Uveitis means inflammation within the eye. It should only be termed equine recurrent uveitis when two or more episodes occur. It is a complex condition, which is the most common cause of blindness in the horse worldwide and a very common cause of chronic eye pain in horses. Patient outcomes are improved by early diagnosis, appropriate therapy and clear understanding of the disease. Recent advances in treatment have helped.
The condition was historically called moon blindness, as when the cause was unknown, the intermittent nature of the disease was suggested to be associated with the phases of the moon. We now know that recurrent equine uveitis is a recurring immune-mediated inflammation of the eye, which after a lifetime of inflammatory episodes is not surprisingly more common in older horses.
ERU is fairly rare in the UK, with around half of those horses that have had uveitis suffering a recurring problem.
ERU is more commonly seen in the USA and in central Europe, particularly in Germany and the Czech Republic. Much of the research into treatments of the disease has been carried out in these countries.
It usually occurs in horses who are more than four years old and often becomes a noticeable problem in mid-adult prime performance years. The disease just affects one eye in about 50% of horse, except for the Appaloosa breed which has 80-87% bilateral uveitis.
Signs of equine recurrent uveitis