Parafoveal retinal vascular response to pattern visual stimulation assessed with OCT angiography

Optical coherence tomography angiography in diabetic retinopathy

There remain many unanswered questions on how to assess and treat the pathology and complications that arise from diabetic retinopathy (DR). Optical coherence tomography angiography (OCTA) is a novel and non-invasive three-dimensional imaging method that can visualize capillaries in all retinal layers. Numerous studies have confirmed that OCTA can identify early evidence of microvascular changes and provide quantitative assessment of the extent of diseases such as DR and its complications. A number of informative OCTA metrics could be used to assess DR in clinical trials, including measurements of the foveal avascular zone (FAZ; area, acircularity, 3D para-FAZ vessel density), vessel density, extrafoveal avascular zones, and neovascularization. Assessing patients with DR using a full-retinal slab OCTA image can limit segmentation errors and confounding factors such as those related to center-involved diabetic macular edema. Given emerging data suggesting the importance of the peripheral retinal vasculature in assessing and predicting DR progression, wide-field OCTA imaging should also be used. Finally, the use of automated methods and algorithms for OCTA image analysis, such as those that can distinguish between areas of true and false signals, reconstruct images, and produce quantitative metrics, such as FAZ area, will greatly improve the efficiency and standardization of results between studies. Most importantly, clinical trial protocols should account for the relatively high frequency of poor-quality data related to sub-optimal imaging conditions in DR and should incorporate time for assessing OCTA image quality and re-imaging patients where necessary.

OCT angiography and its retinal biomarkers [Invited]

Optical coherence tomography angiography (OCTA) is a high-resolution, depth-resolved imaging modality with important applications in ophthalmic practice. An extension of structural OCT, OCTA enables non-invasive, high-contrast imaging of retinal and choroidal vasculature that are amenable to quantification. As such, OCTA offers the capability to identify and characterize biomarkers important for clinical practice and therapeutic research. Here, we review new methods for analyzing biomarkers and discuss new insights provided by OCTA.

Choriocapillary Flow Correlation with Axial Length in High Myopia - An Angiography Study with Optical Coherence Tomography

PURPOSE

To investigate parameters of retinal and choroidal microcirculation quantitatively with optical coherence tomography angiography (OCTA) in high myopic children, and to explore potential correlations with age, axial length (AL), spherical equivalent (SE), and central retinal thickness (CRT).

METHODS

En face angiograms were generated with an OCTA device and evaluated with automated density and flow analyzer algorithms. Perfusion parameters were correlated with age, AL, SE, and CRT using Spearman's rank correlation analysis. Repeatability and reproducibility of perfusion parameter measurements were calculated in a high myopic cohort.

RESULTS

Repeatability and reproducibility of OCTA measurements were good, ranging from 3.6 - 6.5%. Strong positive correlation was identified between age and CRT (rho = 0.673, p = 0.00) as well as between AL and SE (rho = 0.844, p = 0.00). There was a strong negative correlation between AL and choriocapillary flow density (CCFD) (rho = - 0.612, p = 0.00), and a moderate negative correlation between age and superficial parafoveal retinal vessel density (SPRVD) as well as CCFD (rho = - 0.497, p = 0.013 and rho = - 0.483, p = 0.023, respectively).

CONCLUSION

OCTA appears to be a reliable tool for the quantitative investigation of retinal and choroidal microcirculation in a high myopic pediatric cohort. CCFD reduction was associated with increasing AL in this cohort.

Macular superficial vascular density on optical coherence tomography angiography in children with unilateral anisometropic and bilateral hyperopic amblyopia

We analyzed whether macular superficial vascular density (SVD) and foveal vascular zone (FAZ) on optical coherence tomography angiography (OCTA) can distinguish between bilateral ametropic and anisometropic amblyopia. We included 42, 33, and 50 eyes in the bilateral ametropic amblyopia, anisometropic amblyopia, and normal control groups, respectively. Using macular swept-source optical coherence tomography angiography, we measured and analyzed the superficial FAZ areas and five sectoral macular SVDs after magnification correction. The anisometropic amblyopic eye group showed significantly increased foveal SVDs (p < 0.001) and significantly decreased superficial FAZ areas (p < 0.001), compared with the remaining groups. Additionally, the bilateral ametropic amblyopia group had significantly decreased nasal SVDs. SVDs and superficial FAZ areas differed among hyperopic amblyopia subtypes. These findings may reflect vascular distribution differences and macular changes in hyperopic amblyopia subtypes compared with normal eyes.

