Radial peripapillary capillaries (RPCs) comprise a unique network of capillary beds within the retinal nerve fibre layer (RNFL) and play a critical role in satisfying the nutritional requirements of retinal ganglion cell (RGC) axons. Understanding the topographical and morphological characteristics of these networks through in vivo techniques may improve our understanding about the role of RPCs in RGC axonal health and disease. This study utilizes a novel, non-invasive and label-free optical imaging technique, speckle variance optical coherence tomography (svOCT), for quantitatively studying RPC networks in the human retina. Six different retinal eccentricities from 16 healthy eyes were imaged using svOCT. The same eccentricities were histologically imaged in 9 healthy donor eyes with a confocal scanning laser microscope. Donor eyes were subject to perfusion-based labeling techniques prior to retinal dissection, flat mounting and visualization with the microscope. Capillary density and diameter measurements from each eccentricity in svOCT and histological images were compared. Data from svOCT images were also analysed to determine if there was a correlation between RNFL thickness and RPC density. The results are as follows: (1) The morphological characteristics of RPC networks on svOCT images are comparable to histological images; (2) With the exception of the nasal peripapillary region, there were no significant differences in RPC density measurements between svOCT and histological images; (3) Capillary diameter measurements were significantly greater in svOCT images compared to histology; (4) There is a positive correlation between RPC density and RNFL thickness. The findings in this study suggest that svOCT is a reliable modality for analyzing RPC networks in the human retina. It may therefore be a valuable tool for aiding our understanding about vasculogenic mechanisms that are involved in RGC axonopathies. Further work is required to explore the reason for some of the quantitative differences between svOCT and histology.
svOCT has the capacity to provide histology-like anatomical information about human retinal capillary networks in vivo. It may have great potential as a research and diagnostic tool in the management of retinal vascular diseases. Further work is required to clarify the cause of some quantitative differences between svOCT and histology.
Axial length was a significant factor in BMO and BM shape in normal and glaucomatous myopic subjects. Posterior deformation of BM was observed in all eyes and significantly associated with functional glaucomatous damage and age.
Retinal capillary networks are critically linked to neuronal health and disease. The ability to perform accurate in vivo examination of human retinal capillary networks is therefore valuable for studying mechanisms that govern retinal homeostasis and retinal vascular diseases. Speckle variance optical coherence tomography (svOCT) is a non-invasive imaging technique that has the capacity to provide angiographic information about the retinal circulation. The application of this technology for studying human retinal capillary networks however has not been validated in a quantifiable manner. We use a custom-built svOCT device to qualitatively and quantitatively study the various capillary networks in the human perifovea. Capillary networks corresponding to the nerve fibre layer (NFL), the retinal ganglion cell/superficial inner plexiform layer (RGC/sIPL), the deep inner plexiform layer/superficial inner nuclear layer (dIPL/sINL) and the deep inner nuclear layer (dINL) are imaged in 9 normal human subjects. Measurements of capillary diameter and capillary density are made from each of these networks and results are compared to post-mortem histological data acquired with confocal scanning laser microscopy. Additionally, retinal capillary measurements from high-resolution fundus fluorescein angiogram (FA) are directly compared with svOCT images from 6 eyes. We demonstrate that svOCT images of capillary networks are morphologically comparable to microscopic images of histological specimens. Similar to histological images in svOCT images, the capillaries in the NFL network run parallel to the direction of RGC axons while capillaries in the dINL network comprise a planar configuration with multiple closed loops. Capillaries in remaining networks are convoluted with a complex three-dimensional architecture. We demonstrate that there is no significant difference in capillary density measurements between svOCT and histology images for all networks. Capillary diameter was significantly greater in svOCT images compared to histology for all networks. Capillary density measurements were also higher in svOCT compared to FA. The results of this study suggest that in vivo svOCT imaging allows accurate morphometric assessment of capillary networks in the human perifovea and may provide an improved ability to render microvascular detail compared to FA. Therefore, svOCT may have broad clinical applications in the study of human retinal physiology and disease. The difference in quantitative measurements between svOCT and histology may reflect dynamic variations in the retinal microcirculation and warrants further investigation.
This report describes a novel, non-invasive and label-free optical imaging technique, speckle variance optical coherence tomography (svOCT), for visualising blood flow within human retinal capillary networks. This imaging system uses a custom-built swept source OCT system operating at a line rate of 100 kHz. Real-time processing and visualisation is implemented on a consumer grade graphics processing unit. To investigate the quality of microvascular detail acquired with this device we compared images of human capillary networks acquired with svOCT and fluorescein angiography. We found that the density of capillary microvasculature acquired with this svOCT device was visibly greater than fluorescein angiography. We also found that this svOCT device had the capacity to generate en face images of distinct capillary networks that are morphologically comparable with previously published histological studies. Finally, we found that this svOCT device has the ability to non-invasively illustrate the common manifestations of diabetic retinopathy and retinal vascular occlusion. The results of this study suggest that graphics processing unit accelerated svOCT has the potential to non-invasively provide useful quantitative information about human retinal capillary networks. Therefore svOCT may have clinical and research applications for the management of retinal microvascular diseases, which are a major cause of visual morbidity worldwide.
Précis: The Bruch membrane opening (BMO) was posteriorly bowed and the degree of nonplanarity increased in stable and progressive glaucoma subjects. BMO became more posterior relative to the Bruch membrane (BM) in control and both stable and progressive glaucoma subjects. Purpose: To investigate longitudinal changes in morphologic characteristics of the BMO in control and glaucomatous subjects. Materials and Methods: A total of 53 myopic eyes (17 control, 6 suspect, 20 stable glaucoma, and 10 progressing glaucoma) were followed for an average of 4.2±1.4 years and imaged at the baseline and 2 follow-up appointments using a 1060 nm swept-source optical coherence tomography system. BM and BMO were segmented, and 4 morphometric BMO parameters (area, ellipse ratio, nonplanarity, and depth) were measured. Results: There were no significant changes in BMO area or ellipse ratio for all groups. BMO nonplanarity was shown to increase in the glaucoma groups. BMO depth relative to BM increased in all groups except the suspects (control: 8.1 µm/y, P=0.0001; stable glaucoma: 3.5 µm/y, P=0.0001; progressing glaucoma: 14.0 µm/y, P=0.0026). In linear mixed-model analysis, axial length was positively associated with BMO area in all groups except for progressing glaucoma, and with BMO nonplanarity in stable glaucoma. It was not a significant factor to the slopes of the BMO parameters in the ANCOVA analysis of slopes. Conclusions: Longitudinally, BMO increased in nonplanarity in the glaucoma eyes, and its axial position relative to BM became more posterior in both control and glaucoma eyes.
SS-AS-OCT enhances transconjunctival suturing for overfiltering blebs when focal fluid accumulation is visualized.
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