Uveitis in horses can be difficult to diagnose, but early detection is important in order to preserve your horse’s eyesight.

To say a horse has uveitis is like saying he’s lame. In both cases, there are many types, causes, treatments and outcomes of and for the condition. Uveitis simply means there is inflammation inside the eye; specifically, inflammation of the uveal tract, an anatomical section that lines the entire inside of the eye and includes the iris (and pupil). Uveitis is associated with ocular pain, watery discharge, swelling, and a cloudy or red eye. If you look closely, you may notice that a horse with uveitis commonly has a very small or constricted pupil; and usually, horses with uveitis keep their eye tightly closed.


What causes uveitis?

Causes are varied, but include trauma, corneal ulcers, infections, and some systemic illnesses. Often, the cause is not known or ever determined. In most horses, uveitis resolves over the course of two to three weeks, a process that is hastened by the use of medications.

Very commonly, however, when horse owners talk about “uveitis”, they are referring to a special type called Equine Recurrent Uveitis or ERU. Other names include “moon blindness”, “periodic ophthalmia”, and “swamp eye”. ERU is different from regular uveitis because it recurs spontaneously after resolution of the first bout of ocular inflammation, generally at two- to four-month intervals. Although these intervals can be quite variable, and during the quiet time the eyes can seem normal, each flare-up is associated with more damage to the eye. Eventually, the eye may lose vision. In fact, ERU is the leading cause of blindness in horses worldwide.

Recent studies have determined that ERU is caused by an autoimmune reaction between the horse’s immune system and eye tissue. However, we also now know that certain horse breeds may be genetically predisposed to the condition, especially the Appaloosa and Warmblood. Furthermore, exposure to the bacteria Leptospira may help set off this autoimmune reaction.

If your horse is in an environment that can predispose him to leptospiral infections (flooded pastures, access to wildlife or livestock, etc.), please discuss with your veterinarian how you can prevent this disease. A new vaccine against Leptospira pomona, marketed by Zoetis Inc., may help prevent the most common leptospiral infection associated with equine uveitis in the United States.

Preventing eye injury and uveitis

General good farm practices can help prevent eye injury, including the development of uveitis. Remove sharp objects from the barn (old nails are a common culprit), feed loose hay (not directly from a round bale that encourages “head burrowing”), remove low-hanging branches from trees, and cut high weeds in the pasture. Anything with sharp or pointed ends against which a horse can rub his head should be removed from the barn or pasture. Good general healthcare, such as routine deworming, vaccination, and hoof care may also decrease the development of ERU.

Traditional and integrative treatment options

The first treatment for uveitis is to treat the underlying cause, if it can be identified. Your veterinarian may take some blood samples for testing, and in some cases remove some fluid (aqueous humor) from the eye to submit to the lab. Depending on the cause of the uveitis, treatment may involve the use of an oral or injectable antibiotic, such as doxycycline. Generally, for most cases of uveitis, anti-inflammatory medications, both topical (to the eye) and systemic (orally or by injection), are most commonly used. Drugs such as topical corticosteroids (e.g., dexamethasone) and oral non-steroidal anti-inflammatory medications (e.g., flunixin meglumine; Banamine) are very commonly used and are effective for uveitis. In severe cases, injections of these medications into the eye or systemically (under the skin or into the muscle) may also be required. These medications lower inflammation in the eye and help to make it more comfortable. If the pupil is constricted, topical atropine is generally recommended to decrease pain and minimize scarring.

Alternative medications such as herbal therapy or acupuncture are not recommended as the sole mode of treatment for uveitis, but may be helpful in combination with traditional anti-inflammatory medications. New therapies, such as sustained release drug devices (of cyclosporine, for example), stem cell therapy, and gene therapy, are being studied and show great promise for long-term treatment or prevention of new bouts of uveitis and blindness.

Prognosis and the important of prompt treatment

Despite advances in medical treatment, long-term prognosis for maintaining vision in horses with ERU remains poor. A recent study by our group here at North Carolina State University found that five years after diagnosis, over 46% of horses with ERU had gone blind in the affected eye. and many had lost the eye because of the development of cataracts or glaucoma.

Therefore, early recognition and prompt therapy is essential to manage uveitis in horses.

Because of these findings, and the poor prognosis once ERU has developed, you’re encouraged to have your horse examined by an experienced veterinarian if you notice any ocular pain, cloudiness, redness, and/or ocular discharge, especially if they persist longer than six to eight hours, and if you have a Warmblood or Appaloosa horse. Early and aggressive treatment of uveitis may minimize ocular damage and decrease the development or frequency of recurrent episodes. Furthermore, prevention is important and a thorough examination of your barn and pasture is needed to remove even the smallest sharp objects – horses have a unique habit of finding these! Please consult your veterinarian for the latest in preventing and treating this common and devastating eye disease.

At North Carolina State University, the Equine Ophthalmology service is one of the few services in the world dedicated to the care and research of eye diseases in horses. We have studied specifically the cause and treatment of ERU for the past 20 years. In addition, we are leaders in the treatment of equine corneal disease, glaucoma, cataracts, and other causes of blindness. For more information, please visit cvm.ncsu.edu/nc-state-vet-hospital/equine/ophthalmology/.




Dr. Brian Gilger received his veterinary degree from The Ohio State University in Columbus, Ohio. After an ophthalmology residency and masters degree at Auburn University, Dr. Gilger returned to The Ohio State University as an Assistant Professor of Ophthalmology in 1992. In October 1995, Dr. Gilger joined the faculty at North Carolina State University where he is now a Professor of Ophthalmology. Dr. Gilger has been president of the American College of Veterinary Ophthalmologists and is the President of the International Equine Ophthalmology Consortium. He is the head of the Equine Ophthalmology Service at North Carolina State University and has authored over 130 peer-reviewed scientific manuscripts, written over 30 book chapters, and is the editor of five books, including the 2017 publication Equine Ophthalmology, Third Edition.