Haws Syndrome and the cat with the 'third eyelids'
Published 22/05/2012 | 10:29
UNTIL LAST week, Wally had been a healthy young female cat. When she turned up for breakfast one day last week with strange-looking eyes, her owners were perplexed. What was going on with their friendly little cat? The inner of corner of each eye was covered by a flap of some kind. This had never happened before and it didn't look right.
Wally ate her breakfast hungrily, and she seemed perfectly normal in every other way. She was purring, active and playful. But there was definitely something weird going on with those eyes.
Her owners booked an evening appointment to see me, half thinking that it mightn't be necessary. Maybe her eyes would have gone back to normal by lunchtime.
As it turned out, her eyes looked even stranger by the evening, and they were relieved that they'd scheduled their appointment.
When I opened the cat carrier, Wally looked at me as if she was bemused. "Why am I here?" she seemed to be asking. She purred and pressed her head against my hand.
I carried out a thorough physical examination, feeling her all over for oddities like enlarged lymph nodes or any other lumps or bumps. I took her temperature and listened to her heart and lungs. I looked into her ears and examined her eyes with an ophthalmoscope. My conclusion? Wally was a perfectly healthy cat except for the obvious problem: those odd-looking eyes. She was suffering from a common problem in the cat world, known as Haws Syndrome. I explained what was going on to her owners.
Humans have only two sets of eyelids: upper and lower. Cats, like most animals, have an extra set of eyelids that are located on the inner aspect of each eye. These are known, unsurprisingly, as "third eyelids", or to give them their technical name, "nictitating membranes". "Nictitate" is a word that's rarely used these days, but it means "to wink": the third eyelid does precisely this, winking across the eyeball like a windscreen wiper whenever an animal blinks.
Animals are closer to the ground than humans, and their eyes are exposed to far more dust and debris. The third eyelid gives them an extra level of protection: when an animal blinks, not only do the upper and lower eyelids cover the eye, but beneath them, the third eyelid shoots across, providing an extra physical barrier.
The third eyelid isn't made of skin, like the upper and lower eyelids. Instead, it's a thin, membranous structure, similar to a very thin tongue. When it flicks across the surface of the eye, it delicately cleans as it goes, wiping away tiny specks of dirt and spreading lubrication across the eyeball.
Most owners don't even know that their pets have third eyelids. In a normal, healthy animal, the third eyelid is invisible, hiding in a small pocket in the corner of each eye. It only emerges when the animal blinks, and because the upper and lower eyelids are closed when that happens, it's impossible to see it happening.
If you press down gently on your pet's upper eyelid, you can deliberately cause the third eyelid to shoot over the surface of the eye, but it's tricky enough to do this, and I wouldn't recommend that you try. The next time you're at the vet, ask them to show you: it's an interesting part of an animal's anatomy.
So what was going on with Wally? Why were her third eyelids protruding half way across her eye?
She was suffering from a problem that has two names: the technical term is "bilateral protrusion of the third eyelids", and the colloquial name is "Haws Syndrome". Cats with this condition are perfectly healthy in every other way: there is no sign of any underlying eye disease, and there are no other signs of ill health.
There are several possible causes of Haws Syndrome. It's sometimes a side effect of gastro-intestinal disease and can be accompanied by a gastric upset. Sometimes worms are involved, and in Wally's case, I gave her a worm dose to rule this out. In most cases, a mild virus known as a Torovirus is thought to be the underlying cause but this is difficult to prove.
After questioning Wally's owners, I picked up a clue that made the virus seem to be a likely culprit in this case: another cat in the neighbourhood had visited the vet just two weeks previously with precisely the same problem. This other cat had been seen visiting Wally's back garden: the cats must have met, and it seemed likely that the virus had passed from one cat to the other.
The good news is that most cases of Haws Syndrome are "self-limiting". This means that they get better by themselves, usually after two or three weeks. As long as a cat continues to be healthy, hungry and happy, there's no need for treatment. And that's exactly what happened to Wally: he was back to normal within a week.
There is an important PS to this story: protruding third eyelids can also develop as a sign of serious underlying illness, and they should never be ignored. It's important that a vet carries out a detailed inspection of both eyes as well as a physical examination to ensure that there isn't some other, more sinister, cause of the problem. There's a long list of possible causes of protruding third eyelids, and the diagnosis of Haws Syndrome can only be made once these have been ruled out.