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Anatomy and Physiology
Movement
Congenital Abnormalities
Encircling third eyelid
Dermoids
Acquired Abnormalities
Eversion or inversion of the cartilage
Prolapse of the gland of the third eyelid
Plasma cell infiltration of third eyelid
Hypertrophy of lymphoid follicles
Granulomas in horses
Hyperplasia due to actinic irritation
Neoplasia
Also called nictitating membrane or membrana nictitans. This is particularly well developed and functionally important in the bird (Sivak and Glover) in which it is thin and translucent .
Covered with conjunctiva.
T-shaped cartilage for support.
Gland surrounding the base of the cartilage - seromucinous secretion.
Numerous lymph follicles especially on bulbar surface.
Protects the cornea.
Redistributes the tear film.
Adds to tear flow - this is important to keep in mind: if the third eyelid is removed, tear production may be compromised and, if the lacrimal gland ceases to function later, keratoconjunctivitis sicca will develop.
In mammals, normal movement is passive and occurs when the globe is retracted; this results from pressure by the globe on retrobulbar fat which in turn moves causing displacement of the third eyelid by forward pressure at its base.
Birds have special muscle and tendon arrangement whereby they can actively draw the nictitating membrane across the globe (from medial to lateral) . This action serves to distribute tears across the cornea and is important to anterior segment health similar to eyelid blinking in mammals.
Because protrusion of the third eyelid is passive in mammals, it will be seen anytime there is active or passive posterior displacement of the globe. Conditions which are associated with third eyelid protrusion include: enophthalmos, dehydration, loss of body fat, tetanus, microphthalmia, Horner's syndrome and idiopathic protrusion in cats.
The third eyelid also may be displaced due to space occupying orbital lesions such as neoplasms or abscesses.
In this condition the conjunctiva of the third eyelid extends around the globe to various degrees; this may produce a band of tissue which lies over much of the peripheral part of the cornea. Most of the time the condition is not extensive enough to cause clinical problems; surgical excision of the offending tissue in severe cases is the treatment of choice. Seen most frequently in cocker spaniels and beagles.
These are uncommon in this location. If the dermoid is irritating the eye or interfering with function it can either be dissected away or the third eyelid can be removed (this latter procedure should be used only as a last resort).
Outward (eversion) or inward (inversion) curl of the cartilage; the defect usually is in the narrow portion of the cartilage, but can occur anywhere along its length. Seen mainly in the dog.
Eversion more common than inversion.
Occurs spontaneously in certain breeds (Weimaraners, Newfoundlands, Chesapeake Bay retrievers and St. Bernards) usually before a year of age. Cause unknown. May be heritable.
Can occur through injury to the third eyelid.
As a result of irritation, conjunctivitis, keratitis and epiphora may develop, but there usually are no signs of discomfort.
The client probably will complain of a red or pink mass in, or discoloration to, the medial canthal region of the affected eye.
The affected cartilage must be surgically excised
A similar procedure is used for inversion of the cartilage.
Prolapse of the gland of the third eyelid inappropriately is referred to as ‘cherry eye’ by many, including veterinarians. May be bilateral although both sides may not become affected at the same time.
Apparently due to improper attachment of the gland of the third eyelid which leads to looseness. When the gland prolapses, there is vascular congestion which leads to swelling of the gland which gives it a hypertrophied appearance. It may spontaneously regress and return repeatedly.
Seen frequently in dogs, particularly in Boston terriers, American cocker spaniels, English bull dogs and beagles. Rarely seen in species other than the dog.
Although epiphora and conjunctivitis may occur, prolapse of the gland usually is not a problem for the patient. The client, however, often is upset by the large, red mass.
Try to replace and suture the gland to its proper position. This may preserve its lacrimal function.
See the method described by Morgan, et al.. They have based their modification of existing procedures on moderately long-term evaluation of the results of various methods of treatment. This modification may increase the chance of success of gland replacement and continued function.
If surgery to replace the gland fails, or if there is any question about doing the surgery, refer the patient to a specialist. Do not remove the gland unless all else fails!
Particularly in German shepherds; may be related to or associated with chronic superficial keratitis (pannus).
The edges of the third eyelid become thickened, irregular and gray-red to gray-blue; histologically, this appears to be due to infiltration by plasma cells.
Cause is not known.
Strong topical steroids may control the condition - usually must continue on chronic basis.
If medical therapy is unsatisfactory, can try to surgically dissect the thickened material from the third eyelid; follow with antibiotic/steroid (strong) drops for several days then switch to strong steroid alone for continued control. Could also try cryotherapy or radiation (such as strontium). If there is any question as to what to do, refer the patient to a specialist.
This is so-called ‘follicular conjunctivitis.’ The abundant lymphoid tissue normally present on the bulbar surface of the third eyelid often participates in local immune-mediated processes. This results in proliferation of the lymphoid tissue giving rise to many small, pink projections or follicles. Because these represent a reaction to an insult (often chronic), the condition should not be considered a specific entity and treatment should be aimed at the actual cause of the condition (e.g., any chronic inflammatory condition).
Some veterinarians believe that removal of the follicles is the only means of treating the situation. The presence of follicles alone, however, usually is not a problem for the patient. Even when the underlying cause is treated successfully, the follicles may persist, asymptomatically, for months.
Granulomas associated with Habronema larvae may occur in the third eyelid. There will be erythema in and around the region; the center of the mass may abscess or become necrotic. Surgical excision followed by topical antibiotic/steroid preparations usually is effective. May also try topical organophosphates (e.g., echothiophate) or cryotherapy.
In individuals with amelanotic or hypomelanotic third eyelids, there may be hyperplasia of exposed epithelium if they spend time outdoors. This may give the tissue an inflamed appearance or may lead to squamous cell carcinoma. If there is inflammation, it may be controlled by topical steroids; neoplastic transformation should be treated appropriately. Tattooing of the tissue may be the only way of preventing problems of this type.
Neoplasia of the third eyelid is uncommon in the dog. Adenocarcinoma of the gland or hemangioma
Squamous cell carcinoma is seen occasionally - widely excise the affected portion of third eyelid; may require radiation therapy.
Neoplastic lymphocytic infiltration may occur as part of systemic lymphosarcoma
Fibrosarcoma
Squamous cell carcinoma is the most common neoplasm of the third eyelid in horses
If orbital fat protrudes from the incision site after excision of the third eyelid, the conjunctiva of the third eyelid should be over sewn using 6-0 absorbable suture in a simple continuous pattern
Footnotes:
‘Cherry eye’: I mention this only because of tradition. I hope you will join me in never using it so that this tradition can die quietly and quickly.