Update on subthreshold micropulse laser treatment for retinal diseases: A narrative review

Subthreshold micropulse laser (SML) has emerged as a valuable and effective alternative to conventional laser treatments for a variety of retinal diseases, offering therapeutic benefits while minimizing tissue damage. Unlike traditional continuous wave lasers which induce irreversible changes to photoreceptors and retinal pigment epithelial (RPE) cells due to thermal damage, SML delivers energy in short bursts with cooling intervals, maintaining subthreshold temperatures that trigger therapeutic cellular responses without causing visible retinal scarring. We have synthesized the latest evidence on SML's role in managing diabetic macular edema (DME), central serous chorioretinopathy (CSCR), macular edema secondary to retinal vein occlusion, and age-related macular degeneration. Across these conditions, SML demonstrates comparable visual and anatomical outcomes to conventional laser and anti-vascular endothelial growth factor therapies, with notable benefits, including a reduced injection burden in DME and improved choriocapillaris perfusion in CSCR. Additionally, emerging data suggests SML may hold an edge in more complex cases, such as chronic CSCR, pseudophakic macular edema, and dome-shaped maculopathy; however, inconsistencies in laser parameters including wavelength, duty cycle, fluence parameters and spot size continue to pose challenges in standardizing treatment protocols. The "reset theory" of RPE restoration, driven by heat shock protein activation or other described mechanisms, underscores SML's potential to offer sustained, long-term disease control. While current evidence is promising, larger, high-quality studies are still needed to fine-tune treatment settings, improve patient selection strategies, and clarify SML's role alongside other therapies. We provide a comprehensive overview of SML's progress, potential, and future direction in retinal disease management.