Quantification and Repeatability of Vessel Density and Flux as Assessed by Optical Coherence Tomography Angiography

Retinal Microvascular Changes in Association with Endothelial Glycocalyx Damage and Arterial Stiffness in Patients with Diabetes Mellitus Type 2: A Cross-Sectional Study in a Greek Population

PURPOSE

To evaluate the potential association between endothelial glycocalyx damage, as well as arterial stiffness, and the retinal changes on optical coherence tomography (OCT) and OCT-angiography (OCT-A) in patients with type 2 diabetes mellitus (DM).

METHODS

Participants in this cross-sectional study were 65 patients with DM type 2 and 42 age- and gender-matched controls without DM. The demographic and clinical characteristics of the participants were recorded. All patients underwent a thorough ophthalmological examination and multimodal imaging, including fundus photography, OCT, and OCT-A. In addition, evaluation of the endothelial glycocalyx thickness by measuring the perfused boundary region (PBR5-25) of the sublingual microvessel, as well as of the arterial stiffness, by measuring the carotid-femoral pulse wave velocity (PWV), the central aortic pressures and the augmentation index (Aix) was performed. Univariate and multivariate logistic regression analysis was performed for the examination of the potential association between the eye imaging variables and the cardiovascular-related variables. The odds ratios (OR) with the respective 95% confidence intervals (CI) were calculated. A p-value < 0.05 was considered statistically significant.

RESULTS

Patients with DM presented significantly higher PBR5-25 compared to controls without DM (p = 0.023). At the univariate analysis, increased PBR5-25 (≥2.19 μm vs. <2.19 μm) was associated with decreased peripapillary VD at the superior quadrant (univariate OR (95% CI) = 0.34 (0.12-0.93), p = 0.037). Multivariate logistic regression analysis showed that increased PWV (≥13.7 m/s vs. <13.7 m/s) was associated with an increased foveal avascular zone (FAZ) area on OCT-A (p = 0.044) and increased FAZ perimeter (p = 0.048). Moreover, increased Aix (≥14.745% vs. <14.745%) was associated with diabetic macular edema (DME) presence (p = 0.050) and increased perifoveal and parafoveal superior and temporal thickness on OCT (p < 0.05 for all associations).

CONCLUSIONS

Markers of endothelial damage and arterial stiffness were associated with structural and microvascular retinal alterations in patients with DM, pointing out that OCT-A could be a useful biomarker for detecting potential cardiovascular risk in such patients.

The central retina vessel density and foveal avascular zone values of 792 healthy adults using optical coherence tomography angiography

BACKGROUND/OBJECTIVES

To determine normal macular vessel density (VD) and foveal avascular zone (FAZ) values using optical coherence tomography angiography (OCTA) analysis in healthy adults.

SUBJECTS/METHODS

As part of the Prospective Epidemiological Research Studies in Iran (PERSIAN) Organizational Cohort study at Mashhad University of Medical Sciences (POCM), we conducted a cross-sectional study using 3 × 3 and 6 × 6 mm OCTA scans to evaluate the VD of the macular superficial capillary plexus (SCP), deep capillary plexus (DCP), and the FAZ area in healthy adults.

RESULTS

The study included 792 participants, with a mean age of 39.8 ± 6.8 years. There were 359 males with a mean age of 39.9 ± 7.8 years and 440 females with a mean age of 39.4 ± 6 years. The mean values of various parameters were measured, including the right eye whole image SCP and DCP VDs, FAZ area, FAZ perimeter, and fovea VD in a 300 µm wide zone around FAZ (FD). These values were found to be 45.9 ± 2.6%, 50.2 ± 3%, 0.3 ± 0.1mm2, 2.1 ± 0.4 mm, and 50.4 ± 3.3%, respectively. Females and younger participants had significantly higher mean values of whole image SCP and DCP VDs. Additionally, all FAZ parameters had significantly higher values in females, while younger participants had significantly higher mean FD values. Simple linear regression analyses showed that age was negatively correlated with right eye SCP and DCP VDs.

CONCLUSION

Our study established standard SCP and DCP VD values influenced by age and gender. Age correlates negatively with both, DCP VDs correlate negatively with height and weight, and SCP VDs correlate positively with diastolic blood pressure.

CHANGES IN OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY MEASURES THROUGHOUT THE DAY: Diurnal Variation or Test-Retest Variability?

PURPOSE

To evaluate the repeatability and diurnal variation of the retinal vessel density and foveal avascular zone parameters using optical coherence tomography angiography.

