The study aims to enroll 150 eyes. At least 40 eyes will be enrolled with prior focal laser photocoagulation and at least 40 eyes without prior focal laser treatment. After enrollment of 80 eyes (40 with prior treatment and 40 without prior treatment), an interim analysis will be conducted so that focused enrollment strategies can be implemented if the analysis suggests that more subjects in a subgroup should be entered. Approximately half of the eyes will receive each scatter treatment regimen.