Optical Coherence Tomography Angiography of Volumetric Arteriovenous Relationships in the Healthy Macula and Their Derangement in Disease

Purpose

To characterize relative arteriovenous connectivity of the healthy macula imaged by optical coherence tomography angiography (OCTA) using a new volumetric tool.

Methods

OCTA volumes were obtained for 20 healthy controls (20 eyes). Two graders identified superficial arterioles and venules. We implemented a custom watershed algorithm to identify capillaries most closely connected to arterioles and venules by using the large vessels as seeds to flood the vascular network. We calculated ratios of arteriolar- to venular-connected capillaries (A/V ratios) and adjusted flow indices (AFIs) for superficial capillary plexuses (SCPs), middle capillary plexuses (MCPs), and deep capillary plexuses (DCPs). We also analyzed two eyes with proliferative diabetic retinopathy (PDR) and one eye with macular telangiectasia (MacTel) to evaluate the utility of this method in visualizing pathological vascular connectivity.

Results

In healthy eyes, the MCP showed a greater proportion of arteriolar-connected vessels than the SCP and DCP (all P < 0.001). In the SCP, the arteriolar-connected AFI exceeded the venular-connected AFI, but this pattern reversed in the MCP and DCP, with higher venular-connected AFI (all P < 0.001). In PDR eyes, preretinal neovascularization originated from venules, whereas intraretinal microvascular abnormalities were heterogeneous, with some originating from venules and others representing dilated MCP capillary loops. In MacTel, diving SCP venules formed the epicenter of the outer retinal anomalous vascular network.

Conclusions

Healthy eyes showed a higher MCP A/V ratio but relatively slower arteriolar vs. venular flow velocity in the MCP and DCP, which may explain deep retinal vulnerability to ischemia. In eyes with complex vascular pathology, our connectivity findings were consistent with histopathologic studies.

Evaluation of the effect of uncomplicated cataract surgery on retina and optic disc: Optical Coherence Tomography Angiography Study

Purpose

The aim of the present study is to evaluate the effects of uncomplicated cataract surgery on microvascular structure of fovea, parafovea, optic disc, and peripapillary area with optical coherence tomography angiography (OCTA).

Methods

The study included 53 eyes of 53 patients, who undergone uncomplicated cataract surgery. The day before cataract surgery and at the 1st week, 1st month, 3rd month after surgery, best-corrected visual acuity, foveal avascular zone, acircularity index, superficial and deep foveal density, superficial and deep parafoveal density, central macular thickness, peripapillary retinal nerve fiber layer thickness value, and peripapillary vascular density were measured with OCTA.

Results

The mean age of the patients was 62.1 ± 7.2 years (range, 42–69 years) and the sex of the patients was 25 male and 28 female. The foveal avascular zone value was decreased compared to the preoperative value (p < 0.05). There was no significant change in acircularity index postoperatively (p > 0.05). There was a significant increase in superficial and deep foveal density and superficial and deep parafoveal density (p < 0.05). According to preoperative period, peripapillary retinal nerve fiber layer and inside disc capillary density of optic disc increased significantly (p < 0.05). There was no significant change in peripapillary vascular density postoperatively (p > 0.05).

Conclusions

Changes in the vascular density of the retina were detected with OCTA in eyes without ocular or systemic disease, which underwent uncomplicated cataract surgery. In the postsurgical period, OCTA provides important information in the evaluation and follow-up of these changes.

Combining host plant defence with targeted nutrition: key to durable control of hemiparasitic Striga in cereals in sub-Saharan Africa?

Host plant defence mechanisms (resistance and tolerance) and plant nutrition are two of the most widely proposed components for the control of hemiparasitic weeds of the genus Striga in tropical cereal production systems. Neither of the two components alone is effective enough to prevent parasitism and concomitant crop losses. This review explores the potential of improved plant nutrition, being the chemical constituent of soil fertility, to fortify the expression of plant inherent resistance and tolerance against Striga. Beyond reviewing advances in parasitic plant research, we assess relevant insights from phytopathology and plant physiology in the broader sense to identify opportunities and knowledge gaps and to develop the way forward regarding research and development of combining genetics and plant nutrition for the durable control of Striga.

