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A Teary-Eyed Horse May Indicate Moon Blindness

Pet Column for the week of June 29, 2009

Related information:

Services - Ophthalmology

Office of Public Engagement
2001 S. Lincoln Ave.
Urbana, Illinois 61802
Phone: 217/333-2907
Ashley Mitek
Information Specialist

Source - Dr. Amber Labelle
Unless your mare has had a bad breakup with the stallion next door, her watery eyes could indicate a serious problem. While there are many reasons for a horse to have excessive tear production, it's a classic sign of equine recurrent uveitis, also known as moon blindness.

Although years ago it was thought that the disease came and went with the cycles of the moon, today we know that it has nothing to do with the lunar calendar. Unfortunately, "equine recurrent uveitis is the most common cause of vision loss in horses," says Dr. Amber Labelle, an ophthalmology resident at the University of Illinois Veterinary Teaching Hospital in Urbana. Since the disease affects approximately one in ten horses, it's important that a complete ophthalmic examination be performed during pre-purchase exams to detect the disorder.

Uveitis simply means that there is inflammation within the uveal tract of the eye. This area includes three parts: the iris, the ciliary body (which is found around the iris), and the choroid (a layer of tissue that supplies blood to the eye located beneath the retina).

Although they may sound similar, uveitis is not really related to UV radiation. Experts do believe that sunburn-causing UV wavelengths from the sun may exacerbate uveitis, but it is not suspected to be the inciting cause. So those fancy sunglasses you bought for your saddlebred probably won't help with prevention.

One of the reasons equine uveitis is so widespread is because the early clinical signs are very subtle and often are not detected right away. "Extra tearing or occasional squinting are symptoms owners should watch for," explains Dr. Labelle. But she also notes that, "owners often think their horse just has allergies," though in reality it is the beginning signs of the disease.

There are many causes of uveitis. Leptospirosis, a bacterial disease that can also affect humans, is one culprit. However, in many cases the inciting cause is not found, and regardless of the cause, the end result is destruction of sensitive eye tissue by the horse's own immune system.

Unfortunately, Dr. Labelle says, "equine recurrent uveitis is one of the most difficult diseases to treat." The standard protocol of anti-inflammatory medications to decrease inflammation in the eye certainly helps, but it rarely prevents the disease from recurring.

Even with this mainstay of treatment, many horses will eventually lose vision, or at the least, will experience repeated, painful episodes of the disease. But there is hope for better treatment in the future. A veterinary ophthalmologist, Dr. Brian Gilger, has developed a device that is impregnated with a drug that suppresses the immune system and can be surgically placed into the eye of an affected horse. Although the implant is not yet commercially available, it is being used at specialty veterinary hospitals across the country and is showing a great deal of promise.

Because a teary-eyed horse may be the first sign of a much bigger problem, contact your veterinarian immediately if you notice any changes in your horse's eye.