Equine recurrent uveitis (ERU) is the most common cause of blindness in horses worldwide. It is an immune-mediated inflammatory disease of the uveal tract — iris, ciliary body, and choroid — cycling through painful, vision-threatening episodes. Each episode causes cumulative damage.
Causes and Risk Factors
Leptospira interrogans (serovars Pomona and Grippotyphosa) is strongly associated with ERU in the US. Appaloosa horses have a 25-fold increased risk; the LP (leopard complex) allele (PATN1, TRPM1 loci) is associated with ERU susceptibility. Warmbloods are also overrepresented.
Clinical Signs of a Flare-Up
- Blepharospasm: squinting — the most obvious sign
- Epiphora: excessive tearing
- Photophobia: sensitivity to bright light
- Corneal cloudiness or haze: bluish-white opacity
- Miosis: constricted, pinpoint pupil
- Aqueous flare: haziness in the anterior chamber
Treatment
Topical atropine 1% prevents synechiae; overuse reduces gut motility. Topical corticosteroids reduce intraocular inflammation — contraindicated if corneal ulcer present. Systemic NSAIDs reduce pain during a flare.
Surgical options: intravitreal cyclosporine implant (sustained release 3 to 4 years; Gilger et al., Vet Ophthalmol 2010 showed significant flare reduction); pars plana vitrectomy (removes vitreous and Leptospira; excellent results in Warmbloods per Becker et al.); enucleation for non-visual painful eyes.
When to Call the Vet
Call immediately if you notice squinting, cloudiness, excessive tearing, or any eye change. Equine uveitis is never watch-and-see.
Sources: Gilger BC et al. Vet Ophthalmol 2010; Becker M et al. Vet Ophthalmol 2008; Knottenbelt DC, Pascoe RR. Diseases and Disorders of the Horse (2003).
For deeper question-and-answer context on equine eye health and systemic conditions that affect vision, see horse-info.org.