METHODS

Forty-one healthy individuals were measured twice in the morning and once in the evening. Foveal avascular zone area, perimetry, foveal density; superficial and deep capillary plexus (superficial capillary plexus, deep capillary plexus) vessel density, and central macular thickness were evaluated with the intraclass correlation coefficient, coefficient of repeatability, and Bland-Altman plots.

RESULTS

Repeatability was evaluated with two consecutive scans taken in the morning. The coefficient of repeatabilities (%) was 5.4; 4.3, and 8.8 for the foveal avascular zone area, perimetry, and foveal density, respectively, with excellent intraclass correlation coefficients. Intraclass correlation coefficient was poor for parafovea (0.33), whereas excellent for fovea (0.97) in superficial capillary plexus-vessel density. Coefficient of repeatability for fovea and parafovea was 19.19% and 10.43%, respectively. Intraclass correlation coefficient values were poor (0.3-0.4) with 10% to 16% measurement differences in deep capillary plexus-vessel density parameters. Coefficient of repeatabilities for central macular thickness was between 1% and 2% with excellent intraclass correlation coefficient. The analysis on diurnal variation yielded comparable results.

CONCLUSION

Except for the parafoveal vessel density, optical coherence tomography angiography is a highly reproducible device for measuring foveal avascular zone and vessel density using 6 × 6 scans with undilated pupils. However, variation in optical coherence tomography angiography parameters observed throughout the day could be attributed to test-retest variation rather than diurnal rhythm.

Microvascular Changes after Epiretinal Membrane Vitrectomy with Intraoperative Intravitreal Dexamethasone Implant: An OCT Angiography Analysis

BACKGROUND

We aimed to explore microvascular changes evaluated with optical coherence tomography angiography (OCTA) in patients undergoing epiretinal membrane (ERM) pars-plana vitrectomy (PPV) combined with intravitreal Ozurdex implantation, compared with standard PPV. (2) Methods: Prospective interventional analysis on 25 eyes undergoing PPV + Ozurdex (Group A) and 25 eyes undergoing PPV alone. Best corrected visual acuity (BCVA) and OCTA parameters, such as vessel density (VD) of the superficial and deep capillary plexi (SCP and DCP) in the whole 6.4 mm × 6.4 mm and fovea area, were evaluated preoperatively and 3 months after surgery. (3) Results: Postoperative BCVA significantly improved in both groups. No cases of post-operative cystoid macular edema (CME) were reported in Group A vs. two eyes in Group B. In Group A we found a statistically significant increase of SCP's VD in either the whole image (from 42.1 ± 4.1 to 45.6 ± 4.3%, p = 0.01) and the fovea image (from 38.5 ± 7.5 to 41.7 ± 4.2%, p = 0.03). In Group B, we reported no significant variations in the SCP's VDs. In the DCP, VD significantly increased only in the whole image in Group A. Stage 4 ERMs showed the greatest improvement in VD, especially in Group A. (4) Conclusions: Intraoperative Ozurdex prompted a significant BCVA recovery and limited the occurrence of postoperative CME compared to the standard procedure. Moreover, Ozurdex implant is associated with a better restoration of microvascular structure in SCP and DCP.

Reduced Thickness of the Retina in de novo Parkinson's Disease Shows A Distinct Pattern, Different from Glaucoma

Background

Parkinson's disease (PD) patients experience visual symptoms and retinal degeneration. Studies using optical coherence tomography (OCT) have shown reduced thickness of the retina in PD, also a key characteristic of glaucoma.

Objective

To identify the presence and pattern of retinal changes in de novo, treatment-naive PD patients compared to healthy controls (HC) and early primary open angle glaucoma (POAG) patients.

Methods

Macular OCT data (10×10 mm) were collected from HC, PD, and early POAG patients, at the University Medical Center Groningen. Bayesian informative hypotheses statistical analyses were carried out comparing HC, PD-, and POAG patients, within each retinal cell layer.

Results

In total 100 HC, 121 PD, and 78 POAG patients were included. We showed significant reduced thickness of the inner plexiform layer and retinal pigment epithelium in PD compared to HC. POAG patients presented with a significantly thinner retinal nerve fiber layer, ganglion cell layer, inner plexiform layer, outer plexiform layer, and outer photoreceptor and subretinal virtual space compared to PD. Only the outer segment layer and retinal pigment epithelium were significantly thinner in PD compared to POAG.

Conclusions

De novo PD patients show reduced thickness of the retina compared to HC, especially of the inner plexiform layer, which differs significantly from POAG, showing a more extensive and widespread pattern of reduced thickness across layers. OCT is a useful tool to detect retinal changes in de novo PD, but its specificity versus other neurodegenerative disorders has to be established.

