Adaptive Optics Reveals Photoreceptor Abnormalities in Diabetic Macular Ischemia

Perfusion Deficits in Diabetes Without Retinopathy Localize to the Perivenular Deep Capillaries Near the Fovea on OCT Angiography

Purpose

To localize early capillary perfusion deficits in patients with diabetes mellitus (DM) without clinical diabetic retinopathy (DR) using averaged OCT angiography (OCTA).

Design

Retrospective cross-sectional study.

Participants

Patients with DM without DR and healthy controls.

Methods

We measured perfusion deficits in the full retina, superficial capillary plexus (SCP), and deep capillary plexus (DCP) on averaged 3 × 3-mm OCTA images. Perfusion deficits were defined as the percentage of retinal tissue located >30 μm from blood vessels, excluding the foveal avascular zone (FAZ). One eye from each patient was selected based on image quality. We measured deficits in the parafoveal region, the 300 μm surrounding the FAZ, and 300 to 1000 μm surrounding the FAZ. If a capillary layer within one of these regions was significantly different in DM without DR compared with controls, we further characterized the location of perfusion deficit as periarteriolar, perivenular, or the capillaries between these 2 zones.

Main Outcome Measures

Location of increased perfusion deficits in patients with DM without DR compared with controls.

Results

Sixteen eyes from 16 healthy controls were compared with 16 eyes from 16 patients with DM without DR (age 45.1 ± 10.7 and 47.4 ± 15.2 years respectively, P = 0.64). Foveal avascular zone area and perfusion deficits in the entire parafovea and the 300 to 1000-μm ring around the FAZ were not significantly different between groups (P > 0.05 for all). Perfusion deficits in 300 μm around the FAZ were significantly increased in patients with DM without DR in full retinal thickness, SCP, and DCP (P < 0.05 for all). When analyzing the perivenular, periarteriolar, and capillary zones, only the perivenular DCP perfusion deficits were significantly increased (5.03 ± 2.92% in DM without DR and 2.73 ± 1.97% in controls, P = 0.014).

Conclusions

Macular perfusion deficits in patients with DM without DR were significantly increased in the region nearest the FAZ, mainly at the perivenular deep capillaries. Further research on these early changes may improve our understanding of the capillaries most susceptible to vascular injury and disruption during diabetes.

Financial Disclosures

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Microaneurysm detection using high-speed megahertz optical coherence tomography angiography in advanced diabetic retinopathy

PURPOSE

To compare detection rates of microaneurysms (MAs) on high-speed megahertz optical coherence tomography angiography (MHz-OCTA), fluorescein angiography (FA) and colour fundus photography (CF) in patients with diabetic retinopathy (DR).

METHODS

For this exploratory cross-sectional study, MHz-OCTA data were acquired with a swept-source OCT prototype (A-scan rate: 1.7 MHz), and FA and CF imaging was performed using Optos® California. MA count was manually evaluated on en face MHz-OCTA/FA/CF images within an extended ETDRS grid. Detectability of MAs visible on FA images was evaluated on corresponding MHz-OCTA and CF images. MA distribution and leakage were correlated with detectability on OCTA and CF imaging.

RESULTS

47 eyes with severe DR (n = 12) and proliferative DR (n = 35) were included. MHz-OCTA and CF imaging detected on average 56% and 36% of MAs, respectively. MHz-OCTA detection rate was significantly higher than CF (p < 0.01). The combination of MHz-OCTA and CF leads to an increased detection rate of 70%. There was no statistically significant association between leakage and MA detectability on OCTA (p = 0.13). For CF, the odds of detecting leaking MAs were significantly lower than non-leaking MAs (p = 0.012). Using MHz-OCTA, detection of MAs outside the ETDRS grid was less likely than MAs located within the ETDRS grid (outer ring, p < 0.01; inner ring, p = 0.028). No statistically significant difference between rings was observed for CF measurements.

CONCLUSIONS

More MAs were detected on MHz-OCTA than on CF imaging. Detection rate was lower for MAs located outside the macular region with MHz-OCTA and for leaking MAs with CF imaging. Combining both non-invasive modalities can improve MA detection.

Retinal vessel density and choroidal flow changes in oligoarticular juvenile idiopathic arthritis with and without uveitis

PURPOSE

This cross-sectional optical coherence tomography angiography (OCTA) study aimed to assess the macular and optic nerve head (ONH) vascular density, foveal avascular zone, and outer retina and choriocapillaris flow in oligoarticular juvenile idiopathic arthritis (oJIA).

STUDY DESIGN

Prospective.

METHODS

Twenty-two eyes of 22 oJIA patients with uveitis (oJIA-U), 20 eyes of 20 oJIA patients without uveitis (isolated oJIA), and 26 healthy volunteers of similar ages and sexes were investigated. The superficial capillary plexus (SCP) and deep capillary plexus (DCP), ONH, foveal avascular zone (FAZ) parameters, the flow area of the outer retina, and choriocapillaris were evaluated.

RESULTS

Compared with the control group, both the oJIA-U group and isolated oJIA group showed significantly decreased vessel density of parafovea (p = 0.031 and p = 0.047, respectively) in DCP. Choriocapillaris flow area at 1 mm radius was significantly lower in the oJIA-U group compared to the control group (p = 0.001). Choriocapillaris flow area at 2- and 3-mm radius were significantly lower in the oJIA-U group compared to the control group (p < 0.001, for both) and isolated oJIA-U group compared to the control group (p = 0.008 and p = 0.001, respectively). The VD and thickness parameters of SCP and ONH, FAZ, and outer retina flow area were similar between the groups.

CONCLUSIONS

oJIA patients with and without uveitis revealed a decreased vessel density in the deep parafoveal region and choriocapillaris flow. Our findings suggest that retinal choroidal microvascular changes could be evident in oJIA-U patients without posterior segment involvement as well as oJIA patients without uveitis.

Quantitative Analysis of the Vasculature and Cone Photoreceptors in Subjects With Diabetes Without Diabetic Retinopathy

PURPOSE

To characterize any differences in the vasculature and cone photoreceptor packing geometry (CPG) between subjects with diabetes without/no diabetic retinopathy (NDR) and healthy controls.

METHODS

Eight NDR and five controls were enrolled. Optical coherence tomography angiography (OCTA) taken at the macula was used to measure vessel density, vessel length density, and vessel density index (VDI) in three vascular plexuses, namely, the superficial vascular plexus, intermediate capillary plexus, and deep capillary plexus (DCP). The choriocapillaris (CC) flow deficit (FD) was also measured. OCTA images were binarized and processed to extrapolate the parafovea and parafoveal quadrants and the OCTA indices mentioned above. The CC was processed with six different radii to quantify FD. Adaptive optics - scanning laser ophthalmoscopy images were acquired and processed to extract CPG indices, i.e., cone density (CD), cone-to-cone spacing (CS), linear dispersion index, heterogeneity packing index and percent of cells with six neighbors at 3.6° in the temporal retina.

RESULTS

In all eyes, statistically significant differences were found (i) in parafoveal FD across the six radii (p < 0.001) and (ii) in the correlation between the parafoveal temporal quadrant (PTQ) DCP VDI and CS (r = 0.606, p = 0.048). No other significant correlations were found. For OCTA or CPG indices, no significant differences were found between the cohorts in the parafovea or parafoveal quadrants.

CONCLUSIONS

CS is the most sensitive CPG index for detecting alterations in the cone mosaic. The DCP and the cone photoreceptors are significantly correlated, indicating that alterations in the DCP can affect the cones. Future work elucidating the vascular alterations and neurodegeneration present in diabetic eyes should focus on the DCP and multiple CPG indices, not solely CD. Moreover, such alterations are highly localized, hence using larger regions e.g. parafovea versus smaller areas, such as the PTQ, will potentially mask significant correlations.

ASSOCIATION OF MACULAR STRUCTURE WITH MICROPERIMETRY SENSITIVITY FOLLOWING VITRECTOMY FOR PROLIFERATE DIABETIC RETINOPATHY

PURPOSE

To evaluate macular sensitivity using microperimetry in patients with proliferate diabetic retinopathy following vitrectomy and to investigate the relationship between the sensitivity and foveal microstructures with optical coherence tomography/angiography.

METHODS

Eighty-four eyes of 84 patients with proliferative diabetic retinopathy, who were indicated for vitrectomy, had no intraocular surgery history 3 months preoperatively, and were able to ensure fundus examination after the vitrectomy, were included. A logMAR best-corrected visual acuity, macular sensitivity of microperimetry, macular retinal thickness, and macular vessel perfusion using optical coherence tomography/angiography were examined at 1 week, 1 month, and 3 months postoperatively.

