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J.A. Martin, A. Roorda, K. Venkateswaran; Non-Invasive Direct Assessment of Parafoveal Capillary Leukocyte Velocity . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3628.
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Purpose: Alterations in leukocyte velocity have been implicated in many retinal disease processes. However, direct assessment of leukocyte velocity in retinal capillaries has been limited by a reliance on invasive contrast dyes which only allow leukocyte visualization for a short time span. The recent application of adaptive optics in a scanning laser ophthalmoscope has made long-term imaging of parafoveal leukocyte movement possible without contrast dyes. In this study, using an adaptive optics scanning laser ophthalmoscope (AOSLO), we investigated retinal parafoveal capillary leukocyte velocity without contrast dyes. Methods: Seven normal healthy subjects ranging from 17 to 35 years of age with clear ocular media, were imaged using an AOSLO. All subjects were dilated with Tropicamide 1% and phenylephrine hydrochloride 2.5%. An imaging wavelength of 660 nm and a frame rate of 30 Hz were used. The AOSLO field of view was 1.4 degrees by 1.5 degrees. Leukocyte velocity was determined in parafoveal capillaries ranging from the foveal avascular zone to 2.25 degrees from the fovea center. Leukocyte velocity was measured directly from movie segments where leukocytes were clearly visible. Movie segments were extracted from imaging sessions that lasted approximately 1.5 to 2 hours. Results: Leukocyte velocity was determined for all seven subjects. Standard error of the repeated manual measurements of individual leukocyte velocities was ± 0.02 mm/sec. The mean parafoveal leukocyte velocity was 1.19 mm/sec ranging from 0.96 to 1.62 mm/sec. The intersubject variability (standard deviation) was ± 0.20 mm/sec. Leukocytes were not visible in all parafoveal capillaries. Conclusions: Parafoveal capillary leukocyte velocity can be directly and non-invasively measured without the use of contrast dyes using an AOSLO. A shorter imaging wavelength should be used in further studies to allow for increased visualization of leukocyte movement in parafoveal capillaries.
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