Optical coherence tomography angiography in Parkinson's disease: a systematic review and meta-analysis

BACKGROUND

To examine the association between optical coherence tomography angiography (OCTA) retinal measurements and Parkinson's disease (PD).

METHODS

We searched MEDLINE and EMBASE from inception up to November 5th, 2021 for studies examining the differences between OCTA retinal measurements in PD patients and healthy controls. We used the Hartung-Knapp-Sidik-Jonkman random-effects method to combine study-specific standardized mean differences (SMD) in pooled effect estimates and a meta-analytic extension of the E-value metric to quantify the confounding bias capable of nullifying the pooled estimates.

RESULTS

Nine eligible studies for our systematic review were identified through our search strategy. The pooled SMD between the retinal vessel density of PD patients and healthy participants in the whole superficial vascular plexus (SVP), foveal SVP, parafoveal SVP and foveal avascular zone (FAZ) was -0.68 (95% CI: -1.18 to -0.17, p value = 0.02, n = 7 studies), -0.14 (95% CI: -0.88 to 0.59, p value = 0.62, n = 5 studies), -0.59 (95% CI: -1.41 to 0.23, p value = 0.12, n = 5 studies) and -0.20 (95% CI: -0.79 to 0.38, p value = 0.39, n = 5 studies), respectively. An unmeasured confounder would need to be associated with a 3.01-fold, 1.54-fold, 2.81-fold and 1.70-fold increase in the risk of PD and OCTA retinal measurements, in order for the pooled SMD estimate of vessel density in whole SVP, parafoveal SVP and FAZ, respectively, to be nullified.

CONCLUSIONS

Our results provide evidence on an inverse association between whole SVP vessel density and PD.

Retinal Vessel Caliber Measurement Bias in Fundus Images in the Presence of the Central Light Reflex

Purpose

To investigate the agreement between a fundus camera and a scanning laser ophthalmoscope in retinal vessel caliber measurements and to identify whether the presence of the central light reflex (CLR) explains potential discrepancies.

Methods

For this cross-sectional study, we obtained fundus camera and scanning laser ophthalmoscope images from 85 eyes of 85 healthy individuals (aged 50-65 years) with different blood pressure status. We measured the central retinal artery equivalent (CRAE) and central retinal artery vein equivalent (CRVE) with the Knudtson-Parr-Hubbard algorithm and assessed the CLR using a semiautomatic grading method. We used Bland-Altman plots, 95% limits of agreement, and the two-way mixed effects intraclass correlation coefficient for consistency [ICC(3,1)] to describe interdevice agreement. We used multivariable regression to identify factors associated with differences in between-device measurements.

Results

The between-device difference in CRAE (9.5  µm; 95% confidence interval, 8.0-11.1  µm) was larger than the between-device difference in CRVE (2.9  µm; 95% confidence interval, 1.3-4.5  µm), with the fundus camera yielding higher measurements (both P < 0.001). The 95% fundus camera-scanning laser ophthalmoscope limits of agreement were -4.8 to 23.9  µm for CRAE and -12.0 to 17.8  µm for CRVE. The corresponding ICCs(3,1) were 0.89 (95% confidence interval, 0.83-0.92) and 0.91 (95% confidence interval, 0.86-0.94). The between-device CRAE difference was positively associated with the presence of a CLR (P = 0.002).

Conclusions

Fundus cameras and scanning laser ophthalmoscopes yield correlated but not interchangeable caliber measurements. The CLR induces bias in arteriolar caliber in fundus camera images, compared with scanning laser ophthalmoscope images.

Translational Relevance

Refined measurements could yield better estimates of the association between retinal vessel caliber and ophthalmic or systemic disease.

Discriminating Between Compressive Optic Neuropathy With Glaucoma-Like Cupping and Glaucomatous Optic Neuropathy Using OCT and OCTA

Purpose

To discriminate between compressive optic neuropathy with glaucoma-like cupping (GL-CON) and glaucomatous optic neuropathy (GON) by comparing the peripapillary retinal nerve fiber layer (pRNFL) thickness and retinal microvasculature using optical coherence tomography (OCT) and optical coherence tomography angiography (OCTA).

Methods

In this retrospective cross-sectional study, OCT scans were performed on 28 eyes of GL-CON, 34 eyes of GON, and 41control eyes to determine the pRNFL thickness, ganglion cell complex thickness, and cup/disc ratio. OCTA scans were conducted for 12 eyes of GL-CON, 15 eyes of GON, and 15 control eyes to measure the vessel density of the peripapillary and macular areas. Analysis of covariance was used to perform the comparisons, and the area under the curve was calculated.

