Herpes simplex virus (HSV) can cause cold sores around the mouth and can sometimes affect the eye. When the eye is involved we typically see a dendritic corneal ulcer on the surface of the eye. We call it “dendritic” because the infection forms a classic fern-leaf pattern on the cornea. Initial episodes cause eye irritation and a foreign body sensation, though repeat bouts are less painful due to viral deadening of the eye nerves. Deep and repeated infections can cause corneal scarring that may lead to permanent vision loss. The treatment for herpetic eye disease is usually a combination of topical antiviral drops such as Viroptic or Zirgan and an oral antiviral like acyclovir or Valtrex. Whenever we diagnose “herpes virus” in the eye, I like to stress to my patients that this is NOT a sexually transmitted disease that they’ve caught! These viral infections are almost always an activation of HSV-1 (the non-sexual variety of herpes). The majority of the U.S. population is seropositive for HSV-1 with the virus lying dormant in the base of nerves. Only in some people does the virus activate enough to cause skin and eye manifestations. The triggers for this are unknown, but there are many theories about emotional stress, hormones, or environmental conditions that might bring it out.