Association of OCT-A characteristics with postoperative visual acuity after rhegmatogenous retinal detachment surgery: a review of the literature

PURPOSE

Emerging evidence has suggested that macular microcirculation and microstructural changes after rhegmatogenous retinal detachment (RRD) successful reattachment surgery are currently evaluated in detail by OCT-Angiography (OCT-A). New imaging technology has revealed the existence of microscopic macular changes, even in cases that retinal morphology appears to be normal in fundus biomicroscopy. The use of OCT-A for the examination of foveal characteristics has attracted significant attention in recent years as the technique offers a potential explanation of the suboptimal recovery of visual acuity and incomplete restoration of the macula despite anatomical repair. However, the available evidence that is needed to establish the OCT-A parameters as predicting factors in clinical practice is both limited and contradictory.

METHODS

A detailed review of the literature was conducted. The association of OCT-A characteristics with postoperative visual acuity after RRD surgery, including vitrectomy with gas tamponade and in some cases scleral buckle, was extensively analyzed.

RESULTS

A comprehensive update on microcirculation and microstructural changes of the macula using OCT-A after RRD repair may indicate potential factors of functional outcomes in clinical practice.

CONCLUSION

A review of the existing literature sheds light on the microvascular changes of the macular capillary plexus that may significantly affect functional outcomes after RRD surgery. The current article discusses important aspects of key publications on the topic, highlights the importance of long-term effectiveness of these possible prognostic factors and proposes the need for further future research.

Assessment of Anatomical and Functional Macular Changes with Optical Coherence Tomography Angiography After Macula-Off Rhegmatogenous Retinal Detachment Repair

Purpose: To evaluate macular capillary plexus changes with OCT-angiography with regard to macular detachment duration in macula-off rhegmatogenous retinal detachment (RRD).Methods: 23 eyes of 23 patients were included in this retrospective case-control study and were divided into 2 groups. Group-A had a macular detachment duration of 0 to 10 days and group-B of 11 to 30 days. All eyes underwent a single successful pars plana vitrectomy (PPV) and gas tamponade. We analysed the OCT-A characteristics and visual outcomes at 12 weeks postoperatively in the 2 groups. The fellow eye was used as control.Results: Vessel density (VD) and flow density (FD) in the superficial capillary plexus (SCP) were significantly lower in group-B (p < .01) than in group-A and control. FAZ SCP in both groups was significantly larger than the control (p < .01), although it did not differ significantly between the two groups (p = 1.000). BCVA was significantly lower in group-B compared to group-A (p < .01). BCVA was positively correlated with VD SCP in group B (p = .015), but not in group-A. Postoperative BCVA had no correlation with FAZ SCP in both groups.Conclusions: The macular detachment duration could be a predicting factor of flow density in macular capillary plexus which in turn might be an indicator of visual outcomes in chronic cases.

Microbubbles Containing Lysolipid Enhance Ultrasound-Mediated Blood-Brain Barrier Breakdown In Vivo

Ultrasound and microbubbles (MBs) offer a noninvasive method of temporarily enhancing blood-brain barrier (BBB) permeability to therapeutics. To reduce off-target effects, it is desirable to minimize the ultrasound pressures required. It has been shown that a new formulation of MBs containing lysolipids (Lyso-MBs) can increase the cellular uptake of a model drug in vitro. The aim of this study is to investigate whether Lyso-MBs can also enhance BBB permeability in vivo. Female BALB/c mice are injected with either Lyso-MBs or control MBs and gadolinium-DTPA (Gd-DTPA) and exposed to ultrasound (500 kHz, 1 Hz pulse repetition frequency, 1 ms pulse length, peak-negative pressures 160-480 kPa) for 2 min. BBB permeabilization is measured via magnetic resonance imaging (7.0 T) of Gd-DTPA extravasation and subsequent histological examination of brain tissue to assess serum immunoglobulin G (IgG) extravasation (n = 8 per group). An approximately twofold enhancement in BBB permeability is produced by the Lyso-MBs at the highest ultrasound pressure compared with the control. These findings indicate that modifying the composition of phospholipid-shelled MBs has the potential to improve the efficiency of BBB opening, without increasing the ultrasound pressure amplitude required. This is particularly relevant for delivery of therapeutics deep within the brain.