RESULTS

The logMAR best-corrected visual acuity and mean macular sensitivity of patients with proliferative diabetic retinopathy improved postoperatively (P < 0.05). There was a significant correlation between best-corrected visual acuity and mean sensitivity (P < 0.05). Postoperative mean macular sensitivity was significantly correlated with outer retinal thickness in the 0 to 6 mm macular area (P < 0.05) and also significantly correlated with deep capillary plexus perfusion (P < 0.05). Fixation stability and mean macular sensitivity did not show any correlation with glycated hemoglobin, triglyceride, serum total cholesterol, carbamide, and creatinine and duration of diabetes mellitus (P > 0.05).

CONCLUSION

Postoperative mean macular sensitivity was significantly correlated with outer retinal thickness and deep capillary plexus perfusion for patients with proliferative diabetic retinopathy. The authors found that the visual performance of patients can be evaluated by the outer retinal thickness and deep capillary plexus perfusion, so optical coherence tomography/angiography examination can be an important prognostic factor for visual performance in patients.Clinical Trial Registration: This trial is registered with the Chinese Clinical Trial Registry (http://www.chictr.org.cn; Registration No.: ChiCTR2100043399).

Pearls and Pitfalls of Adaptive Optics Ophthalmoscopy in Inherited Retinal Diseases

Adaptive optics (AO) retinal imaging enables individual photoreceptors to be visualized in the clinical setting. AO imaging can be a powerful clinical tool for detecting photoreceptor degeneration at a cellular level that might be overlooked through conventional structural assessments, such as spectral-domain optical coherence tomography (SD-OCT). Therefore, AO imaging has gained significant interest in the study of photoreceptor degeneration, one of the most common causes of inherited blindness. Growing evidence supports that AO imaging may be useful for diagnosing early-stage retinal dystrophy before it becomes apparent on fundus examination or conventional retinal imaging. In addition, serial AO imaging may detect structural disease progression in early-stage disease over a shorter period compared to SD-OCT. Although AO imaging is gaining popularity as a structural endpoint in clinical trials, the results should be interpreted with caution due to several pitfalls, including the lack of standardized imaging and image analysis protocols, frequent ocular comorbidities that affect image quality, and significant interindividual variation of normal values. Herein, we summarize the current state-of-the-art AO imaging and review its potential applications, limitations, and pitfalls in patients with inherited retinal diseases.

Pathological Neurovascular Unit Mapping onto Multimodal Imaging in Diabetic Macular Edema

Diabetic retinopathy is a form of diabetic microangiopathy, and vascular hyperpermeability in the macula leads to retinal thickening and concomitant reduction of visual acuity in diabetic macular edema (DME). In this review, we discuss multimodal fundus imaging, comparing the pathogenesis and interventions. Clinicians diagnose DME using two major criteria, clinically significant macular edema by fundus examination and center-involving diabetic macular edema using optical coherence tomography (OCT), to determine the appropriate treatment. In addition to fundus photography, fluorescein angiography (FA) is a classical modality to evaluate morphological and functional changes in retinal capillaries, e.g., microaneurysms, capillary nonperfusion, and fluorescein leakage. Recently, optical coherence tomography angiography (OCTA) has allowed us to evaluate the three-dimensional structure of the retinal vasculature and newly demonstrated that lamellar capillary nonperfusion in the deep layer is associated with retinal edema. The clinical application of OCT has accelerated our understanding of various neuronal damages in DME. Retinal thickness measured by OCT enables us to quantitatively assess therapeutic effects. Sectional OCT images depict the deformation of neural tissues, e.g., cystoid macular edema, serous retinal detachment, and sponge-like retinal swelling. The disorganization of retinal inner layers (DRIL) and foveal photoreceptor damage, biomarkers of neurodegeneration, are associated with visual impairment. Fundus autofluorescence derives from the retinal pigment epithelium (RPE) and its qualitative and quantitative changes suggest that the RPE damage contributes to the neuronal changes in DME. These clinical findings on multimodal imaging help to elucidate the pathology in the neurovascular units and lead to the next generation of clinical and translational research in DME.

Characterization of the Structural and Functional Alteration in Eyes with Diabetic Macular Ischemia

OBJECTIVE

To investigate the relative effect of disorganization of the retinal inner layers (DRIL) and ellipsoid zone (EZ) loss on visual function in diabetic macular ischemia (DMI).

DESIGN

Prospective cross-sectional observational study.

PARTICIPANTS

Patients with stable treated proliferative diabetic retinopathy (PDR) without center-involved diabetic macular edema were recruited at the Moorfields Eye Hospital from December 2019 to November 2021. The main inclusion criteria were best-corrected visual acuity (BCVA) of ≥ 40 ETDRS letters (Snellen equivalent 20/160) with OCT angiography (OCTA) evidence of DMI in ≥ 1 eye.

METHODS

Each eligible eye of the recruited patients was assessed for BCVA, OCT, and OCTA metrics. The prespecified OCT parameters were DRIL and subfoveal EZ loss. Generalized estimating equations were used.

MAIN OUTCOMES MEASURES

The frequency of DRIL and EZ loss, their relative contributions to vision loss, and their associations with microvascular alterations were evaluated.

RESULTS

A total of 125 eyes of 86 patients with PDR were enrolled; 104 (83%) eyes had a BCVA of ≥ 70 letters. Disorganization of the retinal inner layers was more prevalent than EZ loss (46% [58 eyes] vs. 19% [24 eyes]). On average, the presence of DRIL had a more pronounced impact on vision, retinal thickness, and microvascular parameters than EZ loss. After multivariable adjustment, the odds of coexisting DRIL increased by 12% with every letter decrease in BCVA; however, there was no statistically significant association of subfoveal EZ loss with BCVA. In eyes with DRIL in the absence of EZ loss, the BCVA declined significantly by 6.67 letters compared with eyes with no DRIL nor EZ loss (95% confidence interval [CI], -9.92 to -3.41; P < 0.001). However, if DRIL and EZ loss coexisted, the resultant BCVA was 13.22 letters less than eyes without these structural abnormalities (95% CI, -18.85 to -7.59; P < 0.001).

CONCLUSIONS

In patients with DMI with a Snellen visual acuity of 20/160 or better, eyes with DRIL were associated with more visual function loss and retinal blood circulation alterations than those with subfoveal EZ loss only.

Twenty-five years of clinical applications using adaptive optics ophthalmoscopy [Invited]

Twenty-five years ago, adaptive optics (AO) was combined with fundus photography, thereby initiating a new era in the field of ophthalmic imaging. Since that time, clinical applications of AO ophthalmoscopy to investigate visual system structure and function in both health and disease abound. To date, AO ophthalmoscopy has enabled visualization of most cell types in the retina, offered insight into retinal and systemic disease pathogenesis, and been integrated into clinical trials. This article reviews clinical applications of AO ophthalmoscopy and addresses remaining challenges for AO ophthalmoscopy to become fully integrated into standard ophthalmic care.

Subclinical Retinal Capillary Abnormalities in Juvenile Systemic Lupus Erythematosus without Ocular Involvement

PURPOSE

This study aimed to evaluate subclinical retinal microvascular changes with OCTA in juvenile systemic lupus erythematosus (JSLE) patients without ocular involvement.

METHODS

Ten eyes of 10 JSLE and 13 eyes of 13 age and sex-matched healthy controls (HCs) were enrolled. The superficial (SCP) and deep capillary plexus (DCP), FAZ parameters, the flow area of the outer retina, and choriocapillaris were evaluated using OCTA.

RESULTS

All vessel density (VD) parameters in DCP were significantly lower in JSLE group compared to HCs. There was no significant difference between the groups in VD parameters of both SCP and ONH, FAZ, outer retina and choriocapillaris flow area. All DCP VD parameters showed a good ability to differentiate JSLE from HCs.

CONCLUSION

OCTA could detect retinal vascular impairment in the deep macular region in JSLE patients with normal ocular examination. Furthermore, all DCP VD parameters have a good ability to discriminate JSLE from HCs.

