Cherry eye is a disorder of the nictitating membrane (NM), also called the third eyelid, present in the eyes of dogs and cats. Cherry eye is most often seen in young dogs under the age of two. Common misnomers include adenitis, hyperplasia, adenoma of the gland of the third eyelid; however, cherry eye is not caused by hyperplasia, neoplasia, or primary inflammation. In many species, the third eyelid plays an essential role in vision by supplying oxygen and nutrients to the eye via tear production. Normally, the gland can turn inside-out without detachment. Cherry eye results from a defect in the retinaculum which is responsible for anchoring the gland to the periorbita. This defect causes the gland to prolapse and protrude from the eye as a red fleshy mass. Problems arise as sensitive tissue dries out and is subjected to external trauma Exposure of the tissue often results in secondary inflammation, swelling, or infection. If left untreated, this condition can lead to dry eye syndrome and other complications. Description Cherry eye is most common in young dogs, especially breeds such as Cavalier King Charles Spaniel, English Bulldog, Lhasa Apso, Shih Tzu, West Highland White Terrier, Pug, Bloodhound, American Cocker Spaniel, and Boston Terrier. Cherry eye is rare in felines, but can occur. This defect is most common in the Burmese breed of felines. A similar condition exists in dwarf lop-eared rabbits, which occurs in the harderian gland. Similar surgical treatment is necessary. There is likely a complicated and multigenic component involving genetic risk factors. Some breeds are considered to be more susceptible to its development than others, including the Bulldog, Boston Terrier, Bull Terrier, Lhasa Apso, Cocker Spaniel, St. Bernard, Shar-pei, Shih Tzu and Poodle The NM contains many glands which merge and appear as a single gland. Typically, glands secrete tears for lubrication of the cornea. Lack of anchoring allows the gland to flip up, causing the gland to prolapse. Symptoms include a visible fleshy mass, abnormal tear production, and a discharge or drainage from the eye. Cherry eye is typically diagnosed by examination of the conjunctiva and nictitating membrane. The most obvious symptom of cherry eye is a round fleshy mass in the medial canthus of the eye, similar in appearance to the fruit it is named for. This mass may be unilateral or ‘’bilateral’’. Both eyes may develop cherry eye at different times in the animal's life.