Studies of the retinal microcirculation using human donor eyes and high-resolution clinical imaging: Insights gained to guide future research in diabetic retinopathy

Enabling visualization of GFAP-positive retinal glial cells, neurons and microvasculature in three-dimensions

Glial cells are one of the most numerous cell types in the vertebrate retina and they serve to support neurovascular function. The principal glial cell in the retina is the Müller cell, accounting for approximately 90 % of all retinal glial cells. Müller cells are phenotypically elongated in shape and were first described as 'radial fibers' by Heinrich Müller in 1851. Their structure spans the entire thickness of the retina, through all retinal layers from the internal to external limiting membrane. This unique three-dimensional spatial arrangement enables Müller cells' direct contact with almost all cell types in the retina to perform its function. Despite this, the current study of Müller cells has largely been limited to thin sections or in culture, which provide limited detail about its spatial arrangement and interconnection with other cell types. The novel technique described here enables the three-dimensional visualization of GFAP-positive Müller cell processes in rodent retina and is based on the isolated arterially perfused rat eye preparation. Our micro perfusion technique utilizes the microvasculature as the delivery channel to quickly and effectively preserve all retinal elements. Intravascular labelling enables visualization of the intact three-dimensional retinal microvasculature within its normal neuronal and glial confines. Additional immersion immunolabeling and subsequent clearing with RapiClear® enables the three-dimensional visualization of different retinal elements and their physical interaction. Volume rendering of confocal image stacks acquired from these specimens can facilitate the study of such interactions in normal and disease models to further our understanding. This technique may be replicated in human donor retinae for future investigations to provide insight into Müller cell form and spatial relationship with other cell types.

Microvascular changes in eyes with non-proliferative diabetic retinopathy with or without macular microaneurysms: an OCT-angiography study

PURPOSE

To evaluate different quantitative non-invasive retinal biomarkers of microvascular impairment and neurodegeneration in patients affected by mild and moderate non proliferative diabetic retinopathy (NPDR) with or without macular microaneurysms (MAs).

METHODS

A cross-sectional case-control study. Ninety-seven eyes with NPDR, 49 with no central MAs and 48 with central MAs, underwent color fundus photography and optical coherence tomography (OCT)/OCT-angiography (OCT-A). Thickness of central macula, retinal nerve fiber layer (NFL), ganglion cell layer (GCL+) and NFL + GCL + was evaluated on OCT. FAZ metrics (ImageJ), perfusion and vessel density (PD/VD), and fractal dimension (FD) (MATLAB) were evaluated on 3 × 3 OCT-A slabs of both superficial and deep capillary plexuses (SCP/DCP). All evaluations were performed on the full image and after subdivision in 4 quadrants.

RESULTS

In the MA group, 77 MAs were detected (45.5% in the DCP). The MA group showed: increased FAZ area and perimeter in the SCP (p < 0.01) and DCP (p = 0.02), and reduced circularity index in the SCP (p = 0.03); reduced VD in the SCP (p < 0.01) and reduced PD, VD (p < 0.01) and FD (p = 0.02) in the DCP; decreased VD and FD in the SCP (p = 0.02 and p = 0.05), and in VD and FD in the DCP in the inferior quadrant (p = 0.04 and p = 0.03); a decrease in VD in the SCP in the nasal quadrant (p = 0.05). No differences have been detected in OCT parameters.

CONCLUSIONS

Our results suggest that the presence of central MAs in patients with NPDR may correlate with more pronounced macular microvascular impairment, particularly during the mild and moderate stages of the disease.

The Role of Th17/Treg Axis in Retinal Pathology Associated with Diabetes and Treatment Options

Diabetic retinopathy (DR) is a major complication of diabetes, leading to vision impairment and blindness. The pathogenesis of DR involves multiple factors, including hyperglycemia-induced vascular damage, hypertension, obesity, anemia, immune dysregulation, and disruption of the blood-retinal barrier (BRB). Th17 and Treg cells, two types of CD4+ T cells, play opposing roles in inflammation. Th17 cells are pro-inflammatory, producing cytokines such as IL-17A, while Treg cells help suppress immune responses and promote anti-inflammatory effects. Recent studies highlight the importance of the Th17/Treg balance in retinal inflammation and disease progression in DR. Our literature review reveals an imbalance in DR, with increased Th17 activity and reduced Treg function. This shift creates a pro-inflammatory environment in the retina, worsening vascular leakage, neovascularization, and vision loss. The limited infiltration of Treg cells suggests that Th17 cells may uniquely infiltrate the retina by overwhelming or outnumbering Tregs or increasing the expression of recruiting chemokines, rather than only taking advantage of a damaged BRB. Therapeutic strategies, such as neutralizing IL-17A and enhancing Treg function with compounds like IL-35 or curcumin, may reduce inflammation and retinal damage. Restoring the balance between Th17 and Treg cells could provide new approaches for treating DR by controlling inflammation and preventing further retinal damage.

