Directional Contrast and Observation of Retinal Arterial Retrograde Blood Flow in Out-of-plane Vessels with Laser Doppler Holography

We present a digital method to reveal the axial direction of local blood flow based on the Doppler spectrum asymmetry, called directional contrast. This contrast is overlaid on standard grayscale blood flow images to depict flow towards the camera in red, and flow away from the camera in blue. The local direction of blood flow with respect to the optical axis can be revealed with a high temporal resolution in out-of-plane retinal vessels, allowing to evidence potential blood flow reversal. We demonstrate this capability in an eye affected by high tension glaucoma and central retinal vein occlusion, in which we found a significant diastolic arterial retrograde flow.