Noninvasive and Direct Monitoring of Erythrocyte Aggregates in Human Retinal Microvasculature Using Adaptive Optics Scanning Laser Ophthalmoscopy

PURPOSE. To investigate erythrocyte aggregates in parafoveal capillaries by adaptive optics scanning laser ophthalmoscopy (AO-SLO). METHODS. AO-SLO videos were acquired from the parafoveal areas of one eye in 10 healthy subjects. Erythrocyte aggregates were detected as "dark tails" that were darker regions than vessel shadows. The lengths of the dark tails were measured in target capillaries, and their time-dependent changes in length were analyzed using spatiotemporal images. The dark tail elongation rate was calculated as the change of dark tail length per unit length of the target capillary. RESULTS. The overall average dark tail length was 112.1 +/- 36.9 mu m. The dark tail became longer in a time-dependent manner in every monitored capillary (P < 0.0001). The dark tail elongation rate and average velocity were 0.51 +/- 0.37 and 1.49 +/- 0.36 mm/s, respectively. CONCLUSIONS. AO-SLO can be used for noninvasive and direct monitoring of blood dynamics in the retinal microvasculature without dying agents. Erythrocyte aggregates were detected as dark tails and were elongated in a time-dependent manner in the parafoveal capillaries of normal subjects. Monitoring the characteristics of dark tails has promising potential for evaluating retinal hemodynamics.