The 3th eyelid or nictitating membrane of the dog
The dog has a third eyelid in addition to its upper eyelid and lower eyelid. It is called the nictitating membrane.
This membrane is located in the inner corner of the eye (called the inner canthus).
It consists of a roughly triangular fold of conjunctiva, the base of the triangle of which consists of a free edge usually pigmented in dogs and often hidden by the lower and upper eyelids.
Note carefully!
In some dogs, it happens that the free edge of the nictitating membrane is not pigmented and therefore appears pink (on the right in the photo below).This "anomaly" is of no consequence but can make the membrane more visible, which can easily be confused with prolapse of the nictitating membrane. It may only affect one eye out of the two, especially in dogs with variegated coats.
The dog's nictitating membrane contains:
- a little T-shaped cartilage for support,
- lymphoid follicles,
- a gland, the nictitating gland, at the base of the cartilage. The nictitating gland serves to produce 30-60% of the watery part of the tear film.
The nictitating membrane slides along the eyeball when the dog blinks and thus facilitates the distribution of the tear film and the elimination of debris towards the inner angle of the eye, a bit like a 'a wiper.
Ailments of the 3th eyelid of the dog
The nictitating membrane of the dog can be the seat of various affections among:
Dislocation of the nictitating membrane
Also called prolapse of the nictitating gland, the dislocation of the nictitating gland corresponds to a displacement of the nictitating gland which then moves out of its normal position. This gland is then abnormally exposed to air and light, which causes its irritation. A pinkish to red, smooth and fleshy mass is then observed which suddenly appears at the inner angle of the dog's eye. Young dogs are most commonly affected and the condition most often affects only one eye, although both eyes can be affected (but rarely at the same time). The dislocated gland can then be surgically removed or repositioned in its physiological location.
Several breeds of dogs are known to be predisposed to this condition such as the Beagle, the Cocker Spaniel, the Great Dane, the French Bulldog, the Pekinese, the Basset Hound, the Cane Corso, the Lhasa Apso or even the Shar Pei.
Eversion of the nictitating membrane cartilage
The eversion of the cartilage of the nictitating membrane corresponds to a rolling of the free edge of the nictitating membrane, linked to a faster growth of the posterior part of the T-shaped cartilage than its anterior part. The involvement may affect one or both eyes and is manifested by the formation of a pinkish to red, smooth mass located in the lower part of the eye. It is usually accompanied by chronic conjunctivitis and muco-purulent secretions. Surgical treatment is fortunately possible.
Several dog breeds are predisposed to it, such as the Great Dane (which often associates a dislocation of the nictitating gland with the eversion of the nictitating cartilage), the Berger Picard and the German Shorthaired Pointer.
The prolapse of the nictitating membrane
3th dog eyelid prolapse, also called nictitating gland prolapse, is a condition in which the third eyelid of the eye becomes visible and forms like "a skin over the eye" of the dog.
This anomaly can be congenital or secondary to other eye conditions as more general. The treatment then depends on the cause diagnosed by the veterinarian.
Follicular conjunctivitis
Follicular conjunctivitis is an enlargement of the follicles of the nictitating membrane. This type of conjunctivitis results from exposure to allergens present in the environment (pollen, dust) and generally affects young dogs, seasonally. It concerns more dogs predisposed to atopy such as the Collie or the Labrador as well as those who already have eye problems that predispose them to irritation.
A local treatment based on eye cleaning and the instillation of antibiotic and anti-inflammatory eye drops or ophthalmic ointments is possible. When it is not enough, surgical treatment can be considered in some cases.However, in some cases, this condition may disappear spontaneously after the animal is 2 years old.
Lymphoplasmacytic infiltration of the nictitating membrane
Lymphoplasmacytic infiltration of the nictitating membrane is an autoimmune condition that affects the 3th eyelid of dogs. It is manifested by a thickening of the nictitating membrane and an accumulation of blood in the latter.
The treatment of this condition, which particularly affects the German Shepherd, the Belgian Shepherd, the Shetland, the Collie and the Greyhound, is essentially medical. It is based on the application of ophthalmic ointments based on corticosteroids and/or cyclosporine A.
The nictitating gland cyst
More rarely, it happens that the nictitating gland is the site of the development of a cyst, which leads to a prolapse of the nictitating membrane. Surgical treatment is then possible.
Tumors of the nictitating membrane and gland
The membrane and the nictitating gland can also be the site of the development of benign or malignant tumors. The management then depends on the nature of the tumor that the veterinarian will endeavor to determine.
Foreign bodies under the nictitating membrane
The posterior part of the conjunctival cul-de-sac, or bulbar portion of the nictitating membrane, is a fairly frequent location for foreign bodies and, in particular, for spikelets. The risk is then that the vegetable fragment rubs on the cornea and causes a corneal ulcer.
When there is a foreign body stuck in this place, the veterinarian must remove it, which generally requires local or general anesthesia.