The cornea is the transparent front layer of the eyeball. It is less than 1 millimeter thick and consists of several complex layers. It is the most sensitive part of the body and readily reacts to irritants or stimuli from both outside and inside the eye.

Ulcerative keratitis is corneal inflammation caused by disruption in one or more layers of the cornea, starting from the outside going inward. The disruption (ulcer) may be very shallow, similar to a scrape or an abrasion, or it may be very deep, nearly penetrating all the corneal layers. The deeper the ulcer is, the more vision is threatened.

Corneal ulcers have many causes, including trauma, infections, inborn weaknesses, and nutritional deficiencies.

Once a corneal ulcer occurs, rapid deterioration of the cornea may result.

Corneal ulcers are quite painful, and treatment to reduce discomfort will be given. Further irritation or damage should be prevented. Bright light may be an irritant. Treatment includes use of medicine with or without surgery. Artificial lenses are also used in selected cases.