Andrew W. Kirker

Exacerbation of choroidal and retinal pigment epithelial atrophy after anti-vascular endothelial growth factor treatment in neovascular age-related macular degeneration.

Purpose: To study the progression of retinal pigment epithelium (RPE) and choroidal atrophy in patients with neovascular age-related macular degeneration (AMD) and to assess for a possible association with the number and type of anti–vascular endothelial growth factor treatments. Methods: Patients with neovascular AMD and a minimum of 1-year follow-up were reviewed. Fellow eyes with nonneovascular AMD were used as control eyes. Retinal pigment epithelial atrophy area and choroidal thickness were determined using spectral-domain optical coherence tomography. Multivariable regression models were used for statistical analyses. Results: A total of 415 eyes were included in the study, with a mean follow-up of 2.2 years. Eyes with neovascular AMD had greater progression of RPE atrophy and choroidal atrophy compared with those with nonneovascular AMD (P < 0.001). Progression of RPE atrophy and choroidal atrophy was independently associated with the total number of injections of bevacizumab and ranibizumab (all P values ⩽ 0.001). In the subgroup of 84 eyes with neovascular AMD and without RPE atrophy at baseline, only bevacizumab was associated with the progression of RPE atrophy (P = 0.003). This study likely lacked statistical power to detect an association with ranibizumab in this subgroup. Conclusion: Retinal pigment epithelial atrophy and choroidal atrophy in neovascular AMD seem to be exacerbated by anti–vascular endothelial growth factor treatment. Possible differences between bevacizumab and ranibizumab require further investigation.

Label-Free Density Measurements of Radial Peripapillary Capillaries in the Human Retina

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.

Quantitative Noninvasive Angiography of the Fovea Centralis Using Speckle Variance Optical Coherence Tomography

PURPOSE To demonstrate the utility of speckle variance optical coherence tomography (svOCT), a noninvasive angiographic technique, for evaluating the foveal vasculature. METHODS Twelve normal human eyes were imaged with svOCT (1060-nm, 100-kHz custom-built system) and fluorescein angiography (FA; Topcon TRC-50DX with 5.0 megapixel resolution camera). Manual tracing techniques were used to quantify the foveal vasculature, including foveal avascular zone (FAZ) metrics (area, perimeter, greatest diameter, and lowest diameter). Reproducibility of these measurements was determined. The FAZ was imaged in 25 normal eyes using svOCT and 15 donor eyes using confocal scanning laser microscopy. Retinal capillary plexuses in donor eyes were perfusion-labeled with phalloidin conjugated to Alexa Fluor 546. RESULTS Speckle variance OCT is able to stratify the foveal circulation into inner and deep capillary plexuses as well as reliably quantify and assess the morphometric dimensions of the human FAZ. Capillary density measurements were significantly greater in svOCT than FA (31.2 ± 1.6% vs. 19.3 ± 1.9% of total tissue area; P < 0.001). Measurements were highly reproducible (all P > 0.366). All FAZ metrics were significantly lower in histology than svOCT (all P < 0.001). CONCLUSIONS Speckle variance OCT permits precise, reproducible, and noninvasive visualization of the human foveal vasculature. Speckle variance OCT may become an important adjunct in evaluating patients with retinal vascular diseases.

In vivo optical imaging of human retinal capillary networks using speckle variance optical coherence tomography with quantitative clinico-histological correlation

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.

Comparative analysis of repeatability of manual and automated choroidal thickness measurements in nonneovascular age-related macular degeneration.

PURPOSE We compared the reproducibility and mutual agreement of the subfoveal choroidal thickness measurements by expert raters and an automated algorithm in enhanced depth imaging optical coherence tomography (EDI-OCT) images of eyes with nonneovascular age-related macular degeneration (AMD). METHODS We recruited 44 patients with nonneovascular AMD and EDI-OCT images were acquired. Subfoveal choroidal thickness was measured manually by two expert raters and automatically by a graph-cut-based algorithm. Drusen area was measured using the automated software (version 6) of Cirrus SD-OCT. The manual and automated choroidal thickness measurements were compared in reproducibility, mutual agreement, and correlation with drusen area. RESULTS The mean subfoveal choroidal thickness was 246 ± 63 μm for the first rater, 214 ± 68 for the second rater, and 209 ± 53 for the automated algorithm. Intraclass correlation coefficients (ICC) and 95% confidence intervals (CI) were 0.96 (CI 0.94-0.98) between the raters, 0.85 (CI 0.77-0.90) between the first rater and the automated algorithm, and 0.84 (CI 0.75-0.89) between the second rater and the automated algorithm. Repeat scan measurement ICCs were 0.91 (CI 0.86-0.94) for the first rater, 0.96 (CI 0.94-0.97) for the second rater, and 0.87 (CI 0.80-0.92) for the automated algorithm. Manual and automated measurements were correlated with drusen area. CONCLUSIONS The automated algorithm generally yielded smaller choroidal thickness than the raters with a moderate level of agreement. However, its repeat scan measurement repeatability was comparable to that of the manual measurements. The mean difference between the raters indicated possible biases in different raters and rating sessions. The correlation of the automated measurements with the drusen area was comparable to that of the manual measurements. Automated subfoveal choroidal thickness measurement has potential use in clinical practice and clinical trials, with possibility for reduced time and labor cost.

