Equine Recurrent Uveitis (ERU)

By: Katie Jones, CVT

From time to time owners and veterinarians will occasionally see a horse that has developed Equine Recurring Uveitis; otherwise known as “Moon blindness.” Uveitis can be a painful eye disease of any aged horse. It is the most common inner eye disease and the leading cause of blindness in horses. Uveitis was first discovered in the 1600s with occurrences being linked to the phases of the moon; thus, the name “Moon blindness” came about.

This disease can be caused by several factors; the leading one being a Leptospirosis bacterial infection. Leptospirosis has a spirochete (coiled) shape with flagella along the length of it. This particular shape allows the bacterium to move in a twisting motion, which enables it to move easily in fluid. This bacterium can be found in the environment, specifically in areas of stagnant water or contaminated urine. This bacterium enters the horse either through a break in their skin or the ingestion of infected urine. Uveitis is not directly caused by the exposure to the Leptospirosis bacterium; it is due to the molecular makeup of Leptospirosis being very similar to the structure of the eye. Uveitis is the result of the body’s reaction to the foreign Leptospirosis protein; it attacks both the bacterium as well as the eye due to the similarities.

Besides the development of a Leptospirosis infection, any trauma or inflammation to the ocular barrier (barrier between the blood circulation and the internal eye) can cause the horse to develop uveitis.

Uveitis can affect one or both eyes. Here a few common traits seen in a horse that has fig2_240x180developed an infection: redness, squinting, tearing, and the eye will appear cloudy. As the infection continues to become more of a chronic issue, the horse may develop behavioral issues associated with decreased vision; such as: spooking, bumping into things, and being reluctant to go into dark places.

Horses are not considered to have Equine Recurrent Uveitis until they have had two or more episodes.

fig1_240x180Treatment is focused on preserving vision in the eye and reducing inner eye inflammation due to the body’s immune response. Early examinations of the eye by a veterinarian and treatments are vital to avoid series complications.

If after eye medication treatments the horse is still suffering from recurring episodes, medicated implants can be discussed with a veterinarian. With this option, Cyclosporine implants are surgically placed under the sclera where the eye can constantly absorb the medication. These particular implants will deliver medication for three to four years, and will hopefully prevent future episodes.

Although Equine Recurrent Uveitis can be a serious and devastating disease, with early diagnosis and proper care horses can be fortunate enough to not lose vision in the eye.