Facing the surgical removal of an eye, known medically as enucleation, is an emotional and difficult moment for any horse owner. Equine eyes can suffer from severe conditions such as recurrent uveitis, deep or perforated corneal ulcers, traumatic lacerations, endophthalmitis, or advanced glaucoma. When an eye is blind, chronically painful, or damaged beyond repair, surgical removal often provides profound relief and allows the horse to return to a comfortable, active life.
Traditionally, enucleation in horses was performed almost exclusively under general anesthesia on an operating table. However, general anesthesia carries unique risks in adult horses. Because of these challenges, veterinary surgeons have increasingly developed and refined techniques to remove diseased eyes while the horse remains standing under deep sedation and targeted local nerve blocks. A newly published clinical study explores how well these standing nerve blocks work and whether adding ultrasound guidance makes the procedure safer and more reliable.
UNDERSTANDING THE RISKS OF GENERAL ANESTHESIA IN HORSES
Unlike small animals, horses have massive bodies and powerful flight instincts that make general anesthesia more complex. In healthy horses, the mortality rate associated with general anesthesia is approximately 0.9 percent. Ophthalmic surgeries carry higher overall complication risks than many non-ophthalmic procedures.
A significant portion of this risk occurs during induction and recovery, when an uncoordinated, half-ton animal attempts to stand up on slippery or padded stall surfaces. Fractures, soft tissue injuries, muscle damage from lying down, and cardiovascular stress are ongoing concerns for equine anesthetists. Performing surgery on a standing horse that is calmly sedated and supported in stocks completely bypasses the dangers of an anesthetic recovery stall. In addition, standing surgery often reduces equipment demands and hospital costs.
HOW STANDING EYE SURGERY WORKS: THE NERVE BLOCKS
For a standing surgery to succeed, the horse must feel zero pain and have no reflex urge to move its head or eyelids. Achieving total numbness requires a precise combination of regional nerve blocks.
The nerves responsible for feeling and moving the eye exit the skull and pass through an area behind the eyeball called the retrobulbar muscle cone. This cone-shaped anatomical space contains several cranial nerves that supply sensory feeling to the globe and surrounding structures, as well as the motor nerves that control the muscles that aim the eye. Desensitizing these nerves is accomplished with a retrobulbar anesthesia block, where local anesthetic is deposited behind the globe.
However, the retrobulbar block cannot numb every structure involved in the surgery. The nerve that controls the circular muscle responsible for tightly closing the eyelids—the auriculopalpebral nerve—branches from the facial nerve and runs outside this space along the zygomatic arch. Because it sits away from the eye socket, veterinarians must perform a separate auriculopalpebral nerve block to temporarily paralyze the eyelids and prevent blinking during surgery.
Traditionally, retrobulbar blocks have been performed blindly. The veterinarian relies on external bony landmarks on the horse's skull to guide a long, curved needle over or around the orbital rim into the retrobulbar space. While experienced equine surgeons frequently use this landmark technique with good success, placing a needle blindly into a deep, vascular compartment carries inherent risks, including accidental puncture of the eyeball, bleeding into the socket, or incomplete numbing.
WHAT THE NEW CLINICAL STUDY INVESTIGATED
A recent prospective clinical study evaluated thirty horses that required eye removal to determine the feasibility of standing enucleation and to measure the exact impact of adding ultrasound guidance to the nerve blocks. The horses were divided into two equal groups of fifteen.
Both groups received standardized intravenous sedation, a dorsal retrobulbar injection of mepivacaine, and an auriculopalpebral block using lidocaine. In the first group, the surgeon used a linear ultrasound probe placed on the head to visualize the needle advancing into the tissue behind the eye in real time. In the second group, the surgeon placed the needle using standard anatomical landmarks without ultrasound imaging.
The researchers carefully tracked how long it took to position the needle under ultrasound guidance, the quality of the ultrasound images obtained, changes in eyelid sensation twenty minutes after the injections, and whether the horse tolerated the surgery comfortably without general anesthesia.
