Noninvasive in vivo characterization of erythrocyte motion in human retinal capillaries using high-speed adaptive optics near-confocal imaging

The flow of erythrocytes in parafoveal capillaries was imaged in the living human eye with an adaptive optics near-confocal ophthalmoscope at the frame rate of 800 Hz with a low coherence near-infrared (NIR) light source. Spatiotemporal traces of the erythrocytes were extracted from consecutive images. Custom software based on the Radon transform was developed to measure erythrocyte velocity. The impact of imaging speed on velocity measurement was estimated using images acquired at frame rates of 200, 400, and 800 Hz. NIR light allowed imaging for long periods of time without visually stimulating the retina and disturbing the natural rheological state. High speed near-confocal imaging generated characteristic spatiotemporal erythrocyte traces, enabled direct and accurate erythrocyte velocity measurement, disclosed a distinctively cardiac-dependent pulsatile velocity waveform of the blood flow in retinal capillaries, revealed the effect of the leukocytes on erythrocyte motion, and provided new metrics for precise evaluation of erythrocyte movement. This method may facilitate new investigations on the pathophysiology of retinal microcirculation with applications for ocular and systemic diseases.