will speed things along. If diarrhea is ongoing, your vet may recommend dietary support or treatment for the gut issue, which often helps the eyes improve in parallel.
No eye surgery or long-term medication is needed. The raised third eyelids don’t damage the eyes or cause pain, so the main task is simply waiting it out while addressing any underlying GI problem. In rare cases where the appearance is particularly bothersome or the membranes are significantly obstructing vision, phenylephrine drops can temporarily retract the eyelids, but this isn’t a long-term solution and usually isn’t necessary.
Multi-Cat Households
Because Haws syndrome sometimes clusters among cats in the same home, owners with multiple cats may see more than one cat develop raised third eyelids around the same time. This likely reflects a shared viral or parasitic exposure rather than the syndrome itself being contagious. The underlying gut infection can spread between cats, and some of those cats may then develop the characteristic eye changes. Keeping litter boxes clean, deworming as recommended, and monitoring all cats for diarrhea are reasonable steps if one cat in the household is affected.