7 Diseases of the canine conjunctiva and nictitating membrane (nictitans/third eyelid/membrana nictitans) are common in the dog, and for the most part easily visualized and diagnosed. Examination of both the conjunctiva and nictitating membrane is by direct inspection; occasionally some magnification is useful. Both congenital and traumatic lesions are infrequent, but inflammatory diseases are common and often secondary to lid anomalies, tear deficiency, and abnormal nasolacrimal drainage, among other causes. “Cherry eye” or inflammation and prolapse of the nictitating tear gland is common in young dogs, and surgical re‐positioning of the gland beneath the nictitans is recommended. Some of these dogs are still prone to keratoconjunctivitis sicca (KCS) in the future, so continued monitoring is recommended. Neoplasms of the conjunctiva and nictitans are less frequent than those affecting the eyelids, but are less predictable and decidedly more malignant. Most conjunctival neoplasms require a fairly wide resection, and recurrences are more likely. Adjunctive therapy is often recommended to reduce the possibility of recurrence. Neoplasms of the nictitans usually involve the tear gland, are quite malignant, and usually require excision of the entire nictitans. The nictitans, as an appendix of the medial conjunctiva, functions with passive dorsolateral movements across the cornea. Occasionally, extensions from both the upper and lower margins of the free border of the nictitans occur. These mucosal extensions are often pigmented and extend for several millimeters along the middle of the bulbar conjunctiva. These are generally incidental findings that do not cause clinical signs, but when extensive they can impair nictitans movements. They occur most frequently in the American Cocker Spaniel (Figure 7.1). Figure 7.1 Encircling nictitans in an American Cocker Spaniel. Note the pigmented conjunctival membrane extending from the leading margin of the nictitans laterally. As described in Chapters 5 and 8, dermoids or choristomas are normal skin that develops in abnormal locations (eyelid, conjunctiva, cornea). These raised and sometimes pigmented masses often produce long and irritating coarse hair, which prompts presentation (Figure 7.2). Treatment is careful surgical removal of the entire mass. Figure 7.2 Dermoid of the lateral bulbar conjunctiva in an English Bulldog puppy. Note the mass is lightly pigmented and covered by long coarse hair. Dermoids, if small, are often missed, but when the long coarse hairs begin to grow ocular irritation begins and the condition becomes apparent. Eversion or, less frequently, inversion of the leading margin of the nictitans occurs primarily in the large and giant breeds of dogs (i.e., German Shorthaired Pointer, St. Bernard, Great Dane, and Newfoundland). Presenting clinical signs are epiphora, limited blepharospasm, and a pink raised mass in the medial canthus or in front of the nictitans (Figure 7.3). Closer examination reveals eversion of the leading edge of the nictitans (inversion or curling inward is rare) thereby exposing the nonpigmented bulbar (deeper) surface of the nictitans. Figure 7.3 (A) Everted cartilage of the nictitans in a German Shepherd puppy. Note the leading pigmented margin is absent and folded over (everted) exposing the defective cartilage (see insert: bent cartilage upon removal). (B) Scrolled and everted nictitans cartilage in a young Great Dane. Treatment is surgical removal of the bent or U‐shaped cartilage (see Figure 7.3 insert) located immediately beneath the leading margin and the extensions of the cartilage (not the entire nictitans). Surgery is performed through a small incision on the palpebral conjunctival surface immediately over the defect and often no sutures are required for closure. Incision of the leading margin of the nictitans should be avoided. The immediate postoperative appearance is a normal nictitans. Sometimes the leading margin of the nictitans remains somewhat deformed, but after several days to a few weeks returns to normal position. Recently, a procedure utilizing thermal cautery to straighten the bent cartilage without excision of the deformed segment has been described. “Cherry eye” or the inflammation and prolapse of the tear gland of the nictitating membrane is a common disease of dogs less than 1 year of age, and affects certain breeds more commonly, especially the American Cocker Spaniel, Boston Terrier, Miniature Schnauzer, English Bulldog, and Beagle (Figure 7.4). Some of the same breeds with this disease are also predisposed to KCS. Figure 7.4 (A) Prolapse of both nictitans tear glands in a Boston Terrier puppy. The enlarged and prolapsed glands are anterior to the nictitans leading margin. (B) Close‐up of a 1‐year‐old English Bulldog puppy with a unilateral “cherry eye.” (C) Postoperative appearance of American Cocker Spaniel 1 week later using the intranictitans surgical procedure (an anchoring procedure that permits unrestricted nictitans movements). The history is of recurrent nictitans inflammation and protusion with eventual prolapse of the gland which becomes medically nonresponsive to topical corticosteroids and antibiotics. Close inspection reveals the anterior surface of the nictitans to be normal, but with protraction of the nictitans by thumb forceps, the full extent of the inflamed and prolapsed gland protruding above the leading margins can be appreciated. Surgical correction of “cherry eye” is usually necessary once the gland prolapse occurs. The chance of KCS developing is higher if the gland is left exposed than if it is surgically replaced. There are several surgical procedures (pocket, imbrication, anterior, posterior and intranictitans anchoring), and each has advantages and limitations. The goals of surgery are to replace the gland, reduce its inflammation, and permit continued movement of the nictitans. Recurrences can develop after surgical repositioning, particularly with very large or chronic swellings of the nictitans gland. Long‐term monitoring of these dogs with Schirmer tear tests is recommended as some dogs will develop KCS even after gland replacement surgery. Protrusion of the entire nictitans can be associated with persistent conjunctivitis and epiphora (Figure 7.5). Protrusion can be primary (no antecedent disease detected), or secondary to microphthalmia, enophthalmia, space‐occupying orbital diseases, Horner’s syndrome, tetanus, and other diseases.
Canine Conjunctiva and Nictitating Membrane (Nictitans)
Congenital or Developmental Disease of the Nictitans
Encircling Nictitans
Conjunctival Dermoid
Eversion of Nictitans
Cherry Eye (Inflammation and Prolapse of Nictitans Gland)
Protrusion of Nictitans
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