Evaluating Blood Flow Speed in Retinal Microaneurysms Secondary to Diabetic Retinopathy Using Variable Interscan Time Analysis OCTA

Purpose

To quantify the blood flow speed within retinal microaneurysms (MAs) and investigate the relationship between blood flow speed and clinical characteristics in eyes with diabetic retinopathy (DR).

Methods

Variable interscan time analysis (VISTA) quantifies blood flow speed in the vasculature by measuring how fast optical coherence tomography (OCT) angiography (OCTA) saturates for different interscan times. Macular OCTA imaging was performed in eyes with DR using a high-speed swept-source OCT prototype instrument operating at a 600-kHz A-scan rate. The presence of MAs was determined using OCT B-scans, and three-dimensional MA masks were generated. VISTA flow speed (VFS) was determined within MAs and the retinal capillary plexus (RCP). Intraluminal reflectivity, axial location within the RCP, and the presence of intraretinal fluid (IRF) around the MAs were evaluated.

Results

A total of 123 MAs were detected from 24 eyes of 20 patients with DR. Mean VFS was 1.26 ms-1 (95% confidence interval, 1.16-1.35). MAs with medium and high intraluminal reflectivity had slower VFS than those with low intraluminal reflectivity (P < 0.01) and often had slower VFS than the RCP (P < 0.01). Sixty-six MAs were located near IRF and had slower VFS than the other 57 MAs without surrounding IRF (1.16 ms-1 vs. 1.37 ms-1; P = 0.03).

Conclusions

VISTA OCTA can assess blood flow speed of MAs in relation to other structural features in DR. Decreased blood flow speed in MAs is correlated with the presence of IRF around MAs.

Translational Relevance

We offer a new method that quantifies the blood flow speed of MAs to study the development of diabetic macular edema.

Trajectories of choriocapillaris perfusion in healthy individuals and patients with diabetes mellitus: a prospective cohort study

PURPOSE

To evaluate the longitudinal rate of choriocapillaris flow deficits (CFD) in healthy participants and patients with diabetes mellitus.

METHODS

This prospective cohort study included healthy individuals and diabetic patients without diabetic retinopathy (non-DR) or with mild-to-moderate non-proliferative DR (NPDR). The swept-source optical coherence tomography angiography (OCTA) was adopted for quantifying CFD annually, and linear mixed models were used to analyse the CFD change and its 95% CI overtime.

RESULTS

A total of 1025 individuals were included, including 465 healthy controls, 454 in the non-DR group and 106 in the NPDR group. Significant increase in CFDs was observed in NPDR group (0.423%, 95% CI 0.230% to 0.616%) and non-DR group (0.319%, 95% CI 0.225% to 0.412%), which were higher than the CFD in healthy controls (0.173%, 95% CI 0.079% to 0.266%). After adjusting for other factors, the non-DR and NPDR group had a greater annual elevation of CFD by 0.171% (95% CI 0.060% to 0.283%; p=0.003) and 0.258% (95% CI 0.068% to 0.449%; p=0.008) in comparisons with controls. Furthermore, higher serum creatinine and glycated haemoglobin levels, poorer best-corrected visual acuity, lower OCTA image quality scores and smaller CFD at baseline were independently related to accelerated CFD worsening (all p<0.05).

CONCLUSIONS

The CFD among healthy individuals and patients with diabetes increased consistently overtime, regardless of the presence or absence of DR, suggesting that CFD alterations could be an early indicator of microvascular complications, potentially aiding in the earlier DR detection.

QUANTIFICATION OF CAPILLARY BLOOD FLOW SPEEDS IN DIABETIC RETINOPATHY USING VARIABLE INTERSCAN TIME ANALYSIS OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY

PURPOSE

To investigate retinal capillary plexus capillary flow speed and vessel density in diabetic retinopathy and normal subjects using variable interscan time analysis optical coherence tomography angiography (OCTA).

