Uveitis in Horses

Uveitis is inflammation inside the eye, affecting the uveal tract, which includes the iris, ciliary body, and choroid. In horses, this condition is painful and time-sensitive because inflammation can damage delicate eye structures quickly. Even a horse that only seems mildly squinty can have significant discomfort.

Some horses have a single episode linked to trauma, infection, or another eye problem. Others develop equine recurrent uveitis (ERU), often called moon blindness, where inflammation comes back in repeated flare-ups. ERU is one of the most important eye diseases in horses because it is a leading cause of blindness.

Uveitis may affect one eye or both. Over time, repeated inflammation can lead to corneal scarring, cataracts, glaucoma, retinal damage, and permanent vision loss. That is why early treatment matters, even if the eye looks a little better later the same day.

For pet parents, the key takeaway is simple: a painful eye should never be watched at home for long. If your horse is squinting, tearing, avoiding light, or has a cloudy eye, your vet should examine that eye as soon as possible.

Uveitis is not one single disease. It is a pattern of inflammation that can happen for several reasons. In some horses, the trigger is trauma to the eye, such as a scratch, foreign material, or blunt injury. In others, inflammation develops with infection, including leptospirosis, which has a well-known association with equine recurrent uveitis in North America.

Immune system dysfunction also plays a major role, especially in recurrent cases. ERU is widely considered an immune-mediated disease, meaning the horse's immune system continues to drive inflammation even after the original trigger may be gone. That helps explain why some horses have repeated flare-ups over months or years.

Less common causes include systemic infectious disease, corneal ulcers, intraocular infection, and occasionally cancer or other eye disorders. Sometimes your vet can identify a likely cause, but in many horses the exact trigger is never fully confirmed.

Breed risk matters too. Appaloosas are especially overrepresented in ERU, and some other breeds, including certain draft and warmblood lines, may also be at increased risk. A horse with repeated episodes of a painful eye should be evaluated with recurrence in mind, not only the current flare.

Your vet diagnoses uveitis with a careful eye examination and a full medical history. They will look for signs such as a constricted pupil, aqueous flare, corneal edema, low intraocular pressure, redness, pain, and inflammatory debris inside the eye. Because several eye problems can look alike from a distance, hands-on examination is important.

Testing often includes fluorescein stain to check for a corneal ulcer, because ulcers can change which medications are safe to use. Your vet may also use ophthalmoscopy to examine deeper structures, tonometry to measure eye pressure, and sedation or nerve blocks if the horse is too painful to examine safely.

If recurrent disease is suspected, your vet may recommend additional workup to look for underlying triggers or complications. That can include bloodwork, leptospirosis testing, and referral to a veterinary ophthalmologist. In chronic or severe cases, advanced imaging and specialized exams help guide long-term planning.

Diagnosis is not only about naming the problem. It also helps your vet decide whether the goal is treating a one-time inflammatory episode, managing ERU over the long term, or addressing complications such as cataracts, glaucoma, corneal ulceration, or loss of vision.

Not every case of uveitis can be prevented, especially immune-mediated recurrent disease. Still, there are practical steps that may lower risk or help catch problems early. Prompt treatment of any eye injury, corneal ulcer, or unexplained squinting is one of the most important. Small eye problems can become larger ones fast.

Good barn and pasture management also matters. Reduce exposure to sharp hay stems, dusty environments, and situations where eye trauma is more likely. Fly control and general hygiene can help limit irritation and may reduce exposure to infectious organisms carried in the environment.

Because leptospirosis is associated with ERU in many horses, talk with your vet about local risk, wildlife exposure, standing water, and whether vaccination or other preventive steps make sense in your area. Limiting contact with contaminated water sources and wildlife urine exposure may be part of that conversation.

If your horse has had uveitis before, prevention shifts toward early flare recognition. Keep a close watch for tearing, squinting, light sensitivity, or subtle cloudiness, and contact your vet at the first sign of recurrence. Fast treatment often gives the best chance to protect comfort and vision.