WHAT THE RESEARCHERS FOUND
The study yielded several valuable insights into how these nerve blocks behave in clinical practice:
Overall surgical tolerance was achieved in 63.4 percent of the horses across both groups, representing nineteen out of thirty horses. In the ultrasound-assisted group, 73.3 percent of the horses, or eleven out of fifteen, had a successful block. In the group where the block was placed blindly without ultrasound, 53.3 percent, or eight out of fifteen, had a successful block. While the ultrasound group showed a higher success rate, the statistical difference between the two groups was not significant, meaning the difference could still be influenced by random chance given the relatively small sample size.
Even among the nineteen horses where the initial block succeeded, three horses required additional local anesthetic top-ups during the surgery. This finding highlights that local blocks can wear thin or leave small pockets of feeling, requiring the surgical team to remain attentive and ready to adapt.
The clarity of the ultrasound image had a direct relationship with surgical success. When the surgeon obtained an excellent ultrasound view, the block succeeded in 100 percent of those horses. When the ultrasound view was rated as good, the success rate was 85.7 percent. However, when poor image quality made visualization difficult, the block succeeded in only 40 percent of cases. Needle placement with ultrasound was relatively fast, averaging 5.2 minutes.
Checking eyelid sensation proved to be an excellent predictor of whether the block was deep enough for surgery. Horses that had more completely desensitized eyelid areas twenty minutes after injection were significantly more likely to tolerate the entire surgery without pain.
WHAT THIS STUDY MEANS AND WHAT IT DOES NOT SHOW
When evaluating veterinary medical research, horse owners should understand that one study does not represent settled science, nor does it establish a mandatory new standard of care. This study provides helpful clinical evidence, but it must be viewed in perspective.
First, this investigation involved a small cohort of thirty horses. While the ultrasound group achieved higher success percentages, the difference did not achieve statistical significance. Ultrasound guidance cannot be called strictly necessary based on this study alone, but it shows clear promise when high-quality images can be obtained.
Second, standing retrobulbar anesthesia is not an all-or-nothing technique. Because nearly 37 percent of horses in the study did not achieve adequate surgical numbing from the initial injection alone, and several required top-ups, owners should know that standing eye surgery requires an experienced team. The veterinary team must monitor the patient continuously and be prepared to add local anesthetic or adjust sedation levels if the horse shows any sign of discomfort.
Third, current practice patterns show that blind techniques remain the most common method in the equine veterinary community. In a recent global survey of 238 veterinarians across 25 countries, the dorsal retrobulbar approach was used by 88.8 percent of practitioners, but only 16.1 percent reported using ultrasound guidance for needle positioning. Many surgeons are highly skilled at landmark-based injections, while others are gradually adopting ultrasound equipment as technology becomes more portable and widely available in field and clinic settings. Cadaver research has shown that ultrasound guidance significantly reduces the risk of accidental puncture to the eyeball, which is an important safety consideration when an intact globe is present.
POSTOPERATIVE RECOVERY AND OUTCOMES
For horse owners who must make this decision, multiple clinical reports demonstrate that standing eye removal generally leads to favorable outcomes and high owner satisfaction. When general anesthesia is avoided, horses do not have to endure the physical exhaustion and disorientation of rising from an operating table.
Following standing surgery, some mild complications can occur. Across published clinical studies, short-term complications include moderate postoperative swelling around the socket, minor drainage from the incision, and transient mild colic related to sedation and stress. Serious long-term complications are uncommon. In surveys evaluating horses one or more years after standing eye removal, owners reported high levels of satisfaction with their horses' comfort, cosmetic appearance, and overall quality of life.
Horses adapt remarkably well to living with one eye. Once the chronic pain, inflammation, or infection of a diseased eye is removed, most horses show improved demeanor, appetite, and willingness to work within weeks of their recovery.
WHEN TO CALL YOUR VET
If your horse has recently undergone an enucleation procedure, close daily monitoring of the surgical site and the horse's general attitude is critical. Contact your veterinarian promptly if you observe any of the following signs during recovery:
Active bleeding or persistent, thick foul-smelling discharge from the incision line.
Sudden, severe swelling around the surgical site or down the side of the face.
Signs of abdominal discomfort or colic, including pawing the ground, flank watching, repeated lying down, or a drop in manure output.
A rectal temperature above normal limits, which can signal developing infection.
Loss of appetite, profound lethargy, or signs of head pressing and depression.
Your veterinary surgeon will evaluate your horse's specific ocular disease, general temperament, and health history to determine whether a standing procedure or general anesthesia is the safest and most comfortable choice.