Radial peripapillary capillaries of the retina. II. Possible role in Bjerrum scotoma

Colocalization of Ellipsoid Zone Disruption With Capillary Nonperfusion in Different Retinal Vascular Layers and Choriocapillaris on En Face OCT of Diabetic Patients

PURPOSE

To assess the colocalization of ellipsoid zone (EZ) disruption with nonperfusion in choriocapillaris (CC), retinal superficial capillary plexus (SCP), and deep capillary plexus (DCP) in diabetic patients using en face optical coherence tomography (OCT) and OCT angiography (OCTA).

METHODS

Macular OCT and OCTA scans (3 × 3 mm) of 41 patients with diabetic retinopathy were obtained using an RTVue XR Avanti instrument. After correcting the shadow artifacts, EZ integrity was assessed in the en face OCT slab using the Gaussian mixture model clustering method compared with the corresponding EZ en face OCT of 11 age-matched normal patients. A similar technique was used for detecting capillary nonperfusion using CC en face OCTA. Geometric perfusion density (GPD) maps were also generated for the SCP and DCP. Maps of capillary nonperfusion in the CC, SCP, and DCP were compared pixel by pixel with the map generated from EZ disruption.

RESULTS

Twenty-one patients with diabetic macular edema (DME) and 20 patients with diabetic retinopathy without macular edema were included in this study. In both groups, the overlap of EZ disruption was significantly greater with choriocapillaris nonperfusion than with nonperfusion in the SCP and DCP (dry macular group: 33.15% with CC vs. 0.46% with SCP vs. 1.70% with DCP, p < 0.001; DME group: 29.81% with CC vs. 1.22% with SCP vs. 6.25% with DCP, p < 0.001). In multivariate analysis, after adjusting for stage of diabetic retinopathy and DME, EZ disruption was only associated with nonperfusion in CC (p value = 0.03). According to the linear regression model, there was a statistically significant correlation between logMAR visual acuity and EZ disruption in the dry macular group (p = 0.041).

CONCLUSION

In patients with diabetic retinopathy, choriocapillaris nonperfusion may play a more significant role in photoreceptor loss than retinal nonperfusion.

Vascular density normative data of radial peripapillary capillary plexus in healthy Caucasian subjects

PURPOSE

To establish a normative database for vascular density (VD) of radial peripapillary capillary plexus (RPC) in healthy Caucasian subjects.

METHODS

633 healthy Caucasian subjects underwent a complete ophthalmological examination, including slit-lamp biomicroscopy, best corrected visual acuity measurement with Early Treatment Diabetic Retinopathy Study charts, intraocular pressure measurement, fundus examination, and macular and optic nerve head (ONH) structural optical coherence tomography (OCT). En-face 4.5 × 4.5 mm OCT angiography scans of the RPC plexus were recorded and VD values, automatically provided by the AngioAnalytics™ software, noted. We statistically estimated the impact of age and gender on RPC VD values using a linear mixed model.

RESULTS

560 subjects fully met inclusion criteria and, according to age, were stratified into 5 groups: 18-50 years (77), 51-60 years (160), 61-70 years (110), 71-80 years (132), and ≥ 81 years (81). Overall, mean RPC VD of the whole en-face image was 53.03 ± 4.27%. Age was significantly related to RPC VD values of whole en-face image (r = -0.454; p < 0.0001), which decreased with aging. The linear mixed model disclosed that age has a statistically significant effect on RPC VD values in whole en-face image (p = 0.0006). As age increases, RPC VD values decrease by 0.12 per year. Conversely, no significant gender-related differences were found in terms of RPC VD values of whole en-face image and each parapapillary quadrant analyzing all age group.

CONCLUSIONS

Results show that RPC VD values in healthy Caucasian subjects decrease with aging. These data may be used to create a reference normative database useful for clinical use.

KEY MESSAGES

What is known Radial peripapillary capillary (RPC) plexus, consisting of long parallel capillaries with rare bifurcations and anastomosis and extending straight along the course of the retinal nerve fiber layer to the posterior pole, may be affected early in some optic nerve head (ONH) and retinal diseases. What is new This study reports RPC vascular density (VD) values, automatically measured on optical coherence tomography angiography, in healthy Caucasian subjects, demonstrating that age is negatively related to RPC VD values. Results show that RPC VD values in healthy Caucasian subjects decrease with aging. These data may be used to create a reference normative database useful for clinical use.

Application of Optical Coherence Tomography Angiography in True and Pseudo-Optic Disc Swelling

Purpose

We evaluated the optic disc microvasculature in healthy subjects and patients with optic nerve head drusen (ONHD), active papilledema, and acute nonarteritic anterior ischemic optic neuropathy (NAION) using optical coherence tomography angiography (OCTA).

Methods

This prospective, comparative case series included sixteen eyes with ONHD, thirty-one eyes with active papilledema, sixteen eyes with acute NAION, and thirty-two healthy eyes. The Optovue AngioVue OCT and OCTA Imaging System recorded peripapillary retinal nerve fiber layer (RNFL) thickness and vessel density maps from the radial peripapillary capillary (RPC) slab.

Results

Average RNFL thicknesses were greater in eyes with ONHD, papilledema, and NAION compared to control eyes (all Ps < 0.001), but this parameter did not differ among patient groups. The mean peripapillary vessel density did not differ between the ONHD and control groups (P=1.000), nor between the NAION and papilledema groups (P=0.216). However, this value in the ONHD and control groups was significantly higher than in the NAION and papilledema groups (all Ps < 0.05).

Conclusion

RPC density is influenced during the progression of conditions such as ONHD, papilledema, and NAION. Although a decrease in vessel density values has been observed in cases of true disc edema, further research is necessary to assess the potential of OCTA in differentiating between true and pseudo-optic disc edema.

Optical coherence tomography angiography analysis of the fellow eye in unilateral pseudoexfoliation syndrome

PURPOSE

To compare the macular and optic disc vascular parameters in the unaffected fellow eyes of subjects with unilateral pseudoexfoliation syndrome (PXS) and controls using optical coherence tomography angiography (OCTA).

METHODS

The medical records of 61 eyes of 61 patients were analyzed in a retrospective study. Of these, 30 eyes were unaffected fellow eyes and 31 eyes were control eyes. The vessel density (VD), perfusion density (PD) and foveal avascular zone (FAZ)-related parameters of the superficial capillary plexus (SCP) in the circumpapillary and macular area and the VD and PD of the deep capillary plexus (DCP) in the macular area were measured using OCTA after dilatation and were compared between two groups after adjustment for age, sex and axial length.

RESULTS

There were no statistically significant differences in sex ratio or mean age, central corneal thickness measurements, refractive errors, intraocular pressures and axial length between both groups (all P > 0.05). In the circumpapillary area, inferior VD and PD in the inner zone, as well as average, temporal, inferior, and nasal VD and PD in the outer zone were significantly reduced in the unaffected fellow eyes with unilateral PXS, while the circumpapillary retinal nerve fiber layer (RNFL) thicknesses were similar between groups. In the macular SCP, VDs were significantly lower in all sectors in the inner area and in the outer zones (p < 0.05 for all), PDs were significantly lower in all sectors (p < 0.05 for all) except the nasal sector of the outer zone (p = 0.003 for average, p = 0.029 for superior sector, p = 0.004 for temporal sector, p < 0.001 for inferior sector), and the FAZ circularity (p = 0.037) were significantly lower in the unaffected fellow eyes with unilateral PXS, whereas macular ganglion cell inner plexiform layer (GCIPL) thickness was similar between the two groups.

CONCLUSIONS

Although circumpapillary RNFL and GCIPL thicknesses were similar between the two groups, VDs and PDs in the circumpapillary and macular SCP and FAZ circularity were significantly lower in the fellow eye of subjects with unilateral PXS.

Advances in retinal imaging biomarkers for the diagnosis of cerebrovascular disease

The increasing incidence and mortality rates of cerebrovascular disease impose a heavy burden on both patients and society. Retinal imaging techniques, such as fundus photography, optical coherence tomography, and optical coherence tomography angiography, can be used for rapid, non-invasive evaluation of cerebral microcirculation and brain function since the retina and the central nervous system share similar embryonic origin characteristics and physiological features. This article aimed to review retinal imaging biomarkers related to cerebrovascular diseases and their applications in cerebrovascular diseases (stroke, cerebral small vessel disease [CSVD], and vascular cognitive impairment [VCI]), thus providing reference for early diagnosis and prevention of cerebrovascular diseases.

Characteristics of the radial peripapillary capillary network in patients with COVID-19 based on optical coherence tomography angiography: A literature review

PURPOSE

This review aimed to evaluate the significance of assessing radial peripheral capillary (RPC) network parameters by optical coherence tomography angiography (OCTA) in patients with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection confirmed by polymerase chain reaction.

METHODS

A literature search was conducted in the PubMed database to select high-quality reviews and original articles on the use of OCTA for visualizing the RPC network and calculating RPC parameters.

RESULTS

The study revealed that systemic hypoxia, hypercoagulable state, and inflammation affect the RPC network in patients with coronavirus disease 2019 (COVID-19). Reduced RPC parameters were observed early in the course of SARS-CoV-2 infection and after several months of follow-up. Additionally, there was a correlation between reduced RPC parameters and subsequent thinning of the retinal nerve fiber layer.

