Prolapse of the gland of the third eyelid, sometimes called "cherry eye", is a condition which usually develops during the first year of life. All dogs have three eyelids: an upper, a lower, and a third eyelid that is usually out of sight. The third eyelid acts like a windshield wiper and helps protect the eye. Sometimes the third eyelid can prolapse or pop out and a mass of red tissue will be seen in the inside corner of the eye. affects young dogs, especially Beagles, Cocker Spaniels, Boxers, Neapolitan Mastiffs, Chinese Shar-Peis, Pekingese, and Bulldogs. If one eye has cherry eye, the other eye could be predisposed to it as well. Cherry eye also affects cats. Burmese and Persian cats are more prone to developing this condition than most other cat breeds. If the condition is left untreated, it may go away on its own in two or three weeks, but in other cases it leads to further eye diseases.
The exact cause of the prolapse is unknown but is considered to be a weakness of the connective tissue around the gland. The gland starts to move and becomes irritated. Irritation leads to swelling, clear or mucous discharge, bleeding and ulceration. Left untreated, this may result in conjunctivitis. Eyelids may become inflamed from dermatitis, a bacterial, parasitic, or fungal infection, a metabolic or immune system problem, cancers, trauma or sun damage. It is also a common congenital defect that can be passed from one generation to another.
Treatment involves a surgical procedure where the prolapsed gland is pushed back in its pocket. This procedure can be performed under local anesthesia. The complete removal of the third eyelid is still performed in small animal clinics in some cases, but this type of surgery adversely affects the stability of the tear layer of the eye as this layer is responsible for about 30% of the overall tear production. Removal of a prolapsed gland of the third eyelid predisposes a dog to develop keratoconjunctivitis sicca ("dry eye"). The prognosis for cases treated by replacing the gland is excellent.