Drug prevents herpes return to the eye.

About 400,000 people in the United States suffer from a potentially blinding herpes infection of the eye that tends to recur. A new study suggests a way to thwart the herpes simplex virus and prevent loss of vision.

Kirk R. Wilhelmus of the Baylor College of Medicine in Houston and his colleagues studied 703 people who had reported a previous herpes infection of the eye.

Although the immune system may clear the initial disease, it often doesn't kill the herpes simplex virus, which can remain in hiding for months or even years--causing another round of disease when it revs up again.

The virus can also infect the mouth or genital region. The drug acyclovir prevents recurrence of herpes disease there. Could acyclovir block a flare-up of the disease in the eye as well?

To find out, the researchers gave approximately half the study participants 400 milligrams of acyclovir twice a day for a year, while the controls received a placebo pill. Herpes infections to the eye were recorded.

The researchers observed that acyclovir reduced the recurrence of herpes infection of the eye by 41 percent during the year of treatment. After the acyclovir treatment ended, the number of recurrences increased to match that of the control group. Wilhelmus and his colleagues report their findings in the July 30 New England Journal of Medicine.

The team also noted that the therapy lowered by about 50 percent the risk of a return of the most severe form of the disease, stromal keratitis. Stromal keratitis occurs when the virus invades the inner layer of the eye's cornea where it can lead to scarring and loss of vision.

The study detected no side effects that could be attributed directly to the drug.

The findings suggest that people who have had stromal keratitis should consider taking acyclovir over the long term, perhaps even for life, to prevent a recurrence, says Scott Whitcup of the National Eye Institute in Bethesda, Md.