Optical coherence tomography angiography assessment of 577 nm laser effect on severe non-proliferative diabetic retinopathy with diabetic macular edema

AIM: To quantitatively evaluate the effect of the combined use of 577-nm subthreshold micropulse macular laser（SML）and multi-point mode pan retinal laser photocoagulation（PRP） on severe non-proliferative diabetic retinopathy（NPDR） with central-involved diabetic macular edema（CIDME） using optical coherence tomography angiography（OCTA）.METHODS: In this observational clinical study, 86 eyes of 86 NPDR patients with CIDME who underwent SML and PRP treatment were included. Images were obtained 1 d before laser and post-laser（1 d, 1 wk, 1, 3, and 6 mo） using AngioV ue software 2.0. Best corrected visual acuity（BCVA,LogM AR）, foveal avascular zone area（FAZ）, choriocapillary flow area（Ch F）, parafoveal vessel density（PVD）, capillary density inside disc（CDD）, peripapillary capillary density（PCD）, macular ganglion cell complex thickness（m GCCT）,central macular thickness（CMT）, and subfoveal choroidal thickness（ChT） were compared between pre-and post-laser treatment. RESULTS: BCVA remained stable during 6 mo postlaser therapy（pre-laser vs 6 mo post-laser: 0.53±0.21 vs 0.5±0.15, P>0.05）. PVD, ChF, ChT, CMT, and mGCCT significantly increased 1 d post-laser therapy [pre-laser vs 1 d post-laser: superficial PVD（%）, 40.51±3.42 vs 42.43±4.68;deep PVD（%）, 42.66±3.67 vs 44.78±4.52; ChF, 1.72±0.21 vs 1.9±0.12 mm;; ChT, 302.45±69.74 vs 319.38±70.93 μm; CMT, 301.65±110.78 vs 320.86±105.62 μm; m GCCT, 105.71±10.72 vs 115.46±9.64 μm; P<0.05]. However, PVD, ChF and ChT decreased to less than baseline level at 6 mo postlaser therapy(pre-laser vs 6 mo post-laser: superficial PVD（%）, 40.51±3.42 vs 36.32±4.19; deep PVD（%）, 42.66±3.67 vs 38.76±3.74; Ch F, 1.72±0.21 vs 1.62±0.09 mm;; Ch T, 302.45±69.74 vs 289.61±67.55 μm; P<0.05), whereas CMT and mG CCT decreased to baseline level at 6 mo postlaser therapy（CMT, 301.65±110.78 vs 297.77±90.23 μm; m GCCT, 105.71±10.72 vs 107.05±11.81 μm; P>0.05）. Moreover, FAZ continuously increased while CDD and PCD continuously decreased in 6 mo after laser therapy. CMT and ChT had a significant positive correlation with ChF and PVD in most post-laser stages.CONCLUSION: During a 6-month follow-up period after combined use of SML and PRP therapy, BCVA remained stable and there was a decreased trend in macular edema. Blood flow increased at 1 d post-laser therapy and reduced at 6 mo post-laser therapy.