Uveitis is inflammation of the iris and deeper structures inside the eye. Uveitis may occur as a result of a number of ocular or systemic conditions. Equine recurrent uveitis or ERU is a syndrome of recurrent or chronic episodes of uveitis. It is one of the most common causes of blindness in the horse. It is characterized by repeated episodes of uveitis alternating with periods of quiescence, when the eye is “quiet” or not inflamed. One or both eyes may be involved in the disease. Although the initiating factors are still not completely understood, the overwhelming force causing the ocular damage is clearly immune-mediated.
Clinical signs of “active” ERU include tearing, squinting, pain, sensitivity to light, and a cloudy and/or red eye. The recurrent episodes of intraocular inflammation cause progressive vision-impairing damage, including cataract, retina degeneration and secondary glaucoma. These permanent changes may be seen by a veterinary ophthalmologist even during the “quiet” stages of the disease. During the “quiet” stages, the eye is not painful and minimal inflammation is present.
ERU is thought to be caused by an overly active immune response within the eye. The source may be bacterial (such as Leptospira, Brucella, Salmonella, or Streptococcus), viral, protozoan, or parasitic (such as Onchocerca, Strongylus, or Toxoplasma). There appears to be a genetic predisposition to ERU, as certain breeds such as Appaloosas appear highly predisposed. It is important to remember that the source just initiates the overactive ocular immune process characteristic of ERU. Therefore, although identifying and treating the source of the problem may be recommended, it is not expected to be curative as the horse’s own immune system may perpetuate the disease within the eye. In many cases, the causative agent is never identified.
Treatment is aimed at controlling the inflammation associated with the “active” stages of the disease, alleviating the associated ocular discomfort, treating complicating factors, and preserving vision. Medications should be prescribed by the veterinarian as soon as signs of ERU are noted. For each “active” stage of the disease, it may be necessary to continue treatment of the eye for several weeks to several months, depending on the severity of inflammation. Relapses require re-initiation of treatment. It is recommended to consult with your veterinarian or veterinary ophthalmologist whenever you feel your horse is showing clinical signs as some of the medications used to treat ERU may be contraindicated if another condition, such as a corneal ulceration, is present. During ERU episodes your horse may experience sensitivity to light.
Therefore it may be helpful to keep the horse in a darkened stall with limited exercise during treatment periods and/or to place a UV-protective or fly mask. Some horses may be best treated on a daily basis to reduce the frequency of recurrent episodes.
If you have any questions about Equine Recurrent Uveitis, please do not hesitate to call us at Eye Care for Animals.
