"Equine recurrent uveitis (ERU) is a disease complex characterized by recurring episodes of active uveitis. It is important to note that one bout of uveitis does not equal a diagnosis of ERU. The horse must have evidence for recurring episodes of uveitis to be diagnosed with ERU. This disease is one of the oldest known conditions of the horse. The term “moon blindness” comes from the early and incorrect theory that recurrent episodes were linked to the phases of the moon.
How often does it occur, and which horses are most commonly affected?
Equine recurrent uveitis is thought to have a prevalence of 8% in horses in the United States. (1,2) There appears to be an increased incidence of ERU in the Appaloosa breed. There have been no studies to investigate the prevalence within the Appaloosa breed alone, however, in one study of 112 horses with uveitis, 28 (25%) were Appaloosas. When this was compared to the number of horses without uveitis (10/260 were Appaloosas) the odds of finding uveitis were 8.3 times greater in Appaloosas than in all other breeds combined. (3) Appaloosas also have a greater risk of becoming blind from ERU compared to other breeds. (3)" Equine Recurrent Uveitis (ERU) - Appaloosa coat patterns, coat colour genetics and practical information for breeders of spotted horses - The Appaloosa Project