Peripapillary Perfused Capillary Density in Acute Angle-Closure Glaucoma: An Optical Coherence Tomography Angiography Study

PURPOSE

To compare peripapillary perfused capillary density (PCD) on optical coherence tomography angiography among resolved acute angle-closure (AAC), primary open-angle glaucoma (POAG), and control eyes.

DESIGN

Prospective, cross-sectional, observational study.

METHODS

All patients with resolved AAC or POAG of varying severity and controls were enrolled. We obtained 4.5 × 4.5 mm2 optical coherence tomography angiography images of the optic nerve head. PCD was analyzed using customized software with major vessel removal. Continuous variables were assessed using the analysis of variance and Bonferroni correction test. A marginal model of generalized estimating equations was used to adjust for confounding factors and interocular correlation.

RESULTS

The study included 44 eyes with resolved AAC (mean duration of elevated intraocular pressure, 8.1 ± 10.9 days), 69 eyes with POAG, and 49 control eyes. PCD showed a similar decrease between AAC and POAG eyes (P > 0.99). After adjusting for age and sex, the mean difference in global PCD between each of the POAG stage groups and the AAC group was the highest in the severe POAG group (-3.43; 95% confidence interval [CI], -11.38 to 2.52; P = 0.211), followed by the mild POAG (0.68; 95% CI, -3.26 to 4.62; P = 0.735) and moderate POAG (0.20; 95% CI, -5.21 to 5.61; P = 0.942) groups. The duration of increased intraocular pressure did not affect PCD (P = 0.258 and 0.168 for global and annular PCDs, respectively).

CONCLUSIONS

The degree of microvascular attenuation in AAC eyes was not different from that in POAG eyes.

Vascular changes after vitrectomy for rhegmatogenous retinal detachment: optical coherence tomography angiography study

PURPOSE

To analyse the postoperative foveal avascular zone (FAZ) area, superficial vessel density (SVD) and deep vessel density (DVD) and their correlation with functional (best-corrected visual acuity, BCVA) and anatomical outcomes (foveal macular thickness, FMT) after surgery for rhegmatogenous retinal detachment (RRD) repair.

METHOD

Patients with RRD eyes, successfully treated with a single pars plana vitrectomy (PPV) with gas tamponade and a minimum 12 months follow-up, were re-examined. Foveal avascular zone (FAZ) area, SVD, DVD and FMT were evaluated by using optical coherence tomography angiography (OCTA) and compared to fellow eye.

RESULTS

Fifty-six patients with macula-on and 37 with macula-off RRD were included in the study. In both groups, no difference in FMT and FAZ area was found compared to fellow eyes. In macula-on RRD eyes, a lower parafoveal DVD (p = 0.001) was detected; FAZ area was related to FMT (p = 0.025), and the postoperative BCVA was correlated with parafoveal DVD (p = 0.010) and FAZ area (p = 0.003). In macula-off RRD eyes, lower parafoveal SDV (p = 0.012), and foveal and parafoveal DVD (p = 0.012 and p < 0.001, respectively) were observed. BCVA was related to FAZ area (p = 0.012), foveal SVD (p = 0.005) and parafoveal DVD (p = 0.010).

CONCLUSION

Rhegmatogenous retinal detachment eyes successfully treated with PPV had lower vessel density in the superficial and deep retinal plexus compared to fellow healthy eyes; BCVA was related to FAZ area and vessel density.

Optical coherence tomography reveals light-dependent retinal responses in Alzheimer's disease

Spectral-domain optical coherence tomography (SD-OCT) is an accessible clinical tool for measuring structural changes to the retina, and increasingly as a biomarker for brain-predominant neurodegenerative diseases like Alzheimer's. Information about retinal function can also be extracted from OCT images, but is under-studied, with literature examples often employing challenging protocols or requiring specialized hardware. The first goal of this study was to verify that functional retinal imaging was feasible with a commercially-available SD-OCT device and a clinically practical protocol. Inspired by methods from other functional imaging modalities, we acquired images while repeatedly cycling lights on and off, and spatially normalized retinas to facilitate intra- and inter-individual analyses. In eight healthy young adults, light-dependent increases in reflectivity were easily demonstrated at photoreceptor inner and outer segments, changing by ~7% in bright light and ~3% in dim light. Bright light elicited a subtle (~2%) but consistent light-dependent decrease in reflectivity through much of the rest of the retina, including the avascular outer nuclear layer (ONL). We speculated that some of these changes are influenced by glial function - as through water management - a topic of high interest in neurodegenerative diseases that may involve the glymphatic system. Functional abnormalities in patients with antibodies against aquaporin-4 (n ​= ​3) supported this interpretation. We next compared patients with early-onset Alzheimer's disease (n ​= ​14) to age-matched controls (n ​= ​14), revealing that patients had a relatively exaggerated light-induced change in ONL reflectivity (p ​< ​0.05). Because these measurements can be obtained within 30 ​min, regular use in research and limited clinical settings is feasible.

