This infection is produced by the varicella-zoster virus, the same virus that causes chickenpox. After an initial outbreak of chickenpox (often during childhood), the virus remains inactive within the nerve cells of the central nervous system. But in some people, the varicella-zoster virus will reactivate at another time in their lives. When this occurs, the virus travels down long nerve fibers and infects some part of the body, producing a blistering rash (shingles), fever, painful inflammations of the affected nerve fibers, and a general feeling of sluggishness.
Varicella-zoster virus may travel to the head and neck, perhaps involving an eye, part of the nose, cheek, and forehead. In about 40 percent of those with shingles in these areas, the virus infects the cornea. Doctors will often prescribe oral anti-viral treatment to reduce the risk of the virus infecting cells deep within the tissue, which could inflame and scar the cornea. The disease may also cause decreased corneal sensitivity, meaning that foreign matter, such as eyelashes, in the eye are not felt as keenly. For many, this decreased sensitivity will be permanent.
Although shingles can occur in anyone exposed to the varicella-zoster virus, research has established two general risk factors for the disease: (1) advanced age; and (2) a weakened immune system. Studies show that people over age 80 have a five times greater chance of having shingles than adults between the ages of 20 and 40. Unlike herpes simplex I, the varicella-zoster virus does not usually flare up more than once in adults with normally functioning immune systems.
Be aware that corneal problems may arise months after the shingles are gone. For this reason, it is important that people who have had facial shingles schedule follow-up eye examinations.
Herpes of the eye, or ocular herpes, is a recurrent viral infection that is caused by the herpes simplex virus and is the most common infectious cause of corneal blindness in the U.S. Previous studies show that once people develop ocular herpes, they have up to a 50 percent chance of having a recurrence. This second flare-up could come weeks or even years after the initial occurrence.
Ocular herpes can produce a painful sore on the eyelid or surface of the eye and cause inflammation of the cornea. Prompt treatment with anti-viral drugs helps to stop the herpes virus from multiplying and destroying epithelial cells. However, the infection may spread deeper into the cornea and develop into a more severe infection called stromal keratitis, which causes the body's immune system to attack and destroy stromal cells. Stromal keratitis is more difficult to treat than less severe ocular herpes infections. Recurrent episodes of stromal keratitis can cause scarring of the cornea, which can lead to loss of vision and possibly blindness.
Like other herpetic infections, herpes of the eye can be controlled. An estimated 400,000 Americans have had some form of ocular herpes. Each year, nearly 50,000 new and recurring cases are diagnosed in the United States, with the more serious stromal keratitis accounting for about 25 percent. In one large study, researchers found that recurrence rate of ocular herpes was 10 percent within one year, 23 percent within two years, and 63 percent within 20 years. Some factors believed to be associated with recurrence include fever, stress, sunlight, and eye injury.