The Role of Medical Image Modalities and AI in the Early Detection, Diagnosis and Grading of Retinal Diseases: A Survey

Traditional dilated ophthalmoscopy can reveal diseases, such as age-related macular degeneration (AMD), diabetic retinopathy (DR), diabetic macular edema (DME), retinal tear, epiretinal membrane, macular hole, retinal detachment, retinitis pigmentosa, retinal vein occlusion (RVO), and retinal artery occlusion (RAO). Among these diseases, AMD and DR are the major causes of progressive vision loss, while the latter is recognized as a world-wide epidemic. Advances in retinal imaging have improved the diagnosis and management of DR and AMD. In this review article, we focus on the variable imaging modalities for accurate diagnosis, early detection, and staging of both AMD and DR. In addition, the role of artificial intelligence (AI) in providing automated detection, diagnosis, and staging of these diseases will be surveyed. Furthermore, current works are summarized and discussed. Finally, projected future trends are outlined. The work done on this survey indicates the effective role of AI in the early detection, diagnosis, and staging of DR and/or AMD. In the future, more AI solutions will be presented that hold promise for clinical applications.

Diabetic macular ischaemia- a new therapeutic target?

Diabetic macular ischaemia (DMI) is traditionally defined and graded based on the angiographic evidence of an enlarged and irregular foveal avascular zone. However, these anatomical changes are not surrogate markers for visual impairment. We postulate that there are vascular phenotypes of DMI based on the relative perfusion deficits of various retinal capillary plexuses and choriocapillaris. This review highlights several mechanistic pathways, including the role of hypoxia and the complex relation between neurons, glia, and microvasculature. The current animal models are reviewed, with shortcomings noted. Therefore, utilising the advancing technology of optical coherence tomography angiography (OCTA) to identify the reversible DMI phenotypes may be the key to successful therapeutic interventions for DMI. However, there is a need to standardise the nomenclature of OCTA perfusion status. Visual acuity is not an ideal endpoint for DMI clinical trials. New trial endpoints that represent disease progression need to be developed before irreversible vision loss in patients with DMI. Natural history studies are required to determine the course of each vascular and neuronal parameter to define the DMI phenotypes. These DMI phenotypes may also partly explain the development and recurrence of diabetic macular oedema. It is also currently unclear where and how DMI fits into the diabetic retinopathy severity scales, further highlighting the need to better define the progression of diabetic retinopathy and DMI based on both multimodal imaging and visual function. Finally, we discuss a complete set of proposed therapeutic pathways for DMI, including cell-based therapies that may provide restorative potential.

Clinical significance of metabolic quantification for retinal nonperfusion in diabetic retinopathy

Diabetic retinopathy (DR) is characterized by microvascular changes including ischemia. Degradation and metabolic changes of various retinal cells occur during ischemia. Ischemic region containing more cells will lead to greater metabolic impairment. We analyzed the non-perfusion region (NPR) by integrating histologic mapping with ultra-widefield fluorescein angiography (UWF FA) images. We also investigated the correlations of the weighted ischemic index (ISI) considering the regional distribution of retinal cells with cytokines, macular edema (ME), and neovascularization (NV). In this study, 32 patients with treatment-naïve DR and 21 age-matched control participants were included. The difference between the non-weighted and weighted ISI of NPR with leakage was greatest at the posterior region. The weighted ISI of NPR with leakage was correlated with MCP-1, IL-8, IL-6, PlGF, and VEGF-A levels, while the non-weighted ISI of NPR with leakage was correlated with IL-8 and IL-6 levels. The presence of baseline ME or NV in patients with DR was associated with the weighted ISI, with a stronger association when cones and rods were weighted. The weighted ISI reflecting both metabolic activity and cell distribution demonstrated a better correlation with clinical features and was more valuable in NPR with leakage than non-weighted ISI, which previous studies conventionally used.

Correlation of Optical Coherence Tomography Angiography Characteristics with Visual Function to Define Vision-Threatening Diabetic Macular Ischemia

The thresholds of macular microvasculature parameters associated with mild visual impairment in diabetic macular ischemia (DMI) patients are unclear. Therefore, this prospective observational study is aimed at demonstrating the optical coherence tomography angiography parameters that best correlate with mild visual impairment (<70 Early Treatment Diabetic Retinopathy Study (ETDRS) letters, Snellen equivalent 20/40) in DMI. The study was completed at the Moorfields Eye Hospital from December 2019 to August 2021. A total of 123 eyes of 87 patients with stable-treated proliferative diabetic retinopathy following panretinal photocoagulation were recruited. DMI was defined as an irregular foveal avascular zone (FAZ) area ≥ 0.5 mm2 or a smaller FAZ area with parafoveal capillary dropout in at least one quadrant. The analysis showed that the whole image deep vascular complex vessel density (DVC VD) in the 3 × 3 mm area had the best discriminatory ability to identify participants with mild visual impairment at 41.9% (area under the curve = 0.77, sensitivity 94%, specificity 54%, likelihood ratio [LR] = 2.04), and the FAZ area had the greatest post-test LR = 4.21 at 0.64 mm2. The 3 × 3 mm whole image DVC VD and FAZ area cutoffs are useful for screening vision-threatening DMI, but DVC VD has low specificity.

Contribution of Müller Cells in the Diabetic Retinopathy Development: Focus on Oxidative Stress and Inflammation

Diabetic retinopathy is a neurovascular complication of diabetes and the main cause of vision loss in adults. Glial cells have a key role in maintenance of central nervous system homeostasis. In the retina, the predominant element is the Müller cell, a specialized cell with radial morphology that spans all retinal layers and influences the function of the entire retinal circuitry. Müller cells provide metabolic support, regulation of extracellular composition, synaptic activity control, structural organization of the blood–retina barrier, antioxidant activity, and trophic support, among other roles. Therefore, impairments of Müller actions lead to retinal malfunctions. Accordingly, increasing evidence indicates that Müller cells are affected in diabetic retinopathy and may contribute to the severity of the disease. Here, we will survey recently described alterations in Müller cell functions and cellular events that contribute to diabetic retinopathy, especially related to oxidative stress and inflammation. This review sheds light on Müller cells as potential therapeutic targets of this disease.

Cone Photoreceptors in Diabetic Patients

Purpose

Cones in diabetic patients are at risk due to metabolic and vascular changes. By imaging retinal vessel modeling at high magnification, we reduced its impact on cone distribution measurements. The retinal vessel images and retinal thickness measurements provided information about cone microenvironment.

Methods

We compared cone data in 10 diabetic subjects (28–78 yr) to our published norms from 36 younger and 10 older controls. All subjects were consented and tested in a manner approved by the Indiana University Institutional Review Board, which adhered to the Declaration of Helsinki. Custom adaptive optics scanning laser ophthalmoscopy (AOSLO) was used to image cones and retinal microcirculation. We counted cones in a montage of foveal and temporal retina, using four non-contiguous samples within 0.9–7 deg that were selected for best visibility of cones and least pathology. The data were fit with a two parameter exponential model: ln(cone density) = a ^* microns eccentricity + b. These results were compared to retinal thickness measurements from SDOCT.

Results

Diabetic cone maps were more variable than in controls and included patches, or unusually bright and dark cones, centrally and more peripherally. Model parameters and total cones within the central 14 deg of the macula differed across diabetic patients. Total cones fell into two groups: similar to normal for 5 vs. less than normal for 2 of 2 younger diabetic subjects and 3 older subjects, low but not outside the confidence limits. Diabetic subjects had all retinal vascular remodeling to varying degrees: microaneurysms; capillary thickening, thinning, or bends; and vessel elongation including capillary loops, tangles, and collaterals. Yet SD-OCT showed that no diabetic subject had a Total Retinal Thickness in any quadrant that fell outside the confidence limits for controls.

Conclusions

AOSLO images pinpointed widespread retinal vascular remodeling in all diabetic eyes, but the SDOCT showed no increased retinal thickness. Cone reflectivity changes were found in all diabetic patients, but significantly low cone density in only some. These results are consistent with early changes to neural, glial, or vascular components of the retinal without significant retinal thickening due to exudation.

Retinal Microvasculature and Conjunctival Vessel Alterations in Patients With Systemic Lupus Erythematosus-An Optical Coherence Tomography Angiography Study

Purpose: To evaluate the conjunctival and fundus retinal vessel density in patients with systemic lupus erythematosus (SLE) with optical coherence tomography angiography (OCTA), and to investigate the relationship between vessel density and clinical indicators.

Methods: Twelve patients with SLE (24 eyes) and 12 healthy controls (24 eyes) were recruited. OCTA was used to examine the superficial retina layer (SRL) and deep retina layer (DRL) in the macular retina and conjunctival capillary plexus of each eye. We calculated the density of the temporal conjunctival vessels, fundus microvascular (MIR), macrovascular (MAR) and total MIR(TMI) and compared the results in both groups. We used annular partitioning (C1–C6), hemispheric quadrants, and Early Treatment Diabetic Retinopathy Study partitioning (ETDRS) to analyze changes in the retinal vascular density. Correlation analysis was used to investigate the association between blood capillary density and clinical indicators.

