Third eyelid cartilage eversion in an adult mare.

Purpose: To describe the first report of third eyelid cartilage eversion in an adult American Quarter Horse mare.

Case Presentation: A 22-year-old American Quarter Horse mare presented to the University of Missouri Veterinary Health Center Equine Hospital for a 2-week history of a third eyelid cartilage abnormality of the left eye with no known recent trauma. Complete ophthalmic examination revealed third eyelid cartilage eversion of the left nictitans.