what is Third Eyelid in Cats

If we do not stop to see the eyes of a cat we will notice that these are impressive, many are those who wonder why there is a third eyelid in cats? And it is true, many animals have it, but there are few who know what it is and its function.

What is the third eyelid in cats?

The third eyelid has its scientific name “Tertia palpebra” and is a membrane that many of the mammalian animals have.

It is itself a tissue that is positioned around the cornea, the conjunctiva and the mucous membrane.

This connective tissue membrane is hair-free and its framework is made up of cartilage that is shaped like a “T” or an anchor. In this you can find a gland that is responsible for making a high supply of tear secretion from the eye.

When there is a possibility that the eye may suffer some type of trauma, the outer eyelids (upper and lower) tend to contract and allow the third eyelid to appear.

This acts as a kind of curtain that will cover the eye either partially or completely.

The third eyelid does not have its own muscles, so its movement depends entirely on the external membranes. Once the outer eyelids relax again, the third eyelid will return to its original position and will be hidden.

What function does it have?

The third eyelid in cats, as well as in other animals, fulfills a very important function, since it is responsible for protecting the eyeball of felines in various ways. These functions are:

  • Protects the eye from possible external aggressions that may be suffered. It prevents parasites from entering the eye, in the same way it happens with dirt, dust, sand and other particles that can damage it in one way or another.
  • It is responsible for a large part of the cat’s tear production, since it produces between 30% and 40% of them.
  • It gives a great contribution of defences for the eyeball, in this way there are fewer risks of damage .
  • It is responsible for carrying out expulsions of any foreign object that may have entered the eye or that intends to do so.

Is it normal for my cat to show a lot of the third eyelid?

The answer to this question is simple. No, it is not normal for a feline to constantly see the third eyelid. If your cat begins to see the third eyelid in one or both eyes or has inflammation, it may be an indicator that something is happening, there may be some discomfort in the eyeball, pain or some condition.

According to some research that has been carried out, it is said that the appearance of this membrane could be associated with the appearance of parasites in the intestine of the feline or problems in the digestive system.

Other research indicates that the appearance of this membrane is only associated with eye problems.

Can dehydration cause a prolapse of the nictitating membrane?

The dehydration is one of the reasons why the third eyelid membrane can be made visible. Once there is an extreme lack of water, the appearance of the membrane will be almost immediate.

This will be a clear alarm signal, as it would indicate that the feline’s condition is serious and that it should be taken immediately to a veterinary doctor so that it receives the appropriate treatment and is rehydrated.

You should always keep in mind that, once you notice something unusual in your cat, the ideal is that you take them to the vet, so that it is the professional who indicates if something bad is happening with the feline or not. Never diagnose your pet yourself, as you could put it in serious danger.

What is the Nictitating Membrane?

When we speak of “nictitating membrane” we are referring to the same third eyelid. This is one of the ways this eye membrane is called in cats. Its name comes from the Latin “nictare” which literally means “to blink”.

Other causes why the third eyelid is very visible?

There are many times when the appearance of the third eyelid is related to a pain condition or damage that may have occurred in the eyeball. An example for this is when a feline has an eye disease such as uveitis.

As we have already mentioned previously, there are many experts who also associate the appearance of this ocular membrane with some problems or disorders at the gastrointestinal level, since many cases have indicated that this could be a cause.

There is also a link that says that the appearance of the membrane is associated with the presence of intestinal parasites , although this theory is still very widespread and without a complete foundation.

Among the most common causes of the appearance of the third eyelid we have:

Eye diseases

There are a large number of diseases or traumas associated with the eyes, when there is the presence of eye pain, usually the nictitating membrane makes an appearance to protect the eye.

Constant tearing (which can be watery or purulent), eye redness, photophobia, visible changes in the feline’s pupils, and other symptoms are also noted as symptoms.

When there is a trauma, Horner syndrome may appear, this has among its symptoms the prolapse of the membrane of the third eyelid, in addition to that, it also has symptoms such as pupil contraction, decay of the upper eyelid and strong lacrimation .