Results: OCTA results showed significant differences in the conjunctival microvascular density (p < 0.001). There was no significant difference in MIR, TMI, and MAR in the superficial layers between the SLE and healthy group (p > 0.05). The DRL and DTMI (Deeper TMI) densities were decreased in the macular regions of SLE patients (p < 0.05). In the hemispheric segmentation analysis, the superficial MIR was significantly decreased in the IL (inferior left) region of the SLE patients (p < 0.05), and the deep MIR in the IR (inferior right) region was significantly reduced (p < 0.05). In the ETDRS partitioning analysis, the superficial MIR in the inferior, right, and left subdivisions was significantly decreased in the SLE patients (p < 0.05). In the circular segmentation analysis, the deep MIR in the C1 and C3 regions was significantly reduced in SLE patients (p < 0.05), while the superficial MIR density was decreased only in the C3 region (p < 0.05). The conjunctival vascular density was negatively correlated with the STMI (Superficial TMI) (r = −0.5107; p = 0.0108) and DTMI (r = −0.9418, p < 0.0001). There was no significant correlation between vascular density and SLEDAI-2k (Systemic Lupus Erythematosus Disease Activity Index−2000) (P > 0.05).

Conclusion: Clinically, patients with SLE and patients suspected of SLE should receive OCTA examination in a comprehensive eye examination to detect changes in ocular microcirculation at an early stage.

Analysis of Foveal Microvascular Abnormalities in Patients with Systemic Lupus Erythematosus Using Optical Coherence Tomography Angiography

Purpose: To analyze the abnormalities of foveal microvasculature in patients with systemic lupus erythematosus (SLE).Methods: A cross-sectional study of 41 eyes of patients diagnosed with SLE and 40 eyes of healthy controls. Sections measuring 6 mm×6 mm centered on the fovea were obtained using optical coherence tomography angiography (OCTA).Results: The area and perimeter of foveal avascular zone (FAZ) in SLE patients were greater than those in controls (both p < .05). The parafoveal vessel densities in the deep capillary plexus (DCP) of SLE patients were significantly decreased than those in controls (p < .001). There was a negative correlation between SLE disease activity index and parafoveal vessel density in DCP (p < .05).Conclusion: Enlargement of the FAZ and decline of the parafoveal vessel density of DCP were revealed by OCTA in patients with SLE. Moreover, a negative correlation between parafoveal vessel density in DCP and disease activity index was detected in SLE patients.

Current status and future possibilities of retinal imaging in diabetic retinopathy care applicable to low- and medium-income countries

Diabetic retinopathy (DR) is a leading cause of blindness among adults and the numbers are projected to rise. There have been dramatic advances in the field of retinal imaging since the first fundus image was captured by Jackman and Webster in 1886. The currently available imaging modalities in the management of DR include fundus photography, fluorescein angiography, autofluorescence imaging, optical coherence tomography, optical coherence tomography angiography, and near-infrared reflectance imaging. These images are obtained using traditional fundus cameras, widefield fundus cameras, handheld fundus cameras, or smartphone-based fundus cameras. Fluorescence lifetime ophthalmoscopy, adaptive optics, multispectral and hyperspectral imaging, and multicolor imaging are the evolving technologies which are being researched for their potential applications in DR. Telemedicine has gained popularity in recent years as remote screening of DR has been made possible. Retinal imaging technologies integrated with artificial intelligence/deep-learning algorithms will likely be the way forward in the screening and grading of DR. We provide an overview of the current and upcoming imaging modalities which are relevant to the management of DR.

Assessment of Detailed Photoreceptor Structure and Retinal Sensitivity in Diabetic Macular Ischemia Using Adaptive Optics-OCT and Microperimetry

Purpose

The purpose of this study was to assess density and morphology of cone photoreceptors (PRs) and corresponding retinal sensitivity in ischemic compared to nonischemic retinal capillary areas of diabetic eyes using adaptive optics optical coherence tomography (AO-OCT) and microperimetry (MP).

Methods

In this cross-sectional, observational study five eyes of four patients (2 eyes with proliferative diabetic retinopathy (DR) and 3 eyes moderate nonproliferative DR) were included. PR morphology and density was manually assessed in AO-OCT en face images both at the axial position of the inner-segment outer segment (IS/OS) and cone outer segment tips (COSTs). Retinal sensitivity was determined by fundus-controlled microperimetry in corresponding areas (MP-3, Nidek).

Results

In AO-OCT, areas affected by capillary nonperfusion showed severe alterations of cone PR morphology at IS/OS and COST compared to areas with intact capillary perfusion (84% and 87% vs. 9% and 8% of area affected for IS/OS and COST, respectively). Mean reduction of PR signal density in affected areas compared to those with intact superficial capillary plexus (SCP) and deep capillary plexus (DCP) perfusion of similar eccentricity was -38% at the level of IS/OS (P = 0.01) and -39% at the level of COST (P = 0.01). Mean retinal sensitivity was 10.8 ± 5.4 in areas affected by DCP nonperfusion and 28.2 ± 1.5 outside these areas (P < 0.001).

Conclusions

Cone PR morphology and signal density are severely altered in areas of capillary nonperfusion. These structural changes are accompanied by a severe reduction of retinal sensitivity, indicating the importance of preventing impaired capillary circulation in patients with DR.

Imaging Modalities Employed in Diabetic Retinopathy Screening: A Review and Meta-Analysis

INTRODUCTION

Urbanization has caused dramatic changes in lifestyle, and these rapid transitions have led to an increased risk of noncommunicable diseases, such as type 2 diabetes. In terms of cost-effectiveness, screening for diabetic retinopathy is a critical aspect in diabetes management. The aim of this study was to review the imaging modalities employed for retinal examination in diabetic retinopathy screening.

METHODS

The PubMed and Web of Science databases were the main sources used to investigate the medical literature. An extensive search was performed to identify relevant articles concerning "imaging", "diabetic retinopathy" and "screening" up to 1 June 2021. Imaging techniques were divided into the following: (i) mydriatic fundus photography, (ii) non-mydriatic fundus photography, (iii) smartphone-based imaging, and (iv) ultrawide-field imaging. A meta-analysis was performed to analyze the performance and technical failure rate of each method.

RESULTS

The technical failure rates for mydriatic and non-mydriatic digital fundus photography, smartphone-based and ultrawide-field imaging were 3.4% (95% CI: 2.3-4.6%), 12.1% (95% CI: 5.4-18.7%), 5.3% (95% CI: 1.5-9.0%) and 2.2% (95% CI: 0.3-4.0%), respectively. The rate was significantly different between all analyzed techniques (p < 0.001), and the overall failure rate was 6.6% (4.9-8.3%; I² = 97.2%). The publication bias factor for smartphone-based imaging was significantly higher than for mydriatic digital fundus photography and non-mydriatic digital fundus photography (b = -8.61, b = -2.59 and b = -7.03, respectively; p < 0.001). Ultrawide-field imaging studies were excluded from the final sensitivity/specificity analysis, as the total number of patients included was too small.

CONCLUSIONS

Regardless of the type of the device used, retinal photographs should be taken on eyes with dilated pupils, unless contraindicated, as this setting decreases the rate of ungradable images. Smartphone-based and ultrawide-field imaging may become potential alternative methods for optimized DR screening; however, there is not yet enough evidence for these techniques to displace mydriatic fundus photography.

Novel Foveal Features Associated With Vision Impairment in Multiple Sclerosis

Purpose

To characterize scattering and hyperreflective features in the foveal avascular zone of people with multiple sclerosis (MS) using adaptive optics scanning laser ophthalmoscopy (AOSLO) and to evaluate their relationship with visual function and MS disease characteristics.

Methods

Twenty subjects with MS underwent confocal reflectance and non-confocal split-detection AOSLO foveal imaging. Peripapillary retinal nerve fiber layer thickness was measured using optic nerve optical coherence tomography. Blood pressure, intraocular pressure (IOP), and best-corrected high-contrast visual acuity (HCVA) and low-contrast visual acuity (LCVA) were measured. AOSLO images were graded to determine the presence and characteristics of distinct structures.

Results

Two distinct structures were seen in the avascular zone of the foveal pit. Hyperreflective puncta, present in 74% of eyes, were associated with IOP and blood pressure. Scattering features, observed in 58% of eyes, were associated with decreased HCVA and LCVA, as well as increased MS duration and disability, but were not associated with retinal nerve fiber layer thickness. Hyperreflective puncta and scattering features were simultaneously present in 53% of eyes.

