High-speed adaptive optics ophthalmoscopy for investigation of retinal hemodynamics in the living human eye

To study retinal hemodynamics in blood vessels of various sizes, from capillary to large arterioles and venules, in the living human eye, we developed a high-speed and high-resolution adaptive optics ophthalmoscope. This instrument employs a low coherent superluminescent near-infrared diode (λ=795 nm) as the imaging light source and a high-speed line camera to image the retina in a near-confocal mode through an anamorphic imaging mechanism. To image the erythrocyte flow in vessels with a diameter < 10 μm, retinal images were acquired with a full 2D raster scanning mode of 512 lines/frame. Blood velocity was measured by the spatiotemporal traces of the erythrocytes. To image the erythrocyte flow in vessels with a diameter < 10 μm, the scanner was programmed to stop across the vessel, thereby directly generating the spatiotemporal traces of the erythrocytes within the vessel in this frame. With the full 2D scanning mode over a field of view of 1.2°×1.2°, the ophthalmoscope produced retinal images with cellular-level resolution at a frame rate of 400 frames/second. This mode allows the erythrocytes flowing in the capillaries to be directly measured. With the partial 2D scanning mode, blood velocity in large retinal arterioles near the optic nerve head can be measured. The continuous velocity of the erythrocytes measured by high spatiotemporal resolution retinal imaging renders the fine profile of the erythrocyte movement.