3-Nictitating memb

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NICTITATING MEMBRANE AFFECTIONS

I-INVERSION AND EVERSION OF THE NICTITATING MEMBRANE: -

Definition:

Inversion and eversion of the third eyelid refer to rolling in or rolling out of the free margin of the membrane respectively. Congenital eversion seems to be more common than inversion. The condition may be unilateral or bilateral and seen mostly in young animals but may develop in middle-aged animals. Traumatic injuries and improper suturing of the conjunctival membrane of the nictitating membrane during operations may also result in eversion or inversion.

Symptoms:     

1-Increase visibility of the third eyelid

2-Inversion or eversion of the free margin of the membrane. The curl of the cartilage may occur anywhere between the narrow portion of the cartilage to the free border of the membrane.

3-Slight degree of conjunctivitis and mucoid discharge may be evident

Treatment:

The aim of the treatment is the removal of the abnormally curved part of the cartilage. Sometimes the whole deformed cartilage is removed. The operation is performed under effect of topical or general anesthesia. The free border of the membrane is grasped with Allis tissue forceps and gently elevated. A small amount of normal saline solution is injected between the curved part of the cartilage and the palpebral conjunctiva to separate it from the cartilage. The third eyelid is everted and the incision is made through the bulbar conjunctiva over the deformed part of the cartilage. The cartilage is then dissected and grasped through the wound. A scalpel or scissors are used to excise the deformed part. The wound heals without suturing or if the nictitans gland is exposed, the incision is closed with fine catgut. Topical application of antibiotic-steroid ointment twice daily is indicated for 7 days postoperatively.

II-PROTRUSION OF THE NICTITATING MEMBRANE: -

Causes:

1-Congenital microphthalmos (reduced globe size)

2-Enophthalmos (recession of the globe In the orbit)

3-Diseases accompanied by loss of weight and dehydration (decrease amount of periorbital fat).

4-Encephalitis due to rabies, tetanus or canine distemper and meningitis

5-Postorbital space occupying lesion such as; abscesses, cysts, tumor and hematomas.

6-Homer's syndrome in dogs. It is a partial or complete sympathetic denervation of the eye. The condition manifests itself clinically by miosis of pupil, protrusion of the third eyelid, ptosis, enophthalmos small palpebral fissure and changes in intraocular pressure.

Treatment: Treat the specific cause.

If the protrusion is severe and vision is in paired by the third eyelid, partial excision of the free edge of the membrane is indicated. Topical anesthesia is sufficient and a tenotomy scissors used for excision. The resulting wound is closed with fine number of catgut to prevent prolapse of the remaining cartilage and nictitans gland. Partial excision is better than total one to preserve the function of the membrane and gland. The nictitating membrane is a useful and important structure for the eyeball. The only indications for total excision of the membrane are severe irreparable trauma and malignant neoplasm.

III-HYPERTROPHY OF THE NICTITATING MEMBRANE: -

Definition:

It is a specific inflammatory and degenerative disease of the third eyelid of German Shepards dogs.

Symptoms:

1-The first sign is bilateral inflammation and depigmentation of the nictitating membrane and mucoid discharge is evident.

2-As the process of inflammation progresses, there is thickening and enlargement of the membrane and development of nodular irregular surface. The cause is not established. Biopsy and scraping from the conjunctiva reveal plasma cell and other inflammatory cells.

Treatment:

1-Long term steroid-antibiotic therapy                                                   2-Excision of the third eyelid

IV-NEOPLASMS OF THE NICTITATING MEMBRANE: -

Squamous cell carcinoma is the most common tumor of the third eyelid in all species of animals and unpigmented membranes are more susceptible. Adenoma and adenocarcinoma have been described in dogs.

Treatment:

Surgical removal of the affected area is the treatment of choice, but if the lesion is extensive, radical excision of the entire third eyelid is indicated. If the cartilage is exposed during surgical excision of the tumor, the conjunctival wound is sutured to prevent prolapse of the cartilage or gland. Suturing will speed the process of healing and prevent formation of excessive granulation tissue at the wounded area.

V-ABSCESSES OF THE NICTITATING MEMBRANE: -

Subconjunctival abscesses of the nictitating membrane are most common in cattle and buffaloes. Causes:

Foreign body penetration or trauma appears to be the main cause of the condition.

Symptoms:

The third eyelid protrudes and extends over the cornea obscuring the animal vision.

Treatment:

1-Incision of the abscess at the palpebral surface of the conjunctiva and evacuation of its content

2-Lavage of the abscess cavity and the eyeball with mild antiseptic solution

3-Antibiotic ointment is applied twice daily for 5 successive days.

VI-PROLAPSE OF THE NICTITANS GLAND: -

Prolapse of the nictitans gland over the free border of the third eyelid is also known as hyperplasia, hypertrophy, adenoma of the nictitons gland, or cherry eye. The condition seen frequently in dogs (Beagles and Cocker Spaniels) and reported in cat, sheep, and buffalo. The nictitans gland protrudes from behind the nictitating membrane as a reddish mass over its free border. The normal gland has a connective tissue bands that anchoring it to the periorbital tissues at the base of the membrane. When these bands are not developed properly, the gland moves towards the free edge of the membrane. The movement of the membrane causes the gland to prolapse outwards. Inflammation and hypertrophy of the gland develop as soon as the gland prolapsed

Causes:

1-Congenital, perhaps hereditary weakness of the connective tissue bands between the gland and periorbital tissues.

2-Trauma to the third eyelid or orbit.

Symptoms:

1-A rounded, cherry or pea-like mass appears at the medial canthus of the eyeball. The condition is usually bilateral.

2-Secondary epiphora and conjunctivitis may occur.

Treatment: Surgical excision of the prolapsed gland.

1-Grasp the gland by fixation forceps and apply a mosquito artery forceps at its base for a minute and then cut it by a scissors. An alternative procedure is that the bulbar conjunctiva is incised first over the gland and bluntly dissected from it then the mosquito artery forceps is applied to the base of the gland.

2-Hemorrhage is controlled, if present, by light pressure on the surgical wound for few minutes

3-Antibiotic-corticosteroid ophthalmic ointment is applied twice daily for 5 days postoperatively