My horse has corneal endothelial degeneration. My veterinarian and I have been using a "control" schedule for some time, but I would like some information about the condition.

The cornea of the horse eye is slightly thicker than 1 mm. It consists of outer layers of epithelial cells, a middle stroma made of protein, and a single layer of endothelial cells on the inner surface of the cornea. The endothelial cells contain a pump that normally pumps water out of the cornea. If these endothelial cells and their pump become damaged, the cornea collects water in the stroma and the cornea appears edematous (swollen) or cloudy. The horse is born with a finite number of endothelial cells and produces no more throughout life.

Endothelial cells can become damaged (degenerate) by inflammation (uveitis) and/or physical trauma (such as from a whip injury or a lens dislocation). Since endothelial cells cannot repair themselves, disease of the endothelium is very serious for the horse eye. Equine recurrent uveitis (ERU, or moon blindness) is the most common cause of endothelial degeneration. Controlling ERU can help minimize the damage to the endothelium.