Results

The GON eyes had a significantly thinner pRNFL in the inferior quadrant and greater vertical cup/disc ratio than the GL-CON eyes. In the radial peripapillary capillary segment, the vessel density of the GON in the inferior sectors was significantly lower than in the GL-CON. The superficial macular vessel density in the whole-image, peritemporal, perinasal, and peri-inferior sectors was significantly smaller in the GON group than in the GL-CON group. The best parameter for discriminating between GL-CON and GON was the superficial macular vessel density in the peritemporal sector.

Conclusions

GL-CON eyes showed a characteristic pattern of pRNFL and retinal microvascular changes.

Translational Relevance

GL-CON can be effectively distinguished from GON by detecting the alterations in the pRNFL and retinal microvasculature using OCT and OCTA.

Precision (repeatability and reproducibility) of papillary and peripapillary vascular density measurements using optical coherence tomography angiography in children

Importance

Optical coherence tomography angiography (OCTA) has been widely applied into children, however, few studies have assessed the repeatability and reproducibility of papillary and peripapillary VD in healthy children.

Objective

To assess the precision of papillary and peripapillary vascular density (VD) measurements using optical coherence tomography angiography (OCTA) and analyze the effects of the signal strength index (SSI) and axial length (AL) on precision estimates.

Design setting and participants

This was a prospective observational study. Seventy-eight children aged 6-16 years underwent 4.5 × 4.5 mm OCTA (RTVue XR Avanti) disc scans: two scans by one examiner (repeatability) and two additional scans by another examiner (reproducibility). Within-subject standard deviation (Sw), test-retest reproducibility (TRT), within-subject coefficient of variation (CoV), intraclass correlation coefficient (ICC), and Bland-Altman analysis were performed.

Main outcomes and measures

In repeatability measurement, the fluctuation ranges (minimum to maximum) of VD between intraexaminer A/B in Sw, TRT, CoV, and ICC were (1.05-2.17)% / (1.16-2.32)%, (2.9-6)% / (3.21-6.44)%, (1.9-4.47)% / (2.08-5)%, and (0.588-0.783)% / (0.633-0.803)%, respectively. In reproducibility measurement, the fluctuation ranges of VD in Sw, TRT, CoV, and ICC were 1.11-2.13%, 3.07-5.91%, 1.99-4.41%, and 0.644-0.777%, respectively. VD was negatively correlated with SSI in most sectors of the peripapillary (e.g., inferior nasal, temporal inferior, temporal superior, superior temporal, and superior nasal). AL was positively correlated with inferior temporal VD and negatively correlated with superior nasal VD.

Conclusion and relevance

Optical coherence tomography angiography showed moderate-to-good repeatability and reproducibility for papillary and peripapillary perfusion measurements in healthy children. The SSI value affects most of the peripapillary VD, while AL affects only the temporal inferior and nasal superior peripapillary VD.

Quantitative Evaluation of Retinal Microvascular Abnormalities in Patients With Type 2 Diabetes Mellitus Without Clinical Sign of Diabetic Retinopathy

Purpose

To evaluate microvascular abnormalities in the macula and peripapillary area in diabetic patients without clinical signs of diabetic retinopathy (DR) and compare them with healthy control eyes, using optical coherence tomography angiography (OCTA).

Methods

A prospective study was performed of 49 eyes from 49 diabetic patients without clinical signs of DR and a control group of 52 eyes from 52 healthy normal individuals. The 3 × 3 mm macular scans and 4.5 × 4.5 mm optic disc scans were obtained with the OCTA RTVue-XR Avanti system. Angiograms from the superficial capillary plexus, the deep capillary plexus of the macula scans, and radial peripapillary capillary plexus of the optic disc scans were analyzed with MATLAB. Multivariate binary logistic regression and the least absolute shrinkage and selection operator (LASSO) regression were used to select ideal parameters that distinguish diabetic eyes without DR from normal eyes. A receiver operating characteristic (ROC) curve was generated, and sensitivity and specificity were calculated.

Results

Our final model identified FD-300 (foveal vessel density in a 300-µm-wide region around foveal avascular zone) as the only parameter selected by both the LASSO regression and the final multivariate logistic regression model that significantly differentiates diabetic eyes without clinical signs of DR from healthy normal eyes. The area under the ROC curve of FD-300 was 0.685, and sensitivity and specificity were 65.3% and 71.2%, respectively.

Conclusions

Quantitative evaluation of retinal microvascular abnormalities using OCTA identified FD-300 as a useful biomarker versus the other macular and peripapillary OCTA metrics in the early detection of preclinical diabetic retinal abnormalities.

