Cat Third Eyelid

Cats are fascinating creatures with unique anatomical features, one of which is the third eyelid. Also known as the nictitating membrane, the third eyelid plays a crucial role in a cat's eye health and overall well-being. This article explores the structure and function of the cat's third eyelid, why it might be visible, and whether its appearance is a sign of health or concern.

What is the Cat's Third Eyelid?

The third eyelid, or nictitating membrane, is a translucent or opaque membrane located in the inner corner of a cat's eye, extending across the eye's surface. Unlike the upper and lower eyelids, the third eyelid moves horizontally across the eye.

It serves several important functions, including:

1. Protection:
The third eyelid acts as a protective barrier, shielding the cornea from debris, dust, and potential injury. This is especially important when a cat is hunting, playing, or in an environment with potential hazards.

2. Moisture and Lubrication:
The third eyelid helps spread tears across the eye's surface, keeping it moist and lubricated. This is crucial for preventing dryness and irritation.

3. Immune Defense:
The third eyelid contains lymphoid tissue, which plays a role in the immune response by producing immune cells to combat infections and foreign particles.

4. Wound Healing:
In case of an eye injury, the third eyelid can help protect the damaged area and promote healing by keeping the eye clean and moist.

Why is My Cat's Third Eyelid Showing?

A cat's third eyelid is usually not visible when the cat is awake and healthy. However, there are several reasons why the third eyelid might become visible:

1. Illness or Infection:
One of the most common reasons for a visible third eyelid is illness or infection. This can include viral infections like feline herpesvirus or bacterial infections that cause inflammation and discomfort in the eyes.

2. Dehydration:
Dehydration can cause the third eyelid to become more prominent. Cats that are not drinking enough water or have been vomiting or experiencing diarrhea may show signs of dehydration, including a visible third eyelid.

3. Trauma or Injury:
Eye injuries, such as scratches or foreign objects in the eye, can cause the third eyelid to protrude as a protective response.

4. Pain or Discomfort:
Any source of pain or discomfort in the eye can cause the third eyelid to become more noticeable. This can include conditions like glaucoma, uveitis, or corneal ulcers.

5. Neurological Issues:
Certain neurological conditions can affect the nerves controlling the third eyelid, causing it to become visible. This can occur due to nerve damage, tumors, or other neurological disorders.

6. Sedation or Anesthesia:
After sedation or anesthesia, a cat's third eyelid may be more visible as the cat recovers. This is usually temporary and resolves as the cat becomes fully awake and alert.

7. Systemic Illness:
Certain systemic illnesses, such as gastrointestinal issues, can lead to a condition known as "Haw's syndrome," where both third eyelids become visible without an apparent eye problem.

8. Aging:
Older cats may show their third eyelids more frequently due to decreased muscle tone and elasticity in the eyelids.

Is the Third Eyelid on a Cat Healthy?

The presence of a third eyelid is a normal and healthy feature of a cat's anatomy. However, a visible third eyelid is usually a sign that something is amiss. While the third eyelid itself is not harmful, its appearance can indicate underlying health issues that need to be addressed. Here are some considerations:

1. Normal Appearance:
In a healthy cat, the third eyelid should not be visible when the cat is awake and alert. Occasionally, a slight glimpse of the third eyelid may be seen when a cat is sleeping or very relaxed, which is normal.

2. Signs of Concern:
A third eyelid that remains visible or protrudes over a portion of the eye is a sign that something may be wrong. This could indicate an underlying eye condition, injury, or systemic illness.

3. Bilateral vs. Unilateral Visibility:
If both third eyelids are visible (bilateral), it may suggest a systemic issue such as dehydration, illness, or neurological condition. If only one third eyelid is visible (unilateral), it is more likely due to a localized issue like an eye injury or infection.

4. Duration and Accompanied Symptoms:
The duration of the third eyelid's visibility and any accompanying symptoms are important factors in assessing the situation. If the third eyelid remains visible for an extended period or is accompanied by symptoms like discharge, redness, swelling, or behavioral changes, it is essential to seek veterinary care.

5. Regular Veterinary Check-Ups:
Regular veterinary check-ups are crucial for monitoring a cat's eye health and catching any issues early. If a cat's third eyelid becomes visible, a veterinarian can conduct a thorough examination to determine the underlying cause and recommend appropriate treatment.

Common Conditions Associated with Visible Third Eyelid

Several conditions can cause a cat's third eyelid to become visible. Some of the most common include:

1. Conjunctivitis:
Inflammation of the conjunctiva, the mucous membrane covering the white part of the eye, can cause the third eyelid to appear. This condition may result from infections, allergies, or irritants.

2. Corneal Ulcers:
Ulcers or wounds on the cornea can cause significant pain and discomfort, leading to the third eyelid becoming visible as a protective response.

3. Glaucoma:
Increased pressure within the eye can cause pain and vision changes, often resulting in a visible third eyelid.

4. Uveitis:
Inflammation of the uvea, the middle layer of the eye, can cause redness, pain, and a protruding third eyelid.

5. Haw's Syndrome:
This syndrome is characterized by bilateral protrusion of the third eyelids, often without other symptoms. It is sometimes associated with gastrointestinal issues or systemic illness.

6. Cherry Eye:
Although more common in dogs, cherry eye, a condition where the gland of the third eyelid becomes inflamed and protrudes, can also occur in cats.

Treatment and Care for a Visible Third Eyelid

Treatment for a visible third eyelid depends on the underlying cause. Some potential treatments and care strategies include:

1. Medication:
If the third eyelid is due to an infection or inflammation, medications such as antibiotics, antivirals, or anti-inflammatory drugs may be prescribed.

2. Eye Drops or Ointments:
Lubricating eye drops or ointments can help soothe and protect the eye, especially if dryness or irritation is a factor.

3. Addressing Underlying Conditions:
Treating the underlying cause, whether it's a systemic illness, dehydration, or neurological issue, is crucial for resolving the issue.

4. Surgery:
In some cases, surgical intervention may be necessary, especially if there is a persistent or structural issue with the third eyelid.

5. Home Care:
Owners may need to keep the cat's eye area clean and administer prescribed medications. It's important to follow the veterinarian's instructions carefully.

Conclusion

The third eyelid is an important anatomical feature in cats, serving protective, lubricating, and immune functions. While a healthy third eyelid is typically not visible in a fully awake cat, its appearance can indicate a range of issues, from minor irritations to serious health conditions. Recognizing the signs and seeking prompt veterinary care is essential for ensuring the well-being of your cat. Regular check-ups and proper eye care can help prevent and address issues related to the third eyelid, keeping your feline companion healthy and comfortable.