context: Most people are surprised to find out that two types of herpes viruses -- the one that causes cold sores and the one that causes chickenpox -- can cause a condition called herpetic eye disease. Unlike a separate virus that causes genital herpes, herpetic eye disease is not sexually transmitted. One of the viruses that causes herpetic eye disease is called the varicella-zoster virus. It is the same virus that causes chickenpox and shingles. When this virus affects the eye, it is called herpes zoster ophthalmicus. The other virus that causes herpetic eye disease is called herpes simplex type 1. Herpes simplex type 1 is the same virus that causes cold sores on the lips and mouth. In the eye, it usually causes an infection of the cornea. This infection is called herpes simplex keratitis. Like many viruses, the herpes simplex 1 and varicella-zoster viruses are present in most adults. The viruses in the herpes family usually live around the nerve fibers in humans without ever causing a problem. Occasionally, the viruses will start to multiply, or they will move from one area of the body to another, and that is when herpetic disease breaks out. This often happens when the immune system of the body is weakened by some other health problem. The two types of herpetic eye disease have different symptoms. One thing they have in common, however, is that they can both be very painful, because they affect the nerves directly. The problem is likely to be herpes zoster ophthalmicus if your doctor finds some or all of these symptoms: Pain in and around only one eye Headache and fever Redness, rash, or sores on the eyelids and around the eyes, especially on the forehead A rash on the tip of the nose Redness of the eye Blurry vision Swelling and cloudiness of the cornea The problem is likely to be herpes simplex keratitis if your doctor sees these symptoms: Pain in and around only one eye Redness of the eye Feeling of dirt or "grit" in the eye Overflowing tears Pain when looking at bright light Swelling or cloudiness of the cornea Your doctor might want to use special tests if it looks like herpetic eye disease might be present. The pressure inside the eye will probably be checked, for example. There is also a special dye called fluorescein that the doctor might put into the eye. This dye glows under ultraviolet light and will show the doctor if the virus is causing problems on the surface of the eye. Because herpes is a virus, antibiotics such as penicillin are not an effective treatment. The only drugs that will work against herpes infections are antiviral medications. Your doctor will likely recommend antiviral pills to quicken healing and decrease the severity of the condition. It is important to keep using the medicine for as long as your doctor recommends. Even though the eye might start to look or feel better, the infection could come back if you stop taking your medicine too soon. If the infection is affecting the cornea, eye drops called corticosteroids might also be recommended. Corticosteroids will help control the disease, but they can also raise the pressure in the eyes of some people. If corticosteroids are being used, it is important for the patient to come back to the doctor's office so the pressure can be checked. Another type of eye drop might also be prescribed to keep the pupil dilated. This will help the eye's natural fluids flow, which prevents the pressure from increasing. Unfortunately, herpetic eye disease can be painful even after several days of treatment and even when the eye is starting to look better. This can be discouraging, but it does not mean that the treatment is a failure. The medications are working, and the pain will go away eventually. The same types of eye drops and pills that are used to treat herpes zoster ophthalmicus are often prescribed to treat herpes simplex keratitis. It is also just as important to use the medications as recommended and to keep all appointments with your doctor.