METHODS

High speed swept source OCTA imaging using multiple interscan times was performed over a 5 mm × 5 mm field-of-view with 600 kHz A-scan rate. Second-generation variable interscan time analysis OCTA was used to measure a surrogate marker for capillary blood flow speed, variable interscan time analysis flow speed (VFS), in the superficial and intermediate capillary plexuses VFS , and deep capillary plexus VFS . Vessel density was measured using OCTA.

RESULTS

Fifty-seven eyes with different diabetic retinopathy severity and 37 normal eyes were analyzed. Variable interscan time analysis OCTA provided diverse blood flow speed information, including pseudo-color OCTA and mean flow speed in different regions. Both deep capillary plexus VFS and deep capillary plexus VFS /(superficial and intermediate capillary plexuses) VFS were higher in diabetic retinopathy compared with normal eyes. Elevated deep capillary plexus VFS correlated with decreased deep capillary plexus vessel density in nonproliferative diabetic retinopathy.

CONCLUSION

Variable interscan time analysis OCTA can measure a quantitative biomarker for blood flow speed alterations in diabetic retinopathy and normal eyes as well as the association with vessel density in different capillary plexuses. Variable interscan time analysis OCTA is promising for studies of pathogenesis and early flow alterations, which may precede nonperfusion.

Characterization of the Retinal Circulation of the Mouse

Purpose

Mice are highly used in retinal research because, like humans, mice have vascularized retinas and choroidal circulation. Although the retinal circulation has been well-characterized in development, its stability during adulthood is less understood. To examine this network, we quantified several key metrics of the trilaminar vasculature.

Methods

We used mice (n = 15) with transgenic fluorescent NG2-DsRed (JX: #00824), a vascular-associated label in the retina. One eye per mouse was imaged using confocal microscopy (Nikon A1 Ti2 Eclipse) and traced with ImageJ SNT tools. Using an adaptive optics scanning light ophthalmoscope, additional mice (n = 3) were imaged at single-cell resolution within the living eye to measure the same vasculature.

Results

Across mice, we found a stable retinal circulation that formed and maintained a trilaminar stratification throughout early adulthood at all eccentricities. Bridging these layers, microvessels had five distinct anatomical branching patterns. The superficial, intermediate, and deep plexuses increased in density with depth: 16.14 ± 3.61 mm/mm2, 22.14 ± 6.86 mm/mm2, and 31.01 ± 6.24 mm/mm2, respectively. This patterning was not impacted by eccentricity or age (13-61 weeks). Similar metrics were achieved using adaptive optics scanning light ophthalmoscope in vivo with the same analysis pipeline.

Conclusions

The mouse retinal vasculature was stable up to 50 weeks of age, providing a robust and extensive baseline dataset with which models of retinal vascular and neural disease may be compared. Vessels connecting the laminae were more complex than previously reported and represented a uniquely vulnerable population due to their relatively low density.

Interpericyte Tunneling Nanotubes Are Nonuniformly Distributed in the Human Macula

Purpose

Pericyte-to-pericyte communication via interpericyte tunneling nanotubes (IP-TNTs) is an important mechanism by which spatial and temporal precision in neurovascular coupling is achieved. This study quantifies the distribution and morphologic characteristics of IP-TNTs in the normal human macula.

Methods

Ultra high-resolution, three-dimensional microscopic imaging of 11 perfusion-labeled normal human donor eyes was performed. Immunofluorescent markers for collagen IV, glial fibrillary acidic protein, nuclei, α-smooth muscle actin and phalloidin were used to distinguish IP-TNTs from perfused/nonperfused capillaries and glia processes. IP-TNT length, diameter and density in each capillary plexus was quantified and compared.

Results

IP-TNTs were present in all capillary plexuses. IP-TNTs bridged capillary segments within and between capillary plexuses but did not connect capillaries to arterioles or venules. Mean length of IP-TNTs was 72.6 ± 39.5µm (range 14.0 to 202 µm) and mean diameter was 1.0 ± 0.42µm. IP-TNT length was non-normally distributed with a right-skewed distribution and 43% were 'short' (<55µm). Diameters were greater in the "long" (1.13 ± 0.44 µm) than "short" (0.82 ± 0.33 µm; P < 0.001) IP-TNTs. Density of IP-TNTs was greater in the superficial vascular plexus (3.80 ± 0.69 per 500 µm2) compared to the intermediate (1.85 ± 0.80 per 500 µm2; P < 0. 0001) and deep capillary plexus (1.58 ± 0.84 per 500 µm2; P < 0.0001). No significant difference in IP-TNT density was found between the four macula quadrants (P = 0.98).