CONCLUSIONS

The OCTA examination of the retina and optic disc should be considered in patients with a history of COVID-19 to assess the impact of systemic hypoxia and inflammation on ocular function. Follow-up assessment of these patients is also necessary to understand the potential consequences of ischemia affecting the optic nerve, retina, and choroid.

Optical Coherence Tomography Angiography Vessel Density in Healthy, Glaucoma Suspect, and Glaucoma Eyes

Purpose

To evaluate and compare optical coherence tomography angiography (OCTA) retinal vasculature measurements in healthy, glaucoma suspect (GS), and glaucoma patients.

Methods

One hundred fourteen eyes with good quality OCTA pictures were included from 38 healthy, 38 GS, 38 and primary open-angle glaucoma (POAG) participants. The information on retinal vasculature was summarized as a vessel density map and as vessel density (%), which is the fraction of the flowing vessel area over the total area examined. The superior, inferior, nasal, and temporal quadrants, as well as whole vessel density (wVD) and peripapillary vessel density (ppVD) data taken from the retinal nerve fiber layer, were studied. Global indices of the visual field were correlated with vessel density measurement.

Results

Mean vessel density was significantly lower in POAG eyes compared with GSs and healthy eyes (wVD) 45.34% ± 6.64%, 50.06% ± 1.97% and 53.06% ± 2.12%, respectively (P < 0.001), and ppVD 47.42% ± 7.73%, 47.42% ± 7.73% and 56.074% ± 2.71%, respectively (P < 0.001). A linear relationship between vessel density (wVD and ppVD) and global indices of the visual field (mean deviation [MD] and pattern standard deviation [PSD]) shows a significant (P < 0.001) relation. R 2 is 0.35, 0.36, 0.36, and 0.33 for MD and wVD, PSD and wVD, PSD and ppVD, and MD and ppVD, respectively.

Conclusions

For distinguishing between healthy and glaucoma eyes, OCTA vessel density demonstrated near similar diagnostic accuracy to visual field tests. These findings imply that OCTA measurements reflect damage to tissues important in the pathogenesis of POAG.

Changes of Optic Disc and Macular Vessel Perfusion Density in Primary Angle Closure Glaucoma: A Quantitative Study Using Optical Coherence Tomography Angiograph

INTRODUCTION

This study aims to investigate the changes of retinal vascular system in primary angle closure glaucoma (PACG) and acute primary angle closure (APAC) by optical coherence tomography (OCT) angiograph (OCTA) and to evaluate the diagnostic ability of changes of vessel density (VD) in different sectors and layers of optic disc and macular area in APAC and PACG.

METHODS

In this cross-sectional, observational study, 21 APAC patients (22 eyes) and 21 PACG patients (27 eyes) along with 17 healthy people were enrolled from August 2018 to March 2019. Optic disc region and macular region were imaged using swept-source OCTA system. VD of the macular region was quantified by Image J (1.52a, USA) and Matlab 2018a. The circumpapillary retinal nerve fiber layer (cpRNFL) thickness and ganglion cell complex thickness were obtained by spectral-domain OCT.

RESULTS

Compared with the healthy group, the cpRNFL thickness in superior sector was thicker in the APAC group, and this area had the most diffuse microvascular dropout as well. The difference in the macular superficial capillary plexus (SCP) VD between APAC and the control group was not statistically significant. The area under the ROC curves (AUC) of the total optic disc VD in the radial peripapillary capillary (RPC) layer was higher than the AUC of the papillary VD in the optic nerve head (ONH) layer. Compared to the control group, the total optic disc VD, peripapillary VD, and each quadrant of peripapillary VD were decreased in PACG (p < 0.01). In PACG macular region, SCP VD, and deep capillary plexus (DCP) VD, parafovea VD (except temporal sectors) decreased (p < 0.01). The PACG eyes had a greater decrease percentage of VD in total ONH than total macula. The diagnostic value of the VD in the ONH layer and the RPC layer was similar. The diagnostic value of the SCP VD in the macula was greater than the DCP VD in the macula. The AUC was no significant difference between cpRNFL thickness and the total optic disc VD AUC.

CONCLUSION

Elevated intraocular pressure preferentially affects vascular perfusion in the optic disc region more than the macular region in APAC and PACG. In the APAC eyes, there was a perfusion defect in the optic disc region and an increase in RNFL thickness. In this study, the OCTA vascular parameters have similar performance to the OCT structural parameters for glaucoma diagnosis in PACG.

Age exacerbates the effect of myopia on retinal capillaries and string vessels

The retinal vasculature supplies oxygen and nutrition to the cells and is crucial for an adequate retinal function. In myopia, excessive eye growth is associated with various anatomical changes that can lead to myopia-related complications. However, how myopia-induced ocular growth affects the integrity of the aged retinal microvasculature at the cellular level is not well understood. Here, we studied how aging interacts with myopia-induced alteration of the retinal microvasculature in fourteen marmoset retinas (Callithrix jacchus). String vessel and capillary branchpoint were imaged and quantified in all four capillary plexi of the retinal vasculature. As marmosets with lens-induced myopia aged, they developed increasing numbers of string vessels in all four vascular plexi, with increased vessel branchpoints in the parafoveal and peripapillary retina and decreased vessel branchpoints in the peripheral retina. These myopia-induced changes to the retinal microvasculature suggest an adaptive reorganization of the retinal microvascular cellular structure template with aging and during myopia development and progression.

EVALUATION OF OPTIC DISK AND MACULAR VASCULARITY CHANGES IN CRVO USING OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY

PURPOSE

To quantify changes in optic disk and macular vasculature in patients with central retinal vein occlusion using optical coherence tomography angiography and detect its correlation with visual acuity.

METHODS

The study included 20 eyes of 20 patients with treatment-naive central retinal vein occlusion and 20 age-matched controls. Optical coherence tomography and optical coherence tomography angiographywere performed on the macula and optic disk. Central 1-mm subfield foveal thickness was measured. Vessel densities (VD) of superficial and deep macular capillary plexuses with whole disk VD, inside disk VD, and radial peripapillary capillary plexus were analyzed. Macular ischemia was evaluated by fundus fluorescein angiography. Visual acuity was correlated with measured parameters.

RESULTS

All measured macular and disk VDs differed significantly between cases and controls except inside disk VD. Visual acuity showed a highly significant negative correlation with whole disk VD ( P = 0.005) and radial peripapillary capillary ( P = 0.002), borderline correlation with central subfield foveal thickness ( P = 0.06), and insignificant correlation with macular VDs. Radial peripapillary capillary VD showed a significant correlation with deep parafoveal ( P = 0.04), and superficial and deep perifoveal VDs ( P = 0.01).

CONCLUSION

Optic disk VD could provide more accurate indication of retinal blood supply than macular VD in cases of central retinal vein occlusion with severe macular edema.

Changes in early optical coherence tomography angiography among children and adolescents with type 1 diabetes: Relation to fibroblast growth factor 21

AIMS

Current diagnostic and treatment modalities target late stages of diabetic retinopathy (DR) when retinopathy has already been established. Novel and more sensitive strategies are needed. Optical coherence tomography angiography (OCTA) permits non-invasive visualisation of retinal microcirculation. Fibroblast growth factor-21 (FGF21) plays an important role in glucose and lipid homoeostasis. This study assesses early OCTA changes among children and adolescents with type 1 diabetes (T1DM) compared to fundus photography and correlates them to diabetes-duration, glycaemic control, and FGF21; hence, it determines their value in early detection of DR.

METHODOLOGY

Hundred children and adolescents with T1DM were assessed for diabetes-duration, insulin therapy, hypoglycemia, and diabetic-ketoacidosis frequency, Tanner staging, glycated-haemoglobin (HbA1c), fasting lipids, urinary albumin/creatinine ratio, and serum FGF21. OCTA and fundus photography were done for the studied patients and 100 age, gender, and Tanner matched healthy controls.

RESULTS

The mean age of the children and adolescents with T1DM was 10.84 years, their mean diabetes-duration was 3.27 years and their median FGF21 was 150 pg/ml. FGF21 was significantly higher among children and adolescents with T1DM than controls (p < 0.001). Children and adolescents with T1DM had a significantly larger foveal avascular zone (FAZ) and lower peripapillary and inside-disc capillary densities (p < 0.05); with no significant fundus photography difference (p = 0.155) than controls. FAZ was positively correlated and peripapillary and inside-disc capillary densities were negatively correlated with diabetes-duration, HbA1c, FGF21, and Tanner stage. FGF21 was significantly higher in T1DM children and adolescents having OCTA changes compared to those with normal OCTA (p = 0.002). Multivariate-regression revealed that FAZ is independently associated with diabetes-duration, HbA1c and FGF21.

CONCLUSIONS

OCTA changes start early in children and adolescents with T1DM long before the fundus changes. These changes are correlated with diabetes-duration, puberty, glycaemic, and FGF21.

Quantitative Assessment Parameters of Peripapillary Regions with Branch Retinal Vein Occlusion by Using Optical Coherence Tomography Angiography

PURPOSE

To investigate the baseline parameters of peripapillary regions in both eyes of patients with unilateral branch retinal vein occlusion (BRVO) using optical coherence tomography angiography (OCTA) and their association with best-corrected visual acuity (BCVA).

