Herpes simplex keratitis, also called a dendritic corneal ulcer, is an eye infection caused by the herpes simplex virus, which is the same virus that causes "cold sores" or "fever blisters" near the mouth and nose.  However, you can have a dendritic corneal ulcer without previously having a cold sore.  The infection may follow some mild injury to the eye, or an illness or fever.

A herpes eye infection may start out looking or feeling like the common "pink eye" or conjunctivitis-red, scratchy, watery, and uncomfortable.  You won't be able to see the ulcer in the mirror because it is only about 1/25 of an inch in length.  However, the characteristic dendritic shape can be seen and identified easily with a slit lamp.

Once the infection has started it may run its course and disappear, just as cold sores do.  The problem is that the infections tend to recur, and recurrences are more prone to complications.  The best way to avoid complications is to begin treatment early with eyedrops, ointments, or sometimes pills. Occasionally the virus does not respond to treatment and infect the deeper tissues in the cornea.  Scarring of the cornea can result and it may affect your vision.  Rarely, in extreme cases, corneal scarring or other more severe problems will require a corneal transplant to restore vision.