Conclusions

The distribution of IP-TNTs in the human macula is non-uniform and is associated with the compartmentalized nature of retinal energy consumption and microvascular perfusion. The nonuniform properties of IP-TNTs may predispose distinct vascular beds to injury in conditions such as diabetes.

A High-Fidelity Computational Model for Predicting Blood Cell Trafficking and 3D Capillary Hemodynamics in Retinal Microvascular Networks

Purpose

To present a first principle-based, high-fidelity computational model for predicting full three-dimensional (3D) and time-resolved retinal microvascular hemodynamics taking into consideration the flow and deformation of individual blood cells.

Methods

The computational model is a 3D fluid-structure interaction model based on combined finite volume/finite element/immersed-boundary methods. Three in silico microvascular networks are built from high-resolution in vivo motion contrast images of the superficial capillary plexus in the parafoveal region of the human retina. The maximum tissue area represented in the model is approximately 500 × 500 µm2, and vessel lumen diameters ranged from 5.5 to 25 µm covering capillaries, arterioles, and venules. Blood is modeled as a suspension of individual blood cells, namely, erythrocytes (RBC), leukocytes (WBC), and platelets in plasma. An accurate and detailed biophysical modeling of each blood cell and their flow-induced deformation is considered. A physiological, pulsatile boundary condition corresponding to an average cardiac cycle of 0.9 second is used.

Results

Detailed quantitative data and analysis of 3D retinal microvascular hemodynamics are presented, and their relationship to RBC flow dynamics is illustrated. Blood velocity is shown to have temporal oscillations superimposed on the background pulsatile variation, which arise because of the way RBCs partition at vascular junctions, causing repeated clogging and unclogging of vessels. Temporal variations in RBC velocity and hematocrit are anti-correlated in a given vessel, but their time-averaged distributions are positively correlated across the network. Whole blood velocity is 65% to 85% of RBC velocity, with the discrepancy related to the formation of an RBC-free region, adjacent to the vascular endothelium and typically 0.8 to 1.8 µm thick. The 3D velocity and RBC concentration profiles are shown to be oppositely skewed with respect to each other, because of the way that RBCs "hug" the apex of each bifurcation. RBC deformation is predicted to have biphasic behavior with respect to vessel diameter, with minimal cell length for vessels approximately 7 µm in diameter. The wall shear stress (WSS) exhibits a strongly 3D distribution with local regions of high value and gradient spanning a range of 10 to 80 dyn/cm2. WSS is highest where there is faster flow, greater curvature of the vessel wall, capillary bifurcations, and at locations of RBC crowding and associated thinning of the cell-free layer.

Conclusions

This study highlights the usefulness of high-fidelity cell-resolved modeling to obtain accurate and detailed 3D, time-resolved retinal hemodynamic parameters that are not readily available through noninvasive imaging approaches. The results presented are expected to complement and enhance the interpretation of in vivo data, as well as open new avenues to study retinal hemodynamics in health and disease.

Digital histology of retinal microaneurysms as provided by dense B-scan (DART) OCTA: characteristics and clinical relevance in diabetic retinopathy

BACKGROUND

Retinal microaneurysms (MAs) are among the earliest signs of diabetic retinopathy (DR) and can be classified in several subtypes by non-invasive multimodal retinal imaging. The main aim of the present study is to characterize retinal MAs perfusion properties and their blood flow network connectivity by means of Dense Automatic-RealTime (DART) OCTA technology, checking the relationship with the multimodal retinal imaging classification and testing the clinical impact of DART.

METHODS

A cross-sectional, observational study setting was chosen. Multimodal retinal imaging included confocal multicolour, OCT, OCTA and DART OCTA. We classified retinal MAs accordingly with the recently proposed multimodal retinal imaging classification and we tested the role of DART OCTA for detecting retinal MAs blood flow network connectivity. We also tested the relationship with clinical parameters.

