Read the German translation: Probleme Des 3. Augenlides
Trauma to the Nictitans
Injuries to the third eyelid may cause conjunctival flaps and involve the free margin. Careful appositional suturing as soon as possible after the traumatic event may prevent deformation and shortening of the nictitans. Small flaps of the free margin can be removed. Restoration of a smooth free margin is mandatory.
Inflammatory Conditions of the Nictitans
Most conjunctival disorders will involve the nictitans as well. The lymphocytic plasmacytic infiltration (pannus) of Shepherds will affect most obviously the leading edge of the nictitans. Granulomas may occur in cats after claw injuries.
Eversion of the Third Eyelid
Scrolling of the third eyelid is a uni-or bilateral condition caused by an abnormal curvature of the vertical portion of the T-shaped cartilage. This will evert the free margin of the nictitans. It occurs mostly in dolichocephalic large dog breeds like the Great Dane, Saint Bernard, Newfoundland or Doberman and may be hereditary. However, it may occur in cats, too. Surgical correction involves resection of the scrolled part of the cartilage from the bulbar aspect of the nictitans. The author prefers to combine the resection with a small conjunctival "pocket" as used for the gland reposition (see below) to prevent a prolapse of the nictitans gland postoperatively. Suturing with the knots placed on the anterior surface avoids frictional irritation of the cornea. The author's preferred suture material is vicryl® 6-0.
Prolapse of the Nictitans Gland
Protrusion or prolapse of the nictitans gland ("cherry eye") occurs most commonly in certain dog breeds (brachycephalics as well as giant breeds) and occasionally in cats. A laxity of the connective tissue combined with a lymphoid hyperplasia has been claimed to be the cause of the prolapse. Several techniques for surgical reposition have been described. The author's preference is a modification of the pocket technique described by Morgan et al. (1993). The gland should not be removed as keratoconjunctivitis sicca may occur after resection in predisposed breeds.
Neoplasia of the Third Eye Lid
Adenocarcinoma, hemangioma, hemangiosarcoma and lymphoma as well as squamous cell carcinoma are common neoplasia of the third eyelid. Diagnosis is based on fine needle aspiration biopsy (FNAB) or surgical biopsy. After neoplasia has been confirmed, invasion of the orbit and distant or regional lymph node metastases have to be ruled out. Surgical excision is the treatment of choice for neoplasia other than lymphoma. Excision may be limited to the nictitans and adjacent conjunctiva or may necessitate exenteration of the orbit.
Cysts of the Third Eyelid
Cysts of the third eyelid may occur after surgical repositioning of the prolapsed nictitans gland. Diagnosis is based on FNAB which will reveal clear cystic content. Surgical resection of the cystic wall is usually curative.
Nictitans Prolapse in the Rabbit
In rabbits the third eyelid may be protruding due to orbital venous congestion or backpressure. This is a bilateral condition which may be an indication of mediastinal masses (thymomas) or a cardiac disease. Hyperplasia or cellular infiltration of the Harderian gland may also cause nictitans prolapse which is usually unilateral. Excision of the Harderian gland is curative in those cases.