Does my Dog Have 3 Eyelids?

Yes - your dog does in fact have a 3rd eye lid and did you know, humans used to have one too? A dog's third eye lid is also known as the 'nicitating membrane.' 
Throughout evolution, the third eye lid in humans has shrunk and today is simply a small feature in the inner corner of our eyes, which helps to drain tears and keep debris away from the eyes. 

What does my dogs third eye lid do?

Like humans today, animals have two eye lids that move vertically, the upper and lower eye lids. These eye lids work to protect the eye lids from any debris, damage, sun light and to maintain moisture on the eye balls. It is responsible for creating up to 50% of a dog's tears so is vital to their eye health. 
The third eye lid of dogs and other animals such as cats adds even more protection to the eye ball and is not normally visible. 

Where is the third eye lid on my dog?

A dogs third eye lid is located under their lower eye lid and sits in the corner of the eye. When needed, the third eye lid will extend across the dog's eye to protect it from any damage and helps to spread moisture across the eye ball. 
The third eye lid is opaque in colour and a dog is unable to see through it. It moves horizontally across the eye. 
The third eye lid also contains lymph nodes so helps to prevent eye infections. Unlike the upper and lower eye lids, the third eye lid does not move voluntarily and moves independantly. It is often triggered by the retraction of the dog's eyeball into it's socket (closing it eyes)

Can I see my dogs third eye lid?

in normal circumstances, no. In healthy dogs, their third eye lid is often not visible and will not cause any interruptions to your dogs day to day life. For this reason, if the third eye lid is visible, it's a good indication that there may be a health concern for your dog. Some conditions that can affect the third eye lid in dogs includes;

• Cherry Eye - a condition where the third eye lid tear gland becomes swollen and bright red in colour, swelling out from the edge of the dog's eye. This condition is more common in some breeds than others, including Bulldogs, Beagles and Shih Tzu's. 
• Conjunctivitis - which can be caused by a virus, allergy flare ups or dry eye. This can cause a flare up of the third eye lid and cause it to be exposed from a dog's eye. 
• Poor Health Conditions - such as dehydration, weight loss, malnourishment or any condition that can affect the muscles around a dog's eye, can cause the third eye lid to be exposed. 
  

Should you have any concerns about your dogs third eye lid or their eye health, you should always consult your vet for an examination. If a dogs third eye lid is not functioning correctly, it could lead to eye damage, pain or discomfort for your dog.