Common third eyelid problems in cats

In addition to the upper and lower eyelids that we share with them, cats have a third eyelid, which can also be called the nictitating membrane. It is not usually visible and only occasionally we find it displayed.

Seeing this third eyelid covering the eye is not a sign that we should miss, since it indicates the existence of a health problem. And this can not only be limited to the eye, but, on occasions, accounts for a systemic disease.

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What is the third eyelid?

With the name of third eyelid or nictitating membrane we refer to a membrane that is located in the inner corner of the eye , where it is normally hidden. That is why it is not surprising that we have never seen it, although we have been living with our cat for several years.

On the other hand, some circumstances can cause this membrane to unfold and cover the eye to a greater or lesser extent. This prolapsed gland is the sign of a health problem.

Of course, if we perceive this eyelid when the cat is sleeping, it is not due to any disease, but simply because it has left its eyes ajar. In that case it is not worrisome nor is it necessary to take any action.

What is the third eyelid for?

The main function of this nictitating membrane is to protect and preserve the eyeball from all the elements and foreign bodies that can affect it. Making this third eyelid visible also serves to make us notice that something is wrong with our cat.

Cause of third eyelid prolapse in cats

Sometimes, visualizing the third eyelid is due to a sample of pain due to damage to the eye itself . For example, when the cat suffers from an eye disease such as uveitis. Nictitating membrane prolapse has traditionally been associated with gastrointestinal disorders.

The link between the presence of intestinal parasites and the vision of the third eyelid is widespread. Whatever the cause, the third eyelid may be visible in one or both eyes and is a piece of information that gives a clue to its origin.


Eye diseases

Like uveitis and a number of other eye diseases or trauma and foreign bodies, when there is pain in the eye, the nictitating membrane will unfold for protection. Moreover, we will see other symptoms as aqueous or purulent lacrimation, redness, photophobia, changes in the eyes, etc .

Trauma can cause the so-called Horner syndrome, which includes among its symptoms the prolapse of the nictitating membrane, as well as a constricted pupil or slight drooping of the upper eyelid. Of course, you have to go to the vet.


Dehydration occurs when the cat loses more fluids than it can replace. For example, when you suffer from vomiting and severe diarrhea . Among the symptoms that alert us to dehydration, the prolapse of the nictitating membrane is, perhaps, the most visible.

We can also look at the elasticity of the skin. If we stretch it in the area of ​​the withers, we let go and the skin does not immediately regain its initial position, we are dealing with a dehydrated cat. Dehydration can appear in different degrees , which is what will determine its severity. You have to go to the vet.

Mild cases can be resolved by administering oral or subcutaneous serum. Severe patients require hospital admission to provide intravenous fluids. Of course, the cause of the dehydration must be found out and treated. Dehydration can be life threatening.

Haw syndrome

This syndrome is characterized by the visibility of the nictitating membrane in both eyes without, apparently, the cat showing any discomfort. It may or may not be accompanied by gastrointestinal or parasitic problems. In fact, medication is not recommended unless vision is impaired .

It occurs in cats under three years of age and seems to be related to a neurological or viral problem that makes it impossible to keep this third eyelid in place. Although not serious, you must consult your veterinarian to make a differential diagnosis with the other possible causes of membrane prolapse.


Tumors are a rare cause of visualization of the third eyelid. They are melanomas, lymphomas, leukemia or squamous cell carcinomas that appear on the eyelids and spread. The most common, within the low incidence of these tumors, is adenocarcinoma that affects the gland of the third eyelid .


If this is the case of our cat, once the diagnosis is confirmed, the treatment would go through surgical intervention. Cryotherapy, radiotherapy or laser can also be used, depending on the veterinarian’s decision.


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