deborah y strauss, d.v.m.Equine recurrent uveitis (ERU), also known as “moon blindness” or periodic ophthalmia, is a common disease effecting the equine eye and is the most common cause of blindness in the horse.

Due to the recurrent nature of the disease, the term “moon blindness” dates back to the 1600s when Egyptians believed the ailment was associated with the phases of the moon. Today ERU is mainly recognized as an immune mediated disease, meaning that it is usually caused by an unspecified immune mediated reaction.

There are several causes that have been implicated such as bacteria (Leptospirosis), viruses, parasites (Onchocerciasis), and trauma. ERU, however, is most often considered to be an idiopathic disease, meaning that no specific cause can be identified. ERU is strongly over-represented in the Appaloosa horse breed, however it has been identified in other breeds. ERU is a disease that can be controlled with aggressive medical therapy to maintain partial vision to the horse which is suffering from it.

Due to the environmental exposures that horses experience on a daily basis, their eyes can be adversely effected. Any eye problem a horse is experiencing should be considered an equine emergency and medical treatment needs to be sought immediately.