Principal Inclusion Criteria:  1. 1. Subjects who have participated in a preceding QR-421a study and who may derive benefit from continued treatment with QR 421a, and/or continued follow up, as assessed by the Investigator, in consultation and agreement with the Medical Monitor  Principal Exclusion Criteria:  Presence of any significant ocular or non-ocular disease/disorder (or medication and/or laboratory test abnormalities) which, in the opinion of the Investigator and with concurrence of the Medical Monitor, may either put the subject at risk because of participation in the study, may influence the results of the study, or the subject's ability to participate in the study. This includes but is not limited to a subject who has uncontrolled cystoid macular edema (CME) in the treatment eye. CME is permissible if stable for 3 months (with or without treatment). Past CME is permissible if resolved for more than 1 month. Safety issue during preceding QR-421a study that may compromise subject safety when continued dosing, as determined by the Investigator, and in consultation with the Medical Monitor.