The cornea is the clear covering of the front of the eyeball. The cornea is made up of two basic layers. The structural part is a clear material that makes up the corneal wall, and the second is a very thin live cell surface layer (think of it as a sealing paint over the outside). This outer layer is called the corneal epithelium. If the epithelium is scraped away by traumatic injury, a corneal ulcer is born.

Corneal ulcer is one of the most common eye conditions in horses. Corneal ulcers are painful, causing squinting, tearing, and swelling of the tissues around the eye. They can become infected and quickly spread, endangering the eye. There are many types of corneal ulcers, characterized mostly by how deep they are.

Vets diagnose corneal ulcers and injuries with a careful clinical exam of the eye, and fluorescein staining. This green stain is absorbed by areas that have lost the normal corneal surface covering.

Treatment usually includes systemic anti-inflammatory drugs and ophthalmic antibiotic solutions or ointments. Generally, ointments containing steroids are avoided because this can reduce immunity in the eye and encourage bacterial destruction of the cornea. Full thickness wounds to the cornea can be sutured like a skin wound. This must be done in a meticulous fashion and requires special suture material, instruments and techniques.