Translational Relevance

OCTA may be useful in detecting early retinal microvascular abnormalities in diabetic patients before the clinical findings of DR become visible.

Retinal Oxygen Delivery and Extraction in Ophthalmologically Healthy Subjects With Different Blood Pressure Status

Purpose

To compare retinal oxygen delivery (DO2) and oxygen extraction (VO2) in ophthalmologically healthy subjects with different blood pressure (BP) status.

Methods

In this case-control study, we prospectively included 93 eyes of 93 subjects (aged 50-65 years) from a Dutch cohort (n = 167,000) and allocated them to four groups (low BP, normal BP [controls], treated arterial hypertension [AHT], untreated AHT). We estimated vascular calibers from fundus images and fractal dimension from optical coherence tomography angiography scans. We combined calibers, fractal dimension, BP, and intraocular pressure measurements in a proxy of retinal blood flow (RBF), using a Poiseuille-based model. We measured arterial and venous oxygen saturations (SaO2, SvO2) with a scanning laser ophthalmoscope. We calculated the DO2 and VO2 from the RBF, SaO2, and SvO2. We compared the DO2 and VO2 between groups and investigated the DO2-VO2 association.

Results

DO2 and VO2 were different between groups (P = 0.009, P = 0.036, respectively). In a post hoc analysis, the low BP group had lower DO2 than the untreated AHT group (P = 4.9 × 10-4). The low BP group and the treated AHT group had a lower VO2 than the untreated AHT group (P = 0.021 and P = 0.034, respectively). There was a significant DO2-VO2 correlation (Robs = 0.65, bobs = 0.51, P = 2.4 × 10-12). After correcting for shared measurement error, the slope was not significant.

Conclusions

The DO2 and VO2 were altered in ophthalmologically healthy subjects with different BP status. Future studies could elucidate whether these changes can explain the increased risk of ophthalmic pathologies in those subjects.

Translational Relevance

Understanding the baseline interplay between BP, retinal perfusion, and oxygenation allows for improved evaluation of retinal disease manifestation.

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.

Referenced scans improve the repeatability of optical coherence tomography angiography measurements in normal and glaucoma eyes

AIM

To compare the repeatability of peripapillary perfusion density and flux index measurements on referenced and non-referenced optical microangiography (OMAG) scans in normal, glaucoma suspect and glaucoma eyes.

METHODS

In a cross-sectional study, 48 eyes (33 subjects) underwent three repeat, non-referenced peripapillary OMAG scans in the same session and 43 eyes (25 subjects) underwent three referenced peripapillary OMAG scans. In the referenced scan group, repeat scans (second and the third scan) were acquired exactly on the baseline (first) scan using the 'track to prior scan' option on the device. Repeatability estimates of the mean and four-sector (temporal, superior, nasal and inferior) OMAG measurements on the non-referenced and referenced scans were assessed using within-subject coefficient of repeatability (CR_w) and variation (CV_w).

RESULTS

CR_w (%) of peripapillary perfusion density measurements (range: 2.0-4.1) on non-referenced scans were significantly higher than that on referenced scans (range: 1.4-2.7). CV_w (%) on non-referenced and referenced scans ranged from 1.7 to 3.1 and from 1.2 to 2.1, respectively . CR_w of flux index on non-referenced and referenced scans ranged from 4.4 to 5.8 and from 3.6 to 4.8, respectively. CV_w on non-referenced and referenced scans ranged from 4.1 to 5.2 and from 3.3 to 4.5, respectively.

CONCLUSIONS

Repeatability estimates of OMAG measurements were better on referenced scans compared with non-referenced scans. Perfusion density measurements had lower variability than flux index. OCTA-measured perfusion density of referenced scans is preferable for monitoring vascular change in glaucoma.

U-Shaped Effect of Blood Pressure on Structural OCT Metrics and Retinal Perfusion in Ophthalmologically Healthy Subjects

Purpose

We wanted to investigate the association of blood pressure (BP) status with the ganglion cell-inner plexiform layer (GCIPL) and retinal nerve fiber layer (RNFL) thickness of nonglaucomatous eyes and to elucidate whether this effect is related to vascular metrics proxying retinal perfusion.

Methods

For this case-control study, we prospectively included 96 eyes of 96 healthy subjects (age 50–65) from a large-scale population-based cohort in the northern Netherlands (n = 167,000) and allocated them to four groups (low BP, normal BP [controls], treated arterial hypertension [AHT], untreated AHT). We measured macular GCIPL and RNFL (mRNFL) and peripapillary RNFL (pRNFL) thicknesses with optical coherence tomography (OCT). We estimated retinal blood flow (RBF), retinal vascular resistance (RVR), and autoregulatory reserve (AR) from quantitative OCT-angiography, fundus imaging, BP, and intraocular pressure. We compared structural and vascular metrics across groups and performed mediation analysis.

