Equine Uveitis Study Guide

Overview and Clinical Importance

Equine recurrent uveitis (ERU), also known as moon blindness or periodic ophthalmia, is the most common cause of blindness in horses worldwide. This immune-mediated condition affects 2-25% of horses globally, with approximately 56% of affected horses eventually becoming blind. ERU is characterized by recurrent episodes of intraocular inflammation affecting the uveal tract (iris, ciliary body, and choroid), followed by variable periods of quiescence.

The clinical and economic impact of ERU is substantial: more than 60% of affected horses cannot return to their previous level of work, and many require enucleation due to intractable pain or blindness. Understanding this condition is essential for NAVLE success, as questions frequently test knowledge of clinical signs, breed predispositions, pathophysiology, and treatment approaches.

Anatomy of the Uveal Tract

The uveal tract (also called the uvea) is the middle vascular layer of the eye and consists of three structures. The iris controls pupil size and light entry. The ciliary body produces aqueous humor and contains muscles for accommodation. The choroid provides blood supply to the outer retina. Inflammation of any part of this tract constitutes uveitis.