The cornea is the transparent area at the front of the eyeball. A corneal ulcer is an erosion or open sore in the outer layer of the cornea. It is associated with infection by a bacterium, virus, fungus, or parasite. See also corneal injury.

Corneal ulcers are most commonly caused by an infection with bacteria, viruses, fungi or amoebae. Other causes are abrasions (scratches) or foreign bodies, inadequate eyelid closure, severely dry eyes, severe allergic eye disease, and various inflammatory disorders.

Contact lens wear, especially soft contact lenses worn overnight, may cause a corneal ulcer. Herpes simplex keratitis is a serious viral infection. It may cause repeated attacks that are triggered by stress, exposure to sunlight, or any condition that impairs the immune system.

Fungal keratitis can occur after a corneal injury involving plant material, or in immunosuppressed people. Acanthamoeba keratitis occurs in contact lens users, especially those who attempt to make their own homemade cleaning solutions.

Risk factors are dry eyes, severe allergies, history of inflammatory disorders, contact lens wear, immunosuppression, trauma, and generalized infection.

• Eye pain
• Impaired vision
• Eye redness
• White patch on the cornea
• Sensitivity to light (photophobia)
• Watery eyes
• Eye burning, itching and discharge

• Visual acuity
• Refraction test
• Tear test
• Slit-lamp examination
• Pupillary reflex response
• Keratometry (measurement of the cornea)
• Scraping the ulcer for analysis or culture
• Fluorescein stain of the cornea