Blood flow patterns and kinetics in the choriocapillaris are poorly understood owing to a lack of quantitative ophthalmic imaging techniques for studying microvascular flow in the eye. Compared with the proximal retinal vasculature, the more distal choroidal vasculature is relatively more challenging to probe. Magnetic Resonance Imaging and Doppler Ultrasound can assess the retina and choroid, but do not resolve the finer layers or microvasculature. While Optical Coherence Tomography (OCT) angiography produces high-quality choroidal images, attempts at quantification through Doppler-based methods have had mixed success.
Here, we use a new technique called Dynamic Contrast OCT (DyC-OCT), which tracks the passage of an intravascular scattering contrast agent, to reveal laminar blood flow patterns in the retina and choroid in vivo. While conceptually similar to fluorescence angiography, DyC-OCT has the substantial benefit of depth resolution, which enables separation of retinal and choroidal microvasculature. The scattering contrast agent enables improved angiography of both macro- and microvasculature in the retina and choroid. Blood plasma transit times are measured in individual vessels, while flow and volume are quantified for each of the microvascular layers. As expected, the choriocapillaris had the highest volume and flow. Blood flow rates were estimated with an average retinal blood flow of 9.1 ± 4.3 μL/min and an average choroidal blood flow of 40 ± 18.3 μL/min in the rat eye. These rates are consistent with previous literature. DyC-OCT affords a new perspective on the poorly understood choriocapillaris blood flow and kinetics and may be useful for studying outer retinal diseases.