Acyclovir Prevention Trial: HEDS-APT evaluated the benefit of long-term acyclovir treatment in patients with a recent history of HSV eye disease but no current active disease. To be eligible, a patient must have experienced any kind of ocular herpes simplex infection (blepharitis, conjunctivitis, keratitis, or iridocyclitis) in the preceding year. The infection must have been inactive and untreated for at least the previous 30 days. Patients were randomized to receive either oral acyclovir (400 mg twice a day) or placebo for 1 year. Five followup visits occurred during the 1-year treatment period and an additional three followup visits during the 6-month post-treatment period. Episodes of recurrent HSV eye disease during the trial were treated with topical corticosteroids and antivirals as indicated, but patients continued to receive the oral acyclovir or placebo for the entire 365-day period. The primary outcome was the time to the first recurrence of any type of HSV eye disease in either eye. The recruitment goal was 696 patients.