Why Is My Dog's Third Eyelid Showing?
What Is That Membrane in My Dog's Eye?
Also known as the nictitating membrane or haw, the dog's third eyelid is something most owners aren't aware of until they see it for the first time. All dogs have this membrane found in the inner corner of the eye but it is typically noticed only when it is drawn horizontally across part of the eye. Its color varies depending on the dog's breed and can range from clear to cloudy.
What Does a Dog's Third Eyelid Do?
Deborah S. Friedman, D.V.M. and diplomate with the American College of Veterinary Ophthalmologists has several explanations.
- The third eyelid acts as the dog's "windshield-wiper" for the cornea, effectively removing debris or mucus off of it.
- This membrane is responsible for producing about one-third of the dog's tears, since it has one of the most important tear glands attached at its base, and its lymphoid tissue acts like a lymph node producing antibodies to fight off infections.
- It also helps prevent injuries to the dog's cornea.
In dogs and cats, this membrane is not normally visible other than when the animal is sleeping or suddenly awakens from sleep. Indeed, if you lift the eyelid of a sleeping dog you'll likely see the whole eye covered by the third eyelid.
The dog in my pictures awakened suddenly after resting on my legs, and once she was fully awake, her third eyelid re-positioned normally.
However, the prolonged presence of the third eyelid, even when the dog is bright and alert, often denotes some sort of medical problem.
In the next paragraphs, we will see some common and not-so-common medical issues associated with the abnormal appearance of the dog's third eyelid.
Did you know?
According to Animal Eye Care LLC dogs have two tear glands in each eye; whereas, humans have only one. The orbital tear gland is responsible for producing 60 percent of tears and the third eyelid tear gland produces 40 percent.
Reasons Why the Eye Membrane Might Be Showing
If your dog's third eyelid made a sudden appearance, you may be wondering what's going on. There are several possibilities that range from ocular problems to more systemic autoimmune or neurological disorders.
Canine Eye Problems
- The presence of the third eyelid could be a sign that the dog's eyeball has sunken into its socket, often because of pain and inflammation. The third eyelid covers the eye to protect it from further injury, as in the case of corneal trauma.
- It could also be that the structure meant to hold the third eyelid in place either weakened or got injured.
- A further possibility may include allergic conjunctivitis.
Some dog breeds are prone to prolapse of a gland found in the dog's third eyelid, a condition known as "cherry eye" mostly because of its bright red presence resembling a cherry in the corner of the dog's eye.
This is a congenital disorder found commonly in certain dog breeds such as cocker spaniels, beagles, Boston terriers, and bulldogs.
What happens is the cartilage responsible for supporting the membrane folds over causing the third eyelid to no longer work well as a "windshield wiper." This results in a gland that is exposed and potentially inflamed.
Some neurological diseases may cause loss of function to the nerve that supplies the third eyelid.
Horner's syndrome is a common neurological disorder that occurs suddenly and is characterized by sunken eye, droopy eyelids, droopy facial features, small pupil size, and the prolapse of the third eyelid.
Dilated blood vessels in the affected area cause owners to sometimes report that it feels warmer to the touch. The cause is unknown, but at times it can be triggered by trauma to the head, bite wounds, a herniated disc, a growth pressing on a nerve, a side effect of some medication, or a middle or inner ear disease.
While any dog can develop Horner's, golden retrievers and cocker spaniels are slightly predisposed. Other neurological disorders that can cause a third eyelid to be exposed include tetanus and dysautonomia.
Poor Physical Health
Certain physical conditions that are known for relaxing the muscles found around the eyeball and for causing the settling of the eye deeper into its socket may be a cause for the appearance of the third eyelid.
Dogs who are malnourished, dehydrated, who have lost weight or are generally not feeling well may manifest protrusion of the third eyelid.
Treatment varies depending on the cause. In some cases, a cause is never found. These are referred to as "idiopathic."
Sometimes the issue resolves on its own after several weeks. However, if it turns out to be an eye issue, as with all eye problems, it's best to see a vet, or better, a board-certified veterinary ophthalmologist immediately to prevent potential vision loss.
Questions to Ask
If you visit the vet or are trying to get a better idea of what's going on, here are some questions that can help you determine what's going on with your pet:
- Did your dog bump its head? Or experience any other trauma? You might just need a cold compress on the eye for anywhere from a few to thirty minutes.
- Is the eye okay aside from the third eyelid showing? In that case, and if both eyes don't also react similarly to light, there might be a cranial lesion.
- Is your dog struggling to keep that eye open? This might indicate an eye injury.
- Is there any discharge? This could be a sign of an eye infection.
If your dog's third eyelid appears abnormal, please see your vet immediately for diagnosis and treatment. This article is not to be used as a substitute for veterinary advice.
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Did you know dogs have a third eyelid?
What a Third Eyelid Looks Like
This article is accurate and true to the best of the author’s knowledge. It is not meant to substitute for diagnosis, prognosis, treatment, prescription, or formal and individualized advice from a veterinary medical professional. Animals exhibiting signs and symptoms of distress should be seen by a veterinarian immediately.
Questions & Answers
I understood that 'shark eye' is a sign of stress. Is this the same as the third lid showing itself?
'Whale eye' or 'moon eye,' (I never really heard the term shark eye before) is the term used to depict dogs who are showing the white part of the eye, and yes, you are correct in that it can be seen in situations of stress or aggression.
A classic example is a dog who is guarding a bone. The dog has his head lowered over the bone but he may be looking slightly sideways to make sure nobody comes near, and the whites of the eyes may be showing.
The third eyelid showing is a different situation. This involves a different part of the eye which is the third eyelid which resides in the inner corner of the eye when the dog is alert and awake, but slides over the eye when the dog falls asleep or when the dog is feeling unwell or there is some neurological dysfunction.Helpful 31
My dog had his teeth removed this week and he suddenly has this third eyelid, should I take him to the vet? He is also shaking.
You might want to call your vet to let him know your dog's third eyelid is showing after surgery. Sometimes the stress of a procedure - causes stress that allows other things to crop up. If he is shaking, he may have pain. Has your vet prescribed any pain meds? Hopefully, this is something that will resolve spontaneously.Helpful 9