Whenever it's possible to perform a procedure with the horse standing and sedated, it's better to do that than to use general anesthesia, said Brian Gilger, DVM, MS, Dipl. ACVO, founder of the Equine Ophthalmologic Service at North Carolina State University. His presentation at the 2002 American Association of Equine Practitioners Convention was "How to Prepare for Ocular Surgery in the Standing Horse."

"Horses with orthopedic or other medical problems might be at higher risk for anesthesia complications and should not undergo routine general anesthesia (i.e., general anesthesia for the purpose of a non-emergency procedure)," he began. "Even healthy horses can injure themselves on recovery from general anesthesia and are predisposed to develop colic, cecal impactions, and myositis (inflammation of voluntary muscle) in the post-anesthetic period. Standing procedures require less hospitalization (time), less technical support, less cost and time, and decreased need for surgical and anesthetic equipment and facilities--and thus decreased cost to the horse owner.

"However, there are challenges with standing ocular (eye) surgery--you generally need magnification, and thus the horse must be perfectly still," he continued. "Many (eye) procedures thus require general anesthesia. But with appropriate tranquilization, ocular nerve blocks, and restraint, many ocular surgeries can be performed adequately in standing horses."

Gilger listed the surgical eye procedures that can be done in the standing horse as follows:

Adnexal (appendage-related):

  • Small eyelid mass removal;
  • Eyelid mass biopsy;
  • Small eyelid laceration repair;
  • Conjunctival biopsy;
  • Third eyelid laceration repair; and
  • Third eyelid mass removal or biopsy.


  • Corneal scraping for cytology;
  • Ulcer debridement;
  • Grid keratotomy (a treatment for superficial non-healing corneal ulcers);
  • Superficial keratectomy (small) (removal of a small part of the cornea);
  • Suture of non-perforating corneal laceration; and
  • Removal of superficial corneal foreign body.


  • Aqueocentesis (sampling of eye fluid); 
  • Intraocular injection (i.e., tissue plasminogen activator, which is a blood clot dissolver);
  • Iris cyst laser ablation;
  • Laser cyclophotocoagulation (destroying small blood vessels of the ciliary processes to reduce the secretion of aqueous humor, or eye fluid) for glaucoma; and 
  • Intraocular mass laser ablation.

Tranquilizers and Nerve Blocks

Proper sedation for eye surgery is a must, said Gilger, who recommended detomidine for this surgical purpose. "It lasts about 30-45 minutes, and the horse's head stays still," he explained. "Xylazine and butorphanol aren't recommended because they cause head movement and hyper-reactivity." Twitches or other manual restraint methods aren't usually necessary, he added, although additional sedation might be required for procedures longer than 30-40 minutes.

He went on to describe in detail (with images and video) the procedures for blocking the palpebral nerve (which minimizes upper eyelid movement), the frontal nerve (which decreases upper eyelid sensation), and the retrobulbar nerve with lidocaine.

"The retrobulbar nerve block (with lidocaine) is the key to standing eye surgery," he went on. "It keeps the eye immobile and paralyzes the retractor bulbi muscle (compromising eye sensation, the blink reflex, and vision), and also provides corneal anesthesia. Therefore, stall rest and protection of the eye with lubricants are recommended for two to four hours after surgery." He added that a single temporary suture can be used to close the eyelid for the first 24 hours or so if it's necessary that the horse be transported or will not be monitored closely.

Gilger cautioned that any cultures of the eye surface should be done before surgical preparation of the eye. "Topical anesthetic (proparacaine HCl) and phenylepinephrine are applied to enhance ocular surface anesthesia and to constrict blood vessels in the cornea and conjunctiva to enhance hemostasis (stopping of bleeding) and visibility during surgery," he said. "These can be repeated every 15-20 minutes as needed to maintain effect."

Following these procedures, the eye is immobilized. Additionally, the blocks reduce visual and tactile (touch) stimuli to the eye, thus reducing head and body movements.

From 1996 to 2001, 189 retrobulbar injections were performed at North Carolina State University's College of Veterinary Medicine. Gilger noted that there were only two complications. One was a horse with a hypersensitivity to lidocaine, which resulted in generalized hives and severe retrobulbar swelling (this resolved with medical treatment within three days of surgery). The other horse developed a corneal ulcer after surgery, likely due to corneal exposure from poor eyelid function and desensitization.

Gilger concluded that with proper aseptic technique, sedation, and ocular nerve blocking, "The relatively low complication rate associated with the injection techniques far outweigh risks associated with general anesthesia in horses."

About the Author

Christy M. West

Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

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