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Prolapsed Third Eyelid (Nictitating Membrane) in Dogs

Author: Dr. med. vet. Gisa Löwe | Last modified: 06.11.2025

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ProlapseProlapse refers to the falling out or protrusion of an organ or part of it from its normal position, often through an opening. In animals, this can include, for example, a rectal mucosal prolapse or a vaginal prolapse. of the third eyelid, also known as prolapsed nictitating membraneThe nictitating membrane, also called the third eyelid, is a protective membrane in the inner corner of the eye in dogs and cats. It provides additional protection and moistening of the eye., is a condition in which the dog’s third eyelid, normally hidden in the inner corner of the eye, becomes visible and protrudes over part of the eye.

Can Occur with the Following Diseases:

Basics and possible causes

The third eyelid, also called the nictitating membraneThe nictitating membrane, also called the third eyelid, is a protective membrane in the inner corner of the eye in dogs and cats. It provides additional protection and moistening of the eye., is a thin membrane in the inner corner of a dog’s eye that has a protective function for the eye. It helps protect the eye from foreign objects, distributes tear fluid evenly, and can swell in the event of injury or irritation.

ProlapseProlapse refers to the falling out or protrusion of an organ or part of it from its normal position, often through an opening. In animals, this can include, for example, a rectal mucosal prolapse or a vaginal prolapse. of the third eyelid can have various causes. A common cause is an inflammatory condition or irritation of the eye, which causes the nictitating membraneThe nictitating membrane, also called the third eyelid, is a protective membrane in the inner corner of the eye in dogs and cats. It provides additional protection and moistening of the eye. to protrude to protect the eye. Infections, allergies, or foreign bodies can cause irritation.

Another possible cause is the so-called “Cherry Eye”, in which the gland of the third eyelid protrudes. This gland is responsible for producing part of the tear fluid and can become inflamed or loosen, leading to a visible prolapseProlapse refers to the falling out or protrusion of an organ or part of it from its normal position, often through an opening. In animals, this can include, for example, a rectal mucosal prolapse or a vaginal prolapse..

A prolapsed nictitating membraneThe nictitating membrane, also called the third eyelid, is a protective membrane in the inner corner of the eye in dogs and cats. It provides additional protection and moistening of the eye. can also be a symptom of systemic diseases, such as dehydrationDehydration occurs when the body loses more fluid than it takes in. This can lead to a number of problems, including headaches, Dizziness, and in extreme cases, renal failure or Cardiovascular collapse., neurological disorders, or certain infectiousInfectious describes the ability of a pathogen to be transmitted from one individual to another and trigger an infection. It also refers to diseases caused by such pathogens. diseases. Sometimes the prolapseProlapse refers to the falling out or protrusion of an organ or part of it from its normal position, often through an opening. In animals, this can include, for example, a rectal mucosal prolapse or a vaginal prolapse. occurs in connection with other eye diseases such as corneal ulcers or conjunctivitis.

Typical accompanying symptoms

A visible, pink to reddish tissue that partially or completely covers parts of the eye, often in the inner corner of the eye. This can occur suddenly.
Increased blinking or winking of the affected eye, which may indicate discomfort or irritation.
Tearing or discharge from the eye, which can be clear, yellowish, or greenish, depending on the underlying cause.
Redness or swelling of the eye or surrounding tissues, indicating an inflammatory condition.
The dog may rub its paw over the eye more often or rub its face on furniture, which is a sign of itching or pain.
In some cases, there may be reduced vision if the third eyelid partially blocks the field of vision.

When to visit the vet?

A visit to the vet is absolutely necessary if the prolapseProlapse refers to the falling out or protrusion of an organ or part of it from its normal position, often through an opening. In animals, this can include, for example, a rectal mucosal prolapse or a vaginal prolapse. of the third eyelid occurs suddenly or is accompanied by other symptoms such as severe discharge, redness or obvious pain. These signs may indicate a serious infectionAn infection is the colonization and multiplication of pathogens such as bacteria, viruses, fungi, or parasites in an organism, which often, but not always, leads to a disease. or injury that requires immediate treatment.

If the dog shows signs of systemic diseases, such as lethargy, loss of appetite or fever, a vet should also be consulted as soon as possible. These symptoms may indicate that the prolapsed nictitating membraneThe nictitating membrane, also called the third eyelid, is a protective membrane in the inner corner of the eye in dogs and cats. It provides additional protection and moistening of the eye. is part of a larger health problem.

Even if the prolapseProlapse refers to the falling out or protrusion of an organ or part of it from its normal position, often through an opening. In animals, this can include, for example, a rectal mucosal prolapse or a vaginal prolapse. does not appear immediately threatening, it is advisable to have the situation clarified by a vet in order to determine the underlying cause and start appropriate treatment.

