Equine recurrent uveitis (ERU) is the most common cause of blindness in horses worldwide. This painful inflammatory eye disease causes repeated episodes of ocular inflammation with progressive vision loss.
ERU causes significant ongoing ocular pain during active uveitis episodes — the eye pain equivalent in horses has been compared to severe migraine or acute glaucoma in humans. Horses with active uveitis show behavioural signs of pain including head shaking, reluctance to work, light avoidance, and reduced performance. Between episodes, subclinical inflammation may persist even when the eye appears quiescent, causing cumulative damage with each cycle. Progressive vision loss creates management challenges as the horse adapts — horses with unilateral blindness often compensate well, but bilateral blindness significantly affects safety, rideability, and the horse's confidence. Enucleation of a chronically painful blind eye, while appearing drastic, is often the most welfare-positive option compared to ongoing pain management of an unresolvable condition.