Equine Corneal disease:Scratching the surface by David Gurbacki DVM Horses are uniquely prone to a variety of serious eye injuries. Because of their habits (they forage near the ground and root in tall grasses), the shape of their eyes (large and bulbous), and because of a unique reaction created by the immune system when an eye injury occurs, equine corneal ulcers are both common and serious. In fact, corneal ulceration – also caused ulcerative keratitis – is one of the most common eye problems of horses. And anyone who has had to treat their horse for a corneal ulcer can attest to how serious it can be. Ulcerative keratitis occurs when the cornea – a very thin, clear membrane on the surface of the eye – is disrupted. Trauma to the eye (such as a laceration or puncture) is the most common cause. These injuries usually become infected by bacteria or fungi secondarily, which then initiates a strong immune response. The horse’s white blood cells then migrate to the site of injury and release special enzymes that destroy both the foreign invaders as well as – unfortunately – the normal tissue of the eye. When this happens, the ulcer referred to as a “melting ulcer.” Pain and inflammation on the surface of the eye typically causes secondary inflammation within the eye, called “uveitis,” which then leads to a whole host of other problems. This is why prompt diagnosis and treatment of ulcers is so important. If you notice your horse is suddenly squinting or sensitive to light, if the eyelids are swollen, or if you can see a wound on the surface of the eye (or a “cloudiness” to the cornea, indicative of inflammation), call us immediately day or night as these signs are all potential clues to the presence of a corneal ulcer. The complete ophthalmic exam involves looking at the eye and all the surrounding structures, while placing a local anesthetic to “numb” the eye. A stain is placed on the surface of the eye (fluorescein), and with blue light highlights ulcerated corneal tissue. Our doctors will also swab the surface of the eye, removing cells and debris (and potentially bacteria or fungi) to examine microscopically to determine appropriate therapy and ensure the best prognosis. Treatment of corneal ulcers consists of four important approaches. First, a topical antibiotic or antifungal medication is used to fight infection in the eye. Second, an oral or injectable anti-inflammatory drug (such as Phenylbutazone or banamine) is given to decrease pain and inflammation within the eye. Third, a topical form of atropine is used to keep the pupil dilated, helping to control pain and preventing permanent damage to the inside of the eye. Lastly, topical anti-collagenase medications or patient serum are used to combat the destructive enzymes that degrade the normal tissue of the eye with infection. Examples of anti-collagenase medications include N-acetylcysteine and EDTA. Autologous serum (a component of the horse’s own blood, collected in a tube, spun in a centrifuge and removed sterilely for topical placement into the eye) is another option for combating collagenase activity and is easy and inexpensive to make and use. Aggressive treatment of ulcers is extremely important! Frequent administration (every 2-4 hours) of multiple medications (antibiotics, serum, atropine) is usually recommended depending on the depth of the corneal defect. The eye will need to be reassessed by a veterinarian every week until healed. Complications of untreated ulcers include the “melting” behavior described above and rupture and loss of the eye, and/or glaucoma (increased pressure within the eye), leading to cataracts and vision loss. Our case of the month for October is “Zach”, who had a corneal ulcer. For ease of medication administration which was required 6 times per day, we surgically implanted a Sub-Palpebral Lavage (or SPL) system in the horse’s eye. It involves a thin, flexible tube attached to a small port on one end and a flat, oneway valve on the other end. Medication can be administered through the tubing (usually taped to the horse’s mane part of the way down the neck), avoiding the aversion that is commonly with horses with painful eyes. In this case the SPL was a helpful tool working with a beloved yet difficult, painful and head-shy horse with a serious ulcer. Though Zach needed a lot of nurse care, frequent medications, and careful monitoring, he made a full recovery in 2 weeks! This case was a good example of the importance of early diagnosis and treatment when it comes to the management of corneal ulcers.
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