A cataract is any opacity of the lens or its capsule. There are many small structures and imperfections of the lens that are not cataracts, and harmless. Many types of equine cataracts are nonprogressive and harmless. Equine ophthalmologists are very noncommital when asked to predict the future of a cataract and even argue among themselves over nomenclature and significance. This article talks about the anatomy of the lens, diagnosis, prognosticating the significance of cataracts, and treatment options in horses.

The lens is made up of a thin outer capsule, a thicker cortex that enlarges throughout the life of the horse, and a central nucleus that is completely surrounded by the cortex. The front of the lens is anterior, the back is posterior and around the margin of the lens, as viewed from the front, is called the equatorial. For an illustration: Eye, Sagital Section

Some common findings in the normal lens are:

• Zonules near the equator
• The anterior and posterior Y sutures. These can be quite variable in shape and appearance and are more prominent than in other species.
• Faint dot-like foci
• Incipient cortical refractile bodies