Conclusions

Hyperreflective puncta were associated with parameters affecting ophthalmic perfusion, but they were not associated with MS disease parameters. Scattering features were associated with parameters corresponding to advanced MS, suggesting that they may be related to disease progression. Scattering features were also correlated with reduced visual function independent from ganglion cell injury, suggesting the possibility of a novel ganglion cell–independent mechanism of impaired vision in people with MS.

Photoreceptor cells and RPE contribute to the development of diabetic retinopathy

Diabetic retinopathy (DR) is a leading cause of blindness. It has long been regarded as vascular disease, but work in the past years has shown abnormalities also in the neural retina. Unfortunately, research on the vascular and neural abnormalities have remained largely separate, instead of being integrated into a comprehensive view of DR that includes both the neural and vascular components. Recent evidence suggests that the most predominant neural cell in the retina (photoreceptors) and the adjacent retinal pigment epithelium (RPE) play an important role in the development of vascular lesions characteristic of DR. This review summarizes evidence that the outer retina is altered in diabetes, and that photoreceptors and RPE contribute to retinal vascular alterations in the early stages of the retinopathy. The possible molecular mechanisms by which cells of the outer retina might contribute to retinal vascular damage in diabetes also are discussed. Diabetes-induced alterations in the outer retina represent a novel therapeutic target to inhibit DR.

Assessing the Use of Incorrectly Scaled Optical Coherence Tomography Angiography Images in Peer-Reviewed Studies: A Systematic Review

Importance

Individual differences in axial length affect the lateral magnification of in vivo retinal images and as a result can affect the accuracy of quantitative measurements made from these images. As measurements from optical coherence tomography angiography (OCTA) images are becoming increasingly used in the diagnosis and monitoring of a wide range of diseases, evaluating which studies use correctly scaled images is crucial to their interpretation.

Objective

To perform a systematic literature review to assess the percentage of articles that report correcting the scale of their OCTA images for individual differences in retinal magnification.

Evidence Review

A PubMed (MEDLINE) search was conducted for articles on OCTA retinal imaging published between June 1, 2015, and June 1, 2018. Initial results included 7552 articles. Initial exclusion criteria removed studies of animal models, as well as reviews, letters, replies, comments, and image-based or photographic essays. Articles not written in English and those that required purchase from non-English language websites were excluded. Articles that did not use OCTA for imaging the retina were also excluded. Remaining articles were reviewed in detail to assess whether the OCTA measurements required correct lateral scaling, and if so, whether axial length was reported or used to scale the images. We also determined the number of articles that mentioned the lack of correct lateral scaling as a limitation of the study.

Findings

A total of 989 articles were included in the detailed review. Of these, 509 were determined to require correct image scaling for their analyses, but only 41 (8.0%) report measuring and using axial length to correct the lateral scale of their OCTA images. Furthermore, of the 468 articles that did not correctly scale their images, only 18 (3.8%) mentioned this as a limitation to their study.

Conclusions and Relevance

These findings suggest that most peer-reviewed articles in PubMed that use quantitative OCTA measurements use incorrectly scaled images. This could call into question the conclusions of such studies and warrants consideration by OCTA manufacturers, physicians, authors, journal reviewers, and journal editors.

Adaptive optics ophthalmoscopy: a systematic review of vascular biomarkers

Retinal vascular diseases are a leading cause for blindness and partial sight certifications. By applying adaptive optics (AO) to conventional imaging modalities, the microstructures of the retinal vasculature can be observed with high spatial resolution, hence offering a unique opportunity for the exploration of the human microcirculation. The objective of this systematic review is to describe the current state of retinal vascular biomarkers imaged by AO flood illumination ophthalmoscopy (FIO) and AO scanning laser ophthalmoscopy (SLO). A literature research was conducted in the PubMed and Scopus databases on July 9, 2020. From 217 screened studies, 42 were eligible for this review. All studies underwent a quality check regarding their content. A meta-analysis was performed for the biomarkers reported for the same pathology in at least three studies using the same modality. The most frequently studied vascular biomarkers were the inner diameter (ID), outer diameter (OD), parietal thickness (PT), wall cross-sectional area (WCSA), and wall-to-lumen ratio (WLR). The applicability of AO vascular biomarkers has been mostly explored in systemic hypertension using AO FIO and in diabetes using AO SLO. The result of the meta-analysis for hypertensive patients showed that WLR, PT, and ID were significantly different when compared to healthy controls, while WCSA was not (P < 0.001, P = 0.002, P < 0.001, and P = 0.070, respectively). The presented review shows that, although a substantial number of retinal vascular biomarkers have been explored in AO en face imaging, further clinical research and standardization of procedures is needed to validate such biomarkers for the longitudinal monitoring of arterial hypertension and other diseases.

Quantitative assessment of vascular density in diabetic retinopathy subtypes with optical coherence tomography angiography

Background

Quantitative assessment of vascular density (VD) of retinal and choriocapillaris (CC) in various stages of diabetic retinopathy (DR) using spectral domain optical coherence tomography angiography (SD OCTA).

Methods

188 eyes of 97 participants were recruited in this cross-sectional study. The macular OCTA (3x3mm) scan was performed and the computer algorithm assessed VD at the level of superficial capillary plexus (SCP), deep capillary plexus (DCP) and CC.

Results

All measured parameters were decreased in retinal VD at the more extreme stages of DR, with the exception of SCP foveal VD. There was a constant pattern of decrease in VD of CC from normal cases to cases of NDR and NPDR and then a slight increase occurred in the PDR stage but never touching the normal quantities. Age, fasting blood sugar, and years of diabetes mellitus were correlated with reduced VD in different segments. Multivariate linear regression analysis showed that best-corrected visual acuity (BCVA) was positively correlated with parafoveal VD at SCP and VD of foveal area at CC. VD of all subfields of macular area except foveal DCP VD showed reduced levels in diabetic macular edema (DME) patients compared to those without DME.

Conclusions

The findings of the study endorse retina VD changes as a potential biomarker for DR development before retinopathy becomes clinically evident. It seems that parafoveal VD of SCP and foveal VD of CC are good biomarkers to predict VA in the diabetic patients.

Near-infrared fundus autofluorescence alterations correlate with swept-source optical coherence tomography angiography findings in patients with retinitis pigmentosa

Thirty-eight patients from 37 families with retinitis pigmentosa (RP) underwent macular 6 × 6-mm swept-source optical coherence tomography angiography (SS-OCTA) and 30° near-infrared fundus autofluorescence (NIR-FAF) acquisitions in one eye. Superficial vascular complex (SVC), deep capillary complex (DCC) and choriocapillaris (CC) angiograms were registered with NIR-FAF acquisitions to comparatively assess subjects with and without central area of preserved NIR-FAF (APA). On the subset of patients showing an APA, the vessel densities for SVC and DCC and flow deficits for CC were assessed in three directions (superior, inferior and temporal) from the fovea and compared to healthy 1:1 age-matched controls. Nine patients with no APA had evidence of severe central OCTA alterations at all levels, especially in the DCC. In the other 29 subjects presenting APA, all OCTA parameters were similar to healthy eyes within the APA, where the retina preserves its structural integrity. Outside the APA, both the DCC and CC were significantly reduced in all directions. These alterations are probably related to the outer retinal atrophy outside the APA. Comparing OCTA to other imaging modalities is helpful to determine the potential interest of OCTA findings as an outcome measure for disease status and progression.

Three-dimensional composition of the photoreceptor cone layers in healthy eyes using adaptive-optics optical coherence tomography (AO-OCT)

Purpose

To assess the signal composition of cone photoreceptors three-dimensionally in healthy retinas using adaptive optics optical coherence tomography (AO-OCT).

Methods

Study population. Twenty healthy eyes of ten subjects (age 23 to 67).

Procedures. After routine ophthalmological assessments, eyes were examined using AO-OCT. Three-dimensional volumes were acquired at 2.5° and 6.5° foveal eccentricity in four main meridians (superior, nasal, inferior, temporal). Cone densities and signal compositions were investigated in four different planes: the cone inner segment outer segment junction (IS/OS), the cone outer segment combined with the IS/OS (ISOS+), the cone outer segment tips (COST) and full en-face plane (FEF) combining signals from all mentioned cone layers. Additionally, reliability of a simple semi-automated approach for assessment of cone density was tested.

Main outcome measures. Cone density of IS/OS, IS/OS+, COST and FEF. Qualitative depiction and composition of each cone layer. Inter-rater agreement of cone density measurements.

