Equine recurrent uveitis (ERU) is a nasty disease, causing searing pain and loss of use. Adding insult to injury, the disease keeps coming back, often resulting in blindness.
This disease frequently frustrates veterinarians such as Mary Lassaline, DVM, PhD, MA, Dipl. ACVO—even to the point of despair, she said—because ERU remains an expensive and unrewarding disease to treat. But as researchers learn more about the ins and outs of the disease, they’re finding ways to improve treatment.
“ERU is the number one cause of blindness that comes with important emotional and economic strings attached,” said Lassaline, a large animal ophthalmologist at the University of California, Davis, during her presentation at the 2017 American Association of Equine Practitioners Convention, held Nov. 17-21 in San Antonio, Texas. “In one retrospective study, approximately 15% of affected horses are euthanized, and by the time many horses are referred to a specialist, the horse’s disease is already at an advanced stage. Up to 25% of horses are already blind by the time they are referred.”
“In that same retrospective study, many horses with ERU already underwent a career change or had reduced activity, and about 50% tested positive for leptospirosis,” she added.
To review briefly, ERU is an immune-mediated form of uveitis—inflammation of the uveal tract, which comprises the iris, muscular ciliary body, and choroid. Uveitis is a painful condition, and chronic uveitis can cause permanent changes in the eye, including cataracts, glaucoma, and retinal detachment.
“There are multiple causes for ERU, and despite the importance of this disease, ERU remains incurable,” said Lassaline.
In light of these facts, she encouraged practitioners to approach horses with painful eyes in a systematic and standardized fashion to optimize chances of treatment success:
- Recognize uveitis promptly. It is characterized by miosis (excessive constriction of the pupil); a painful, red, and cloudy eye; and low intraocular pressure.
- Stain every eye. Corneal ulcers can also cause squinting, tearing, redness, and cloudiness. Staining the eye with a fluorescent dye can distinguish them from uveitis.
- Always do a fundic exam to assess the structures in the back of the eye. “You can use a smartphone and an app that has a camera plus the light to perform a fundic exam easily and thoroughly,” Lassaline said.
To diagnose ERU, the horse must have uveitis that has recurred or is persistent. In addition, veterinarians use a standardized grading scheme for ERU (e.g., on a scale of 1 to 5) to achieve an early diagnosis and assess treatment success.
“In some ways, ERU is akin to laminitis, a recurrent and lifelong, life-altering condition,” said Lassaline.
In terms of treatment, Lassaline recommended administering topical steroids, topical atropine to dilate the eye, and systemic nonsteroidal anti-inflammatory drugs. Cyclosporine implants, which veterinarians surgically place in the eye (in the suprachoroidal space), can reduce the frequency and severity of ERU flare-ups and can last for at least 48 months.
Wrapping up, Lassaline reminded veterinarians that commercially available leptospirosis vaccines are not labeled to prevent or treat ERU.