is exquisitely painful and will lead to many of the eye pain symptoms listed earlier with a few other distinctive characteristics of its own. Specifically, it is common to see blood, pus or fibrin within the anterior chamber of the eye and engorged blood vessels within the sclera. Sometimes, however, the symptoms may be as subtle as the eyelashes of the affected eye pointing down, rather than straight out. There are essentially two forms of primary uveitis: acute uveitis and recurrent uveitis. Interestingly, acute uveitis from any underlying condition can potentially lead a horse to develop the immunemediated equine recurrent uveitis that many commonly refer to as “moon blindness.” Each uveitis episode causes some degree of damage to the structures of the eye, creating a problematic long-term prognosis. More severe secondary conditions include corneal scarring, cataract formation, glaucoma From left: AN EXAMPLE OF and retinal degeneration. EYELASHES POINTING The potential causes DOWN RATHER THAN of acute uveitis can be PERPENDICULAR TO separated into infectious CORNEAL SURFACE. and noninfectious. As A REPAIRED the list of potential causEYELID LACERATION. es is almost endless, your
veterinarian will likely perform other diagnostic tests aside from a thorough eye exam. Laboratory tests such as complete blood count, serum biochemistry analysis and infectious disease serologic tests may be needed. The infectious causes of uveitis range from bacterial infections, such as leptospirosis (often implicated as the cause for equine recurrent uveitis), streptococcus and E. coli, to viral diseases like equine herpesvirus-1 and equine infectious anemia. Other infections such as tooth-root or hoof abscesses have also been identified as causes, as have parasitic onchocerca infections. Noninfectious origins, such as trauma and neoplasia, can also cause acute uveitis. The common denominator in developing acute uveitis is damage to the uveal tract that allows protein to leak into the aqueous of the eye, which leads to the associated symptoms. If an underlying cause can be identified, then treatment centers around that cause. If an underlying cause cannot be identified,
symptomatic treatment of the eye itself becomes the main focus. The primary objective is eliminating the inflammation and thus the pain from the eye. This is where a careful eye examination becomes of paramount importance. Topical steroids, such as prednisolone or dexamethasone, are often the first medications of choice for uveitis, as they are powerful anti-inflammatories with excellent corneal penetration ability. However, if a corneal abrasion is present, the use of these medications can be profoundly detrimental to the eye. Other mainstay medication choices for acute uveitis involve the use of atropine and systemic anti-inflammatories like phenylbutazone or flunixin as well as the addition of aspirin.
Laceration of the Eyelid
Thanks to the anatomical location of the eye on the horse’s head, and the very nature of horses, laceration of the eyelid is an extremely common eye condition. These injuries are often identified rapidly by owners, but in some cases, given the varied housing conditions of horses, it can be days before the injury is identified and the horse presents for examination. The eyelid possesses excellent blood flow, completely contrary to the cornea, which allows for rapid and efficient healing. Surgical correction is the only treatment option for eyelid lacerations, and these can almost always be performed with the horse heavily sedated and standing. Should you encounter an eyelid laceration, it is imperative that you resist the urge to cut off the hanging strip of lid, regardless of the condition you find it in initially. Removal of the affected portion of lid causes exposure keratitis down the road, effectively producing recurring corneal ulcerations simply because the horse has no way to protect its globe. After suturing the laceration, your veterinarian will perform a thorough eye exam to rule out the presence of any other eye trauma that could lead to more severe problems going forward. Many other conditions can affect horses’ eyes, with ulcerative keratitis, uveitis and eyelid lacerations being the most commonly encountered. Anything we, as the advocates for our equine companions, can do to intervene promptly when eye pain is encountered will ultimately lead to a happier and healthier horse. This begins with never assuming we know what is going on in and around the eye without a proper examination by a veterinarian. Initiating an appropriate therapeutic plan from the beginning improves not only healing but often the long-term prognosis for the eye. H Megan Tracy Petty, DVM, is an associate equine veterinarian at Tularosa Equine Clinic in Tularosa, New Mexico. A born and raised Texan, Petty is an active member of the Texas Thoroughbred Association, serving as the current president of the Paddock Foundation and board member of the Texas Thoroughbred Educational Fund. She enjoys spending time with her husband, Bryan, and their dogs Maverick and Ray on their work-in-progress horse farm, Creekside Farm, in Bent, New Mexico. AMERICAN RACEHORSE • FALL 2017 63