Long-Term Intraocular Pressure Dynamics After Selective Stromal Melanin Modulation: A Testable Mechanistic Framework

Background: Conventional aqueous outflow is regulated by trabecular meshwork (TM) cells, juxtacanalicular extracellular matrix (ECM), and Schlemm’s canal (SC) endothelium. Iris-directed laser pigment modification, unlike selective laser trabeculoplasty (SLT), does not directly irradiate the outflow tissues. Whether an iris-derived particulate response could be followed by a lasting change in outflow homeostasis is unknown. Objective: To integrate experimental findings on pigment processing, monocyte signaling, SC junctional mechanotransduction, and cytokine-associated matrix remodeling into a falsifiable hypothesis for long-term intraocular pressure (IOP) trajectories after selective stromal melanin modulation (SSMM). Methods: A targeted, non-systematic synthesis examined primary experimental work on pigment–TM interactions, SLT-associated monocytes, FYN–VE-cadherin signaling, PIEZO1/TRPV4 responses, TNF/IL-1–MMP interactions, and outflow ECM biology. Evidence is distinguished as directly demonstrated, transferred across experimental contexts, or specific to SSMM. A Goldmann-equation sensitivity analysis estimates the outflow-facility changes implied by hypothetical pressure shifts under fixed assumptions. Synthesis: Two potentially concurrent responses are proposed: a rapidly reversible component involving TM tone and SC endothelial permeability, and a slower, unproven component involving ECM and cell–matrix feedback. Experiments support monocyte-mediated changes in outflow following SLT, FYN-dependent SC permeability in mice, and cytokine-driven MMP induction in TM cultures. Other experiments demonstrate that pigment loading can instead increase outflow resistance, and that the TM protease response depends on the phagocytic substrate. Neither a beneficial response nor multi-year persistence has been demonstrated after SSMM. Conclusion: A transient-to-persistent shift in outflow homeostasis is an experimentally testable possibility, not an established outcome of SSMM. Competing pathways, washout studies, direct outflow measurements, and standardized longitudinal human observations are required to determine whether any sustained IOP change exists and why.