Equine Cataracts Study Guide

Overview and Clinical Importance

Cataracts are opacities of the crystalline lens that interfere with the transmission of light to the retina, resulting in varying degrees of visual impairment. In horses, cataracts represent a significant cause of blindness and are important to recognize during prepurchase examinations and routine ophthalmic evaluations.

Cataracts are estimated to be present in 5% to 7% of all horses with otherwise normal eyes. If we consider that approximately 8% of all horses are affected by equine recurrent uveitis (ERU), and nearly all of these horses develop some degree of cataract formation, the clinical significance of this condition becomes apparent.

Anatomy and Physiology of the Equine Lens

The crystalline lens is a biconvex, transparent structure located posterior to the iris and pupil, suspended by zonular fibers (lens zonules) attached to the ciliary body. In horses, the lens is notably large compared to other domestic species.