A “hot” eye—one that is cloudy and irritated with a constricted pupil—is a true emergency. One of its causes, a particularly nasty bacterial uveitis, can cause eventual blindness in 50-100% of its victims especially in Appaloosa’s. Thus, a veterinarian’s prompt assessment and treatment are crucial.

“A “hot” eye is a classic presentation for a horse with uveitis, or inflammation of the middle layer of the eye called the uvea,” said Ann Dwyer, DVM, of Genesee Valley Equine Clinic, in Scottsville, New York, at the 2015 American Association of Equine Practitioners Convention, held Dec. 5-9 in Las Vegas.

During a Sunrise Session brought to attendees by Zoetis, Dwyer reminded equine veterinarians about the key features of the inner eye and how they reside in a “privileged” area of the body because of the blood-ocular barrier. The horse’s body essentially perceives all proteins and other cellular antigens (substances the immune system produces antibodies against) inside the eye as nonself, or, “in other words, molecules that the immune system would classify as foreign and react to,” she said.

In cases of uveitis, the blood-ocular barrier becomes leaky and, “All bets are off! Immune cells, T cells specifically, flood into the eye and essentially go crazy, causing damage and inflammation because so many structures deep to the uvea look foreign,” said Dwyer.

Affected eyes are painful, blepharospastic (winking due to involuntary eyelid muscle contraction), teary, and sensitive to light. In some cases the horse has a flare (cloudy appearance), blood ve