“Equine recurrent uveitis has been an interest of mine for as long as I’ve been an ophthalmologist,” began Brian C. Gilger, DVM, MS, Dipl. ACVO. “Unfortunately, it’s still an interest because we can’t seem to get this disease under control.”

While a cure for equine recurrent uveitis (ERU) remains elusive, veterinarians have learned how to best control this devastating disease and are continuously working to unravel new treatment options. Gilger, professor of ophthalmology at the North Carolina State University College of Veterinary Medicine, reviewed the current diagnostic, treatment, and management options for ERU at the 2012 American Association of Equine Practitioners’ Focus on Ophthalmology conference, held Sept. 6-8 in Raleigh, N.C.

Gilger stressed that there is a difference between ERU and “garden variety” uveitis, and he discussed aspects of both during the presentation.

Types and Signs of ERU

Gilger explained that there are three distinct types of ERU that can affect horses: classic, insidious, and posterior.

Classic, or anterior, ERU is the most common type, and is characterized by concurrent bouts of pain and inflammation which last approximately two weeks. This “active” period is followed by a period of quiet (which lasts for an unknown amount of time), Gilger said, which is followed by another active spell. This pattern continues indefinitely until the eye goes blind, he said.

Gilger explained that insidious, or subclinical, uveitis can be challenging for owners and veterinarians alike. Although affected horses typically don’t show signs of pain, low-grade inflammation remains in the eye after the active phase, damaging the internal structures. Affected horses often slowly develop signs of chronic ERU (more on that in a moment), but owners might not recognize disease presence until significant damage is done. “It’s sad,” Gilger said. “You have an owner come in, eager to do something (to help the horse), but the eye’s already blind.”

Finally, posterior uveitis is the least common type seen in the United States. With this syndrome, the majority of the associated inflammation develops behind the lens, Gilger said. Association vitreal opacities, degeneration, and infiltration are common, as is retinal detachment, he said.

Gilger noted that classic and insidious ERU are common in Appaloosa horses, insidious ERU is common in draft horses, and posterior ERU is commonly seen in Warmblood horses.

Clinical signs of active ERU include:

• Photophobia (sensitivity to light);
• Blepharospasm (squinting);
• Corneal edema;
• Aqueous flare (small “floaters” in the front chamber of the eye);
• Hypopyon (pus in the eye);
• Miosis (pupillary constriction);
• Vitreous haze (a haze in the gel that fills the eyeball between the lens and the retina); and
• Chorioretinitis (inflammation of the choroid and retina).

Signs of chronic ERU include:

• Corneal edema;
• Iris fibrosis and hyperpigmentation;
• Posterior synechia (adhesion of the iris to the capsule of the lens);
• Corpora nigra degeneration (the irregular body at the edge of the iris that shades the pupil);
• Miosis;
• Cataract formation;
• Vitreous degeneration and discoloration; and
• Retinal degeneration.

Causes and Diagnosis

“There’s a big controversy about what actually sets this off,” Gilger said, noting that there are several different theories about the pathogenesis of both uveitis and ERU.

“It’s becoming more and more likely we have a genetic component to this,” he noted. Additionally, environmental factors, ocular injury, certain infections (such as leptospirosis), and the presence of certain cells (such at T-lymphocytes, or T-cells) are each believed to contribute to disease development.

“The clinical diagnosis of ERU is based on the presence of characteristic clinical signs and a history of documented recurrent or persistent episodes of uveitis,” Gilger explained. He noted that in most horses, a normal uveitic spell lasts for two to three weeks before it calms down, even without therapy. Multiple occurrences points to ERU.

“If it’s a first bout of inflammation, this is one you really need to work up (examine) carefully,” he said. If recurrence is observed, the diagnosis is typically ERU.

At that point, treating and managing ERU becomes the priority.

Treatment and Management

Traditional medical treatments for ERU are aimed at reducing inflammation and minimizing ocular damage, Gilger said; however they will not effectively prevent recurrence. Common medical treatment includes topical and systemic non-steroidal anti-inflammatory drugs (NSAIDs, most often flunixin meglumine) and corticosteroids.

“Other medications used to prevent or decrease severity or recurrent episodes, such as aspirin, phenylbutazone, and various herbal treatments have limited efficacy and potential detrimental effects on the gastrointestinal and hematologic systems when used chronically in the horse,” Gilger added.

He recommends slowly weaning horses off these treatments as active episodes subside. Many horses, he said, respond well to medical treatment if it is implemented early and aggressively.

If medical treatment proves unsuccessful, surgical intervention might be a viable option. Current surgical options include a vitrectomy (CV) and the implantation of a sustained-release cyclosporine device (CsA).

Although simply removing the cells and vitreous from inside the eye might “sound remarkably straight forward,” Gilger said, a vitrectomy is a very expensive option and carries a high complication rate, such as cataract development. Thus, if surgery is required, some veterinarians are more inclined to recommend a CsA device.

In these cases, a surgeon implants a small disc (about 6 millimeters in diameter and weighing about 25 milligrams) into the sclera of the affected eye, Gilger said, adding that the entire procedure takes about 15 minutes, on average. The device will release medication to the eye at a predetermined dosage for at least four years, he said. Currently, he said, more than 500 procedures have been completed worldwide, and owners have reported a significant decrease in the number of active episodes affected horses have.

Even with aggressive treatment, affected horses can go blind in a matter of years, Gilger said.

Once acute episodes are under control, Gilger said, there are several relatively simple steps owners of affected horses can take on a daily basis to help keep their charges healthy. For instance, changing stable or pasture mates if ocular injury is common or has occurred can help keep a uveitic horse healthy. Additionally, decreasing their sun exposure can help keep them comfortable.

Other management practices Gilger recommended include:

• Increase insect and rodent control, and use a quality fly mask with ultraviolet protection;
• Decrease dust;
• Change bedding;
• Eliminate sharp objects from around the barn and pasture;
• Eliminate low branches;
• Decrease training and show schedule, and minimize trailering;
• Avoid using hay nets;
• Maintain proper hoof and dental care, as well as deworming and vaccination schedules; and
• Ensure a proper diet.

Take-Home Message

Equine recurrent uveitis and uveitis are two different diseases, Gilger stressed. Although there is no cure for ERU, an immune-mediated disease, treatment is often effective in controlling clinical signs and active episodes.