Results

Compared to controls, GCIPL was thinner in the low BP group (P = 0.013), treated hypertensives (P = 0.007), and untreated hypertensives (P = 0.007). Treated hypertensives exhibited the thinnest mRNFL (P = 0.001), temporal pRNFL (P = 0.045), and inferior pRNFL (P = 0.034). The association of GCIPL thickness with BP was mediated by RBF within the combined low BP group and controls (P = 0.003), by RVR and AR within the combined treated hypertensives and controls (P = 0.001, P = 0.032), and by RVR within the combined untreated antihypertensives and controls (P = 0.022).

Conclusions

Inner retinal thinning was associated with both tails of the BP distribution and with ineffective autoregulation. Longitudinal studies could clarify whether these defects can explain the reported glaucomatous predisposition of these population groups.

Non-invasive electrophysiology in glaucoma, structure and function-a review

Glaucoma, its early diagnosis, and monitoring of interventions remain an ongoing challenge. We here review developments in functional assessment and its relation to morphology, evaluating recent insights in electrophysiology in glaucoma and highlighting how glaucoma research and diagnostics benefit from combined approaches of OCT and electrophysiological investigations. After concise overviews of OCT and non-invasive electrophysiology in glaucoma, we evaluate commonalities and complementarities of OCT and electrophysiology for our understanding of glaucoma. As a specific topic, the dynamic range (floor effects) of the various techniques is discussed.

Detection of the Microvascular Changes of Diabetic Retinopathy Progression Using Optical Coherence Tomography Angiography

Purpose

To investigate microvascular parameters that are related to the severity of diabetic retinopathy (DR) with optical coherence tomography angiography (OCTA).

Methods

In total, 105 eyes from 105 diabetic patients were recruited in this prospective cross-sectional study, including 37 eyes with no clinical signs of DR (NoDR), 43 eyes with nonproliferative diabetic retinopathy (NPDR), and 25 eyes with proliferative diabetic retinopathy (PDR). Angiogram images from the parafoveal superficial capillary plexus (SCP), the deep capillary plexus (DCP), and the radial peripapillary capillary plexus were analyzed, and metrics were compared among groups. Multivariate regression analysis was used to identify the best OCTA parameters that could distinguish DR severity among groups.

Results

Parafoveal vessel diameter index in the SCP and vessel density (VD) in the DCP showed the strongest correlation with the severity of DR (P < 0.01). Extrafoveal avascular area in the SCP was the parameter that could most distinguish NoDR from NPDR (P < 0.01) with sensitivity and specificity of 83.72% and 78.38%, respectively. VD in the DCP also was the most sensitive biomarker to distinguish NPDR from PDR (P < 0.01) with sensitivity and specificity of 84.00% and 79.07%, respectively.

Conclusions

The microvascular changes in the SCP and DCP in DR may have different characteristics that could be identified with specific OCTA parameters. OCTA serves as a promising technology to discriminate eyes with different severity of DR.

Translational Relevance

Our study investigated OCTA metrics and severity of DR. At different stages of DR, ophthalmologists may focus on specific OCTA parameters to predict the progression of retinopathy in individual patients.

Developing a normative database for retinal perfusion using optical coherence tomography angiography

Visualizing and characterizing microvascular abnormalities with optical coherence tomography angiography (OCTA) has deepened our understanding of ocular diseases, such as glaucoma, diabetic retinopathy, and age-related macular degeneration. Two types of microvascular defects can be detected by OCTA: focal decrease because of localized absence and collapse of retinal capillaries, which is referred to as the non-perfusion area in OCTA, and diffuse perfusion decrease usually detected by comparing with healthy case-control groups. Wider OCTA allows for insights into peripheral retinal vascularity, but the heterogeneous perfusion distribution from the macula, parapapillary area to periphery hurdles the quantitative assessment. A normative database for OCTA could estimate how much individual's data deviate from the normal range, and where the deviations locate. Here, we acquired OCTA images using a swept-source OCT system and a 12×12 mm protocol in healthy subjects. We automatically segmented the large blood vessels with U-Net, corrected for anatomical factors such as the relative position of fovea and disc, and segmented the capillaries by a moving window scheme. A total of 195 eyes were included and divided into 4 age groups: < 30 (n=24) years old, 30-49 (n=28) years old, 50-69 (n=109) years old and >69 (n=34) years old. This provides an age-dependent normative database for characterizing retinal perfusion abnormalities in 12×12 mm OCTA images. The usefulness of the normative database was tested on two pathological groups: one with diabetic retinopathy; the other with glaucoma.

