About That Third Eyelid

Dogs have lots of wonderful and fascinating quirks, but did you know that they also have an extra eyelid? Yep, this inner eyelid, known as a nictitating membrane, provides extra protection against scratches and debris. It plays an important role, especially considering all the scurrying dogs tend to do in bushes and grass. Located under the lower eyelid on the inner corner of the eye, it’s also responsible for spreading moisture across the eye and keeping the eye healthy. The third eyelid isn’t visible to us - in fact, if you do see it then it may be a sign you need to take your dog to the vet. It could be a sign of eye issues such as cherry eye, Horner’s syndrome, or conjunctivitis.

Another interesting fact? Humans also had a third eyelid, but it shrank throughout evolution to become the plica semilunaris - a small structure near the tear duct. It still plays a role in keeping our tears drained and debris flushed from our eyes.