Do dogs have a third eyelid?

Just like cat, dogs do indeed have a third eyelid – but what is it for and are there any conditions which can affect it?  In this article, Holidays4Dogs finds out more.

The technical name for the third eyelid is, ‘niticans’ or the ‘nictitating membrane’ and is located in the corner in each of the dog’s eyes. Its purpose is to protect and lubricate the eye since it has a major tear gland attached to the base.

The third eyelid can vary in colour depending on the individual dog and while it is generally pigmented a grey colour, it can also be almost clear.  When the dog is sleeping, the third eyelid closes underneath the top and bottom lids to partially cover the eyeball.  If your dog wakes quickly from sleep, you may notice the third eyelid as it slips back behind the eye.

Because you can’t normally see the dog’s third eyelid under normal circumstances, it can be useful to know what this might mean should you notice that the membrane in the corner of his eye is constantly visible, as this could indicate that something is wrong.

It could be something as simple as your dog feeling off colour if the third membrane is showing, but there are a few more serious conditions that it could point to, so always get him checked by your vet if you are concerned – this is particularly important if the membrane or any part of the eye is swollen, red or weepy.

One of the most common conditions relating to the eyelids is, ‘cherry eye’ and refers to a condition where the third eyelid gland has prolapsed and is seen as a smooth pink or red lump on the edge of the eyelid which looks rather like a small fruit – hence the term, cherry eye.  This can cause the dog some significant discomfort and there can be other complications such as conjunctivitis as a result.

Cherry eye is generally regarded as congenital disorder and is particularly know to affect certain breeds more than others.  Bassets, Bulldogs, Spaniels, Newfoundlands and Pugs are some of the breeds more commonly affected by cherry eye.

If the condition is treated very early on, it is possible to gently massage the tear gland back into place using warm compresses and eye drops (dog specific).  However, this doesn’t always mean that the condition will clear up for good and the safest way to treat cherry eye is to seek veterinary advice.  For chronic conditions, surgery is usually the only option and your vet will attempt to reattach the duct back into place.  As a last resort the duct can be removed but this will almost certainly result in the dog needing lifelong treatment to manually lubricate the eye in the absence of this important tear duct.

A less common, but similar condition to cherry eye is, ‘scrolled cartilage’ and involves one section of the cartilage on the third eyelid growing more rapidly than the rest, which results in a scrolling effect.  The condition can be confused with cherry eye as the resulting redness and swelling looks very similar.  Scrolled cartilage will almost certainly need operating on toe removed the affected cartilage.  Both conditions can affect one or both eyes.

If you notice that your dog’s third eyelid is visible while he is awake, it is always a sensible precaution to have him checked out by your vet to find out exactly what the problem is.