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Why Can I See My Dog’s Third Eyelid? Vet Approved Facts and FAQs

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By Nicole Cosgrove

a blue french bulldog with infected eyes showing its third eyelid

Vet approved

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Reviewed & Fact-Checked By

Dr. Lauren Demos

DVM (Veterinarian)

The information is current and up-to-date in accordance with the latest veterinarian research.

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Locking eyes with your dog is one of the most rewarding moments as a dog parent, and there is so much we can tell during that eye gaze about our companions. However, while we read how they may be feeling, we may notice some physical attributes that weren’t there before. Perhaps this time, you noticed something extra in the corner of their eye.

It could be your dog’s third eyelid or nictitating membrane, which all dogs have. The third eyelid is always there but is not noticed because it is usually hidden. However, if it can be seen, it usually indicates something is wrong with the eye. If you can see your dog’s third eyelid, read on to figure out why it could be.

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Why Do Dogs Have a Third Eyelid?

Your dog has eyelids to protect their eyes, but dogs have a third one under the lower eyelid on the inner corner of the eye. It is also known as the nictitating membrane and has three parts which are:

  • The conjunctiva, which is a thin protective membrane.
  • T-shaped cartilage
  • A tear gland held in place by the cartilage

A dog’s third eyelid and the other eyelids serve to protect the eyes in various ways, such as :

  • Protection from being scratched, especially while walking or running, thanks to the blink reflex.
  • Keeps the eyes moist by spreading tears. Every time your dog blinks, the eyelids stimulate more tears while draining away the old ones. The third eyelid is responsible for 50% of a dog’s tears.
  • Tears contain immunoglobulins to protect the eyes from infection.
  • It removes any debris from the eye.
close up of a dog's eye showing its third eyelid
Image Credit: Robert Avgustin, Shutterstock

Why Can I See My Dogs Third Eyelid?

In healthy, awake dogs, the third eyelid isn’t seen unless the dog is dozing off or suddenly waking up. If your dog’s third eyelid is visible for a prolonged period, it might be suffering from an infection, cherry eye, neurological disorder, or poor physical health.

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General Eye Problems

  • Visibility of the third eyelid may indicate that the dog’s eyeball has sunken into its socket, frequently due to discomfort and inflammation.
  • If your dog’s eye has abnormally small eyes due to a congenital abnormality, then the third eye may be visible, or it can result from the eye shrinking due to a severe injury or inflammation.
  • It is possible that the support system intended to keep the third eyelid in place deteriorated or is injured.

Cherry Eye

Cherry eye is the most common ailment regarding the third eyelid. It is the name given for a prolapsed gland that has moved out of its usual position. The gland that is now exposed may become swollen and red. Cherry eye is more common in some breeds than others. The connective tissues that hold the third eyelid gland in place may be weaker in some species; it is suspected that there is a genetic component present in dogs that have cherry eye.

While it may look unpleasant, cherry eye appears worse than what a dog feels. However, it can lead to secondary problems that are more severe such as corneal ulcers and chronic dry eye.

Cane corso with cherry eye being looked at by the vet
Image Credit: Todorean-Gabriel, Shutterstock


Conjunctivitis is also known as pink eye. While pink eye is commonly known among humans, it can occur in dogs too. The third eyelid is made of the conjunctiva, and when this tissue becomes inflamed (conjunctivitis), the mucous membranes enlarge, become irritated, and change color to a brighter pink or red.

There are many causes of conjunctivitis in dogs, which include:
  • Dry eye
  • Allergies
  • Trauma to the eye
  • Debris or foreign objects, such as grass
  • Virus
Common signs include:

Horner’s Syndrome

Horner’s Syndrome is a nerve disorder that affects the eye and facial muscles, causing the eye to droop, the eyelid to protrude, or the pupil to constrict. It usually happens on one side of the face, and the third eyelid may become more pronounced and inflamed. The causes of Horner’s syndrome are varied and usually unknown but can include a brain injury or tumor, infections, and spinal cord lesions.

Depending on how severe it is, Horner’s syndrome typically goes away on its own in a few weeks or months. However, it might be a sign of a more serious medical condition.

Poor health

The third eyelid can also be seen in canines that are malnourished, dehydrated, or underweight. When a dog is ill, the soft tissues behind the eye may contract, sinking the eye backward and causing the third eyelid to be raised and more visible.

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How are Third Eyelid Issues Treated?

The primary cause for the visibility of a dog’s third eyelid will determine which treatment is needed, but treatment can often include:

  • Flushing the eye to remove debris or using ophthalmic forceps to remove any foreign object
  • Medications to treat infection
  • Suturing of large cuts
  • Surgery for cherry eye

Antibiotics and painkillers are likely to be part of the after-care regimen, depending on how intensive the repair operation was.

vet examining dog's eye
Image By: Ermolaev Alexander, Shutterstock

How to Care for Your Dog Eyelids

It is best to leave your dog’s eyelid alone unless there is an issue. Dogs with allergies and brachycephalic breeds are more susceptible to eyelid irritation, so it’s helpful to clean their eyes regularly. You can use a cotton ball with water to gently wipe your dog’s eyes but never use chemicals or soap.

If you notice anything abnormal with your dog’s eyes, such as swelling, redness, discharge, color changes, or growths, you should have your veterinarian have a look as soon as possible.

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All dogs have a third eyelid, but it usually can’t be seen. If you can see your dog’s third eyelid, it is typically a sign of an eye issue or poor health. In severe cases, it will usually be inflamed or protruding.

The most common ailment regarding a dog’s third eyelid is cherry eye, which isn’t painful for your dog but can lead to secondary ailments that may be more severe. Anytime you notice something out of the ordinary with your companion, it’s better to be safe than sorry and get your friend to the vet for a proper diagnosis.


Featured Image Credit: Deborah Lee Rossiter, Shutterstock

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