Uveitis (Equine Recurrent Uveitis- ERU) follows a bout of acute Uveitis. It is an autoimmune response in the eye. There are many factors that can lead to Uveitis, including ocular trauma, parasites, bacterial infections, etc.
Not all horses that experience acute Uveitis will develop chronic Uveitis.
If anti-inflammatory treatment, and treatment specific to the cause of the inflammation (whether it be antibiotics, parasite removal, anti-parasitic medication, steroids, etc.) are not effective, the eye may need to be removed.