Herpetic simplex keratitis is a form of keratitis (inflammation of the cornea) caused by recurrent herpes simplex virus in the cornea. Also known as eye herpes, the symptoms usually resemble those of common conjunctivitis with pain, burning, irritation, photophobia, reduced visual acuity and redness.

There are two major types of the herpes virus. Type I is the most common and primarily infects the face (mouth, lips and eyes), type II is the sexually transmitted form of herpes, infecting the genitals. When active, both types cause clusters of blisters commonly known as cold sores or fever blisters.

Once herpes simplex is present in the eye, it typically infects the eyelids, conjunctiva and cornea. It can also infect the inside of the eye but this is much less common.

If the infection is superficial, involving only the corneas outer layer, the initial infection may clear up on its own and can heal with no scarring or further problems. However, if the infection reactivates and involves the deeper layers of the cornea (which can happen after numerous activations) the infection may lead to permanent severe scarring of the cornea. The herpes simplex virus may also cause blood vessels to grow onto the cornea which can also lead to significant visual impairment.

Mild infections can be treated with topical ointments and sometimes oral antiviral medication. The affected area of the cornea can also be gently scraped to remove the diseased cells. In the most severe cases where scarring and loss of vision has occurred, a corneal transplant may be required.