A randomized pilot study comparing subthreshold vs threshold diode laser photocoagulation (PC) in the reduction of drusen associated with age-related macular degeneration

Purpose. To determine whether diode laser grid PC using subthreshold (invisible) lesions results in reduction in drusen equal to threshold (visible) lesions and to compare these results to controls. Methods. We enrolled 146 patients (217 eyes) with dry AMD in a multicenter pilot study. Each eligible eye had at least 5 large soft drusen and visual acuity of >20/63. Bilateral eligible eyes (71 patients) were randomly assigned to receive diode laser (IRIS OcuLight SLx) PC in one eye and observation in the other; unilateral eligible eyes (75 patients) were randomized to either treatment or observation. Treatment eyes were further randomized to threshold or subthreshold PC. Results. Both treated groups showed a reduction in drusen during the course of the follow-up period. None of the observed eyes had a reduction in drusen. Disappearance of drusen was faster initially in the threshold treatment subgroup (43% (23/53) vs 18% (9/49) at 3 months), but gradually equalized in both threshold and subthreshold subgroups during the follow-up period: 80% vs 36% at 6 months; 88% vs 75% at 12-18 months. Three cases of acute choroidal neovascular membranes (CNVM) were induced by visible laser burns early in the study. No cases of geographic atrophy occurred in any treated eyes. Conclusion. Subthreshold diode laser PC decreases the amount of drusen present in dry AMD eyes with minimal side effects. These results are helpful in the design of a larger multicenter randomized study to determine whether reduction of drusen may reduce the incidence of CNVM formation in eyes with dry AMD.