The Dog Third Eyelid: Unveiling Its Purpose and Functions

June 25, 2023

The Dog Third Eyelid: A Closer Look

Dogs are filled to the brim with astounding anatomical wonders—none more so than their eyes, which serve as a window to their health and emotions. We're all familiar with their expressive outer eyelids, but there's another facet that often remains under the radar—the dog's third eyelid. In this extensive manual, we'll venture into the fascinating realm of the third eyelid, unearthing its role, tasks, and prevalent concerns. So, buckle up, folks, because we're about to delve into the enigma of this extraordinary canine attribute.

Our furry pals, you see, have a tear gland located in this extra eyelid, crucial for normal tear production. This gland is responsible for up to 50% of the tear film that keeps the surface of the cornea moist and healthy. When everything's in its normal position, you'd barely notice it. Yet, this seemingly unobtrusive feature plays an essential role in maintaining the health of the soft tissues of the eye.

The normal tear film, fortified by the third eyelid, forms a protective barrier and provides essential nutrients to the cornea. This extra layer of defense is key to our dogs' vision, helping them see the world in all its vibrant glory.

In the upcoming sections, we'll delve into some common issues and the role of medications in addressing them. So, stick around and get ready for a deep dive into the intriguing world of the dog third eyelid.

close up of dogs third eyelid

The dog third eyelid, also known as the nictitating membrane or haw, is an additional protective layer found in the inner corner of a dog's eye. This translucent membrane serves several crucial functions, ensuring the well-being and health of the dog's eyes.

1. Anatomy of the Dog Third Eyelid

The dog third eyelid is a specialized structure consisting of connective tissue, muscles, and a thin layer of mucous membrane. It is located below the lower and upper eyelids, hidden from view in normal circumstances. When activated, it moves across the eye's surface, providing an extra layer of protection.

2. Purpose and Functions of the Dog Third Eyelid

The dog third eyelid has multiple essential purposes and functions, contributing to a dog's eye health and protection.

2.1. Lubrication and Moisture Regulation

One of the primary functions of the dog third eyelid is to produce tears and distribute them across the cornea. Tears play a vital role in lubricating the eyes and maintaining their moisture. This helps prevent dryness and irritation, ensuring optimal eye health.

2.2. Protection against Foreign Objects

The third eyelid acts as an additional shield, protecting the dog's eye from potential harm caused by foreign objects. It serves as a barrier against dust, debris, and other particles that may come into contact with the eyes, reducing the risk of injury.

2.3. Protection during Physical Activity

During intense physical activity or situations that pose a higher risk to the dog's eyes, the third eyelid may be activated. It provides an extra layer of protection, minimizing the potential for injuries that could arise from impact or accidental contact.

2.4. Tear Drainage and Distribution

The dog third eyelid aids in tear drainage, allowing excess tears to flow away from the eye and into the nasolacrimal duct. This helps maintain the proper balance of tears and prevents an overflow that could lead to discomfort or visual impairment.

close up a golden retriever third eyelid

Puzzling Problems: Navigating the Dog Third Eyelid's Complications

Even though the extra eyelid plays a key role in keeping our furry friends' eyes moist and warding off debris, it's not immune to its own set of issues. So, let's dive into the common challenges related to the dog third eyelid.

  1. Battling the Cherry Eye

When the eyelid gland, nestled within the third eyelid, decides to make an unannounced appearance, it results in a condition endearingly called the cherry eye. The prolapsed gland can make your pooch's eye resemble a red, inflamed mass—not a pleasant sight, I must say. It could be a tad uncomfortable for your dog, but with the right veterinary guidance, it's nothing you can't handle.

  1. The Tale of Third Eyelid Prolapse

Our next story is about the third eyelid that oversteps its boundary—otherwise known as third eyelid prolapse. When the extra eyelid juts out unusually, it could be due to a range of culprits from trauma to infection. It's a call to arms for prompt veterinary care, ensuring your four-legged buddy doesn't have to bear unnecessary discomfort.

  1. Inflammation and Infection: Uninvited Guests

In some unfortunate instances, the dog's third eyelid might play host to inflammation and infection. Symptoms include everything from the telltale signs of redness and swelling to outright discomfort. The causes could be as varied as an allergy or a pesky foreign object that overstayed its welcome. Your trusted vet will be the best detective in identifying the root cause and serving up the right treatment.

  1. When the Third Eyelid Plays Peek-a-boo

There might be times when your dog's third eyelid decides to take center stage, becoming more visible than normal. While it might give you a bit of a start, remember that it could be a sign of an underlying issue. As always, your vet will be the best guide to assess the situation and rule out any hidden threats.

  1. Tumors and Growths: Unpleasant Surprises

While they aren't common guests, tumors and growths could sometimes decide to make an appearance on or near the dog's third eyelid. These abnormal masses could be harmless or malignant, but it's not worth playing the guessing game. An immediate visit to the veterinary ophthalmologist is the wisest course of action for a swift diagnosis and treatment plan.

  1. A Case of Eye Irritation and Discharge

If your dog's third eyelid is grappling with inflammation or infection, it could cause your pup's eye to be irritated and release a discharge. The eye may turn red, watery, or even release a thicker, pus-like discharge—not the most delightful of sights. Yet, it's crucial to consult your vet promptly. They can help you uncover the underlying cause and come up with an effective treatment plan to help your dog feel better in no time.


The dog third eyelid, or nictitating membrane, plays a vital role in maintaining the health and protection of a dog's eyes. Understanding its purpose and functions can help dog owners identify potential issues and seek appropriate veterinary care. Regular eye examinations, proper hygiene, and prompt attention to any changes or abnormalities can contribute to the overall well-being of a dog's eyes. Remember, if you notice any concerning signs related to the dog third eyelid, consult with a veterinarian for a thorough evaluation and guidance.

Frequently Asked Questions (FAQs)

What is the purpose of the dog third eyelid?

The dog third eyelid serves various functions, including lubrication, protection against foreign objects, tear distribution, and drainage.

Why is my dog's third eyelid visible?

Visible third eyelid can indicate an underlying health issue or eye condition. It is recommended to consult with a veterinarian for a proper evaluation.

How can I prevent eye issues related to the dog third eyelid?

Regular veterinary check-ups, maintaining good eye hygiene, and avoiding exposure to potential eye irritants can help prevent eye issues.

Can cherry eye be treated without surgery?

In some cases, non-surgical treatment options may be attempted, but surgery is often necessary to address cherry eye effectively.

Is the dog third eyelid unique to dogs?

No, other animals, including cats and some birds, also possess a third eyelid, although its appearance and functions may vary.

Can a dog live without the third eyelid?

While the third eyelid serves important functions, dogs can still live a relatively normal life if it becomes damaged or needs to be surgically removed. However, veterinary guidance is essential in such cases.

Leave a Reply

Your email address will not be published. Required fields are marked *