RESULTS

We included 206 retinal MAs of 36 DR eyes. We categorized retinal MAs as red (70; 34%), mixed (106; 51%) and green (30; 15%), corresponding to precise characteristics on structural OCT and both (regular) enface and DART OCTA images. The agreement between en-face and DART OCTA techniques for detecting MAs perfusion was very high (overall ICC 0.98; p < 0.01). However, DART OCTA provided clearer visualization than enface OCTA for detecting the blood flow network connectivity of retinal MAs, especially looking at the afferent and efferent MAs capillaries. Multimodal retinal imaging classification of retinal MAs provided significant correlations with DR duration, DR stage, and macular capillary non-perfusion.

CONCLUSIONS

DART OCTA provided several new insights on retinal MAs characteristics and their blood flow network connectivity.

AI-based 3D analysis of retinal vasculature associated with retinal diseases using OCT angiography

Retinal vasculature is the only vascular system in the human body that can be observed in a non-invasive manner, with a phenotype associated with a wide range of ocular, cerebral, and cardiovascular diseases. OCT and OCT angiography (OCTA) provide powerful imaging methods to visualize the three-dimensional morphological and functional information of the retina. In this study, based on OCT and OCTA multimodal inputs, a multitask convolutional neural network model was built to realize 3D segmentation of retinal blood vessels and disease classification for different retinal diseases, overcoming the limitations of existing methods that can only perform 2D analysis of OCTA. Two hundred thirty sets of OCT and OCTA data from 109 patients, including 138,000 cross-sectional images in normal and diseased eyes (age-related macular degeneration, retinal vein occlusion, and central serous chorioretinopathy), were collected from four commercial OCT systems for model training, validation, and testing. Experimental results verified that the proposed method was able to achieve a DICE coefficient of 0.956 for 3D segmentation of blood vessels and an accuracy of 91.49% for disease classification, and further enabled us to evaluate the 3D reconstruction of retinal vessels, explore the interlayer connections of superficial and deep vasculatures, and reveal the 3D quantitative vessel characteristics in different retinal diseases.

Characterizing Presumed Displaced Retinal Ganglion Cells in the Living Human Retina of Healthy and Glaucomatous Eyes

Purpose

The purpose of this study was to investigate the large somas presumed to be displaced retinal ganglion cells (dRGCs) located in the inner nuclear layer (INL) of the living human retina. Whereas dRGCs have previously been studied in mammals and human donor tissue, they have never been investigated in the living human retina.

Methods

Five young, healthy subjects and three subjects with varying types of glaucoma were imaged at multiple locations in the macula using adaptive optics optical coherence tomography. In the acquired volumes, bright large somas at the INL border with the inner plexiform layer were identified, and the morphometric biomarkers of soma density, en face diameter, and spatial distribution were measured at up to 13 degrees retinal eccentricity. Susceptibility to glaucoma was assessed.

Results

In the young, healthy individuals, mean density of the bright, large somas was greatest foveally (550 and 543 cells/mm2 at 2 degrees temporal and nasal, respectively) and decreased with increasing retinal eccentricity (38 cells/mm2 at 13 degrees temporal, the farthest we measured). Soma size distribution showed the opposite trend with diameters and size variation increasing with retinal eccentricity, from 12.7 ± 1.8 µm at 2 degrees to 15.7 ± 3.5 µm at 13 degrees temporal, and showed evidence of a bimodal distribution in more peripheral locations. Within and adjacent to the arcuate defects of the subjects with glaucoma, density of the bright large somas was significantly lower than found in the young, healthy individuals.

Conclusions

Our results suggest that the bright, large somas at the INL border are likely comprised of dRGCs but amacrine cells may contribute too. These somas appear highly susceptible to glaucomatous damage.

Spatially resolved imaging of human macular capillaries using adaptive optics-enhanced optical coherence tomography angiography