Results

Mean overall cone density at all eccentricities was highest at the FEF plane (21.160/mm²), followed by COST (20.450/mm²), IS/OS+ (19.920/mm²) and IS/OS (19.530/mm²). The different meridians and eccentricities had a significant impact on cone density, with lower eccentricity resulting in higher cone densities (p≤.001), which were highest at the nasal, then temporal, then inferior and then superior meridian. Depiction of the cone mosaic differed between all 4 layers regarding signal size and packing density. Therefore, different cone layers showed evident but not complete signal overlap. Using the semi-automated technique for counting of cone signals achieved high inter-rater reliability (ICC > .99).

Conclusions

In healthy individuals qualitative and quantitative changes in cone signals are found not only in different eccentricities and meridians, but also within different photoreceptor layers. The variation between cone planes has to be considered when assessing the integrity of cone photoreceptors in healthy and diseased eyes using adaptive optics technology.

Standardization of OCT Angiography Nomenclature in Retinal Vascular Diseases: First Survey Results

PURPOSE

To develop a consensus nomenclature for OCT angiography (OCTA) findings in retinal vascular diseases.

DESIGN

Online survey using the Delphi Method.

PARTICIPANTS

Members of The Retina Society, the European Society of Retina Specialists, and the Japanese Retina and Vitreous Society.

METHODS

An online questionnaire on OCTA terminology in retinal vascular diseases was sent to members of The Retina Society, the European Society of Retina Specialists, and the Japanese Retina and Vitreous Society. The respondents were divided into 2 groups ("experts" vs. "users") according to the number of their publications in this field. The respondents who had more than 5 publications in the field of OCTA and retinal vascular diseases were considered the OCTA "experts" group.

MAIN OUTCOME MEASURES

Consensus and near consensus on OCTA nomenclature.

RESULTS

The complete responses of 85 retina specialists were included in the analysis. Thirty-one were categorized as "experts." There was a consensus in both groups that OCTA parameters such as foveal avascular zone (FAZ) parameters, areas of nonperfusion, and presence of neovascularization (NV) should be implemented in the identification and staging of diabetic retinopathy (DR) and that OCTA can be applied to differentiate between ischemic and nonischemic retinal vein occlusion (RVO). Diabetic macular ischemia (DMI) also can be assessed via OCTA. Further, there was consensus that the terminology should differ on the basis of the underlying causes of decreased vascular flow signal. There was disagreement in other areas, such as which terms should be applied to describe decreased OCTA signal from different causes, the definition of wide-field OCTA, and how to quantify DMI and area of decreased flow signal. These discrepancies form the basis for the upcoming expert Delphi rounds that aim to develop a standardized OCTA nomenclature.

CONCLUSIONS

Although there was agreement in some areas, significant differences were found in many areas of OCTA terminology among all respondents, but also between the expert and user groups. This indicates the need for standardization of the nomenclature among all specialists in the field of retinal vascular diseases.

Association Between Alterations of the Choriocapillaris Microcirculation and Visual Function and Cone Photoreceptors in Patients With Diabetes

Purpose

The purpose of this study was to investigate the association between the choriocapillaris microcirculation and the visual function and cone photoreceptor structure in patients with diabetes.

Methods

Thirteen control subjects and 26 patients with type 2 diabetes were recruited. The patients with diabetes were divided into three groups based on the grade of diabetic retinopathy (DR). The retinal sensitivity (RS) was evaluated using microperimetry. Cone photoreceptor mosaics were imaged using an adaptive optics retinal camera, and the cone heterogeneity packing index (HPi) was calculated. Optical coherence tomography angiography (OCTA) images of the choriocapillaris were obtained using spectral-domain OCTA, and the area of flow deficit (FD) was evaluated. All parameters were evaluated in the foveal and parafoveal areas.

Results

The study included four patients with diabetes without retinopathy, 12 patients with nonproliferative diabetic retinopathy (NPDR), and 10 patients with proliferative diabetic retinopathy (PDR). The foveal and parafoveal FDs were correlated significantly (fovea, r = −0.58; P = 0.046 and r = −0.82; P = 0.003; parafovea, r = −0.59; P = 0.044 and r = −0.72; and P = 0.019, respectively) with the RS in patients with NPDR and PDR, but not in control and no diabetic retinopathy (NDR) groups. There were no differences in the foveal HPi among the groups.

Conclusions

Impaired choriocapillaris microcirculation is associated with impaired visual function but not cone photoreceptor integrity in eyes with DR.

Three-dimensional assessment of para- and perifoveal photoreceptor densities and the impact of meridians and age in healthy eyes with adaptive-optics optical coherence tomography (AO-OCT)

An adaptive optics optical coherence tomography (AO-OCT) system is used to assess sixty healthy eyes of thirty subjects (age 22 to 75) to evaluate how the outer retinal layers, foveal eccentricity and age effect the mean cone density. The cone mosaics of different retinal planes (the cone inner segment outer segment junction (IS/OS), the cone outer segment combined with the IS/OS (ISOS+), the cone outer segment tips (COST), and the full en-face plane (FEF)) at four main meridians (superior, nasal, inferior, temporal) and para- and perifoveal eccentricities (ecc 2.5° and 6.5°) were analyzed quantitatively. The mean overall cone density was 19,892/mm² at ecc 2.5° and 13,323/mm² at ecc 6.5°. A significant impact on cone density was found for eccentricity (up to 6,700/mm² between ecc 2.5° and 6.5°), meridian (up to 3,700/mm² between nasal and superior meridian) and layer (up to 1,400/mm² between FEF and IS/OS). Age showed only a weak negative effect. These factors as well as inter-individual variability have to be taken into account when comparing cone density measurements between healthy and pathologically changed eyes, as their combined effect on density can easily exceed several thousand cones per mm² even in parafoveal regions.

Promises and pitfalls of evaluating photoreceptor-based retinal disease with adaptive optics scanning light ophthalmoscopy (AOSLO)

Adaptive optics scanning light ophthalmoscopy (AOSLO) allows visualization of the living human retina with exquisite single-cell resolution. This technology has improved our understanding of normal retinal structure and revealed pathophysiological details of a number of retinal diseases. Despite the remarkable capabilities of AOSLO, it has not seen the widespread commercial adoption and mainstream clinical success of other modalities developed in a similar time frame. Nevertheless, continued advancements in AOSLO hardware and software have expanded use to a broader range of patients. Current devices enable imaging of a number of different retinal cell types, with recent improvements in stimulus and detection schemes enabling monitoring of retinal function, microscopic structural changes, and even subcellular activity. This has positioned AOSLO for use in clinical trials, primarily as exploratory outcome measures or biomarkers that can be used to monitor disease progression or therapeutic response. AOSLO metrics could facilitate patient selection for such trials, to refine inclusion criteria or to guide the choice of therapy, depending on the presence, absence, or functional viability of specific cell types. Here we explore the potential of AOSLO retinal imaging by reviewing clinical applications as well as some of the pitfalls and barriers to more widespread clinical adoption.

Reversed Neurovascular Coupling on Optical Coherence Tomography Angiography Is the Earliest Detectable Abnormality before Clinical Diabetic Retinopathy

Diabetic retinopathy (DR) has traditionally been viewed as either a microvasculopathy or a neuropathy, though neurovascular coupling deficits have also been reported and could potentially be the earliest derangement in DR. To better understand neurovascular coupling in the diabetic retina, we investigated retinal hemodynamics by optical coherence tomography angiography (OCTA) in individuals with diabetes mellitus (DM) but without DR (DM no DR) and mild non-proliferative DR (mild NPDR) compared to healthy eyes. Using an experimental design to monitor the capillary responses during transition from dark adaptation to light, we examined 19 healthy, 14 DM no DR and 11 mild NPDR individuals. We found that the only structural vascular abnormality in the DM no DR group was increased superficial capillary plexus (SCP) vessel density (VD) compared to healthy eyes, while mild NPDR eyes showed significant vessel loss in the SCP at baseline. There was no significant difference in inner retinal thickness between the groups. During dark adaptation, the deep capillary plexus (DCP) VD was lower in mild NPDR individuals compared to the other two groups, which may leave the photoreceptors more susceptible to ischemia in the dark. When transitioning from dark to ambient light, both diabetic groups showed a qualitative reversal of VD trends in the SCP and middle capillary plexus (MCP), with significantly decreased SCP at 5 min and increased MCP VD at 50 s compared to healthy eyes, which may impede metabolic supply to the inner retina during light adaptation. Mild NPDR eyes also demonstrated DCP dilation at 50 s and 5 min and decreased adjusted flow index at 5 min in light. Our results show altered neurovascular responses in all three macular vascular plexuses in diabetic subjects in the absence of structural neuronal changes on high resolution imaging, suggesting that neurovascular uncoupling may be a key mechanism in the early pathogenesis of DR, well before the clinical appearance of vascular or neuronal loss.

