Direct and Noninvasive Assessment of Parafoveal Capillary Leukocyte Velocity

Purpose Alterations in leukocyte velocity have been implicated in many retinal disease processes. However, direct and objective assessment of leukocyte velocity in retinal capillaries has been limited by a reliance on invasive contrast dyes that allow leukocyte visualization only for a short time span. The recent application of adaptive optics in a scanning laser ophthalmoscope (AOSLO) has made long-term imaging of parafoveal leukocyte movement possible without contrast dyes. In this study, using the AOSLO, we demonstrate a new method to investigate retinal parafoveal capillary leukocyte velocity. Design Experimental study. Participants Six normal healthy subjects ranging from 25 to 35 years of age with clear ocular media. Methods The parafoveal zone of the retina was imaged in all subjects using an AOSLO. Main Outcome Measures Leukocyte velocity was determined in the parafoveal capillaries including the foveal avascular zone border. Leukocyte velocity was measured directly from movie segments in which the leukocytes were clearly visible. Results The mean parafoveal leukocyte velocity for 6 subjects was 1.37 mm/second, ranging from 0.77 to 2.10 mm/second. Leukocytes were not visible in all parafoveal capillaries. Conclusions Parafoveal capillary leukocyte velocity can be directly and noninvasively measured without the use of contrast dyes using an AOSLO.