METHODS

Forty-eight unilateral BRVO patients were enrolled. The 4.5 × 4.5 mm disc angiogram was acquired in the BRVO eyes and fellow eyes using the OCTA. Radial peripapillary capillary (RPC), whole vessel density, and retinal nerve fiber layer (RNFL) thickness in different regions and optic nerve head (ONH) analysis were automatically calculated. The partition includes the whole image, peripapillary, superior hemifield, inferior hemifield, eight equally divided sectors, and nine evenly divided square areas.

RESULTS

All vessel density and capillary vessel density in the whole and peripapillary regions of BRVO eyes were significantly lower than those in fellow eyes. The RNFL peripapillary thickness in BRVO eyes was significantly higher than those in fellow eyes. In eyes with supertemporal vein occlusion, all vessel density both in the superior hemifield and in the G12 region was significantly reduced compared with that in the fellow eyes. The capillary vessel density was significantly lower in the superior hemifield, superior temporal (ST), superior nasal (SN), and temporal superior (TS) areas than in the fellow eyes. The RNFL thickness in the NI, IN, TI, and TS sectors was significantly higher than in fellow eyes (all P < 0.05).

CONCLUSIONS

OCTA provided quantitative information on peripapillary vascular density and RNFL thickness changes in BRVO. Branch retinal vein occlusion not only affects the blood vessel density in the macular area but also decreases the radial peripapillary capillaries. The capillary density is mainly affected in the affected hemifield but not in the unaffected hemifield.

Acute effects of coffee consumption on the microcirculation of macula and optic nerve head

Purpose: This study aimed to evaluate the acute changes in retinal vasculature following coffee consumption. Methods: This is an interventional case series. The subjects were 22 healthy young adults. They were asked to rest in a silent room for 15 min; then, their heart rate, blood pressure, and arterial oxygen saturation pressure were measured with a single patient monitoring system. Optical coherence tomography (OCT) and OCT angiography (OCT-A) imaging of the disc and macula were performed for both eyes of the subjects. These measurements were repeated 45 min after drinking a cup of 450 ml of coffee containing a standard dose of 130 mg of caffeine. Macular and optic nerve head neurovasculature changes were assessed. Results: The results of our study did not show a significant change in peripapillary retinal nerve fiber layer thickness and neural structural and vascular parameters of the optic nerve head. Although assessments of macular vasculature showed a significant decrement in superficial (p = 0.01) and deep vessel density (p = 0.05) at parafovea, vessel densities (VDs) at the fovea, and deep capillary plexus at perifovea showed no significant change. Conclusion: Consuming one cup of coffee (150 mg caffeine) statistically changes central foveal thickness and parafoveal blood flow but likely does not have a clinical impact in healthy young adults.

Evaluation of Radial Peripapillary Capillary Density in G6PD Deficiency: An OCT Angiography Pilot Study

Glucose-6-phosphate-dehydrogenase (G6PD) deficiency is an inherited enzymatic disorder causing hemolytic anemia. The purpose of this pilot study was to compare vascular density (VD) values of the radial peripapillary capillary (RPC) plexus in G6PD-deficient and G6PD-normal men, using optical coherence tomography angiography (OCTA).

METHODS

46 G6PD-deficient men and 23 age-matched male controls were included. A complete ophthalmological evaluation, consisting of slit-lamp biomicroscopy, best-corrected visual acuity, intra-ocular pressure measurement, structural optical coherence tomography, and OCTA scanning of the optic nerve head, was performed. The en-face angioflow images were carefully analyzed and the VD values of the RPC plexus were measured using the AngioAnalytics™ software embedded in the OCTA device. Medical conditions, including systemic hypertension, hypercholesterolemia, and diabetes mellitus, were also investigated.

RESULTS

G6PD-deficient eyes showed higher values of VD in all peripapillary sectors, but a statistical significance (p = 0.03) was reached only in the infero-temporal sector. There were no significant differences in terms of hypercholesterolemia, systemic arterial hypertension, and diabetes mellitus between the two study groups.

CONCLUSION

Results show that VD values of the RPC plexus are higher in G6PD-deficient men than in G6PD-normal subjects, but a statistically significant difference was found only in the inferior temporal sector. Overall, our preliminary findings support the hypothesis that the RPC layer of G6PD-deficient men consists of a denser vascular network, which may contribute to offering protection against ocular atherosclerotic vasculopathies.

Towards standardizing retinal optical coherence tomography angiography: a review

The visualization and assessment of retinal microvasculature are important in the study, diagnosis, monitoring, and guidance of treatment of ocular and systemic diseases. With the introduction of optical coherence tomography angiography (OCTA), it has become possible to visualize the retinal microvasculature volumetrically and without a contrast agent. Many lab-based and commercial clinical instruments, imaging protocols and data analysis methods and metrics, have been applied, often inconsistently, resulting in a confusing picture that represents a major barrier to progress in applying OCTA to reduce the burden of disease. Open data and software sharing, and cross-comparison and pooling of data from different studies are rare. These inabilities have impeded building the large databases of annotated OCTA images of healthy and diseased retinas that are necessary to study and define characteristics of specific conditions. This paper addresses the steps needed to standardize OCTA imaging of the human retina to address these limitations. Through review of the OCTA literature, we identify issues and inconsistencies and propose minimum standards for imaging protocols, data analysis methods, metrics, reporting of findings, and clinical practice and, where this is not possible, we identify areas that require further investigation. We hope that this paper will encourage the unification of imaging protocols in OCTA, promote transparency in the process of data collection, analysis, and reporting, and facilitate increasing the impact of OCTA on retinal healthcare delivery and life science investigations.

Variability in Retinal Neuron Populations and Associated Variations in Mass Transport Systems of the Retina in Health and Aging

Aging is associated with a broad range of visual impairments that can have dramatic consequences on the quality of life of those impacted. These changes are driven by a complex series of alterations affecting interactions between multiple cellular and extracellular elements. The resilience of many of these interactions may be key to minimal loss of visual function in aging; yet many of them remain poorly understood. In this review, we focus on the relation between retinal neurons and their respective mass transport systems. These metabolite delivery systems include the retinal vasculature, which lies within the inner portion of the retina, and the choroidal vasculature located externally to the retinal tissue. A framework for investigation is proposed and applied to identify the structures and processes determining retinal mass transport at the cellular and tissue levels. Spatial variability in the structure of the retina and changes observed in aging are then harnessed to explore the relation between variations in neuron populations and those seen among retinal metabolite delivery systems. Existing data demonstrate that the relation between inner retinal neurons and their mass transport systems is different in nature from that observed between the outer retina and choroid. The most prominent structural changes observed across the eye and in aging are seen in Bruch's membrane, which forms a selective barrier to mass transfers at the interface between the choroidal vasculature and the outer retina.

Longitudinal In Vivo Changes in Radial Peripapillary Capillaries and Optic Nerve Head Structure in Non-Human Primates With Early Experimental Glaucoma

Purpose

There is conflicting evidence regarding whether a loss of radial peripapillary capillaries (RPCs) precedes neuronal loss in glaucoma. We examined the time course of in vivo changes in RPCs, optic nerve head (ONH) structure, and retinal nerve fiber layer thickness (RNFLT) in experimental glaucoma (EG).

Methods

Spectral domain optical coherence tomography images were acquired before and approximately every two weeks after inducing unilateral EG in nine rhesus monkeys to quantify mean anterior lamina cribrosa surface depth (ALCSD), minimum rim width (MRW), and RNFLT. Perfused RPC density was measured from adaptive optics scanning laser ophthalmoscope images acquired on the temporal half of the ONH. The time of first significant change was quantified as when values fell and remained outside of the 95% confidence interval established from control eyes.

Results

Mean ALCSD and/or MRW were the first parameters to change in eight EG eyes. RPC density changed first in the ninth. At their first points of change, mean ALCSD posteriorly deformed by 100.2 ± 101.2 µm, MRW thinned by 82.3 ± 65.9 µm, RNFLT decreased by 25 ± 14 µm, and RPC density decreased by 4.5 ± 2.1%. RPC density decreased before RNFL thinning in 5 EG eyes. RNFLT decreased before RPC density decreased in two EG eyes, whereas two EG eyes had simultaneous changes.

Conclusions

In most EG eyes, RPC density decreased before (or simultaneous with) a change in RNFLT, suggesting that vascular factors may play a role in axonal loss in some eyes in early glaucoma.

Repeatability of Peripapillary OCT Angiography in Neurodegenerative Disease

Purpose

To assess the repeatability of peripapillary OCT angiography (OCTA) in those with Alzheimer disease (AD), mild cognitive impairment (MCI), Parkinson disease (PD), or normal cognition.

Design

Cross-sectional.

Participants

Patients with a clinical diagnosis of AD, MCI, PD, or normal cognition were imaged. Those with glaucoma, diabetes mellitus, vitreoretinal pathology, and poor-quality images were excluded.