Repeatability of Peripapillary Optical Coherence Tomography Angiography Parameters in Older Adults

Purpose:

This work assesses the intrasession repeatability of capillary perfusion density (CPD) and capillary flux index (CFI) measurements on peripapillary optical coherence tomography angiography (OCTA) in healthy eyes of older adults.

Methods:

In this cross-sectional study, healthy volunteers aged 50 years or older underwent 4.5 × 4.5 mm OCTA imaging centered on the optic nerve head using Zeiss Cirrus HD-5000 AngioPlex (Carl Zeiss Meditec). Two consecutive images were acquired in the same eye during a single study session. CPD and CFI were assessed using AngioPlex Software (version 11.0.0.29946) for the radial peripapillary capillary plexus (average over whole scan area) and 4 quadrants (superior, inferior, temporal, and nasal). CPD and CFI repeatability was assessed by intraclass correlation (ICC), mean interocular differences using 2-tailed t test, and association with age using generalized estimating equations.

Results:

A total of 150 images were acquired from 75 eyes of 47 patients. For CPD, ICC results ranged from 0.7160 (nasal CPD) to 0.9218 (average CPD). For CFI, ICC results ranged from 0.6167 (temporal CFI) to 0.8976 (inferior CFI). Temporal CFI was significantly different between right and left eyes of the same patient ( P = .03). CPD and CFI decreased with age in all analyses (average CPD β coefficient –0.00172, P < .001; average CFI β coefficient −0.00278, P < .001).

Conclusions:

Moderate to good repeatability was observed for most peripapillary OCTA metrics; temporal measurements were least repeatable for CPD and CFI. Peripapillary CPD and CFI decrease with age even beyond the fifth decade in healthy older adults.

Retinal blood flow in critical illness and systemic disease: a review

BACKGROUND

Assessment and maintenance of end-organ perfusion are key to resuscitation in critical illness, although there are limited direct methods or proxy measures to assess cerebral perfusion. Novel non-invasive methods of monitoring microcirculation in critically ill patients offer the potential for real-time updates to improve patient outcomes.

MAIN BODY

Parallel mechanisms autoregulate retinal and cerebral microcirculation to maintain blood flow to meet metabolic demands across a range of perfusion pressures. Cerebral blood flow (CBF) is reduced and autoregulation impaired in sepsis, but current methods to image CBF do not reproducibly assess the microcirculation. Peripheral microcirculatory blood flow may be imaged in sublingual and conjunctival mucosa and is impaired in sepsis. Retinal microcirculation can be directly imaged by optical coherence tomography angiography (OCTA) during perfusion-deficit states such as sepsis, and other systemic haemodynamic disturbances such as acute coronary syndrome, and systemic inflammatory conditions such as inflammatory bowel disease.

CONCLUSION

Monitoring microcirculatory flow offers the potential to enhance monitoring in the care of critically ill patients, and imaging retinal blood flow during critical illness offers a potential biomarker for cerebral microcirculatory perfusion.

Combined Multi-Modal Assessment of Glaucomatous Damage With Electroretinography and Optical Coherence Tomography/Angiography

Purpose

To compare the diagnostic performance and to evaluate the interrelationship of electroretinographical and structural and vascular measures in glaucoma.

Methods

For 14 eyes of 14 healthy controls and 15 eyes of 12 patients with glaucoma ranging from preperimetric to advanced stages optical coherence tomography (OCT), OCT-angiography (OCT-A), and electrophysiological measures (multifocal photopic negative response ratio [mfPhNR] and steady-state pattern electroretinography [ssPERG]) were applied to assess changes in retinal structure, microvasculature, and function, respectively. The diagnostic performance was assessed via area-under-curve (AUC) measures obtained from receiver operating characteristics analyses. The interrelation of the different measures was assessed with correlation analyses.

Results

The mfPhNR, ssPERG amplitude, parafoveal (pfVD) and peripapillary vessel density (pVD), macular ganglion cell inner plexiform layer thickness (mGCIPL) and peripapillary retinal nerve fiber layer thickness (pRNFL) were significantly reduced in glaucoma. The AUC for mfPhNR was highest among diagnostic modalities (AUC: 0.88, 95% confidence interval: 0.75-1.0, P < 0.001), albeit not statistically different from that for macular (mGCIPL: 0.76, 0.58-0.94, P < 0.05; pfVD: 0.81, 0.65-0.97, P < 0.01) or peripapillary imaging (pRNFL: 0.85, 0.70-1.0, P < 0.01; pVD: 0.82, 0.68-0.97, P < 0.01). Combined functional/vascular measures yielded the highest AUC (mfPhNR-pfVD: 0.94, 0.85-1.0, P < 0.001). The functional/structural measure correlation (mfPhNR-mGCIPL correlation coefficient [rs]: 0.58, P = 0.001; mfPhNR-pRNFL rs: 0.66, P < 0.001) was stronger than the functional-vascular correlation (mfPhNR-pfVD rs: 0.29, P = 0.13; mfPhNR-pVD rs: 0.54, P = 0.003).

