Did you know that dogs have six eyelids — three for each eye? Many owners don’t, at least until something goes wrong with one of the third eyelids that are normally hidden from view.
First a little anatomy. We are all familiar with a dog’s upper and lower eyelids that function very much like ours. The third eyelids, or nictitating membranes, as they are also called, normally lie underneath the lower lids. When they close and cover the eyes, owners often mistakenly think that their dog’s eyes are rolling back in their head.
Third eyelids serves as an extra layer of eye protection for dogs who, at least in the past, spent a lot of time running through brush and grass and digging in the dirt, which can lead to debris in the eyes and wounds to the cornea. Third eyelids sweep dirt and other material off of the surface of the eyes and keep the eyes moist. They also harbor a lot of tissue associated with the immune system and help heal any eye wounds or infections that do develop. When a dog has an injury to the eye, the third eyelid will often be raised to cover it. In these cases, I think of the third eyelid as a natural Band-Aid to the eye.
But the condition that most often brings third eyelids to an owner’s attention is cherry eye — more officially known as a third eyelid gland prolapse. The gland in question produces tears and is normally invisible since it is anchored by connective tissue on the inner surface of the third eyelid. When that connective tissue is weaker than normal, the attachments can break down, allowing the gland to slip from behind the third eyelid. It looks like (and is) a lump of pink or red tissue at the inner corner of the dog’s eye. Sometimes a gland will protrude every so often and then go back to its normal position before the final, permanent prolapse occurs.
Any dog can develop cherry eye, but is most often seen in Cocker Spaniels, Beagles, Boston Terriers, English Bulldogs, Lhasa Apsos, and Pekingese. It is thought that a combination of facial anatomy (prominent eyes) and a genetic weakness in the connective tissue that normally holds third eyelids in place is to blame. Often one eye will be affected initially, but with time the other gland will also prolapse.
There is no way to prevent cherry eye from developing in at-risk dogs, but thankfully the condition is not too difficult to treat. A veterinarian can perform one of a couple of different surgeries that put the gland back in a more normal position and hold it there. In the past, we used to surgically remove the affected gland, but too often that created another problem, dry eye (keratoconjunctivitis sicca), since we were removing the gland that was responsible for approximately one-third of tear production in the affected eye.
Dr. Jennifer Coates
Image: Seregraff / Shutterstock