Methods

Each eligible eye of each participant underwent 2 OCTA 4.5 × 4.5-mm peripapillary scans in a single session using a Zeiss Cirrus HD-OCT 5000 with AngioPlex (Carl Zeiss Meditec). The Zeiss software (v11.0.0.29946) quantified measures of perfusion in the radial peripapillary capillary (RPC) plexus in 4 sectors (superior, nasal, inferior, temporal). The average of these sectors was calculated and reported.

Main Outcome Measures

Radial peripapillary capillary plexus perfusion was quantified using 2 parameters: capillary perfusion density (CPD) and capillary flux index (CFI). Intraclass correlation coefficients (ICCs) were used to quantify repeatability. For subjects who had both eyes included, the average values of each scan pair were used to assess interocular symmetry of CPD and CFI.

Results

Of 374 eyes, 46 were from participants who had AD, 85 were from participants who had MCI, 87 were from participants who had PD, and 156 were from participants who had normal cognition. Capillary perfusion density ICC in AD = 0.88 (95% confidence interval [CI], 0.79-0.93), MCI = 0.95 (0.92-0.96), PD = 0.91 (0.87-0.94), and controls = 0.90 (0.87-0.93). Capillary flux index ICC in AD = 0.82 (0.70-0.90), MCI = 0.87 (0.80-0.91), PD = 0.91 (0.87-0.94) and controls = 0.85 (0.79-0.89). There were no significant differences in interocular variation in average CPD and CFI in AD, MCI, or PD (all P > 0.05). Isolated interocular sectoral CPD differences were noted in AD (nasal, P = 0.049; temporal, P = 0.024), PD (nasal, P = 0.036), and controls (nasal, P = 0.016). Interocular differences in CFI in the superior sector in MCI (P = 0.028) and in average CFI for controls (P = 0.035) were observed.

Conclusions

Peripapillary OCTA repeatability in AD, MCI, and PD is good-excellent and similar to those with normal cognition. Insignificant interocular asymmetry in peripapillary OCTA suggests neurodegeneration may proceed uniformly; future studies may reveal the appropriateness of single-eye imaging.

Predictors of Peripapillary and Macular Optical Microangiography Measurements in Healthy Eyes

PRECIS

The vessel density (VD) and perfusion density (PD) generated by optical microangiography (OMAG) is significantly affected by the signal strength (SS). Sex, hypertension, diabetes, and axial length did not have any statistically significant effect on these measurements.

PURPOSE

The aim was to assess the effect of subject-related factors (age, sex, systemic hypertension, diabetes, and axial length) and machine-related factor (SS) on VD and PD generated by OMAG in peripapillary and macular regions.

METHODS

In an observational, cross-sectional study of 200 eyes of 100 healthy individuals (age: 18 to 80 y), mean and sectoral VD and PD were calculated on disc and macular scans. Effect of subject-related and machine-related factors on VD and PD parameters were evaluated using multivariate mixed effect models.

RESULTS

Mean±SD peripapillary and macular VD of the study population was 18.56±1.11 and 20.59±1.85 mm-1, respectively. Mean peripapillary and macular PD was 46.43±3.22% and 37.61±3.26%, respectively. Sex, hypertension, diabetes, and axial length did not have any statistically significant effect on the OMAG measurements (P>0.05 for all associations). However, the SS had significant effect on the OMAG measurements. Mean peripapillary and macular VD on scans with SS of 10 was 1.4 and 3.79 mm-1 greater, respectively, than that on scans with SS of 7. Mean peripapillary and macular PD on scans with SS of 10 was 4.43% and 7.85% greater, respectively, than that on scans with SS of 7.

CONCLUSION

Significant association exists between SS of the scan and the optical coherence tomography angiography measurements generated by OMAG even when the scans have acceptable SS as recommended by the manufacturer (≥7). This needs to be considered while interpreting optical coherence tomography angiography measurements.

Optic disc and peripapillary vessel density measured with optical coherence tomography angiography and its associations in Chinese adults: a large population-based study

PURPOSE

To investigate the optic disc and peripapillary vessel density, as well as its ocular and systemic associations, in healthy eyes among adult Chinese population.

METHODS

A population-based cross-sectional eye survey was conducted on Chinese adults residing in Hong Kong. 1891 eyes from 1891 participants who completed 4.5×4.5 mm optical coherence tomography angiography scans were recruited. Among the 1891 eyes, 404 were excluded due to low scan quality, optic disc or retinal disorders and non-Chinese ethnicity. The vessel densities (VDs) at nerve fibre layer plexus (NFLP) at both optic disc and peripapillary were collected for analysis. Multiple linear regression analysis was performed to determine the ocular and systemic associations of NFLP VD.

RESULTS

The study included 1487 participants (men: 41.2%) with a mean age of 48.8±15.4 years. The mean NFLP VD of the whole en face image, inside disc and peripapillary region was 53.8%, 42.7% and 60.3%, respectively. In the multivariable model, decreased NFLP VDs were significantly associated with older age, male gender, longer axial length (AL) and lower Signal Strength Index.

CONCLUSIONS

This large population-based cross-sectional study provided quantitative data of optic disc and peripapillary NFLP VD which may serve as a normative reference for clinical use. Apart from age, gender and AL, the scan signal strength also should be taken into consideration during the assessment of NFLP VD.

Energy Metabolism in the Inner Retina in Health and Glaucoma

Glaucoma, the leading cause of irreversible blindness, is a heterogeneous group of diseases characterized by progressive loss of retinal ganglion cells (RGCs) and their axons and leads to visual loss and blindness. Risk factors for the onset and progression of glaucoma include systemic and ocular factors such as older age, lower ocular perfusion pressure, and intraocular pressure (IOP). Early signs of RGC damage comprise impairment of axonal transport, downregulation of specific genes and metabolic changes. The brain is often cited to be the highest energy-demanding tissue of the human body. The retina is estimated to have equally high demands. RGCs are particularly active in metabolism and vulnerable to energy insufficiency. Understanding the energy metabolism of the inner retina, especially of the RGCs, is pivotal for understanding glaucoma’s pathophysiology. Here we review the key contributors to the high energy demands in the retina and the distinguishing features of energy metabolism of the inner retina. The major features of glaucoma include progressive cell death of retinal ganglions and optic nerve damage. Therefore, this review focuses on the energetic budget of the retinal ganglion cells, optic nerve and the relevant cells that surround them.

Macula Structure and Microvascular Changes in Recent Small Subcortical Infarct Patients

Purpose: This study aimed to assess the macula structure and capillaries in the macula and optic nerve head in recent small subcortical infarct (RSSI) patients. Methods: This observational cross-sectional study included 40 RSSI patients and 46 healthy controls. Optical coherence tomography angiography was used to image the capillaries in the macula and optic nerve head. An inbuilt algorithm was used to measure the densities in the microvasculature of the macula [superficial retinal capillary plexus (SRCP) and deep retinal capillary plexus (DRCP)] and optic nerve head [radial peripapillary capillary (RPC)] and thickness around the optic nerve head, peripapillary retinal nerve fiber layer (pRNFL). Results: Densities in RPC (P < 0.001), SRCP (P = 0.001), and DRCP (P = 0.003) were reduced in RSSI patients when compared with healthy controls. The pRNFL thickness was thinner (P < 0.001) in RSSI patients than healthy controls. In the RSSI group, the SRCP density significantly correlated with the DRCP density (rho = 0.381, P = 0.042). The pRNFL thickness displayed a significant relationship with the RPC density (rho = 0.482, P = 0.003) in the RSSI group. Conclusions: RSSI patients showed interrupted capillary plexuses leading to its significant impairment and neurodegeneration. Our report provides insight into the macula capillary microcirculation changes in RSSI.

Peripapillary and Macular Vessel Density Measurement With Optical Coherence Tomography Angiography in Exfoliation Syndrome

PRECIS

Although peripapillary retinal nerve fiber layer thickness (RNFLTs) and vessel density (VD) values were similar to healthy group, eyes with exfoliation syndrome had significantly lower superficial macular VDs and minimum ganglion cell analysis values.

PURPOSE

To compare peripapillary and macular perfused capillary densities with optical coherence tomography angiography (OCT-A) between patients with eyes having exfoliation syndrome (XFS) and normal age-matched healthy controls.

PATIENTS AND METHODS

This cross-sectional study included patients diagnosed with XFS from December 2017 to January 2020 at the Glaucoma Department. Peripapillary and parafoveal superficial VDs were obtained using OCT-A. The RNFLTs and ganglion cell analysis values were compared.

RESULTS

Thirty-nine eyes of 39 XFS patients (26 women; mean age, 69.0±8.1 y) and 39 eyes of 39 healthy patients (25 women; mean age, 68.0±8.6 y) were enrolled. There were no statistically significant differences in sex or age distribution, central corneal thickness measurements, refractive errors, or intraocular pressures between both groups (all P>0.05). There were no statistically significant differences in the peripapillary VD or peripapillary RNFLT between XFS eyes and healthy eyes (P>0.05 for all). In the macular region, most superficial VD parameters were significantly reduced in the XFS group (P=0.02 for parafoveal VD, P=0.04 for both hemifields). While the average ganglion cell and internal plexiform layer (GCL+IPL) values were similar between groups (P=0.19), the minimum GCL+IPL value was lower in the XFS group than in the healthy group (P=0.03).

