The "Eyes" Have It, but What Is It?
- rickmillertx1
- Aug 31
- 3 min read
What's Wrong With My Puppy's Eye?
by Nancy Miller
8/29/2025
The answer to that question is, "Absolutely NOTHING!"
The first time we saw this, we first thought she was going blind, a "veil" was growing over her eye, a deformity; something was horribly wrong. Immediately, we rushed her to the vet, thinking he'd send us to our veterinary ophthalmologist. After a thorough examination, he pronounced, 'Her eyes are completely healthy. You're just seeing her third eyelid."
What? Dogs have three eyelids? I remembered hearing something about cats having three eyelids, but they are strange creatures who can see in the dark. Guess what? Although a dog's night vision isn't as acute as a cat's, they still see much better in the dark than you or I, and it has nothing to do with a third eyelid.
Then what is this third eyelid?
The third eyelid, or the nictitating membrane, is a triangular membrane of conjunctival (think conjunctivitis = pink eye) tissue located in the inner corner under the lower eyelid. It's often called the inner eyelid. It can be a pinkish, whitish, or grayish color and is translucent as you can see in the picture.
What's the purpose?
As it sweeps across the surface of the eye, it
provides protection and cleans by removing debris, a blade of grass, an eyelash and by shielding the cornea from scratches and UV rays.
distributes a tear film from a gland within to keep the eye lubricated. Attached to its base is one of the most important tear glands that produces 50% of a dog's tears.
provides immunity with the lymphoid tissue that it contains, helping fight off infection.
protects the dog's eye, especially if she is walking or running through brush where her eye can easily be scratched.
is an important part of keeping your dog's eyes healthy and functional.
Why don't we usually see it?
For the most part, it stays hidden, but it can be seen if the dog is sleepy, relaxed, or if the eye is irritated and there's a problem. The picture above is of a two-week-old puppy whose eyes had just recently opened, which can be another time the third eyelid is visible. It can also be normal to see this inner eyelid from time to time, but if it doesn't retract, or if it looks red and inflamed, see your vet.
Why do I sometimes see it when my dog is sleeping?
The third eyelid acts as a barrier for the eye, especially during sleep. It continues to produce tears to lubricate and cleanse the eye. Some dogs may sleep with their eye(s) partially open, and the inner eyelid is often visible in this position. It's more obvious in short-snouted dogs because their eye sockets are smaller making the eyes more prominent.
Can there be problems with the third eyelid?
The most common problem is called Cherry Eye when the protrusion of the eyelid gland pops out and appears as a bright red mass in the inner corner of the eye. This occurs when the ligament holding the tear gland ruptures. It usually occurs in younger dogs, but we once had a senior dog who had cherry eye. Surgery is usually the best option, but for our senior dog, the risk of anesthesia wasn't worth the surgery since the dog was not in any discomfort. The risk of eye infection was greater for her, however, because the eye was not being continually cleansed and lubricated which could have led to dry eye.
Another problem is conjunctivitis, more commonly known as pink eye. It can be caused by a virus, allergies, trauma to the eye such as a scratch, a foreign body, or dry eye. Symptoms are redness; swelling; cloudy, yellow or greenish discharge; squinting, and/or excessive blinking. Treatment requires topical and/or oral meds as distributed by your vet to treat the inflammation or infection.
Basically, the third eyelid is an amazing piece of anatomy with relatively few problems, but if you do see any of the warning signs as detailed in this blog, call your vet.
In the meantime, learn the art of making gentle, non-threatening eye contact with your dog. It strengthens your bond with your dog if done correctly. But that's for another blog!
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