A cat’s eyes are truly a fascinating feature. They can vary in size, shape, and color, and each set is uniquely beautiful.
If you haven’t paid a special attention to your cat’s eyes, and now you looked at them from up close, and noticed a third eyelid, this was certainly surprising and even scary for you.
The third eyelid, or the nictitating membrane, is something that is actually inherent in all animals, including cats. It is located next to the nose, in the inner corner of the eye, and serves to protect the cat's eye. However, while your kitty has an open eye, this eyelid will not be visible to you.
So why does my cat have a visible third eyelid, but doesn't show any other symptoms?
There are five common explanations for this occurrence in felines. Let’s check them out and find out in which situations the third eyelid showing might be dangerous for your cat’s health.
1. When A Cat Is Completely Relaxed
Seeing a cat’s third eyelid without any other symptoms present is completely normal in a situation when she’s totally relaxed or tired.
You're most likely to notice this phenomenon when your cat is either asleep or just beginning to doze off.
These are the moments when your cat is totally comfortable, and sleeping and napping are also the times when you might see her, for example, with her mouth open.
While your cat’s eyes are half-closed, if you take a good look, you’ll be able to see her third eyelid.
The most probable reason why you haven’t seen it before is because the cat’s third eyelid moves very quickly, and chances are you probably haven’t observed your cat carefully while she was sleeping.
This is completely natural to happen in felines, and nothing you should be worried about.
2. Anesthesia
Almost all cats will eventually go into a medical procedure when they will be given sedation or anesthesia.
This might sound scary for pet parents whose cats are about to go under anesthesia for the first time.
However, as Sheilah Robertson and her associates [1] explain, general anesthesia is essential in feline veterinary medicine, since, without it, surgeries and some other diagnostic procedures and treatment modalities wouldn’t be possible.
You should be aware that there are potential anesthesia side effects in cats, and one of them is third eyelid showing.
This effect might be present for several hours after your cat has woken up out of sedation, but it should stop being visible in about 24 hours after the procedure.
If you still continue to see your cat’s third eyelid even after this period, you should consult your veterinarian.
You can watch the video below to get the visual demonstration of a cat’s third eyelid.
3. Vaccination
The essential part of being a cat parent is taking care of your pet’s well-being, meaning estimating right how often to take her to the vet, and, of course, ensuring that she gets all the necessary vaccinations on time.
According to PetMD, there are core and noncore feline vaccines. Core vaccines are the ones recommended for all cats, regardless of their lifestyle conditions. The two most important core vaccines are FVRCP and rabies vaccines.
Vaccinations are absolutely essential and necessary for cats, but they might cause certain side effects. Your cat showing her third eyelid might be one of them.
Not all cats are equally sensitive to vaccines. Some might experience side effects such as lethargy, fever, or vomiting, while others will only show the third eyelid.
When your cat receives a vaccine, her body responds by producing antibodies since it perceives the vaccine as a virus. This might cause your cat’s nictitating membrane to start showing.
This symptom should disappear in a couple of hours after your cat has received the vaccine. If it doesn’t go away, you should call your veterinarian.
4. Haws Syndrome
If you notice your cat showing the third eyelid on both of her eyes, this could be a sign of Haws syndrome in her.
As the Veterinary Partner points out, this condition isn’t associated with diseases inside or outside of the cat’s eyeball, and this is why you probably won’t be able to notice any other symptoms in your pet.
The exact cause of Haws syndrome isn’t known, but it's most commonly associated with gastrointestinal disorders in cats.
To set up the diagnosis, the veterinarian will undertake a detailed physical examination of your cat, including an ophthalmic examination.
In most cases, there won’t be a specific treatment for Haws syndrome. A cat’s third eyelid should stop being visible in a couple of days.
If this doesn’t happen, and if your cat starts showing signs of GI disorders, such as vomiting or diarrhea, then your vet might suggest further diagnostic tests.
5. Horner’s Syndrome
The protrusion of the third eyelid in your cat can be a sign of a medical condition called Horner's syndrome, even though you are unable to notice any other symptoms in her.
As WebMD explains, this is a neurological condition that affects cats and other animals as well, such as dogs and horses.
Horner's syndrome in cats is most commonly related to an underlying disease, and, ultimately, a prognosis for the cat’s recovery will depend on the exact cause of the syndrome in her.
Some of the underlying causes are neck injuries, ear infections, spinal cord injuries, and even some types of tumors. In most cases, Horner’s syndrome affects one eye in cats, but it’s also possible to occur in both eyes.
In this situation, it’s necessary to have your cat examined by a veterinarian. If he confirms Horner’s syndrome in her, he will prescribe the treatment in accordance with the underlying cause.
Therefore, treatment might include eye drops, phenylephrine drops, but also chemotherapy, or even surgery.
Summary
What could cause a cat third eyelid showing with no other symptoms?
As we have seen, there are a couple of reasons for this occurrence. If you only see this while your cat is napping or sleeping, you don’t have to worry, since this is considered perfectly normal.
The third eyelid can also become apparent after a cat has been under anesthesia or immediately following a vaccination. Under normal circumstances, her eyes should return to their usual appearance within a few hours.
Still, a cat showing a third eyelid, but without any other symptoms, could also indicate Haws or Horner’s syndrome in her.
Just to be sure, you should observe your kitty’s eyes after you notice this. If the third eyelid is still visible a day after you first noticed it, you should have her checked by a veterinarian.
It might be nothing, but it’s always better to be safe than sorry.
References:
[1] Robertson SA, Gogolski SM, Pascoe P, Shafford HL, Sager J, Griffenhagen GM. AAFP Feline Anesthesia Guidelines. Journal of Feline Medicine and Surgery. 2018;20(7):602-634. DOI, Retrieved September 6, 2023.
