Enucleation is the surgical procedure used for removal of one or both of a horse’s eyes. In horses this procedure is most commonly used in cases of severe trauma to the globe or chronic painful ocular disease in order to improve the patient’s comfort. The procedure is typically well tolerated by horses, and many animals with a unilateral enucleation can return to their previous discipline.
Severe Ocular Trauma: This may include penetrating wounds or rupture of the globe, where restoration of a non-painful, functional eyeball is highly unlikely.
Chronic Ocular Disease: Most commonly this is performed for chronic uveitis (equine recurrent uveitis or moon blindness), severe corneal ulceration, or glaucoma. Ocular neoplasm is rare in the horse but may also be an indication for enucleation. These disorders may become refractory to medical management or the horse may continue to have pain despite conservative therapy.
Typically the decision for enucleation is based on outward examination of the globe. Some additional diagnostics which may be implemented include ultrasound of the globe, tonometry (or measuring of the intraocular pressure) to diagnose glaucoma, or advanced imaging such as CT or MRI.
Enucleation may be performed under general anesthesia or with standing sedation and local anesthesia, depending on the temperament of the horse, exact characteristics of the disease, and surgeon preference. After administering local and/or general anesthesia the surgical site is aseptically prepared, eye examined for any abnormalities which could not be identified prior to surgery, and the final surgical plan finalized. Straight-forward enucleation involves the removal of the globe and supporting soft tissues (third eyelid, conjunctiva, and the eyelid margins) and can be performed using several possible techniques depending on surgeon preference and the pathology necessitating enucleation. At the end of this surgery, the globe will be removed, and the eyelids will be closed, resulting in the skin fully covering the empty socket (Figure 1). Occasionally, intraorbital prostheses will be placed prior to skin closure, which may reduce some of the pitting that occurs after healing. Prostheses can increase the postoperative infection risk and should not be used in cases of infection of neoplasia.
More rarely alternative techniques may be used, which may remove more or less tissue than an enucleation. Evisceration involves removing the contents of the globe while preserving the scleral shell, which is then filled with an implant or prosthesis to maintain orbital volume and cosmetic appearance. This will make it appear that a globe is still present, however the inner contents were removed, and no vision is present. This procedure is rarely performed and can only be used with a small number of disease processes, however this provides a more cosmetic outcome than enucleation.
Exenteration involves removing the entire contents of the orbit, including the eyeball, associated muscles, and surrounding tissues. This procedure is more extensive than enucleation and is used to address extensive disease or neoplastic involvement within the orbit.
While rare, potential surgical complications may include post-operative infection, hemorrhage, damage to surrounding structures (such as the optic nerve or orbital vessels), inadequate closure of the eyelids, or post-operative swelling and discomfort
Pain management, antimicrobial therapy, and incision care are routine following surgery. Feeding horses off the ground for several days following surgery may help to reduce swelling of the surgery site. Often, horses were blind in the affected eye prior to removal and adjustment to having an eye removed is uneventful, but horses who sustained an acute injury necessitating enucleation may have more of an adjustment period. It is important to keep these horses in a safe, familiar area while they adjust to their new world. Most horses adapt to enucleation very well, and horses with unilateral enucleation often can return to their previous profession. For horses suffering from chronic ocular pain enucleation can significantly improve their quality of life, and many owners describe their older horses showing an energy they hadn’t seen in months to years.
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