CONCLUSION

Although structural test results, especially peripapillary RNFLT and mean GCL+IPL, were similar between the healthy and XFS groups, macular VD values were lower in XFS eyes. Our findings implicate microvascular damage can be the mechanism underlying XFS-related changes and indicate that it precedes significant structural damage.

3D Retinal Vessel Density Mapping With OCT-Angiography

Optical Coherence Tomography Angiography (OCTA) is a novel, non-invasive imaging modality of retinal capillaries at micron resolution. Recent studies have correlated macular OCTA vascular measures with retinal disease severity and supported their use as a diagnostic tool. However, these measurements mostly rely on a few summary statistics in retinal layers or regions of interest in the two-dimensional (2D) en face projection images. To enable 3D and localized comparisons of retinal vasculature between longitudinal scans and across populations, we develop a novel approach for mapping retinal vessel density from OCTA images. We first obtain a high-quality 3D representation of OCTA-based vessel networks via curvelet-based denoising and optimally oriented flux (OOF). Then, an effective 3D retinal vessel density mapping method is proposed. In this framework, a vessel density image (VDI) is constructed by diffusing the vessel mask derived from OOF-based analysis to the entire image volume. Subsequently, we utilize a non-linear, 3D OCT image registration method to provide localized comparisons of retinal vasculature across subjects. In our experimental results, we demonstrate an application of our method for longitudinal qualitative analysis of two pathological subjects with edema during the course of clinical care. Additionally, we quantitatively validate our method on synthetic data with simulated capillary dropout, a dataset obtained from a normal control (NC) population divided into two age groups and a dataset obtained from patients with diabetic retinopathy (DR). Our results show that we can successfully detect localized vascular changes caused by simulated capillary loss, normal aging, and DR pathology even in presence of edema. These results demonstrate the potential of the proposed framework in localized detection of microvascular changes and monitoring retinal disease progression.

Differences in the multicolour imaging features between the superficial and deep vascular occlusions

Purpose To describe the multicolour imaging (MI) findings in superficial and deep vascular plexus occlusions.

METHODS

In this retrospective observational study, patients diagnosed with central retinal artery and branch retinal artery occlusion, cotton-wool spot, paracentral acute middle maculopathy and acute macular neuroretinopathy between January 2018 and June 2019 were included. Colour fundus photograph, optical coherence tomography and MI of these patients were analysed.

RESULTS

A total of 41 eyes of 40 patients were included in this study. In eyes with central retinal artery occlusion, MI showed white areas in the retina with orange foveal centre. In eyes with branch retinal artery occlusion, MI showed white area along the affected retinal quadrant without an orange foveal centre. In pure superficial vascular plexus occlusions as in cotton-wool spots, the lesion was identified on MI as a white lesion. On MI, paracentral acute middle maculopathy showed parafoveal white areas with orange foveal centre while acute macular neuroretinopathy on MI parafoveal greyish-white areas with normal foveal centre.

CONCLUSION

En-face images using MI technology can provide yet another way to identify the level of retinal vasculature involvement which complements the existing gold standard of optical coherence tomography imaging.

The Effect of Software Versions on the Measurement of Retinal Vascular Densities Using Optical Coherence Tomography Angiography

BACKGROUND

The goal of the study was to determine the effect of different software versions on the measurement of retinal vessel densities using optical coherence tomography angiography (OCTA) in normal subjects.

METHODS

Thirty-two eyes of eighteen healthy subjects were imaged using two OCTA devices: the Optovue RTVue and the Zeiss Cirrus. The macular 3 × 3 mm scan protocol was used. The images acquired using the Optovue OCTA device were exported using two different software versions in the system and compared to the images acquired through the Zeiss OCTA. In addition, the Optovue OCTA images were exported after manual adjustment of the segmentation boundaries according to the intraretinal layer definition. The densities of the superficial vascular plexus (SVP) and deep vascular plexus (DVP) were measured using fractal analysis by box-counting (Dbox).

RESULTS

Both the vessel densities of the SVP and DVP acquired using the Optovue OCTA device were significantly different when compared to those from the Zeiss OCTA device (all, P <.05). No significant difference was found between the vessel densities of the SVP exported using both the new and old versions of Optovue (P >.05). However, the DVP exported using the new Optovue software version was significantly different compared to those exported using the old version (P <.05). The vessel densities of the SVP and DVP were related among the Optovue OCTA software versions and manual adjustment method (r ranged from 0.55 to 0.77; all P <.05).

CONCLUSION

This is the first study to determine that different software versions with various intraretinal layer segmentation methods affect the vessel density measurements of the SVP and DVP.

Evaluation of radial peripapillary capillary density in patients with newly diagnosed iron deficiency anemia

PURPOSE

To investigate the effects of iron deficiency anemia (IDA) on radial peripapillary capillary vessel density (RPCvd) and retinal nerve fiber layer (RNFL) thickness.

METHODS

Forty patients with IDA, and 46 healthy participants, were enrolled in this study. Optical coherence tomography angiography was used to determine RNFL thickness and RPCvd measurements. In addition, hemoglobin (Hb), hematocrit (HCT), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), and ferritin laboratory values were evaluated.

RESULTS

Analysis of retinal regions (whole images, peripapillary, superior-hemi, inferior-hemi, inferior-nasal, inferior-temporal, temporal-inferior, temporal-superior, superior-nasal) showed that RPCvd values were significantly lower in patients with IDA compared to the control group values (p < 0.05 for all). However, there were no significant differences in RNFL thickness values between the IDA patient group and the control group (p > 0.05 for all). In addition, there were significant positive correlations between RPCvd values and hematological values for Hb, HCT, MCV, MCH, MCHC, and ferritin.

CONCLUSION

It is important to identify changes in retinal vascularity to prevent possible ocular problems in patients with IDA. Specifically, the significant positive correlations between RPCvd values and hematological values suggest that anemia treatment is important for optic nerve perfusion.

Structural and Microvascular Changes in the Macular Are Associated With Severity of White Matter Lesions

Purpose: This study aimed to characterize the microvascular and structural changes in the macular that occur in white matter hyperintensities (WMH) using optical coherence tomographic angiography. We also aimed to explore the association between macular microvascular and structural changes with focal markers of brain tissue on MRI in WMH using the Fazekas scale.

Methods: This study enrolled healthy participants who were stroke- and dementia-free. MRI was used to image the cerebral white matter lesions, and Fazekas scale was used to evaluate the severity of the white matter lesions. Optical coherence tomography angiography (OCT-A) was used to image the radial peripapillary capillaries (RPCs), macular capillary plexuses [superficial capillary plexus (SCP) and deep capillary plexus (DCP)] and thickness around the optic nerve head, peripapillary retinal nerve fiber layer (pRNFL).

Results: Seventy-four participants were enrolled and divided into two groups according to their Fazekas score (Fazekas scores ≤ 1 and ≥2). Participants with Fazekas score ≥2 showed significantly reduced RPC density (P = 0.02) and DCP density (P = 0.012) when compared with participants with Fazekas score ≤ 1. Participants with Fazekas score ≥2 showed reduced pRNFL (P = 0.004) when compared to participants with Fazekas score ≤ 1. Fazekas scores were significantly associated with the pRNFL thickness (Rho = −0.389, P = 0.001), RPC density (Rho = −0.248, P = 0.035), and DCP density (Rho = −0.283, P = 0.015), respectively.

Conclusions: Microvascular impairment and neuro-axonal damage are associated with the disease cascade in WMH. We have shown that RPC and DCP densities are significantly affected, and these impairments are associated with the severity of the disease and cognitive function. OCT-A could be a useful tool in quantifying the retinal capillary densities in WMH.

Quantitative analysis of radial peripapillary capillary plexuses in patients with clinically unilateral pseudoexfoliation syndrome

PURPOSE

The aim of this study was to image the radial peripapillary capillary vessel densities (RPCvds) of the affected eyes and fellow unaffected eyes of individuals with unilateral pseudoexfoliation syndrome (PES) using optical coherence tomography angiography (OCTA) and to compare the RPCvds with those of normal age-matched individuals.

METHODS

The eyes were divided into three groups: the pseudoexfoliative material (PXM)-positive eyes of patients with clinically unilateral PES (study eyes), the fellow eyes of the PXM-positive patients (fellow eyes), and the eyes of healthy patients (control eyes). Those patients with glaucomatous findings, including peripapillary hemorrhaging, cupping, notching, focal thinning of the neuroretinal rim, or intraocular pressure readings greater than 21 mmHg, were excluded from the study. The RPCvd (%), peripapillary retinal nerve fiber layer (RNFL) thickness (μm), cup/disc area ratio, rim area (mm²), disc area (mm²), and cup volume (mm³) were automatically calculated via OCTA.

RESULTS

This cross-sectional comparative prospective study included 128 eyes of 88 patients: 40 PXM-positive eyes, 40 fellow eyes, and 48 control eyes. The RPCvds and RNFL thicknesses in the peripapillary region were significantly lower in the study eyes than in the fellow eyes and the control eyes (p = 0.011 and p = 0.011, p = 0.009 and p = 0.004, respectively). There were no significant differences between the fellow eyes and the control eyes with regard to the RPCvd and RNFL values in any region (p > 0.05 for all).

