Disorders of the Cornea in Horses
The cornea protects the front of the eye and is also important in focusing light on the retina at the back of the eye. Because the cornea is critical for proper vision, it is important to address any disorders or injuries promptly.
Inflammation and swelling of the outer cornea (superficial keratitis) is common in all domestic species. The most common sign is the development of blood vessels in the cornea. In addition, the cornea often becomes cloudy due to fluid build-up, cellular infiltrates, pigmentation, or the formation of fibrous tissue. If ulcers (sores on the cornea, see below) are present, signs of pain—excessive tearing and squinting—may be obvious. If only one eye is affected, an injury (including one caused by a foreign object) is often the cause. If both eyes are affected, the inflammation may be associated with a lack of tears; abnormalities in the shape, outline, or form of the eyelids; or infection. Your veterinarian will try to identify the underlying cause of the inflammation, because improvement may not occur until the cause is resolved.
Inflammation and swelling within the cornea involves the deep connective tissue that provides the structure of the cornea. It is referred to as interstitial keratitis. It is present in all longterm and in many short-term, severe cases of anterior uveitis (inflammation within the front portion of the eye). Swelling of the cornea is often very noticeable. Some generalized diseases can cause this type of inflammation in one or both eyes, including blood infections (septicemia) in newborn foals and body-wide fungal infections. In these cases, therapy is directed at the inflammation of the eye, the generalized infection, or both. A specific disorder of persistent inflammation in the front of the eye (keratouveitis) occurs in horses; the outlook and response to treatment for this condition are poor.
Corneal ulcers are sores that develop on the cornea. They are common in horses. This disorder has the potential to affect vision unless the cause is promptly diagnosed and treated. Many equine corneal ulcers occur as a result of injury to the eye, but equine herpesvirus infection can also cause corneal ulceration.
The depth of the ulcer cant range from superficial to deep. Untreated, deep ulcers can lead to perforation of the cornea and protrusion (prolapse) of the iris. Secondary bacterial or fungal infections are common and can worsen ulcers.
To detect small ulcers, a veterinarian may put drops of fluorescein dye into the eye. Superficial ulcers are usually controlled with topical antibiotics and correction of any mechanical factors (such as rolled eyelids or a foreign object in the eye). In addition, veterinarians often prescribe medications to reduce eye pain. Medical treatment of deep ulcers is similar to that of superficial ulcers, but many deep ulcers also require surgical grafts to strengthen and maintain the integrity of the cornea.
Corneal ulcers may be complicated by a fungal invasion; this is termed equine ulcerative keratomycosis. The fungus, which is normally present in the conjunctiva, multiplies rapidly after injury to the cornea and causes inflammation and ulcers. The diagnosis is confirmed by identifying the fungus in cells from the cornea. Treatment must begin promptly to avoid vision loss and includes both therapy with antifungal drugs and surgery. Even with prompt treatment, keratomycosis causes blindness in about 25% of affected eyes.
Syndromes of very slow-healing and recurrent superficial ulcers also occur in horses. In such cases, a herpesvirus is often the cause. Initial treatment involves removal of the dead, damaged, or infected tissue of the ulcer, followed by prescription topical medication.
Corneal stromal abscesses are pus-filled sores in the connective tissue of the cornea. In horses, they may be caused by healing ulcers or defects of the cornea and the trapping of bacteria or fungi (or both) within the connective tissue after healing tissue is formed. A white to yellow material in the connective tissue is surrounded by an intense inflammation and swelling of the cornea and formation of blood vessels. In addition, there may be a variable but sometimes intense inflammation of the anterior uvea (the front portion of the eye). Treatments include topical and, in some cases, whole-body antibiotics, antifungal drugs, drugs to reduce pain, and nonsteroidal anti-inflammatory drugs. In addition, surgery may be required to remove the abscess and promote corneal healing.
Injuries to the eye can cut or tear the cornea. Corneal lacerations are highly painful. Lacerations of the cornea are common in horses and can usually be treated with surgery to close the wound. The eyelids may be temporarily sutured together to protect the eye.
Severe lacerations or perforations of the cornea can result in:
The outlook depends on size and position of the laceration, the presence of other injuries to the eye or body, sex and age of the horse, and how long ago the injury occurred. Your veterinarian may recommend topical and oral medications after surgery to control pain, inflammation, and infection. Possible complications include significant corneal scarring, cataracts, glaucoma (increased pressure within the eye), bacterial infections within the eye, and blindness.
Also see professional content regarding disorders of the cornea in animals.