Factors predicting final visual outcome in quiescent proliferative diabetic retinopathy

To investigate factors reflecting visual outcome and macular perfusion in quiescent proliferative diabetic retinopathy (PDR) patients after panretinal photocoagulation (PRP). We included 118 patients with quiescent PDR who had completed PRP. All participants had standardized interview to determine ocular history, smoking status, cardiovascular risk factors, and history of diabetic mellitus (DM). Foveal avascular zone (FAZ) area, retinal vessel density (VD) and vessel length density (VLD) were measured using optical coherence tomography angiography. VD was negatively correlated with hypertension, diabetic foot, HbA1c, and time after PRP (β =  − 0.181, P = 0.046; β =  − 0.231, P = 0.020; β =  − 0.244, P = 0.010; β =  − 0.278, P = 0.029). FAZ area of superficial capillary plexus and deep capillary plexus (DCP) was positively correlated with DM duration and diabetic foot (β = 0.178, P = 0.047; β = 0.293, P = 0.002; β = 0.252, P = 0.045; β = 0.304, P = 0.002). Macular perfusion state in patients with quiescent PDR was associated with diabetic foot, DM duration, HbA1c, and time after PRP. Of note, diabetic foot showed the strongest correlation with macular perfusion among various systemic factors. VLD, especially in DCP was associated with poor visual outcome.

MULTILEVEL ISCHEMIA IN DISORGANIZATION OF THE RETINAL INNER LAYERS ON PROJECTION-RESOLVED OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY

PURPOSE

To examine the relationship between ischemia and disorganization of the retinal inner layers (DRIL).

METHODS

Cross-sectional retrospective study of 20 patients (22 eyes) with diabetic retinopathy presenting to a tertiary academic referral center, who had DRIL on structural optical coherence tomography (OCT) using Spectralis HRA + OCT (Heidelberg Engineering, Heidelberg, Germany) and OCT angiography with XR Avanti (Optovue Inc, Fremont, CA) on the same day. Optical coherence tomography angiography images were further processed to remove flow signal projection artifacts using a software algorithm adapted from recent studies. Retinal capillary perfusion in the superficial capillary plexuses, middle capillary plexuses, and deep capillary plexuses, as well as integrity of the photoreceptor lines on OCT was compared in areas with DRIL to control areas without DRIL in the same eye.

RESULTS

Qualitative assessment of projection-resolved OCT angiography of eyes with DRIL on structural OCT demonstrated significant perfusion deficits compared with adjacent control areas (P < 0.001). Most lesions (85.7%) showed superimposed superficial capillary plexus and/or middle capillary plexus nonperfusion in addition to deep capillary plexus nonflow. Areas of DRIL were significantly associated with photoreceptor disruption (P = 0.035) compared with adjacent DRIL-free areas.

CONCLUSION

We found that DRIL is associated with multilevel retinal capillary nonperfusion, suggesting an important role for ischemia in this OCT phenotype.

Diabetic photoreceptors: Mechanisms underlying changes in structure and function

Based on clinical findings, diabetic retinopathy (DR) has traditionally been defined as a retinal microvasculopathy. Retinal neuronal dysfunction is now recognized as an early event in the diabetic retina before development of overt DR. While detrimental effects of diabetes on the survival and function of inner retinal cells, such as retinal ganglion cells and amacrine cells, are widely recognized, evidence that photoreceptors in the outer retina undergo early alterations in diabetes has emerged more recently. We review data from preclinical and clinical studies demonstrating a conserved reduction of electrophysiological function in diabetic retinas, as well as evidence for photoreceptor loss. Complementing in vivo studies, we discuss the ex vivo electroretinography technique as a useful method to investigate photoreceptor function in isolated retinas from diabetic animal models. Finally, we consider the possibility that early photoreceptor pathology contributes to the progression of DR, and discuss possible mechanisms of photoreceptor damage in the diabetic retina, such as enhanced production of reactive oxygen species and other inflammatory factors whose detrimental effects may be augmented by phototransduction.

New developments in angiography for the diagnosis and management of diabetic retinopathy

The most common microvascular complication of diabetes is diabetic retinopathy, the leading cause of blindness in adults of working age. Our understanding of the vascular changes in diabetic retinopathy was enhanced by the demonstration of fluorescein angiography (FA) in the human retina for the first time in 1961. It was subsequently integrated with digital fundoscopic imaging to become an invaluable technique in evaluation of the retinal vasculature. The recent development of OCT-angiography (OCT-A) has revolutionized the clinician's ability to examine the retinal vasculature without the need for injection of a contrast dye. By coupling OCT, which can provide noninvasive cross-sectional imaging of the central retina, with angiography in OCT-A, one can reveal retinal perfusion by allowing visualization of the depth-resolved retinal capillary plexus. OCT-A has allowed for more precise delineation of changes in the retinal microvasculature, specifically the alterations of retinal vasculature and loss of capillary perfusion from chronic microvascular occlusion in diabetic retinopathy.

Acute Hyperglycemia Reverses Neurovascular Coupling During Dark to Light Adaptation in Healthy Subjects on Optical Coherence Tomography Angiography

Purpose

To test the hypothesis that hyperglycemia perturbs neurovascular\ coupling and compromises retinal vascular response during transition from dark to light in healthy subjects using optical coherence tomography angiography (OCTA).

Methods

Ten eyes of 10 healthy subjects were tested, first during fasting and then after receiving a 75-g oral glucose solution. In both sessions, OCTA imaging was done in the dark-adapted state and at 50 seconds, 2 minutes, 5 minutes, and 15 minutes of ambient light. Parafoveal vessel density (VD) and adjusted flow index (AFI) were calculated for the superficial capillary plexus (SCP), middle capillary plexus (MCP), and deep capillary plexus (DCP), and vessel length density was calculated for the SCP. These measurements were compared among conditions after adjusting for age, refractive error, and OCTA scan quality.

Results

Hyperglycemia leads to a complete reversal of dark/light adaptation trends in VD and AFI in all layers of the inner retina. In the dark, there is significantly decreased VD in the DCP in hyperglycemia. With a transition to light in hyperglycemia, we observed decreased VD in the SCP, increased vessel density in the MCP and DCP, and decreased AFI in all three layers.

Conclusions

Our results show that hyperglycemia significantly disrupts neurovascular coupling in healthy eyes, with potential metabolic deficits affecting photoreceptor oxygen demands during dark adaptation and the inner retina during light exposure. In pathological states, such as diabetic retinopathy, where the vasculature is already attenuated, retinal neurons may be exquisitely vulnerable to intermittent hyperglycemic challenge, which should be the focus of future studies.

Computer-aided fixation detection using retinal birefringence in multi-modal ophthalmic systems: Computer, electronics, algorithms

Many diagnostic and some therapeutic ophthalmic devices require a reliable complementing method to track the direction of gaze or just to validate fixation of the eye on a presented target. This would allow acquisition of artefact-free robust images of the fovea and the surrounding macula. So far, there have been only few attempts to provide fast and dependable fixation information to an optical imaging system in real time, to guide image acquisition. The author's lab has developed several instruments that detect the location of the fovea using retinal birefringence scanning (RBS), proven to be very effective. Here, an RBS-based fixation detection subsystem is proposed, designed to operate conjointly with a number of ophthalmic imaging technologies. Combining RBS with such technologies is not trivial, because RBS uses polarized light and polarization-sensitive optics, while most other modalities don't. The polarization optics was optimized by means of enhanced computer modeling. Both the electronic hardware and the software were designed for fast and reliable performance. Because many retinal imaging systems are used in pediatric settings, extensive audio-visual circuitry was employed for efficient attention/fixation attraction. The optomechanics has been optimized for robust data acquisition. This computer-aided conjoint system employs true anatomical information from the back of the eye and needs no calibration. The prototype instrument uses a decision-making logic based on four frequencies generated during scanning. The results reveal the applicability of RBS as an adjunct fixation monitoring modality, showing promise to remove the limitation imposed by eye movements upon advanced ophthalmic imaging technologies.

