In vivo characterization of blue-light-induced peripheral arterial photorelaxation using functional OCT

Precise and spatially controlled modulation of peripheral arterial tone is important for treating microvascular disorders. Current pharmacological vasodilators are typically systemic and lack local specificity. Light-induced photorelaxation has been proposed as an alternative method for vascular modulation. However, its structural and hemodynamic effects in vivo have not been fully characterized. In this study, real-time functional optical coherence tomography (OCT) was used to visualize and quantify blue-light-induced peripheral arterial photorelaxation in living mice. Arteries in the femoral, tail, and auricular regions were exposed to 473-nm blue-light stimulation and imaged using OCT angiography and Doppler OCT to monitor changes in vessel diameter and blood flow. Blue-light stimulation induced rapid, reversible, and artery-selective vasodilation with minimal effects on adjacent veins. Flow velocity decreased during stimulation, whereas the increase in vessel cross-sectional area resulted in higher volumetric blood flow. The vasodilatory response was retained in single opsin-deficient mouse models (Opn3^-/^-, Opn4^-/^-, and Opn5^-/^-) but was absent in Opn4/Opn5 double-knockout mice, indicating a cooperative role of non-visual opsins. These findings demonstrate increased local perfusion during optical stimulation and highlight the potential of photorelaxation as a spatially targeted approach to vascular modulation.