The outer boundary on each OCT angiogram was determined at the layer that was just above the layer depicting the small branches of the retinal arterioles and venules that connect the capillaries of the inner retinal plexus ( Fig. To depict the RPC network and minimize inclusion of the capillaries of the inner retinal plexus, the segmentation of the inner border was fixed at the vitreous cavity, and that of the outer border was moved down manually from the internal limiting membrane (ILM) toward the RNFL in the cross-sectional OCT B-scan with overlaying blood flow. 6 The capillaries of the inner retinal plexus under the RPC network connected to the small branches of the retinal arterioles and venules, and their spread is obviously not in parallel with the nerve fibers. The ganglion cell layer has one or more capillary layers, which were referred to as the “inner retinal plexus” by Spaide et al. 6, 13 The RPC network is the most superficial of the retinal vasculature and courses parallel to the nerve fibers. 11 Two scans of the superior and inferior optic disc were obtained using the Angio Disc mode. 1), which was a modification of the method of de Carlo et al.
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Thirteen OCT angiograms (3 × 3 mm) were obtained using the Angio Retina mode in adjacent regions of the posterior pole by moving the software scanning area without changing fixation ( Fig.
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Each OCT angiogram was created using orthogonal registration and merging of two consecutive scan volumes. 10 The Avanti OCT provides 70,000 A-scans/second to acquire OCT angiograms consisting of 304 × 304 A-scans. Subjects were imaged using the commercially available spectral-domain OCT (RTVue XR Avanti Optovue, Inc., Fremont, CA, USA) with AngioVue software to obtain en face OCT angiograms as previously described. In the current study, using wide-field montage OCTA, we analyzed quantitatively the features of the RPC network and the relationship between the RPC density and RNFL thickness in normal human eyes. However, in their svOCT studies, the field of view was small (636.5 μm 2), and the extent of the entire RPC network and the differences in the RPC in each retinal region were undetermined. Those authors also compared the morphologic characteristics and density of the RPC on en face svOCT images with histologic images in human donor eyes and showed that the en face OCTA technique using svOCT may be reliable for analyzing the RPC network in human retinas. 9 quantitatively studied the RPC using speckle variance OCT (svOCT) and reported a positive correlation between the RPC density and RNFL thickness in the same healthy human eyes. 6 clearly showed wide-field montage images of the RPC network in the human retina for the first time. 6 Using en face OCTA with application of the split-spectrum amplitude-decorrelation angiography algorithm, Spaide et al. 4 – 12 En face OCTA technology enables layer-by-layer evaluation of the chorioretinal vascular structures, allowing the RPC network to be visualized separately. Recently, several optical coherence tomography angiography (OCTA) methods have been developed and are gaining in popularity for three-dimensional noninvasive chorioretinal vascular imaging. The RPC is present in the superficial peripapillary retina in proportion to the RNFL thickness, supporting the idea that the RPC may be the vascular network primarily responsible for RNFL nourishment. Montage OCT angiograms can visualize expansion of the RPC network. The RPC density also was correlated significantly ( r = 0.64, P < 0.0001) with the RNFL thickness, with the greatest density in the inferotemporal region.
Capillary-free zones beside the first branches of the arterioles were significantly ( P < 0.0001) narrower than those beside the second ones.
The RPC at the temporal retina was detected as far as 7.6 ± 0.7 mm from the edge of the optic disc but not around the perifoveal area within 0.9 ± 0.1 mm of the fovea. The correlation between the RPC density and the retinal nerve fiber layer (RNFL) thickness measured by an OCT circle scan was investigated. To evaluate the RPC density, the montage images were binarized and skeletonized. En face 3 × 3-mm OCT angiograms of multiple locations in the posterior pole were acquired using the RTVue XR Avanti, and wide-field montage images of the RPC were created.
Twenty eyes of 20 healthy subjects were recruited. We quantitatively analyzed the features of a radial peripapillary capillary (RPC) network visualized using wide-field montage optical coherence tomography (OCT) angiography in healthy human eyes.
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