The Macular Photocoagulation Study (MPS) comprised three randomized clinical trials: the Senile Macular Degeneration Study (SMDS), the Ocular Histoplasmosis Study (OHS), and the Idiopathic Neovascularization Study (INVS). The goal was to determine whether, in patients with visual symptoms due to choroidal neovascularization outside the fovea (at least 200 microns from the center of the foveal avascular zone and a best corrected visual acuity of 20/100 or better caused by senile macular degeneration (now known as age-related macular degeneration), histoplasmosis, or idiopathic causes, argon blue-green laser photocoagulation prevents significant loss of visual acuity. Based on the study findings, the authors recommended that eyes with well-defined extrafoveal choroidal neovascular membranes should be treated with argon blue-green laser photocoagulation to prevent or delay significant loss of visual acuity.