To assess the efficacy of scanning laser ophthalmoscopy in the retro mode, employing a new dark-field aperture, for detecting laser spots created by subthreshold diode laser micropulse photocoagulation. Interventional case series. setting: Institutional. patients: Eight consecutive patients (8 eyes) with clinically significant diabetic macular edema and 1 patient (1 eye) with macular edema attributable to branch vein occlusion underwent subthreshold diode laser micropulse photocoagulation. Scanning laser ophthalmoscopy images were obtained before and immediately after subthreshold laser photocoagulation. Application of the laser was done under 3 different sets of conditions with a 15% duty cycle for 0.2 seconds in the micropulse mode: condition I was 200-μm spots at 200% of the threshold power in the continuous wave mode, condition II was 200-μm spots at 300%, and condition III was 125-μm spots at 250% or 300%. The laser-treated area was monitored on both color images and by scanning laser ophthalmoscopy (F-10, NIDEK, Gamagori, Japan). Immediately after subthreshold laser photocoagulation, there were no obvious laser scars affecting the treated area in any of the patients on color images. Scanning laser ophthalmoscopy with a diode laser in the retro mode showed no obvious changes after treatment under condition I. However, conditions II and III resulted in dark spots at the sites where the laser had been applied in 5 out of 7 patients. Scanning laser ophthalmoscopy in the retro mode is useful to detect sites of subthreshold micropulse laser application. The dark spots detected by retro mode scanning laser ophthalmoscopy are probably related to swelling of the pigment epithelium after laser application. This method is useful to confirm the invisible spots created by subthreshold diode laser micropulse photocoagulation. Copyright © 2010 Elsevier Inc. All rights reserved.