CONCLUSION

Lower RPCvds could provoke capillary deficiency and deterioration of the perfusion of the optic nerve head in patients with PES.

Peripapillary Vessel Density In Unilateral Preperimetric Glaucoma

Purpose

To investigate vessel density (VD) of radial peripapillary capillaries (RPC) and structural alterations in patients with unilateral preperimetric glaucoma (PPG) using optical coherence tomography angiography (OCTA).

Methods

This cross-sectional observational study included 13 untreated patients with unilateral PPG. PPG eyes had larger excavation and abnormal thinning of retinal nerve fiber layer (RNFL) and/or ganglion cell complex (GCC) compared with fellow eyes (F). Both RNFL and GCC thickness in F were statistically within normal limits and/or borderline. The RPC VD on optic disc (idVD), of peripapillary (ppVD) and whole image (wiVD) scan area was measured. Twenty healthy eyes (H) served as controls. Structural and vascular parameters obtained by spectral-domain OCT/OCTA (Optovue; Fremont, CA) were compared between PPG, F and H.

Results

Mean RNFL and GCC average thickness in microns differed significantly (p<0.001) between PPG (82.4±7.1, 81.4±5.9), F (91.0±7.1, 88.5±3.8) and H (103.5±6.0, 99.3±5.7). PPG compared with F showed significantly (p<0.001) lower mean ppVD (43.8%±3.0% versus 47.8%±3.2%) and wiVD (45.9%±3.5% versus 50.1%±3.9%). Mean ppVD (49.7%±2.4%) and wiVD (52.6%±3.0%) in H were not significantly higher than in F. Mean idVD showed no significant differences among the 3 groups. Areas under the receiver operating characteristic curves (AUROCs) for RNFL, GCC, ppVD and wiVD between PPG and H were excellent (>0.9). AUROCs between F and H demonstrated an excellent diagnostic ability for structural parameters and a poor one (<0.7) for vascular parameters.

Conclusion

Affected eyes of patients with unilateral PPG demonstrated significant RPC dropout. Clinically unaffected eyes showed thinner structural parameters but no significant microvasculature differences compared with non-glaucomatous eyes. Diagnostic ability of peripapillary vascular parameters was not superior to structural measurements. Microvascular dysfunction seems to be an early but not a primary event in glaucoma continuum at the stage of undetectable visual field loss. OCTA can be useful in early glaucoma diagnosis.

Macular Vessel Density and Ganglion Cell/Inner Plexiform Layer Thickness and Their Combinational Index Using Artificial Intelligence

PURPOSE

To evaluate the relationship between macular vessel density and ganglion cell to inner plexiform layer thickness (GCIPLT) and to compare their diagnostic performance. We attempted to develop a new combined parameter using an artificial neural network.

METHODS

A total of 173 subjects: 100 for the test and 73 for neural net training. The test group consisted of 32 healthy, 33 early, and 35 advanced glaucoma subjects. Macular GCIPLT and vessel density were measured using Spectralis optical coherence tomography and Topcon swept-source optical coherence tomography, respectively. Various regression models were used to investigate the relationships between macular vessel density and GCIPLT. A multilayer neural network with one hidden layer was used to determine a single combined parameter. To compare diagnostic performance, we used the area under the receiver operating characteristic curve (AUROC).

RESULTS

Correlation analyses in all subjects showed a significant correlation between macular vessel density and GCIPLT in all sectors (r=0.27 to 0.56; all Ps≤0.006). The fitness of linear, quadratic, and exponential regression models showed clinically negligible differences (Akaike's information criterion=714.6, 713.8, and 713.3, respectively) and were almost linear. In differentiating normal and early glaucoma, the diagnostic power of macular GCIPLT (AUROC=0.67 to 0.81) was much better than that of macular vessel density (AUROC=0.50 to 0.60). However, when vessel density information was incorporated into GCIPLT using the neural network, the combined parameter (AUROC=0.87) showed significantly enhanced diagnostic performance than all sectors of macular vessel density and GCIPLT (all Ps≤0.043).

CONCLUSIONS

Macular vessel density was significantly decreased in glaucoma patients and showed an almost linear correlation with macular GCIPLT. The diagnostic performance of macular vessel density was much lower than that of macular GCIPLT. However, when incorporated into macular GCIPLT using an artificial neural network, the combined parameter showed better performance than macular GCIPLT alone.

Evaluation of radial peripapillary capillary density in patients with Fuchs uveitis syndrome

PURPOSE

To quantitatively analyze the microcirculation in the peripapillary sectors in the affected eyes and fellow unaffected eyes of individuals with unilateral Fuchs uveitis syndrome (FUS) using optical coherence tomography angiography (OCTA), and to compare the radial peripapillary capillary vessel density (RPCvd) with normal and age-matched individuals.

METHODS

Eyes were divided into three groups based on the involvement of the FUS: FUS-positive eye of patients (study eye), fellow eye of FUS-positive patients (fellow eye), and the control eye for the control group (control eye). RPCvd (%) and peripapillary retinal nerve fiber layer (RNFL) thickness (μm) at eight equal sectors and two equal hemispheres were automatically calculated in peripapillary region via OCTA.

RESULTS

This study included 105 eyes of 71 patients: 34 FUS-positive eyes of 34 patients, 34 fellow eyes of FUS-positive patients, and 37 control eyes of 37 patients. RPCvd was significantly lower in study eyes than in fellow and control eyes in the peripapillary region (p = 0.044 and p = 0.005, respectively). There was no significant difference between fellow eyes and control eyes regarding RPCvd in any region (p > 0.05 for all). There were no significant differences between the three groups regarding peripapillary RNFL values (p > 0.05 for all).

CONCLUSION

OCTA is a novel technology for imaging of the RPC network in patients with FUS. Lower radial peripapillary capillary vessel density in FUS could induce capillary insufficiency and impairment of ocular blood flow to optic nerve head.

Comparison of vascular parameters between normal cynomolgus macaques and healthy humans by optical coherence tomography angiography

BACKGROUND

The metabolic activity of retina is higher than other human tissues and is crucial to the vision. Cynomolgus macaques is widely used in ophthalmic disease research. The evaluation and comparison of macular and optic disc vascular circulation parameters between normal adult cynomolgus macaques and healthy adult humans using OCT-A can promote better use of nonhuman primate models in studies of ophthalmic vascular disease.

METHODS

Twelve normal adult cynomolgus macaques with a mean age of 4.91 ± 0.43 years were studied for data collection. The macula of 28 adult healthy humans (14 males and 14 females), with a mean age of 25.11 ± 6.21 years and the optic discs of 9 adult healthy humans (4 males and 5 females) with a mean age of 28.56 ± 6.78 years were measured. The vessel density (VD) was measured using an RTVue XR with AngioVue. The scan sizes of the macular and optic discs were 3 × 3 mm and 4.5 × 4.5 mm, respectively.

RESULTS

OCT-A can image the superficial and deep capillary plexuses and radial peripapillary capillary network. In RPC layer of the optic disc, the VD in the nasal quadrant was lower than the VD in the inferior temporal quadrant. Similarities and significant differences in VD between healthy humans and cynomolgus macaques were obtained using OCT-A.

CONCLUSIONS

This study provides normal vascular parameters for adult cynomolgus macaques using OCT-A to help establish an optical parameter database for cynomolgus macaques and compare VD between healthy humans and cynomolgus macaques to promote choroid-retinopathy research.

TRIAL REGISTRATION

Current Controlled Trials NCT03692169 , retrospectively registered on 26 sept 2018.

Is "normal tension glaucoma" glaucoma?

Primary open angle glaucoma (POAG) represents a distinct disease entity with elevated intraocular pressure (IOP) as the main risk factor, even though the reasons for why the IOP is elevated remains to be elucidated. It is considered that normal tension glaucoma (NTG) is a subtype of POAG, comprising a special form of glaucomatous neurodegeneration or glaucomatous optic neuropathy (GON) almost exactly the same as that seen in POAG, but the IOP, as named, remains in the statistically normal range. Actually the disease entity of NTG has been a profound confusion and it is difficult to be accurately conceptualized. One of the reasons is that the IOP is closely linked to the occurrence of GON in POAG but not in NTG, and for the latter, it seems that GON is secondary to a number of local or systemic disorders. In recent years, increasing evidences suggest that NTG or IOP independent GON is a non-glaucomatous disease with different disease entities from POAG and with more diverse and complex etiologies. Here we hypothesized that NTG, at least for those with recognizable primary diseases, is not a glaucomatous disease; instead, it represents a group of disorders with GON as a characteristic clinical feature or phenotype.

Changes in vessel density of the patients with narrow antenior chamber after an acute intraocular pressure elevation observed by OCT angiography

Background

Although the pathogenesis of glaucoma is not fully understood,an elevated intraocular pressure (IOP) is a major factor contributing to its development and progression. The aim of this study was to investigate the changes in the vessel densities of the macula and optic nerve head (ONH) after an acute elevation in the intraocular pressure (IOP) observed using optical coherence tomography angiography (OCTA).

