Corneal ulceration occurs when there has been loss of the corneal epithelium and exposure of the underlying corneal stroma. It is common in horses and is a sight-threatening disease that requires prompt, early attention and aggressive accurate treatment.

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.

Corneal ulcers can range from simple, superficial abrasions in the corneal epithelium to full-thickness corneal perforations with iris prolapse. However, no matter how small or superficial a corneal ulcer may be, it is still highly susceptible to infection and still requires quick, appropriate treatment. Corneal ulcers can be traumatic or non-traumatic, and may be sterile or infected (usually bacterial but sometimes fungal).

Corneal ulcers are detected during an eye exam through florescein staining.