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Equine Recurrent Uveitis

Information for the veterinarian and horse owner

Equine recurrent uveitis (ERU), or “moon blindness,” is the most common cause of blindness in horses. Studies done at NC State College of Veterinary Medicine and elsewhere have determined that the cause of ERU is an over-reaction of the horse’s immune system, which causes inflammation in the eye. Usually this occurs after an initial ocular injury or infection. In most horses, ERU causes episodes of ocular irritation such as corneal cloudiness, pain, discharge, and a small pupil. The episodes usually become more severe and frequent, until the eye becomes blind.

Traditional treatment of ERU is usually effective in controlling the active inflammation, but there is no effective way to prevent the recurrent episodes typical of ERU. Because of these problems, we have worked on developing methods to prevent recurrent episodes of uveitis, such as use of sustained release cyclosporine.

Mature cataract induced by ERU; horses that lose vision from cataracts caused by ERU are poor candidates for cataract surgery.

Mature cataract induced by ERU; horses that lose vision from cataracts caused by ERU are poor candidates for cataract surgery.

Cyclosporine

Cyclosporine is an immunosuppressant drug that is commonly used for treatment to prevent organ transplant rejection and for treatment of dry eyes in dogs. Cyclosporine is the ideal drug to prevent the recurrence of immune-mediated ocular inflammation. It suppresses the activity of the T-lymphocyte, which is the most common infiltrating cell in ERU eyes.

However, cyclosporine eyedrops or ointment do not penetrate past the cornea. Therefore it cannot get into the eye to treat the uveitis. Oral cyclosporine would likely be too toxic and expensive to give a horse to prevent ERU.

Corneal disease caused by steroid use and iridal damage due to ERU; horses that develop corneal disease from ERU pose further medical treatment challenges.

Corneal disease caused by steroid use and iridal damage due to ERU; horses that develop corneal disease from ERU pose further medical treatment challenges.

Sustained-release cyclosporine

Studies performed at NC State have shown that reservoir devices placed into the eye can allow long-term (more than 4 years) release of low levels of cyclosporine. Studies have shown that the implants are safe and effective in decreasing inflammation in the equine eye. Clinical studies in horses with ERU have shown excellent control of the disease. However, this is an experimental device and not approved for use in horses by the FDA.

Is my horse a candidate?

The best candidates for the implant are those with the following characteristics:

  • ERU is controllable with traditional medication, but the horse has frequent recurrences
  • The horse has good vision between episodes
  • The horse has minimal scarring in the eye and no cataract formation
  • There is no retinal degeneration and has good retinal function
  • The horse does not have other systemic illnesses (such as a high titer to leptospirosis)

Your veterinarian’s examination will help determine if your horse is a good candidate.

The 6mm diameter non-dissolvable cyclosporine implant developed by Dr. Brian Gilger’s Ocular Immunology, Toxicology and Drug Delivery Laboratory.

The 6mm diameter non-dissolvable cyclosporine implant developed by Dr. Brian Gilger’s Ocular Immunology, Toxicology and Drug Delivery Laboratory.

Who can do the surgery?

There are veterinary ophthalmologists in nearly all areas of the US who are or will be trained to perform the implant surgery. Please call us to determine the closest ophthalmologist in your area.

What are the success rates?

This is an experimental procedure, however, long-term results have shown that greater than 80% of horses have ERU controlled. Some horses have lost vision after implantation.

Support us!

Cyclosporine implants have been studied, tested, and manufactured at the Comparative Ophthalmology Research Laboratory at North Carolina State University College of Veterinary Medicine. A large amount of time and money has been spent to develop these devices specifically for the treatment of equine uveitis.

Please support our laboratory and our efforts in the treatment of equine uveitis by donating to the Equine Uveitis Research Fund in care of the North Carolina Veterinary Medical Foundation, 1060 William Moore Drive, Box 8401, Raleigh, NC 27607. Telephone 919.513.6660.

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Contact

Dr. Brian Gilger
Comparative Ophthalmology Research Laboratory
Phone: 919.513.6659
Fax: 919.513.6711
Email: NCStateOphthalmology@ncsu.edu

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