Symptom recognition for animal owners and veterinary diagnostic procedures

For the pet owner, the prolapseProlapse refers to the falling out or protrusion of an organ or part of it from its normal position, often through an opening. In animals, this can include, for example, a rectal mucosal prolapse or a vaginal prolapse. of the third eyelid is relatively easy to recognize, as the normally hidden tissue suddenly becomes visible. It is important to carefully observe the affected eye and watch out for additional symptoms such as discharge or redness.

The vet will carry out a thorough examination of the eye to determine the cause of the prolapsed nictitating membraneThe nictitating membrane, also called the third eyelid, is a protective membrane in the inner corner of the eye in dogs and cats. It provides additional protection and moistening of the eye.. This may include an examination with a special light source and a magnifying glass to check the eye for foreign bodies, injuries or signs of infectionAn infection is the colonization and multiplication of pathogens such as bacteria, viruses, fungi, or parasites in an organism, which often, but not always, leads to a disease..

In addition, the vet can carry out special tests, such as a Schirmer tear test to measure tear production, or a fluorescein stain to detect corneal ulcers. In some cases, blood tests or other diagnostic tests may be necessary to rule out systemic diseases.

What can pet owners do and professional therapy options

Until the veterinary examination, pet owners should try to keep the affected eye clean and avoid further irritation. A soft, damp cloth can be used to gently remove any discharge around the eye.

It is important to prevent the dog from rubbing the eye, as this could make the problem worse. A protective collar, also known as an Elizabethan collar, can help protect the eye until veterinary treatment is possible.

Avoid using over-the-counter eye drops or ointments without veterinary advice, as these could worsen the situation or be inappropriate for the underlying cause. The best course of action is to see a vet as soon as possible to get an appropriate diagnosisA diagnosis is the identification of a disease or condition by its symptoms and/or results from diagnostic tests. It is the first step in the management and treatment of patients. and treatment.

Outlook on current research

Current research into prolapseProlapse refers to the falling out or protrusion of an organ or part of it from its normal position, often through an opening. In animals, this can include, for example, a rectal mucosal prolapse or a vaginal prolapse. of the third eyelid in dogs focuses on various aspects to develop a better understanding and effective treatment options. Scientists are investigating the exact mechanisms that lead to prolapseProlapse refers to the falling out or protrusion of an organ or part of it from its normal position, often through an opening. In animals, this can include, for example, a rectal mucosal prolapse or a vaginal prolapse. of the third eyelid. In particular, the role of genetic factors and breed predispositions is being analyzed. Studies show that certain dog breeds such as Cocker Spaniels, Beagles and Basset Hounds have a higher susceptibility to this symptom. Genetic studies aim to identify specific genes that are associated with this susceptibility. These findings could support targeted breeding programs in the future to minimize the risk.

Another focus of the research is on the development and evaluation of new treatment methods. Traditionally, surgery has been considered the standard treatment to return the third eyelid to its normal position. However, there is an increasing number of studies dealing with conservative treatment methods such as special eye medications and therapeutic massages. These approaches may be less invasiveInvasive describes medical procedures or pathogens that enter the body or penetrate tissue. In medicine, invasive procedures can range from minimally invasive techniques to open surgery. and more suitable for certain cases. The effectiveness and long-term stability of such treatments are the focus in order to find out whether they represent a viable alternative to surgery.

The role of environmental factors is also being investigated to understand how external influences can affect the occurrence of prolapsed nictitating membraneThe nictitating membrane, also called the third eyelid, is a protective membrane in the inner corner of the eye in dogs and cats. It provides additional protection and moistening of the eye.. Researchers are analyzing whether environmental conditions such as air pollution or allergens increase the risk or worsen symptoms. Such information could lead to preventive measures that reduce the occurrence of this symptom. In addition, innovative diagnostic procedures are being tested that enable early detection. Advances in imaging technology and molecular diagnostics could enable more precise and less invasiveInvasive describes medical procedures or pathogens that enter the body or penetrate tissue. In medicine, invasive procedures can range from minimally invasive techniques to open surgery. diagnoses.

Overall, the research aims to provide more comprehensive information about the causes and best treatment approaches for prolapseProlapse refers to the falling out or protrusion of an organ or part of it from its normal position, often through an opening. In animals, this can include, for example, a rectal mucosal prolapse or a vaginal prolapse. of the third eyelid in dogs. Through the integration of genetic, therapeutic and environmental findings, scientists hope to sustainably improve the quality of life of affected dogs.

