In the second trial, 381 patients were recruited, all of whom had severe fibrovascular proliferations and useful vision in at least one eye. Eligible eyes were assigned either to early vitrectomy or to conventional management. Conventional management included photocoagulation when indicated, with vitrectomy if a severe vitreous hemorrhage occurred and failed to clear spontaneously during a 6-month waiting period or if retinal detachment involving the center of the macula -occurred. After randomization and treatment, all patients were examined at 6-month intervals for 2 years and annually thereafter. Comparisons of visual acuity distributions between experimental and control groups were made.