UC Davis

The purpose of this retrospective study was to identify the types and causes of disorders that primarily or specifically afflict the membrana nictitans of birds. Seventeen wild, domestic, and pet exotic birds examined by the Ophthalmology Services at three institutional referral centers were identified with lesions of the third eyelid. Lesions were unilateral in 16 birds. Traumatic injury, with (three birds) and without (four birds) an associated foreign body, was the predominant cause of lesions. Neoplasia, presumed dystrophic mineralization, and inflammation with or without infection were equally represented (three birds each). One probable congenital malformation was identified. We conclude that although many specific and nonspecific external ocular disorders incidentally involve the membrana nictitans to a minor degree, clinically important primary disorders of the third eyelid seem distinctly uncommon in birds. © 1996 by the Association of Avian Veterinarians.