Frequently asked questions

What is the third eyelid in dogs? The third eyelid, also called the nictitating membraneThe nictitating membrane, also called the third eyelid, is a protective membrane in the inner corner of the eye in dogs and cats. It provides additional protection and moistening of the eye., is a thin membrane in the inner corner of the dog’s eye. It protects the eye and distributes tear fluid.
How do I recognize a prolapsed nictitating membraneThe nictitating membrane, also called the third eyelid, is a protective membrane in the inner corner of the eye in dogs and cats. It provides additional protection and moistening of the eye. in my dog? ProlapseProlapse refers to the falling out or protrusion of an organ or part of it from its normal position, often through an opening. In animals, this can include, for example, a rectal mucosal prolapse or a vaginal prolapse. of the third eyelid is characterized by a visible, often reddish or pink massIn pathology, the term "mass" is used to describe an abnormal lump or growth in the body. A mass can form in the skin or subcutaneous tissue, or even inside the body. The causes can be benign (not cancer) or malignant (cancer). that protrudes in the inner corner of the eye. It may be accompanied by watery eyes or irritation.
What are the causes of prolapseProlapse refers to the falling out or protrusion of an organ or part of it from its normal position, often through an opening. In animals, this can include, for example, a rectal mucosal prolapse or a vaginal prolapse. of the third eyelid? The prolapseProlapse refers to the falling out or protrusion of an organ or part of it from its normal position, often through an opening. In animals, this can include, for example, a rectal mucosal prolapse or a vaginal prolapse. can be caused by genetic predispositionA predisposition is an innate inclination or susceptibility of an organism to certain diseases or conditions. In dogs and cats, there may be a genetic predisposition to certain conditions such as hip dysplasia or certain heart diseases., injuries, infections or inflammatory conditions. Certain breeds are more susceptible to this symptom.
Is a prolapsed nictitating membraneThe nictitating membrane, also called the third eyelid, is a protective membrane in the inner corner of the eye in dogs and cats. It provides additional protection and moistening of the eye. painful for the dog? The prolapseProlapse refers to the falling out or protrusion of an organ or part of it from its normal position, often through an opening. In animals, this can include, for example, a rectal mucosal prolapse or a vaginal prolapse. itself can be uncomfortable and cause irritation, but it is not necessarily painful. However, it can lead to complications that can be painful, such as infections or ulcers.
How is prolapseProlapse refers to the falling out or protrusion of an organ or part of it from its normal position, often through an opening. In animals, this can include, for example, a rectal mucosal prolapse or a vaginal prolapse. of the third eyelid diagnosed? A vet usually diagnoses the prolapseProlapse refers to the falling out or protrusion of an organ or part of it from its normal position, often through an opening. In animals, this can include, for example, a rectal mucosal prolapse or a vaginal prolapse. by a physical examination of the eye. Further tests may be necessary to identify underlying causes.
Can a prolapsed nictitating membraneThe nictitating membrane, also called the third eyelid, is a protective membrane in the inner corner of the eye in dogs and cats. It provides additional protection and moistening of the eye. heal on its own? In some cases, the prolapseProlapse refers to the falling out or protrusion of an organ or part of it from its normal position, often through an opening. In animals, this can include, for example, a rectal mucosal prolapse or a vaginal prolapse. may resolve on its own, especially if it was caused by temporary irritation. However, treatment is often necessary to permanently resolve the problem.
What treatment options are there for a prolapsed nictitating membraneThe nictitating membrane, also called the third eyelid, is a protective membrane in the inner corner of the eye in dogs and cats. It provides additional protection and moistening of the eye.? Treatment can be conservative, such as with eye drops or massages, or surgical to return the third eyelid to its position. The choice of treatment depends on the severity and the cause.
Is surgery to correct the prolapseProlapse refers to the falling out or protrusion of an organ or part of it from its normal position, often through an opening. In animals, this can include, for example, a rectal mucosal prolapse or a vaginal prolapse. risky? As with any surgery, there are risks, but most procedures to correct prolapsed nictitating membraneThe nictitating membrane, also called the third eyelid, is a protective membrane in the inner corner of the eye in dogs and cats. It provides additional protection and moistening of the eye. are routine and have a high success rate. The risks and benefits should be discussed with the vet.
Can prolapseProlapse refers to the falling out or protrusion of an organ or part of it from its normal position, often through an opening. In animals, this can include, for example, a rectal mucosal prolapse or a vaginal prolapse. of the third eyelid be prevented? PreventionPrevention includes measures taken to prevent diseases or injuries. In veterinary medicine, this includes vaccinations, parasite control, and health monitoring. is difficult, especially with genetic predispositions. However, regular eye examinations and avoiding eye injuries can be helpful in minimizing the risk.
What happens if a prolapsed nictitating membraneThe nictitating membrane, also called the third eyelid, is a protective membrane in the inner corner of the eye in dogs and cats. It provides additional protection and moistening of the eye. is left untreated? If the prolapseProlapse refers to the falling out or protrusion of an organ or part of it from its normal position, often through an opening. In animals, this can include, for example, a rectal mucosal prolapse or a vaginal prolapse. is left untreated, this can lead to chronicChronic refers to a condition or disease that is long-lasting or permanent. Chronic diseases often develop slowly and can lead to persistent or recurring health problems over time. irritation, infections or permanent eye damage. Early diagnosisA diagnosis is the identification of a disease or condition by its symptoms and/or results from diagnostic tests. It is the first step in the management and treatment of patients. and treatment are important to avoid complications.