Tumors are one of the less frequent causes for the appearance of the third eyelid. Among the squamous cells that most appear on the eyelids of cats we have: melanomas, lymphomas, leukemia and carcinomas. 

Adenocarcinoma is one of the most common tumors within their low impact, this carcinoma directly affects the nictitating membrane making it frequently visible.

If I want to cure it, what is the treatment of the third eyelid in cats?

Since there are several causes that the third eyelid is visible, the treatments that should be used for its cure will also look different. Each one will be made from the symptoms that the cat presents.

Depending on the cause that causes the prolapse of the nictitating membrane, one or the other treatment should be carried out. Let’s get to know some of them:

  1. In the event that it occurs due to dehydration, it is recommended that the feline be provided with food that is moist and that it has access to plenty of water, in this way the dehydration process can be stopped. However, even if these steps are carried out, you should go to the veterinarian, the prolonged lack of fluids in the animal’s body can be very dangerous and will require medical supervision.
  2. When we talk about felines that suffer from conjunctivitis, eye wounds, invasion of foreign bodies into the eye or cancer, the first thing to do is obtain a diagnosis from the veterinarian, since it will only be it who says what treatment will be carried out based on the symptoms and the cause of the appearance of the third eyelid. One of the most common treatments in these cases is eye drops and some other medications, it will depend on the severity of the condition.

In the case of cancer, it will be the veterinarian who indicates which treatment is best for the feline, always taking into account a good quality of life and its health.

  • When we talk about the presence of the third eyelid due to Haw syndrome, it does not need a particular treatment, since it will disappear when the intestinal problems, which evidenced the membrane, also disappear.
  • In the event that the nictitating membrane prolapse is due to genetic origins, it will be the veterinarian who will say the treatment to follow. Certain medical studies should be carried out, especially if the membrane is affecting the feline’s vision or if it is causing any kind of discomfort, pain or discomfort.

In these cases, surgical intervention may be necessary, although that will only be determined by the veterinary professional. 

What is Haw syndrome?

This is the term used when the presence of the nictitating membrane is linked to the fact that the cat suffers from some intestinal problem, intense diarrhea, vomiting or parasites.

This syndrome affects cats that are older than 3 years, however, there is no distinction in the breed of cats or sex of the feline. 

Diagnosis can be achieved through the installation of a sympathomimetic agent. Changes in the post-ganglionic sympathetic system usually respond to medications in an average of 20 minutes.

If there is prolapse or inflammation, what do I do?

In the event that you realize that your cat has a prolapse in the membrane of the third eyelid or that it is inflamed, the first and most advisable thing is to go to a veterinarian. This will be the one who performs an examination and the proper diagnosis that will allow you to know the causes that have caused some of these symptoms.

It will be the same doctor who will prescribe the appropriate treatment to be administered to your feline and treat the condition that causes the symptom and to help the membrane return to its place of origin.

In the worst case, is third eyelid surgery necessary?

The surgery of the third eyelid is necessary if conventional treatment does not work or if the disease afflicting the animal has caused severe damage to the membrane.

A third eyelid surgery is not too invasive. However, it will require complete sedation and complex care, because if it is not done in the correct way, the surgeon could affect the vision or the eye of the feline.

It will be the veterinarian who will decide whether or not it is necessary for the cat to undergo surgery for the correction of the third eyelid in cats. In some cases, depending on the disease causing the appearance, it will be strictly necessary to carry out this surgical intervention.

There are many cats that have had to undergo corrective surgery for these cases, however, there are more that, with the appropriate treatment, can improve without having to go through an operating room.

Everything will depend on the cause for which the visualization of the nictitating membrane occurs and on how effective the treatment that is prescribed for the feline is.

In the event that the cause is dirt, trauma, or another simple factor, the treatment is straightforward and will not require surgery.

Now that you know everything about the third eyelid in cats, we would like you to leave a comment on the subject or tell us if you have had any experience with a feline that had any of these problems with its nictitating membrane.

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