Methods

This was a prospective comparative study of subjects with narrow anterior chamber angles who underwent laser peripheral iridotomies (LPIs). The IOP was measured before and one hour after the LPI. The retinal vessel densities of the macula and ONH were measured using OCTA at the baseline and one hour after the LPI.

Results

A total of 64 eyes of 51 individuals were enrolled in this study, and 58 eyes of 43 individuals finally completed the study with a mean IOP rise of 10.5 ± 7.6 mmHg after the LPI. Based on the magnitude of the rise in the IOP, we divided the subjects into three groups: group A = IOP rise ≤10 mmHg, group B = 10 mmHg < IOP rise ≤20 mmHg, and group C = IOP rise > 20 mmHg. The vessel density did not differ after the acute IOP elevation in either the macular region or papillary region in group A or group B (p > 0.05), but there was a significant difference in group C (p < 0.05). However, when the subjects were not separated into groups, the vessel densities of the ONH and macular region did not differ between the measurements obtained at the baseline and one hour after the LPI (p > 0.05). The correlation existed in peripapillary and macular vessel density (p < 0.05).

Conclusion

In these subjects with narrow antenior chamber, an acute mild or moderate IOP elevation for one hour after the LPI did not affect the vessel density in the macula or ONH, as examined using OCTA. However, when the IOP rise was greater than 20 mmHg, the macular and papillary vessel density decreased significantly.

Segmentation of the Four-Layered Retinal Vasculature Using High-Resolution Optical Coherence Tomography Angiography Reveals the Microcirculation Unit

Purpose

To differentiate the four layers of the retinal vessel network in the human macula and examine their morphologic features using high-resolution optical coherence tomography angiography (HR-OCTA).

Methods

Macular areas measuring 464 × 464 pixels of 10 right eyes of 10 healthy subjects without ocular disease were scanned 10 times using a HR-OCTA device. Averaged OCTA images were created. Based on clear decorrelation signals, four vascular slabs were segmented, comprising one each in the retinal nerve fiber layer (RNFL), ganglion cell layer (GCL), and top and bottom of the inner nuclear layer (INL). Qualitative features and quantitative measurements in each slab were compared with those in conventionally segmented slabs.

Results

HR-OCTA isolated four layers of vascular plexuses in the macula that followed the corresponding anatomic layers. Segmentations for the RNFL revealed that radial peripapillary capillaries (RPCs) extended to the central macular area. The RPCs followed relatively straight and long paths, with few apparent feed points and anastomoses. The GCL slab enhanced visualization of the capillary-free zones around the arteries and arterioles and helped to differentiate arterial and venous systems. The arterioles and venules were linked by capillaries that were arranged in a mesh-like fashion, with multiple arteriolar feed points and anastomoses. Vascular plexuses in the top and bottom of the INL consisted of capillaries in a vortex arrangement. The center of these vortex arrangements was consistent with the venules in the GCL.

Conclusions

HR-OCTA can differentiate the four layers of vascular plexuses in the human macula and elucidate their angiographic features.

Optical coherence tomography angiography measured capillary density in the normal and glaucoma eyes

Purpose

To compare the diagnostic ability of optical coherence tomography angiography (OCT-A) derived radial peripapillary capillary (RPC) measured capillary density (CD) and inside the optic nerve head (ONH) CD measurements to differentiate between the normal and primary open angle glaucoma (POAG) eyes.

Methods

AngioVue disc OCT-A images were obtained and assessed in 83 eyes of POAG patients and 74 age matched healthy eyes. RPC CD was quantitatively measured in the peripapillary area within 3.45 mm circle diameter around the ONH and inside the ONH in 8 equally divided sectors, using Bar – Selective Combination of Shifted Filter Responses method after the suppressing large vessels. Area under receiver operating characteristic (AUROC) curve was used to assess the diagnostic accuracy of the two scanning regions of CD to differentiate between the normal and POAG eyes.

Results

The mean peripapillary RPC density (0.12 ± 0.03) and mean ONH CD (0.09 ± 0.03) were significantly lower in POAG eyes when compared to the normal eyes (RPC CD: 0.17 ± 0.05, p < 0.0001 and ONH CD 0.11 ± 0.02, p = 0.01 respectively). The POAG patients showed 29% reduction in the RPC CD and 19% reduction in the ONH CD when compared to the normal eyes. The AUROC for discriminating between healthy and glaucomatous eyes was 0.784 for mean RPC CD and 0.743 for the mean ONH CD.

Conclusions

Diagnostic ability of OCT-A derived peripapillary CD and ONH CD was moderate for differentiating between the normal and glaucomatous eyes. Diagnostic ability of even the best peripapillary average and inferotemporal sector for RPC CD and average and superonasal sector for the ONH CD was moderate.

Microstructure of Parapapillary Atrophy Is Associated With Parapapillary Microvasculature in Myopic Eyes

PURPOSE

To evaluate the clinical characteristics of beta-parapapillary atrophy (β-PPA) in myopic eyes and determine whether the microstructure of β-PPA is associated with parapapillary microvasculature by using optical coherence tomography (OCT) angiography.

DESIGN

Cross-sectional study.

METHODS

This study included 80 subjects with myopia with β-PPA. Spherical equivalent (SE) refractive error, axial length, horizontal tilt angle, and the width of β-PPA were evaluated. The microstructure of β-PPA and subfoveal choroidal thickness were evaluated using enhanced-depth imaging OCT and eyes were classified into 3 groups based on the presence of Bruch membrane (BM): a PPA_+BM-only group, a PPA_+BM and PPA_-BM group, and a PPA_-BM-only group. Superficial and deep parapapillary vessel density was measured using OCT angiography. Clinical characteristics were compared among the groups and linear regression analysis was performed to explore the relationship between the parapapillary microvasculature and microstructure of β-PPA.

RESULTS

The mean axial length and SE refractive error of the participants were 26.47 ± 1.17 mm and -6.28 ± 2.71 diopters, respectively. The PPA_+BM-only group had a more inferiorly rotated optic disc (P = .025), larger β-PPA (P < .001), and lower superficial and deep parapapillary vessel density (both P < .001) compared with those of the PPA_-BM-only group. Multivariate linear regression analysis showed that the average PPA_+BM width on horizontal scans was significantly associated with superficial and deep parapapillary vessel density (P = .034 and P = .003, respectively).

CONCLUSIONS

Significant differences were observed in the microvasculature according to the microstructure of β-PPA. PPA_+BM width was closely correlated with superficial and deep parapapillary vessel density. Longitudinal studies are needed to elucidate the role of β-PPA in the development and progression of glaucoma in myopic eyes.

A method for age-matched OCT angiography deviation mapping in the assessment of disease- related changes to the radial peripapillary capillaries

PURPOSE

To present a method for age-matched deviation mapping in the assessment of disease-related changes to the radial peripapillary capillaries (RPCs).

METHODS

We reviewed 4.5x4.5mm en face peripapillary OCT-A scans of 133 healthy control eyes (133 subjects, mean 41.5 yrs, range 11-82 yrs) and 4 eyes with distinct retinal pathologies, obtained using spectral-domain optical coherence tomography angiography. Statistical analysis was performed to evaluate the impact of age on RPC perfusion densities. RPC density group mean and standard deviation maps were generated for each decade of life. Deviation maps were created for the diseased eyes based on these maps. Large peripapillary vessel (LPV; noncapillary vessel) perfusion density was also studied for impact of age.

RESULTS

Average healthy RPC density was 42.5±1.47%. ANOVA and pairwise Tukey-Kramer tests showed that RPC density in the ≥60yr group was significantly lower compared to RPC density in all younger decades of life (p<0.01). Average healthy LPV density was 21.5±3.07%. Linear regression models indicated that LPV density decreased with age, however ANOVA and pairwise Tukey-Kramer tests did not reach statistical significance. Deviation mapping enabled us to quantitatively and visually elucidate the significance of RPC density changes in disease.

CONCLUSIONS

It is important to consider changes that occur with aging when analyzing RPC and LPV density changes in disease. RPC density, coupled with age-matched deviation mapping techniques, represents a potentially clinically useful method in detecting changes to peripapillary perfusion in disease.

Optical Coherence Tomography Angiography in Glaucoma Care

PURPOSE

To provide the reader with information on the principal techniques of optical coherence tomography angiography (OCTA); the current literature on OCTA reproducibility; its applications to glaucoma detection and monitoring of progression; and the role of OCTA in the assessment of the vascular component in glaucoma pathogenesis.

METHODS

A literature review of the pertinent publications for the OCTA in relation to the development, techniques, and its use in glaucoma was carried out.

RESULTS

Rapid improvements in optical coherence tomography (OCT) technology have allowed for enhancement of both image resolution and scanning speed, and the development of vascular assessment modality. OCTA is the non-invasive in vivo imaging of the vasculature located within the retina and optic nerve head area. The principle of OCTA is to use the variations in OCT signals caused by moving particles as the contrast mechanism for imaging of flow. Several algorithms which aim to maximize the contrast signal and minimize the noise have been developed including the phase-based techniques, intensity-based techniques (e.g., split-spectrum amplitude decorrelation angiography (SSADA)), and complex-based techniques (e.g., optical microangiography (OMAG)). With its reliable technique, high image resolution, and current availability, OCTA has been widely used in the assessment of posterior segment diseases including glaucoma in which ocular perfusion dysfunction has been proposed as a pathophysiological mechanism.

