Dogs have three eyelids. All dogs are born naturally with three eyelids. That third eyelid is called “the nictitating membrane” or “haw”. They are the same in different breeds and sizes of dogs, however the pigmentation varies from breed to breed. Some can be cloudy while others can be very clear.
When the haw closes, the dog’s eye looks as if it’s rolling back in its head. In fact, when dogs sleep, sometimes the upper and lower eyelids open, making it seem as the eyeballs are completely white because the membrane is closed.These eyelids are simple muscle and skin folds that protect the eyeball by clearing debris and mucus off of the cornea. The gland of the third eyelid, also, produces about one third of the dog’s tears. Finally, it helps protect the dog’s cornea from injuries.