Conclusions

The combination of ERG measures and OCT-A improved diagnostic performance and enhanced understanding of pathophysiology in glaucoma.

Translational Relevance

Multimodal assessment of glaucoma damage improves diagnostics and monitoring of disease progression.

Microcirculatory model predicts blood flow and autoregulation range in the human retina: in vivo investigation with laser speckle flowgraphy

In this study, we mathematically predict retinal vascular resistance (RVR) and retinal blood flow (RBF), we test predictions using laser speckle flowgraphy (LSFG), we estimate the range of vascular autoregulation, and we examine the relationship of RBF with the retinal nerve fiber layer (RNFL) and ganglion cell complex (GCC). Fundus, optical coherence tomography (OCT), and OCT-angiography images, systolic/diastolic blood pressure (SBP/DBP), and intraocular pressure (IOP) measurements were obtained from 36 human subjects. We modeled two circulation markers (RVR and RBF) and estimated individualized lower/higher autoregulation limits (LARL/HARL), using retinal vessel calibers, fractal dimension, perfusion pressure, and population-based hematocrit values. Quantitative LSFG waveforms were extracted from vessels of the same eyes, before and during IOP elevation. LSFG metrics explained most variance in RVR (R² = 0.77/P = 6.9·10^-9) and RBF (R² = 0.65/P = 1.0·10^-6), suggesting that the markers strongly reflect blood flow physiology. Higher RBF was associated with thicker RNFL (P = 4.0·10^-4) and GCC (P = 0.003), thus also verifying agreement with structural measurements. LARL was at SBP/DBP of 105/65 mmHg for the average subject without arterial hypertension and at 115/75 mmHg for the average hypertensive subject. Moreover, during IOP elevation, changes in RBF were more pronounced than changes in RVR. These observations physiologically imply that healthy subjects are already close to LARL, thus prone to hypoperfusion. In conclusion, we modeled two clinical markers and described a novel method to predict individualized autoregulation limits. These findings could improve understanding of retinal perfusion and pave the way for personalized intervention decisions, when treating patients with coexisting ophthalmic and cardiovascular pathologies.NEW & NOTEWORTHY We describe and test a new approach to quantify retinal blood flow, based on standard clinical examinations and imaging techniques, linked together with a physiological model. We use these findings to generate individualized estimates of the autoregulation range. We provide evidence that healthy subjects are closer to the lower autoregulation limit than thought before. This suggests that some retinas are less prepared to withstand hypoperfusion, even after small intraocular pressure rises or blood pressure drops.

Evaluation of microvascular changes in optic disc and retina by optical coherence tomography angiography during Valsalva maneuver

PURPOSE

Optical coherence tomography angiography (OCTA) is an increasingly widespread imaging tool that allows the visualization of the microvascular structures of the eye. It should be kept in mind in clinical practice, Valsalva maneuver (VM) may have an effect on OCTA findings. We aimed to evaluate the effect of VM on the optic nerve and retinal blood flow parameters measured by OCTA.

METHODS

Sixty age- and sex-matched healthy volunteers were included into this prospective study. Optic disc status for radial peripapillary capillary (RPC) network [whole image, inside disc and peripapillary capillary densities], superficial and deep capillary plexus whole, foveal, parafoveal and perifoveal densities and foveal avascular zone (FAZ) densities of volunteers were examined by OCTA both at rest and during VM.

RESULTS

The mean age of the subjects was 31.48 ± 7.49 (18-50) years and 51.7% were male. Superficial whole, parafoveal and perifoveal vessel densities were found to be significantly decreased during VM (p = 0.008, p= 0.015, p = 0.017, respectively). Lower levels of deep whole, parafoveal and perifoveal vessel densities were also detected while VM (p < 0.001 for all). However, there were no significant differences in terms of foveal vessel and FAZ densities. Additionally, VM significantly decreased RPC densities for whole image, inside and peripapillary capillary (p = 0.005, p < 0.001, p = 0.039, respectively).

CONCLUSION

VM may cause a significant decrease in optic nerve and para-perifoveal blood flow. Therefore, patient instruction about not holding breath is required before OCTA scanning.