How to Surgically Remove the Third Eyelid in the Standing Horse

1. Introduction
Diseases that can affect the nictating membrane or third eyelid of the horse include neoplasia, traumatic lacerations, and inflammatory/infectious processes.^1,2  Squamous cell carcinoma is, by far, the most reported neoplastic condition associated with the third eyelid in the horse.¹  Diagnosis often requires surgical biopsy for definitive diagnosis. Most often, an excisional biopsy is taken, which combines diagnostics and treatment in the same procedure. Strontium probe brachytherapy, cryotherapy, or hyperthermia, when available, is occasionally used after excision of the third eyelid to prevent reoccurrence of neoplasia.³

Horses with neoplasia of the nictating membrane are often referred to veterinary surgical centers to have removal of the membrane performed under general anesthesia. The anesthetic risks and financial costs associated with general anesthesia can be prohibitive to some horse owners. Biopsy or removal of the third eyelid can be performed in a safe, routine fashion in the standing horse using appropriate sedation and local anesthesia. In addition to avoiding anesthetic and post-operative anesthetic complications, standing surgery for removal of the third eyelid is very economical.^4–6  Standing surgery for removal of the third eyelid can also be safely performed in the field.⁷ [...]