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Shigeta Arichika, Akihito Uji, Masanori Hangai, Sotaro Ooto, Nagahisa Yoshimura; Distribution of vessels with dark tails in the parafoveal capillary network monitored by adaptive optics scanning laser ophthalmoscopy. Invest. Ophthalmol. Vis. Sci. 2013;54(15):6062.
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© ARVO (1962-2015); The Authors (2016-present)
Adaptive optics scanning laser ophthalmoscopy (AOSLO) provides a unique opportunity for objective and noninvasive study of vessels with dark tails, which correspond to erythrocyte aggregation. In this study, we investigated the distribution of vessels with dark tails in the parafoveal capillary network using our prototype AOSLO system developed by Canon Inc.
The imaging light wavelength of AOSLO was 840 nm, and the frame rate was 32 or 64 Hz. The scan area at the retina was either 1.4 × 1.4° or 1.4 × 2.8°, and this was sampled at 200 × 200 pixels or 200 × 400 pixels, respectively. The AOSLO videos were recorded for 2-4 seconds per scan area, and 10-25 scan areas were obtained for each of 3 healthy subjects (aged 23-38 years) who had no ocular or systemic diseases to ensure total coverage of the parafoveal area. After the capillary images were constructed as projections of the sequential division images, those covering an area ranging from 0 to 0.15 mm peripheral to the edge of the foveal avascular zone (FAZ) and in which most of the capillary network appeared as a single layer were cropped and used for analyses. Vessels with and without dark tails were identified and their entire lengths were measured independently. Moreover, the boundary of the FAZ was divided into 2 categories based on the presence or absence of vessels with dark tails.
In all 3 subjects, the vessels could be divided into 2 categories based on the presence or absence of dark tails. No time-dependent change was observed in distribution of vessels with dark tails. The total length of vessels with and without a dark tail was 3.01 mm and 5.44 mm, respectively. The lengths of vessels with and without a dark tail at the boundary of the FAZ were 0.70 mm and 1.42 mm, respectively. The average ratio of the length of a vessel with a dark tail relative to the length of a vessel without a dark tail was 0.55 in the parafoveal area and 0.54 on the boundary of the FAZ.
AOSLO imaging revealed the existence of 2 pathways of dark tail flow in the parafoveal capillary network. Vessels with dark tails tended to be shorter than those without dark tails.
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