Documenting the organization of the retinal capillaries is of importance to understand the visual consequences of vascular diseases which may differentially affect the microvascular layers. Here we detailed the spatial organization of the macular capillaries in ten healthy human subjects using a prototypic adaptive optics-enhanced optical coherence tomography angiography (AO-OCTA) system. Within the central 6° × 6°, the radial peripapillary capillaries and the superficial, intermediate and deep vascular plexuses (SVP, IVP and DVP, respectively) were consistently resolved. In 8 out of the 10 eyes, the capillary segments composing the perifoveal arcade (PFA) were perfused only by the SVP, while drainage of the PFA showed more variability, comprising a case in which the PFA was drained by the DVP. Around the center, a distinct central avascular zone could be documented for each layer in 7 of the 10 cases; in three eyes, the IVP and SVP merged tangentially around the center. In all eyes, the foveal avascular zone was larger in the DVP than in the SVP and IVP. In one eye with incomplete separation of the inner foveal layers, there was continuity of both the SVP and the IVP; a central avascular zone was only present in the DVP. The diversity of perfusion and drainage patterns supported a connectivity scheme combining parallel and serial organizations, the latter being the most commonly observed in perifoveal vessels. Our results thus help to further characterize the diversity of organization patterns of the macular capillaries and to robustly analyze the IVP, which will help to characterize early stages of microvascular diseases.

Temporary alleviation of MAPK by arbutin alleviates oxidative damage in the retina and ARPE-19 cells

Dry age-related macular degeneration (AMD) is one of the main diseases that causes blindness in humans, and the number of cases is increasing yearly. However, effective treatments are unavailable, and arbutin (ARB) has been reported to have antioxidant, anti-inflammatory, and anti-aging effects in other age-related diseases. However, whether ARB can be used to treat dry AMD remains unknown. To explore the therapeutic potential and molecular mechanism of arbutin in the treatment of dry AMD. MTT assays, reactive oxygen species (ROS) production assays, flow cytometry assays, qPCR and western blotting were used to assess the impact of ARB on human RPECs induced by H2O2. A transcriptome sequencing assay was used to further explore how ARB acts on human RPECs treated with H2O2. Hematoxylin and eosin (H&E) staining and total antioxidant capacity (T-AOC) assays were used to observe the impact of ARB on mouse retina induced by sodium iodate. ARB counteracted the H2O2-induced reduction in human RPECs viability, ARB reversed H2O2-induced cellular ROS production by increasing the expression of antioxidant-related genes and proteins, ARB also reversed H2O2-induced cell apoptosis by altering the expression of apoptosis-related genes and proteins. Transcriptome sequencing and western blotting showed that ARB reduced ERK1/2 and P-38 phosphorylation to prevent H2O2-induced oxidation damage. The in vivo experiments demonstrated that ARB protected against retinal morphology injury in mice, increased serum T-AOC levels and increased antioxidant oxidase gene expression levels in the mouse retina induced by sodium iodate. We concluded that ARB reversed the H2O2-induced decrease in human RPECs viability through the inhibition of ROS production and apoptosis. The ERK1/2 and P38 MAPK signaling pathways may mediate this process. ARB maintained retinal morphology, increased serum T-AOC level and improved the expression of antioxidant oxidase genes in mice.

Detection of capillary abnormalities in early diabetic retinopathy using scanning laser ophthalmoscopy and optical coherence tomography combined with adaptive optics

This study tested if a high-resolution, multi-modal, multi-scale retinal imaging instrument can provide novel information about structural abnormalities in vivo. The study examined 11 patients with very mild to moderate non-proliferative diabetic retinopathy (NPDR) and 10 healthy subjects using fundus photography, optical coherence tomography (OCT), OCT angiography (OCTA), adaptive optics scanning laser ophthalmoscopy (AO-SLO), adaptive optics OCT and OCTA (AO-OCT(A)). Of 21 eyes of 11 patients, 11 had very mild NPDR, 8 had mild NPDR, 2 had moderate NPDR, and 1 had no retinopathy. Using AO-SLO, capillary looping, inflections and dilations were detected in 8 patients with very mild or mild NPDR, and microaneurysms containing hyperreflective granular elements were visible in 9 patients with mild or moderate NPDR. Most of the abnormalities were seen to be perfused in the corresponding OCTA scans while a few capillary loops appeared to be occluded or perfused at a non-detectable flow rate, possibly because of hypoperfusion. In one patient with moderate NPDR, non-perfused capillaries, also called ghost vessels, were identified by alignment of corresponding en face AO-OCT and AO-OCTA images. The combination of multiple non-invasive imaging methods could identify prominent microscopic abnormalities in diabetic retinopathy earlier and more detailed than conventional fundus imaging devices.

Retinal vasculature of different diameters and plexuses exhibit distinct vulnerability in varying severity of diabetic retinopathy

OBJECTIVES

To study the changes in vessel densities (VD) stratified by vessel diameter in the retinal superficial and deep vascular complexes (SVC/DVC) using optical coherence tomography angiography (OCTA) images obtained from people with diabetes and age-matched healthy controls.

