The Mystery of the Feline Third Eyelid: Unveiling Its Secrets and Functions

Why Do Cats Have a Third Eyelid?

Why Do Cats Have a Third Eyelid? -  An Overview

Cats, with their grace and agility, have always fascinated us. The third eyelid, the nictitating membrane, is a lesser-known yet intriguing aspect of their anatomy. This 1200-word blog will explore why cats have a third eyelid, its functions, health indications, and more.

Understanding the Third Eyelid in Cats

The third eyelid is a triangular piece of tissue located closest to the nose in the corner of each eye. It's more prominent in some animals than in others, and in cats, it's usually visible only partially or when they are unwell.

Evolutionary Perspective

From an evolutionary standpoint, the third eyelid is believed to have developed as an extra protective layer for the eyes. For ancestors of modern cats, which were hunters, this membrane played a crucial role in protecting their eyes from debris, branches, and even during fights.

The Protective Function

The primary function of the third eyelid in cats is protection. It acts as a shield, guarding the eye from potential harm caused by dust, dirt, or any foreign objects. It also serves to keep the eye’s surface moist and clean.

Contribution to Vision

While the third eyelid doesn’t directly improve vision, it helps maintain the health of the cornea and overall eye by spreading tears and clearing away debris. This indirectly supports the cat's excellent vision.

Role in Eye Health

The third eyelid contains a special gland that produces a significant portion of the tear film. This gland is essential in keeping the eye moist and ensuring that the tear film is spread evenly across the eye’s surface.

Indicators of Health Issues

The appearance of the third eyelid can be an indicator of health issues in cats. If it becomes more visible than usual, it could be a sign of dehydration, eye infection, or other systemic illnesses. A protruding third eyelid should not be ignored and warrants a veterinary check-up.

Common Third Eyelid Problems

Common issues with the third eyelid include prolapse of the gland (also known as "cherry eye"), inflammation, or injury. These conditions can lead to discomfort and, if left untreated, more serious eye problems.

Treatment and Care

Treatment for third eyelid problems depends on the underlying cause. Infections might require antibiotic or anti-inflammatory eye drops, while more serious conditions like a prolapsed gland may need surgical intervention.

Nictitating Membrane and Hydration Status

The visibility of the third eyelid can sometimes be linked to a cat’s hydration status. Dehydration can cause the eyes to sink slightly, making the third eyelid more prominent.

Differences Across Species

While many animals have a third eyelid, its development and visibility vary across species. In cats, it's more developed than in humans but less so than in some birds and reptiles.

Impact on Cat Behavior

The third eyelid usually doesn’t impact a cat's behavior. However, if a cat is persistently pawing at its eye or seems bothered, it could indicate a problem with the third eyelid or the eye itself.

Regular Eye Checks

Regularly checking your cat's eyes can help catch any issues with the third eyelid early. Look for signs like excessive tearing, redness, or a noticeable increase in the visibility of the third eyelid.

Nutritional Support for Eye Health

Good nutrition plays a role in maintaining eye health, including the health of the third eyelid. Ensure your cat’s diet is balanced and rich in essential nutrients, vitamins, and minerals.

The Role of Genetics

Genetic factors can influence the size and functioning of the third eyelid. Some breeds may have more prominent third eyelids, while in others, it’s rarely visible.

Myths and Misconceptions

There are several myths surrounding the third eyelid in cats. It’s important to understand that its visibility isn't always a sign of illness and can be a normal physiological response in some situations.

Stress and the Third Eyelid

Stress can affect a cat’s overall health and may sometimes manifest in eye-related symptoms, including changes in the appearance of the third eyelid.


The third eyelid is a fascinating and important part of a cat’s anatomy, providing essential protection and contributing to overall eye health. Understanding its functions and the signs that indicate a problem can help cat owners ensure their pets’ eyes remain healthy.

In summary, the cat's third eyelid is more than just an intriguing anatomical feature; it plays a vital role in maintaining eye health and function. As cat owners, being aware of how to care for and monitor this part of your cat's anatomy is key to ensuring their long-term health and comfort. By paying attention to the health of their eyes, including the third eyelid, you play an important role in your cat's overall well-being.