Avoiding general anesthesia for surgery in horses, when possible, is not only safer for the horse and surgeons but also more economical for the owner. However, not all surgeries can be performed without anesthesia, partly because the procedure is too uncomfortable for the horse to remain awake (even if sedated and given pain medications) and also because the area being operated on might be too hard to reach in the awake animal. A surgery that could go either way is removal of the third eyelid due to cancer; an equine ophthalmologist recently presented research on the two anesthesia approaches at the American Association of Equine Practitioners convention, held Nov. 18–22 in San Antonio, Texas.
Surgeons perform nictitating membrane (third eyelid) removal most frequently in horses with squamous cell carcinoma of the third eyelid. A successful outcome means complete removal of the third eyelid to ensure all cancer cells have been removed and the tumor does not recur.
Amber Labelle, DVM, MS, Dipl. ACVO, assistant professor of comparative ophthalmology at the University of Illinois Urbana-Champaign’s Veterinary Teaching Hospital, said, “Proving that the method of anesthesia does not influence the rate of recurrence encourages veterinarians to perform the procedure under local anesthesia, which is safer for the patient.
"The purpose of this study was to compare the outcomes of horses which had their third eyelids surgically removed using sedation and local anesthesia with those who had them removed under general anesthesia. Our hypothesis was that recurrence of cancer would not be more common in the local anesthesia group than it was in the general anesthesia group.”
In their study Labelle and colleagues examined the medical records of 26 horses that had their third eyelid removed while standing with sedation and pain medications. They contacted the horses’ owners for follow-up data and compared outcomes to those of horses that had the same procedure performed under general anesthesia.
“Recurrence of neoplasia only occurred in two of the 26 horses, which is not any more frequent than what is seen in horses that underwent general anesthesia,” relayed Labelle. “In addition, the only long-term complication was a mild ocular discharge that was not associated with any damage to the eye.”
Not all horses are amenable to this approach, however. “Third eyelid excision is most likely to be successful when the tumor is confined to the third eyelid alone,” Labelle cautioned.
If a veterinarian pursues this surgery, he or she should submit the excised tissue for laboratory examination after excision to ensure all cancerous tissue has been removed.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.