Herpes simplex keratitis is a kind of inflammatory affection of the cornea due to the infection of herpes simplex virus. Usually, the invading virus cannot give rise to the disease but may, only when the body's resistance is weak. One eye is often affected, and sometimes both simultaneously or one after another. In clinic, the disease manifests the main symptom of dendritic or geographic or discoid inflammatory focus of the cornea. With a repeated and protracted course, the case can greatly affect a patient's vision or even cause blindness if it is not treated immediately. In most cases, the infection of herpes simplex virus type I is the cause of the disease.