Brett Robinson, DVM
Eye problems in horses are extremely common. Last year alone, our group practice performed 100 eye exams on horses experiencing signs of eye pain or trauma. If you have ever dealt with an equine eye problem, you know the importance of early recognition and appropriate treatment. The aim of this article is to help you gain a better understanding of common conditions and how your veterinarian might manage them.
To begin an eye exam, your vet will review your horse’s medical history. Then he or she will evaluate the horse for comfort and eye symmetry, examine the structures surrounding the eyeball, assess vision and reflexes, apply a fluorescent stain, and examine the back of the inside of the eye using a magnifying lens with a special light source. For certain conditions, veterinarians will measure intraocular pressures and dilate the pupil. In all cases, treatment goals are to preserve vision, decrease pain, and prevent infection and recurrence.
Horses are particularly vulnerable to ocular trauma because their eyes are large and positioned on the sides of the head. Corneal ulcers are one of the most common eye conditions caused by trauma. The cornea is a transparent membrane in the front of the eye. Fluorescein stain dye adheres to and enables the veterinarian to identify defects there. Corneal pathology (disease or damage) generally results in opacity, and various color changes can accompany this process. Other signs include squinting, eyelid swelling, and discharge.
Corneal ulcer treatment and prognosis depend on the defect’s depth. For uncomplicated (small and superficial) ulcers the veterinarian might prescribe a topical antibiotic to prevent infection, in addition to oral and/or topical anti-inflammatory drugs. If the pupil is small (a pain response called miosis), the practitioner might apply a topical medication such as atropine for dilation. For complicated (infected, deep, large diameter) ulcers, hospital referral is ideal, because the eye might need medication every few hours and close monitoring. If a corneal ulcer fails to respond to medial therapies, is significantly deep, or has a “melting” appearance, vets usually recommend surgery to remove the dead and infected tissue and place a conjunctival graft. If corneal ulcers are treated early and aggressively, the prognosis for vision can be good.
Eyelid lacerations are also common results of trauma. The classic case is an avulsion (tearing) that occurs when the horse “catches” the eyelid on a sharp object. After examining for concurrent eye damage, the veterinarian usually sedates the horse, administers local anesthesia, prepares the skin, and repairs the laceration. Aftercare typically involves systemic anti-inflammatories and antibiotics. If treated promptly, prognosis is good.
Another common eye issue is conjunctivitis. The conjunctiva is the mucous membrane covering the inside of the eyelids and white part of the eye. Clinical signs of conjunctivitis include ocular discharge, redness, and swelling of these tissues. Causes include allergies and insect hypersensitivity, which veterinarians can treat with anti-inflammatories, antihistamines, and environmental modifications.
Uveitis is an inflammatory condition of the middle layer of the eye. Complications associated with uveitis are the number one cause of blindness in horses worldwide. Uveitis is categorized as acute or chronic/recurrent. Veterinarians base their initial diagnosis on clinical signs of squinting, ocular discharge, corneal edema (swelling), blood or pus in the anterior (front) chamber, and miosis, among others. Veterinarians consider uveitis to be immune mediated with multiple causes, both infectious (Leptospirosis, Streptococcus, equine influenza, and equine herpesvirus, to name a few) and noninfectious (trauma or tumors). Sometimes, vets cannot identify a cause and must treat the eye symptomatically. Treatment consists of topical medication to dilate the pupil, topical anti-inflammatories (corticosteroids or non-steroidal anti-inflammatories), topical immunosuppressants, and systemic anti-inflammatories. Most horses with the acute form initially respond well to symptomatic treatment, but the long-term prognosis might be guarded because of recurrence, and each inflammatory episode causes further eye damage.
Medical therapies for eye disease can be prolonged and fraught with complications. In cases that cannot be treated for financial or medical reasons, practitioners might recommend enucleation (removing the eye). Study results show that horses can return successfully to a variety of disciplines following enucleation, and owners report satisfaction with the procedure and outcome.
If you suspect an issue with your horse’s eye, remember that early detection and veterinary attention will help ensure the best possible outcome.
Article provided courtesy of The Horse, an AAEP Media Partner.