Measuring flicker induced vasodilation at a high spatial and temporal resolution in the human retina.
Neurovascular coupling (NVC) is a crucial process in which blood flow is dynamically adjusted to meet the metabolic demands of active neurons. In this study, we introduce an innovative method for in-vivo imaging of retinal blood vessel dilation in response to visible light stimulation, offering insights into the functional regulation of retinal blood flow. Using high-resolution, high-speed phase contrast imaging, we continuously monitored retinal vessel dynamics in eight healthy subjects, capturing precise temporal and spatial changes in vessel size under both stimulated and baseline conditions. We have measured a significant vessel dilation of 5.2% {+/-} 1.6% (4.4 {micro}m {+/-} 1.3 {micro}m) during flicker-stimulation compared to a dilation of 2.5% {+/-} 1% (2.1 {micro}m {+/-} 0.9 {micro}m) without stimulation. The flexibility of our method also allowed for the exploration of various acquisition and stimulation settings, broadening possibilities for investigating neurovascular coupling in the retina. This work not only enhances our understanding of neurovascular coupling but also has the potential to identify new biomarkers for vision-impairing conditions and neurodegenerative diseases. SignificanceNeurovascular coupling is a fundamental mechanism of the brain which locally regulates blood flow in response to changes in neuronal activity. Here, we present a new imaging technique that enables measuring vasodilation in response to visible light stimulation of the neurons at high spatial and temporal resolution in the living human retina. Owing to the unprecedented measurement precision of the presented technique, we provide new insights into the inner working of functional blood flow regulation in the retina. Clinically, this method holds promise for vascular dysfunction early detection, which can improve diagnosis of retinal and neurodegenerative diseases, as well as assist the development of new targeted therapies.