Painful inflammation and ulceration of the outer surface (cornea) of the eye because of infection with the herpes virus. Most herpes infections of the eye are caused by type 1 herpes simplex virus, the type of herpes virus that causes fever blisters and cold sores. Prompt treatment with antiviral drugs (eye drops or pills) can prevent the infection from penetrating more deeply into the eye surface, where it is difficult to control and more likely to result in permanent damage. People who have had one outbreak of herpes keratitis are likely to have another, often as a result of fever, stress, exposure to sunlight, or eye injury. Herpes keratitis is the most common infectious cause of corneal blindness in the United States.