Retinal angiography with real-time speckle variance optical coherence tomography

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.

Quantitative Comparison of Retinal Capillary Images Derived By Speckle Variance Optical Coherence Tomography With Histology.

PURPOSE The purpose of this study was to correlate human retinal capillary network information derived from a prototype speckle variance optical coherence tomography (svOCT) device with histology to determine the utility of this instrument for quantitative angiography. METHODS A retina location 3 mm superior to the optic disk was imaged with svOCT in 14 healthy human eyes. Qualitative and quantitative features of capillary networks, including capillary diameter and density, were compared with perfusion-labeled histological specimens from the same eccentricity. Twelve human donor eyes with no history of eye disease were used for histological comparisons. RESULTS svOCT was able to clearly distinguish the morphological features of the nerve fiber layer capillary network, the retinal ganglion cell (RGC) layer capillary network, the capillary network at the border of the inner plexiform layer and superficial boundary of the inner nuclear layer, and the capillary network at the boundary of the deep inner nuclear layer and outer plexiform layer. The morphological features of these networks were highly comparable to those in previous histological studies. There were no statistical differences in mean capillary diameter between svOCT images and histology for all networks other than the RGC capillary network. Capillary density measurements were significantly greater in svOCT images, except in the RGC capillary network. CONCLUSIONS 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.

Optical coherence tomography-based correlation between choroidal thickness and drusen load in dry age-related macular degeneration.

Purpose: Spectral domain optical coherence tomography can be used to measure both choroidal thickness and drusen load. The authors conducted an exploratory study using spectral domain optical coherence tomography to determine if a correlation between choroidal thickness and drusen load exists in patients with dry age-related macular degeneration. Methods: Forty-four patients with dry age-related macular degeneration were recruited. The drusen area and volume were determined using the automated software algorithm of the spectral domain optical coherence tomography device, and choroidal thickness was measured using enhanced depth imaging. Correlations were determined using multivariable and univariable analyses. Results: The authors found an inverse correlation between choroidal thickness and drusen load (r = −0.35, P = 0.04). Drusen load was also correlated with visual acuity (r = 0.32, P = 0.04). A correlation between choroidal thickness and visual acuity was suggested (r = −0.22, P = 0.21). Conclusion: Spectral domain optical coherence tomography can be used to assess the correlation between drusen load and choroidal thickness, both of which show a relationship with visual acuity. The measurement of these outcomes may serve as important outcome parameters in routine clinical care and in clinical trials for patients with dry age-related macular degeneration.

Optical coherence tomography-based measurement of drusen load predicts development of advanced age-related macular degeneration.

PURPOSE To determine whether baseline drusen load, as measured using spectral-domain optical coherence tomography (SD OCT), is a useful predictor of development of advanced age-related macular degeneration (AMD). DESIGN Retrospective cohort study. METHODS setting: Academic clinical practice. study population: All patients with non-neovascular AMD and no retinal pigment epithelial (RPE) atrophy at baseline who were seen between 2007 and 2012 in a single academic retina practice. A minimum of 1 year of follow-up was required. observation: Drusen load (area and volume) was assessed using automated SD OCT software algorithms. main outcome measure: RPE atrophy area, assessed using an automated SD OCT software algorithm, and the development of neovascular AMD. RESULTS Eighty-three patients met the inclusion criteria with a mean age of 80 years and a mean follow-up time of 2.8 years. Repeated-measures analysis of variance showed an association between drusen area (P = .005) and drusen volume (P = .001) and the development of RPE atrophy. We also found an association between drusen area (P = .001) and drusen volume (P = .001) and the development of neovascular AMD. CONCLUSIONS Drusen load, as measured using SD OCT, is associated with the development of RPE atrophy and neovascular AMD. SD OCT assessments of drusen load are simple and practical measurements that may be useful in stratifying the risk of developing advanced AMD. These measurements have potential applications in both routine clinical care and clinical trials.

Automatic detection of subretinal fluid and sub-retinal pigment epithelium fluid in optical coherence tomography images

Age-related macular degeneration (AMD) is the leading cause of blindness in developed countries. Subretinal fluid (SRF) and sub-retinal pigment epithelium (sub-RPE) fluid are signs of AMD and can be detected in optical coherence tomography images. However, manual detection and segmentation of SRFs and sub-RPE fluids are laborious and time consuming. In this paper, a novel pipeline is proposed for automatic detection of SRFs and sub-RPE fluids. First, top and bottom layers of retina are segmented using a graph cut method. Then, a Split Bregman-based segmentation method is used to segment dark regions between layers. These segmented regions are considered as potential fluid candidates, on which a set of features are generated. After that, a random forest classifier is trained to distinguish between the true fluid regions from the falsely detected fluid regions. This method shows reasonable performance in a leave-one-out evaluation using a dataset from 21 patients.