The authors of this prospective cohort study set out to report the changes on Spectral Domain-OCT of PASCAL panretinal laser photocoagulation (PRP) treatment for proliferative diabetic retinopathy (PDR) or severe nonproliferative DR (NPDR) and the retinal morphology, from one hour to 21 weeks postoperatively. SD-OCT was performed along the vascular arcades in treated areas, imaging as many of the laser spots as possible. OCT images taken one hour after PASCAL treatment (mean power, 926±434 mW; median, 1,000 mW; n=27 eyes) demonstrated acute morphologic changes including retinal pigment epithelial (RPE) detachment. Laser burns were characterised by bands of increased optical reﬂectivity that localised to the outer retina, extending from the outer plexiform layer to the photoreceptor layer and RPE. Above each burn, there was upward displacement of the outer plexiform layer toward the inner nuclear layer. The retinal structure in between burns remained unaltered, with no evident damage because of the photocoagulation. RPE detachment was observed in 23 of 27 eyes imaged one hour after treatment. Of the laser spots imaged, 36.1% had RPE detachments and 48.4% of them occurred at the spot edges. Only average laser power and average laser energy were signiﬁcantly associated with the percentage of pigment epithelium detachments (PEDs) observed one hour after treatment. At laser powers of 550mW or greater, RPE detachment was observed in every eye. The same was true in eyes that received an average laser energy of 12mJ or greater. No RPE detachments were seen in the one to two week follow-up group. On subsequent follow-up the burns had contracted in horizontal and vertical axis and were less reflective. Burn contraction appeared to plateau three to six weeks after treatment. There was downward deﬂection of the inner retina at each burn, contrasting with the upward deﬂection seen one hour after treatment. RPE seems morphological similar to its pre-treatment structure by three weeks. A small but significant improvement in visual acuity pre and post treatment was noted. This study provides comprehensive insight into the immediate pathophysiological changes after PASCAL treatment and the evolution of these lesions thereafter.