METHODS

We quantified the VD based on vessel diameter categorized as <10, 10-20 and >20 μm in the SVC/DVC obtained on 3 × 3 mm2 OCTA scans using a deep learning-based segmentation and vascular graph extraction tool in people with diabetes and age-matched healthy controls.

RESULTS

OCTA images obtained from 854 eyes of 854 subjects were divided into 5 groups: healthy controls (n = 555); people with diabetes with no diabetic retinopathy (DR, n = 90), mild and moderate non-proliferative DR (NPDR) (n = 96), severe NPDR (n = 42) and proliferative DR (PDR) (n = 71). Both SVC and DVC showed significant decrease in VD with increasing DR severity (p < 0.001). The largest difference was observed in the <10 μm vessels of the SVC between healthy controls and no DR (13.9% lower in no DR, p < 0.001). Progressive decrease in <10 μm vessels of the SVC and DVC was seen with increasing DR severity (p < 0.001). However, 10-20 μm vessels only showed decline in the DVC, but not the SVC (p < 0.001) and there was no change observed in the >20 μm vessels in either plexus.

CONCLUSIONS

Our findings suggest that OCTA is able to demonstrate a distinct vulnerability of the smallest retinal vessels in both plexuses that worsens with increasing severity of DR.

Differential artery-vein analysis improves the OCTA classification of diabetic retinopathy

This study investigates the impact of differential artery-vein (AV) analysis in optical coherence tomography angiography (OCTA) on machine learning classification of diabetic retinopathy (DR). Leveraging deep learning for arterial-venous area (AVA) segmentation, six quantitative features, including perfusion intensity density (PID), blood vessel density (BVD), vessel area flux (VAF), blood vessel caliber (BVC), blood vessel tortuosity (BVT), and vessel perimeter index (VPI) features, were derived from OCTA images before and after AV differentiation. A support vector machine (SVM) classifier was utilized to assess both binary and multiclass classifications of control, diabetic patients without DR (NoDR), mild DR, moderate DR, and severe DR groups. Initially, one-region features, i.e., quantitative features extracted from the entire OCTA, were evaluated for DR classification. Differential AV analysis improved classification accuracies from 78.86% to 87.63% and from 79.62% to 85.66% for binary and multiclass classifications, respectively. Additionally, three-region features derived from the entire image, parafovea, and perifovea, were incorporated for DR classification. Differential AV analysis further enhanced classification accuracies from 84.43% to 93.33% and from 83.40% to 89.25% for binary and multiclass classifications, respectively. These findings highlight the potential of differential AV analysis in augmenting disease diagnosis and treatment assessment using OCTA.

Current understanding of subclinical diabetic retinopathy informed by histology and high-resolution in vivo imaging

The escalating incidence of diabetes mellitus has amplified the global impact of diabetic retinopathy. There are known structural and functional changes in the diabetic retina that precede the fundus photography abnormalities which currently are used to diagnose clinical diabetic retinopathy. Understanding these subclinical alterations is important for effective disease management. Histology and high-resolution clinical imaging reveal that the entire neurovascular unit, comprised of retinal vasculature, neurons and glial cells, is affected in subclinical disease. Early functional manifestations are seen in the form of blood flow and electroretinography disturbances. Structurally, there are alterations in the cellular components of vasculature, glia and the neuronal network. On clinical imaging, changes to vessel density and thickness of neuronal layers are observed. How these subclinical disturbances interact and ultimately manifest as clinical disease remains elusive. However, this knowledge reveals potential early therapeutic targets and the need for imaging modalities that can detect subclinical changes in a clinical setting.

Role and molecular mechanism of Salvia miltiorrhiza associated with chemical compounds in the treatment of diabetes mellitus and its complications: A review

Diabetes mellitus (DM) is one of the most prevalent diseases worldwide, greatly impacting patients' quality of life. This article reviews the progress in Salvia miltiorrhiza, an ancient Chinese plant, for the treatment of DM and its associated complications. Extensive studies have been conducted on the chemical composition and pharmacological effects of S miltiorrhiza, including its anti-inflammatory and antioxidant activities. It has demonstrated potential in preventing and treating diabetes and its consequences by improving peripheral nerve function and increasing retinal thickness in diabetic individuals. Moreover, S miltiorrhiza has shown effectiveness when used in conjunction with angiotensin-converting enzyme inhibitors, angiotensin receptor blockers (ARBs), and statins. The safety and tolerability of S miltiorrhiza have also been thoroughly investigated. Despite the established benefits of managing DM and its complications, further research is needed to determine appropriate usage, dosage, long-term health benefits, and safety.