CONCLUSION

OCTA may enhance our knowledge of glaucoma pathogenesis and offer an improvement in our ability to detect glaucomatous change.

Effect of Surgical Intraocular Pressure Lowering on Peripapillary and Macular Vessel Density in Glaucoma Patients: An Optical Coherence Tomography Angiography Study

PURPOSE

To measure the influence of surgically induced intraocular pressure lowering on peripapillary and macular vessel density in glaucoma patients using optical coherence tomography angiography.

METHODS

Twenty-one eyes of 21 patients with open-angle glaucoma scheduled for filtering surgery were enrolled prospectively. Using optical coherence tomography angiography, vessel density was quantified within the peripapillary and macular regions, before and 1 month after filtering surgery. Change in vessel density was calculated for all analyzed areas.

RESULTS

One month after surgery, the mean intraocular pressure reduction was 44.2%±4.8% (range, 15.2% to 77.1%). The mean change in vessel density for the whole peripapillary area was 0.065±0.88% (P=0.788). In the macular region, the mean change in vessel density was -0.022%±0.691% (P=0.405) with significant changes only within the inferotemporal area of patients with predominantly superior visual field defects (-1.86%±1.43%, P=0.024).

CONCLUSIONS

Optical coherence tomography angiography allowed very limited measurement of intraocular pressure lowering-induced changes on the vessel density of the peripapillary and macular regions in glaucoma patients.

Wide-Field OCT Angiography Investigation of the Relationship Between Radial Peripapillary Capillary Plexus Density and Nerve Fiber Layer Thickness

Purpose

To characterize the density and distribution of the radial peripapillary capillary plexus (RPCP) and its relationship with retinal nerve fiber layer (NFL) thickness in healthy subjects.

Methods

Using spectral-domain optical coherence tomography (OCT), split-spectrum amplitude decorrelation angiography algorithm and automated montaging, wide-field OCT angiography (OCTA) was used to measure the RPCP capillary density (CD) and NFL thickness. Polar sector-average CD and thickness maps were also created on each eye.

Results

Wide-field OCTA (8 × 8 mm) in 10 healthy eyes from 10 subjects demonstrated the distribution of the RPCP throughout the posterior pole. RPCP-CD decreases with distance from the disc, but along the arcuate nerve fiber bundles relatively dense (> half maximum density) RPCP extends more than 5 mm from the disc and includes regions superior to and inferior to the macula. The RPCP-CD and NFL thickness are highly correlated (R² = 0.85, P < 0.001) and fit well with a nonlinear stacked-layer model. The model fit suggests that the RPCP is present when the NFL is thicker than 17.9 μm and reaches a ceiling area density of 84% and that the RPCP has an apparent volume density of 19% at the current instrument transverse resolution. This indicates that capillary overlap can be expected to occur when NFL thickness reaches 40 μm.

Conclusions

The wide distribution of dense overlapping RPCP suggests that wider (up to 8 mm vertical and 7 mm horizontal) OCTA scans may be better investigate capillary loss in the early stages of glaucoma or other optic neuropathies.

Optical coherence tomography angiography: A comprehensive review of current methods and clinical applications

OCT has revolutionized the practice of ophthalmology over the past 10-20 years. Advances in OCT technology have allowed for the creation of novel OCT-based methods. OCT-Angiography (OCTA) is one such method that has rapidly gained clinical acceptance since it was approved by the FDA in late 2016. OCTA images are based on the variable backscattering of light from the vascular and neurosensory tissue in the retina. Since the intensity and phase of backscattered light from retinal tissue varies based on the intrinsic movement of the tissue (e.g. red blood cells are moving, but neurosensory tissue is static), OCTA images are essentially motion-contrast images. This motion-contrast imaging provides reliable, high resolution, and non-invasive images of the retinal vasculature in an efficient manner. In many cases, these images are approaching histology level resolution. This unprecedented resolution coupled with the simple, fast and non-invasive imaging platform have allowed a host of basic and clinical research applications. OCTA demonstrates many important clinical findings including areas of macular telangiectasia, impaired perfusion, microaneurysms, capillary remodeling, some types of intraretinal fluid, and neovascularization among many others. More importantly, OCTA provides depth-resolved information that has never before been available. Correspondingly, OCTA has been used to evaluate a spectrum of retinal vascular diseases including diabetic retinopathy (DR), retinal venous occlusion (RVO), uveitis, retinal arterial occlusion, and age-related macular degeneration among others. In this review, we will discuss the methods used to create OCTA images, the practical applications of OCTA in light of invasive dye-imaging studies (e.g. fluorescein angiography) and review clinical studies demonstrating the utility of OCTA for research and clinical practice.

Retinal vasculature in glaucoma: a review

Despite the critical impact of glaucoma on global blindness, its aetiology is not fully characterised. Elevated intraocular pressure is highly associated with glaucomatous optic neuropathy. However, visual field loss still progresses in some patients with normal or even low intraocular pressure. Vascular factors have been suggested to play a role in glaucoma development, based on numerous studies showing associations of glaucoma with blood pressure, ocular perfusion pressure, vasospasm, cardiovascular disease and ocular blood flow. As the retinal vasculature is the only part of the human circulation that readily allows non-invasive visualisation of the microcirculation, a number of quantitative retinal vascular parameters measured from retinal photographs using computer software (eg, calibre, fractal dimension, tortuosity and branching angle) are currently being explored for any association with glaucoma and its progression. Several population-based and clinical studies have reported that changes in retinal vasculature (eg, retinal arteriolar narrowing and decreased fractal dimension) are associated with optic nerve damage and glaucoma, supporting the vascular theory of glaucoma pathogenesis. This review summarises recent findings on the relationships between quantitatively measured structural retinal vascular changes with glaucoma and other markers of optic nerve head damage, including retinal nerve fibre layer thickness. Clinical implications, recent new advances in retinal vascular imaging (eg, optical coherence tomography angiography) and future research directions are also discussed.

Optical Coherence Tomography Angiography Vessel Density in Healthy, Glaucoma Suspect, and Glaucoma Eyes

Purpose

The purpose of this study was to compare retinal nerve fiber layer (RNFL) thickness and optical coherence tomography angiography (OCT-A) retinal vasculature measurements in healthy, glaucoma suspect, and glaucoma patients.

Methods

Two hundred sixty-one eyes of 164 healthy, glaucoma suspect, and open-angle glaucoma (OAG) participants from the Diagnostic Innovations in Glaucoma Study with good quality OCT-A images were included. Retinal vasculature information was summarized as a vessel density map and as vessel density (%), which is the proportion of flowing vessel area over the total area evaluated. Two vessel density measurements extracted from the RNFL were analyzed: (1) circumpapillary vessel density (cpVD) measured in a 750-μm-wide elliptical annulus around the disc and (2) whole image vessel density (wiVD) measured over the entire image. Areas under the receiver operating characteristic curves (AUROC) were used to evaluate diagnostic accuracy.

Results

Age-adjusted mean vessel density was significantly lower in OAG eyes compared with glaucoma suspects and healthy eyes. (cpVD: 55.1 ± 7%, 60.3 ± 5%, and 64.2 ± 3%, respectively; P < 0.001; and wiVD: 46.2 ± 6%, 51.3 ± 5%, and 56.6 ± 3%, respectively; P < 0.001). For differentiating between glaucoma and healthy eyes, the age-adjusted AUROC was highest for wiVD (0.94), followed by RNFL thickness (0.92) and cpVD (0.83). The AUROCs for differentiating between healthy and glaucoma suspect eyes were highest for wiVD (0.70), followed by cpVD (0.65) and RNFL thickness (0.65).

Conclusions

Optical coherence tomography angiography vessel density had similar diagnostic accuracy to RNFL thickness measurements for differentiating between healthy and glaucoma eyes. These results suggest that OCT-A measurements reflect damage to tissues relevant to the pathophysiology of OAG.

Relationship Between Retinal Perfusion and Retinal Thickness in Healthy Subjects: An Optical Coherence Tomography Angiography Study

Purpose

To investigate the relationship between retinal perfusion and retinal thickness in the peripapillary and macular areas of healthy subjects.

Methods

Using spectral-domain optic coherence tomography and split-spectrum amplitude decorrelation angiography (SSADA) algorithm, retinal perfusion and retinal thicknesses in the macular and peripapillary areas were measured in healthy volunteers, and correlations among these variables were analyzed.

Results

Overall, 64 subjects (121 eyes) including 28 males and 36 females with a mean ± SD age of 38 ± 13 years participated. Linear mixed-models showed that vessel area density was significantly correlated with the inner retinal thickness (from the inner limiting membrane to the outer border of the inner nucleus layer; P < 0.05), but not with the thickness of the full retina (P > 0.05) in the parafoveal area. The area of the foveal capillary-free zone was negatively correlated with the inner and full foveal thicknesses (all P < 0.001). In the peripapillary area, the vessel area density was positively correlated with the thickness of the retinal nerve fiber layer (P < 0.001).

Conclusions

In healthy subjects, retinal perfusion in small vessels was closely correlated with the thickness of the inner retinal layers in both the macular and peripapillary areas.