Impact of Subthreshold Micropulse Laser on the Vascular Network in Diabetic Macular Edema: An Optical Coherence Tomography Angiography Study

<b>Objectives</b>: To evaluate the short- and long-term effects of subthreshold micropulse laser (SMPL) treatment on the microvascular network in diabetic macular edema (DME). <b>Methods</b>: This 12-month prospective study included 67 eyes (67 patients) with mild DME and good best-corrected visual acuity (BCVA), randomized into SMPL (33 eyes) or sham (34 eyes) groups. Assessments were performed at baseline (T1), 3 months (T2), and 12 months (T3). Optical coherence tomography (OCT) and OCT angiography (OCTA) were used to measure central retinal thickness (CRT), macular thickness (MT), macular volume (MV), foveal avascular zone (FAZ) area, microaneurysm (MA) count, and vessel parameters in the superficial capillary plexus (SCP) and deep capillary plexus (DCP). <b>Results</b>: The SMPL group showed a greater relative reduction in FAZ area in the SCP at 3 months (3.21 ± 13.03% vs. -5.73 ± 13.3%; <i>p</i> = 0.032) with a trend toward significance at 12 months (2.37 ± 12.47% vs. -3.3 ± 7.92%; <i>p</i> = 0.086) compared to the sham group. No changes in FAZ size, MA count, and other microvascular parameters were observed in either group. In the SMPL group, BCVA improved at 3 months (T2 > T1, <i>p</i> = 0.003); CRT decreased at 12 months (T2 > T3, <i>p</i> = 0.023); MT decreased at 12 months (T2 > T3, <i>p</i> = 0.006) and MV decreased at 12 months (T2 > T3, <i>p</i> = 0.007). No changes were detected in the sham group. No treatment-related complications occurred. <b>Conclusions</b>: SMPL may improve the macular microvasculature in mild DME by reducing FAZ size in the SCP. It provides visual and functional benefits while maintaining a favorable safety profile.