Optic Disc and Macular Vessel Density Measured by Optical Coherence Tomography Angiography in Open-Angle and Angle-Closure Glaucoma

There is distinct pathogenesis between primary open-angle glaucoma (POAG) and primary angle-closure glaucoma (PACG). Although elevated intraocular pressure (IOP) is the major risk factor for glaucoma, non-IOP risk factors such as vascular abnormalities and lower systolic/diastolic perfusion pressure may play a role in the pathogenic process. This study aimed to compare the vessel density (VD) in the optic disc and macula using optical coherence tomography angiography (OCTA) between POAG and PACG eyes. Thirty-two POAG eyes, 30 PACG eyes, and 39 control eyes were included. All the optic disc VD parameters except the inside disc VD were significantly lower in glaucomatous eyes than in control eyes. Compared with PACG eyes, only the inferior temporal peripapillary VD was significantly lower in POAG eyes. The parafoveal VD was significantly lower in each quadrant in glaucomatous eyes than in control eyes. The central macular and parafoveal VD did not differ between POAG and PACG eyes. In conclusion, the inferior temporal peripapillary VD was significantly reduced in POAG eyes compared with PACG eyes, while PACG eyes showed a more evenly distributed reduction in the peripapillary VD. The distinct patterns of VD change may be associated with the different pathogenesis between POAG and PACG.

Detection of Reduced Retinal Vessel Density in Eyes with Geographic Atrophy Secondary to Age-Related Macular Degeneration Using Projection-Resolved Optical Coherence Tomography Angiography

PURPOSE

To compare retinal vessel density in eyes with geographic atrophy (GA) secondary to age-related macular degeneration (AMD) to age-matched healthy eyes by using projection-resolved optical coherence tomography angiography (PR-OCTA).

DESIGN

Prospective cross-sectional study.

METHODS

Study participants underwent macular 3- × 3-mm OCTA scans with spectral domain OCTA. Reflectance-compensated retinal vessel densities were calculated on projection-resolved superficial vascular complex (SVC), intermediate capillary plexus (ICP), and deep capillary plexus (DCP). Quantitative analysis using normalized deviation compared the retinal vessel density in GA regions, 500-μm GA rim regions, and non-GA regions to similar macular locations in control eyes.

RESULTS

Ten eyes with GA and 10 control eyes were studied. Eyes with GA had significantly lower vessel density in the SVC (54.8 ± 2.4% vs. 60.8 ± 3.1%; P < 0.001), ICP (34.0 ± 1.5% vs. 37.3 ± 1.7%; P = 0.003) and DCP (24.4 ± 2.3% vs. 28.0 ± 2.3%; P < 0.001) than control eyes. Retinal vessel density within the GA region decreased significantly in SVC, ICP, and DCP. Retinal vessel density in the GA rim region decreased in SVC and ICP but not in DCP. The non-GA region did not significantly deviate from normal controls. Eyes with GA had significantly reduced photoreceptor layer thickness; but similar nerve fiber layer, ganglion cell complex, inner nuclear layer, and outer plexiform layer thickness.

CONCLUSIONS

Eyes with GA have reduced retinal vessel density in SVC, ICP, and DCP compared to those in controls. Loss is greatest within regions of GA. Vessel density may be more sensitive than retinal layer thickness measurement in the detection of inner retinal change in eyes with GA.

Repeatability of ocular surface vessel density measurements with optical coherence tomography angiography

Background

To determine the repeatability of measurements of ocular surface vessel density in normal and diseased eyes using optical coherence tomography angiography (OCTA).

Methods

Ten normal eyes, 10 pinguecula eyes, and 10 pterygium eyes of 30 volunteers were subjected to OCTA (AngioVue Imaging System, Optovue, Inc.). For scanning, we used the corneal adapter module. Each eye was scanned three times in the nasal and temporal directions, separately. AngioVue software was used to generate the ocular surface vessel density. Ocular surface vessel density was defined as the proportion of vessel area with blood flow to the total measurement area (3 × 3 mm²). Intersession repeatability of the measurement was summarized as the coefficient of variation (CV), and intraclass correlation coefficients (ICC) were calculated by variance component models.

