A corneal ulcer is a painful open sore on the cornea of the horse's eye. It is a serious condition which requires early recognition and aggressive treatment from a veterinarian, no matter how small or superficial they may appear. They are a common occurrence in horses and the severity can range from minor, superficial abrasions in the outer layer of the cornea, to full-thickness corneal perforations with iris prolapse. It can cause significant pain and discomfort to the horse and is potentially a sight-threatening disease if left untreated.
Corneal ulcers can be caused by trauma or microtrauma, resulting from conjunctival foreign body (plant material, metal, glass, hay, and so on), chemical toxin, or environmental objects (fences, branches, stall components). The corneal epithelium of the horse serves as a barrier against invasion of potentially pathogenic bacteria or fungi normally present on the surface of the cornea and conjunctiva. A horse with a corneal ulceration can allow bacteria or fungi to potentially invade the cornea and cause a secondary infection.