Argon laser photocoagulation for ocular histoplasmosis. Results of a randomized clinical trial.

The Ocular Histoplasmosis Study (OHS) is a multicenter controlled clinical trial designed to determine whether argon laser photocoagulation is useful in preventing severe visual acuity loss in eyes with choroidal neovascular membranes (NVMs) 200 to 2,500 microns from the center of the foveal avascular zone and evidence of ocular histoplasmosis. Eligible patients were assigned to photocoagulation (n = 124) or to observation only (n = 121) groups. Recruitment of patients who have extrafoveal NVMs for the OHS has been terminated because more untreated eyes than treated eyes had experienced severe visual acuity loss. At the most recent follow-up visit (median follow-up, 18 months), 34.2% (39/114) of untreated eyes v 9.4% (11/117) of treated eyes had lost six or more lines of visual acuity from the baseline level. The superiority of argon laser photocoagulation was evident in all subgroups and at every point in follow-up time, indicating that patients who meet the eligibility criteria will benefit from treatment. Follow-up of all patients continues in order to assess long-term results of treatment.