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Cyclosporine Implants for 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.ERU causes, in most horses, frequent 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 the cyclosporine implant, which is designed to prevent recurrent episodes of uveitis.

Cyclosporine A

Cyclosporine A 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 does 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.

Slow-release, intravitreal cyclosporine

Experimental studies done at NC State by Dr. Brian Gilger and Dr. Janice Allen have shown that reservoir devices placed into the eye can allow long-term (more than 5 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 yet for use in horses by the FDA.

Is my horse a candidate?

The best canidates 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.

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, so although long-term results are not known, early results are very promising. However, 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, 4700 Hillsborough Street, Box 8401, Raleigh, NC 27606. Telephone 919.513.6660, Fax 919.513.6105.

More on Equine Recurrent Uveitis

Contact

Dr. Brian Gilger or Dr. Mike Davidson
Comparative Ophthalmology Research Laboratory
North Carolina State University
College of Veterinary Medicine
4700 Hillsborough Street
Raleigh, NC 27606
Phone: 919.513.6659
Fax: 919.513.6711
Email: cvm_ophth@ncsu.edu

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