Stem cell factor protects against chronic ischemic retinal injury by modulating on neurovascular unit

Retinal ischemia is a significant factor in various vision-threatening diseases, but effective treatments are currently lacking. This study explores the potential of stem cell factor (SCF) in regulating the neurovascular unit as a therapeutic intervention for retinal ischemic diseases. A chronic retinal ischemia model was established in Brown Norway rats using bilateral common carotid artery occlusion (BCCAO). Subsequent SCF treatment resulted in a remarkable recovery of retinal function, as indicated by electroretinogram, light/dark transition test, and optokinetic head tracking test results. Histological examination demonstrated a significant increase in the number of retinal neurons and an overall thickening of the retina. Immunofluorescence confirmed these findings and further demonstrated that SCF treatment regulated retinal remodeling. Notably, SCF treatment ameliorated the disrupted expression of synaptic markers in the control group's BCCAO rats and suppressed the activation of Müller cells and microglia. Retinal whole-mount analysis revealed a significant improvement in the abnormalities in retinal vasculature following SCF treatment. Transcriptome sequencing analysis revealed that SCF-induced transcriptome changes were closely linked to the Wnt7 pathway. Key members of the Wnt7 pathway, exhibited significant upregulation following SCF treatment. These results underscore the protective role of SCF in the neurovascular unit of retinal ischemia rats by modulating the Wnt7 pathway. SCF administration emerges as a promising therapeutic strategy for retinal ischemia-related diseases, offering potential avenues for future clinical interventions.

Variability in Capillary Perfusion Is Increased in Regions of Retinal Ischemia Due to Branch Retinal Vein Occlusion

Purpose

To investigate alterations in macular perfusion variability due to branch retinal vein occlusion (BRVO) using a novel approach based on optical coherence tomography angiography (OCTA) coefficient of variation (CoV) analysis.

Methods

Thirteen eyes of 13 patients with macular ischemia due to BRVO were studied. Multiple consecutive en face OCTA images were acquired. Bias field correction, spatial alignment, and normalization of intensities across the images were performed followed by pixelwise computation of standard deviation divided by the mean to generate a CoV map. Region of interest-based CoV values, derived from this map, for arterioles, venules, and the microvasculature were compared between regions with macular ischemia and control areas of the same eye. Control areas were regions of the same macula that were not affected by the BRVO and had normal retinal vascular structure as seen on multimodal imaging and normal retinal vascular density measurements as quantified using OCTA.

Results

CoV increased by a mean value of 17.6% within the microvasculature of ischemic regions compared to the control microvasculature (P < 0.0001). CoV measurements of microvasculature were consistently greater in the ischemic area of all 13 eyes compared to control. There were no differences in CoV measurements between ischemic and control areas for arterioles (P = 0.13) and venules (P = 1.0).

Conclusions

Greater variability in microvasculature perfusion occurs at sites of macular ischemia due to BRVO. We report a novel way for quantifying macular perfusion variability using OCTA. This technique may have applicability for studying the pathophysiology of other retinal vascular diseases.

Frontiers in diabetic retinal disease

Diabetic retinal disease (DRD) remains a leading cause of vision loss and blindness globally. Although treatments can be effective when given at vision-threatening stages of DRD, there is a lack of knowledge about the earliest mechanisms leading to the development of clinically evident DRD. Recent advances in retinal imaging methods for patients with diabetes allow a more precise and granular characterization of the different stages of DRD than is provided by the classic Diabetic Retinopathy Severity Scale based on fundus photographs. In addition, recent clinical studies have yielded more information on how to adjust blood glucose levels, lipid levels and blood pressure to minimize the risk of DRD. Given the incomplete success of current therapies, there is a critical need for better understanding of the mechanisms underlying DRD and novel treatment targets that address the entire neurovascular retina. Moreover, the causes for interindividual variability in the development of DRD in patients with similar glycemic history and other metabolic factors are not yet clarified either. Finally, greater focus on patients' experience with visual disabilities and treatment effects should be addressed in research in this field.