Retinal Capillary Plexus Pattern and Density from Fovea to Periphery Measured in Healthy Eyes with Swept-Source Optical Coherence Tomography Angiography

Optical coherence tomography angiography is evolving towards wider fields of view. As single widefield acquisitions have a lower resolution, preventing an accurate segmentation of vascular plexuses in the periphery, we examined the retinal vascularisation from the macula to the periphery in all retinal quadrants, using 3 × 3-mm volume scans, to obtain montages with sufficient image resolution up to 11 mm from the foveal centre. Images were qualitatively and quantitatively analysed, using C- and B-scan approaches to calculate the capillary density (CD) and the interplexus distance (IPD). Three vascular plexuses (i.e., superficial vascular plexus: SVP, intermediate capillary plexus: ICP, and deep capillary plexus: DCP) were observed up to the mid-periphery in all sectors. The CD of the SVP decreased from about 5 mm of eccentricity, along with ganglion cell density decrease. The CD of the ICP progressively decreased from the fovea towards the periphery, along with the retinal thinning and then vanished from 8 to 9 mm of eccentricity, becoming undetectable beyond. This ICP disappearance resulted in an increased IPD between the SVP and the DCP in an area known to be frequently affected by capillary drop-out in diabetic retinopathy. The DCP only showed a slightly decreased CD towards the retinal periphery.

Associations between Macular OCT Angiography and Nonproliferative Diabetic Retinopathy in Young Patients with Type 1 Diabetes Mellitus

METHODS

OCTA of both eyes was performed in a cross-sectional study of 14 to 30-year-old individuals with at least 10-year duration of T1D and controls recruited from the Norwegian Atherosclerosis and Childhood Diabetes (ACD) study. Vessel density (VD) and foveal avascular zone (FAZ) area in the superficial and deep capillary plexus (SCP and DCP), total retinal volume (TRV), and central macular thickness (CMT) were calculated using automated software. Univariate and multivariate ordered logistic regression (OLR) models were used accordingly.

RESULTS

We included 168 control eyes and 315 T1D eyes. Lower VD in DCP (OR 0.65, 95% CI 0.51-0.83), longer diabetes duration (OR 1.51, 95% CI 1.22-1.87), and higher waist circumference (OR 1.08, 95% CI 1.02-1.14) were significantly associated with progression of NPDR. VD in SCP and DCP were significantly lower in T1D patients without diabetic retinopathy than in controls.

CONCLUSIONS

Sparser VD in DCP is significantly associated with severity of NPDR, supporting that OCTA might detect the earliest signs of NPDR before it is visible by ophthalmoscopy.

Characterization of Retinal Structure in ATF6-Associated Achromatopsia

Purpose

Mutations in six genes have been associated with achromatopsia (ACHM): CNGA3, CNGB3, PDE6H, PDE6C, GNAT2, and ATF6. ATF6 is the most recent gene to be identified, though thorough phenotyping of this genetic subtype is lacking. Here, we sought to test the hypothesis that ATF6-associated ACHM is a structurally distinct form of congenital ACHM.

Methods

Seven genetically confirmed subjects from five nonconsanguineous families were recruited. Foveal hypoplasia and the integrity of the ellipsoid zone (EZ) band (a.k.a., IS/OS) were graded from optical coherence tomography (OCT) images. Images of the photoreceptor mosaic were acquired using confocal and nonconfocal split-detection adaptive optics scanning light ophthalmoscopy (AOSLO). Parafoveal cone and rod density values were calculated and compared to published normative data as well as data from two subjects harboring CNGA3 or CNGB3 mutations who were recruited for comparative purposes. Additionally, nonconfocal dark-field AOSLO images of the retinal pigment epithelium were obtained, with quantitative analysis performed in one subject with ATF6-ACHM.

Results

Foveal hypoplasia was observed in all subjects with ATF6 mutations. Absence of the EZ band within the foveal region (grade 3) or appearance of a hyporeflective zone (grade 4) was seen in all subjects with ATF6 using OCT. There was no evidence of remnant foveal cone structure using confocal AOSLO, although sporadic cone-like structures were seen in nonconfocal split-detection AOSLO. There was a lack of cone structure in the parafovea, in direct contrast to previous reports.

Conclusions

Our data demonstrate a near absence of cone structure in subjects harboring ATF6 mutations. This implicates ATF6 as having a major role in cone development and suggests that at least a subset of subjects with ATF6-ACHM have markedly fewer cellular targets for cone-directed gene therapies than do subjects with CNGA3- or CNGB3-ACHM.

The impact of ganglion cell layer cysts in diabetic macular oedema treated with anti-vascular endothelial growth factor

PURPOSE

To investigate the prevalence and impact of ganglion cell layer cysts (GCLC) in patients with diabetic macular oedema (DME) under continuous anti-vascular endothelial growth factor (VEGF) therapy.

METHODS

The clinical findings and spectral domain optical coherence devices of baseline visits and follow-up after 12-24 and 36 months of DME patients under continuous anti-VEGF therapy were retrospectively collected and analysed for the impact of GCLC cysts. Previously established prognostic parameters were also assessed.

RESULTS

A total of 110 eyes of 110 DME patients (mean age 64 ± 10 years) were included. At baseline, 17% eyes had GCLC. With GCLC, the best-corrected visual acuity (BCVA) improvement was in mean 8.4 ± 2.4 Early-Treatment-Diabetic-Retinopathy-Study (ETDRS) letters less over the course of 36 months compared to the group lacking GCLC (p = 0.0009). Eyes with GCLC showed 68 ± 23.4 μm less central retinal thickness (CRT) decrease than eyes lacking GCLC (p < 0.0001). In the linear mixed effect models including external limiting membrane disruption, disintegration of inner retinal layer and epiretinal membrane, GCLC remained a statistical significant factor for the outcome parameter CRT, but missed statistical significance for BCVA.

CONCLUSION

Ganglion cell layer cysts (GCLC) seem to impact outcome in DME in patients receiving long-term treatment. This prognostic factor warrants further evaluation in the context of already well-established outcome parameters.

Optical coherence tomography angiography in diabetic retinopathy: a review of current applications

Background

Diabetic retinopathy (DR) is a leading cause of vision loss in adults. Currently, the standard imaging technique to monitor and prognosticate DR and diabetic maculopathy is dye-based angiography. With the introduction of optical coherence tomography angiography (OCTA), it may serve as a potential rapid, non-invasive imaging modality as an adjunct.

Main text

Recent studies on the role of OCTA in DR include the use of vascular parameters e.g., vessel density, intercapillary spacing, vessel diameter index, length of vessels based on skeletonised OCTA, the total length of vessels, vascular architecture and area of the foveal avascular zone. These quantitative measures may be able to detect changes with the severity and progress of DR for clinical research. OCTA may also serve as a non-invasive imaging method to detect diabetic macula ischemia, which may help predict visual prognosis. However, there are many limitations of OCTA in DR, such as difficulty in segmentation between superficial and deep capillary plexus; and its use in diabetic macula edema where the presence of cystic spaces may affect image results. Future applications of OCTA in the anterior segment include detection of anterior segment ischemia and iris neovascularisation associated with proliferative DR and risk of neovascular glaucoma.

Conclusion

OCTA may potentially serve as a useful non-invasive imaging tool in the diagnosis and monitoring of diabetic retinopathy and maculopathy in the future. Future studies may demonstrate how quantitative OCTA measures may have a role in detecting early retinal changes in patients with diabetes.

Retinal Sensitivity Loss Correlates with Deep Capillary Plexus Impairment in Diabetic Macular Ischemia

Purpose

To assess retinal sensitivity and retinal morphologic changes of capillary nonperfused areas in diabetic macular ischemia.

Methods

Observational cross-sectional study. Patients were examined at IRCCS—Bietti Foundation, Rome, Italy. Fourteen consecutive diabetic eyes showing outer retinal changes on spectral domain optical coherence tomography B-scan were included. Ten eyes of ten diabetic patients with normal outer retinal structure on SD-OCT were included as controls. All eyes underwent optical coherence tomography angiography (OCTA) and MP1 microperimetry. To explore the outer retina findings and localized areas of capillary nonperfusion at the superficial and deep capillary plexus, we used the Spectralis HRA + OCTA (Heidelberg Engineering, Heidelberg, Germany). The B-scans as either normal or having outer retinal disruption and the enface images at the level of the superficial and/or deep capillary plexus were evaluated to identify areas of capillary nonperfusion.

Results

Fourteen eyes of 12 consecutive type 2 diabetic patients with outer retinal disruption on SD-OCT showed that areas of capillary nonperfusion of the deep capillary plexus were colocalized to areas of reduced retinal sensitivity.

Conclusions

On optical coherence tomography angiography, areas of capillary nonperfusion of deep capillary plexus due to macular ischemia are associated with photoreceptor structural abnormalities and retinal sensitivity loss on microperimetry. This highlights that the health status of deep capillary plexus and not only the choroid is important to the oxygen requirements of the photoreceptors in patients with diabetic macular ischemia. Also, the anatomical and functional consequences of these findings might help to explore the efficacy of new therapy into the macular area in clinical practice.