Results

The CVs were less than 5% in all subjects, and the ICCs exceeded 0.9; thus, all measurements showed good repeatability. The nasal vessels densities differed significantly between healthy eyes and eyes with pterygium (P < 0.05); however, there was no significant difference between healthy eyes and eyes with pinguecula (P = 0.466).

Conclusions

These results suggest that measurement of ocular surface vessel density by OCTA in normal eyes and eyes with pterygium and pinguecula is repeatable. This preliminary research describes a quantitative and visual method for assessing vessel density of the ocular surface with a high level of consistency.

Immediate Changes in Peripapillary Retinal Vasculature after Intraocular Pressure Elevation -an Optical Coherence Tomography Angiography Study

Purpose: To investigate changes in peripapillary retinal vessel density after acute intraocular pressure (IOP) elevation caused by laser peripheral iridotomy (LPI) in primary angle-closure suspects (PACS) by optical coherence tomography angiography (OCTA).Materials and Methods: Ninety-seven participants with PACS were included in this cross-sectional observational study. OCTA and IOP measurement were performed at baseline and 1 h after LPI. PACS eyes were further divided into three groups according to IOP increase 1 h after LPI (group 1 = IOP elevation <5 mmHg, 42eyes; group 2 = IOP elevation ≥5 mmHg and <10 mmHg, 34 eyes; group 3 = IOP elevation ≥10 mmHg, 21eyes). The changes of vessel density in radial peripapillary capillary (RPC) and entire retina were compared among groups.Results: When all eyes were included, the vessel density of RPC and entire retina 1 h after LPI were significantly decreased compared to the baseline (RPC: 64.5 ± 7.9 vs.67.8 ± 6.8, P < .001; retina: 86.3 ± 4.6 vs.88.3 ± 3.8, P < .001). There were significant differences among the three groups in the RPC and retinal vessel density at 1 h after LPI (RPC: 67.4 ± 7.3 vs. 63.2 ± 7.6 vs. 60.9 ± 7.5, P = .003; retinal: 87.7 ± 4.0 vs. 85.8 ± 4.5 vs. 84.3 ± 5.2, P = .015). In group 2 with an increased IOP from 5 mmHg to 10 mmHg, the reduction of vessel density in the RPC was more significant than that of the entire retina (RPC vs. retina: 7.1 ± 10.0% vs. 3.0 ± 4.4%, P = .006).Conclusions: LPI-induced IOP spikes resulted in a decrease in retina vessel density with PACS eyes by OCTA. The reduction of RPC vessel density was more significant than that of the entire retina in the subgroup of IOP increase from 5 to 10 mmHg. This suggests that vessel density in RPC was more sensitive to IOP increase than that of the entire retina in the peripapillary area.

Hemodynamic Response of the Three Macular Capillary Plexuses in Dark Adaptation and Flicker Stimulation Using Optical Coherence Tomography Angiography

Purpose

To assess retinal microvascular reactivity during dark adaptation and the transition to ambient light and after flicker stimulation using optical coherence tomography angiography (OCTA).

Methods

Fifteen eyes of 15 healthy participants were dark adapted for 45 minutes followed by OCTA imaging in the dark-adapted state. After 5 minutes of normal lighting, subjects underwent OCTA imaging. Participants were then subjected to a flashing light-emitting diode (LED) light and repeat OCTA. Parafoveal vessel density and adjusted flow index (AFI) were calculated for superficial (SCP), middle (MCP), and deep capillary plexuses (DCP), and then compared between conditions after adjusting for age, refractive error, and scan quality. SCP vessel length density (VLD) was also evaluated. Between-condition capillary images were aligned and subtracted to identify differences. We then analyzed images from 10 healthy subjects during the transition from dark adaptation to ambient light.

Results

SCP vessel density was significantly higher while SCP VLD was significantly lower during ambient light and flicker compared to dark adaptation. There was a significant positive mean value for DCP “flicker minus dark or light,” suggesting more visible vessels during flicker due to changes in flow, dilation, or vessel recruitment. We found a significant, transient increase in SCP and decrease in both MCP and DCP vessel density during the transition from dark to light.

Conclusions

We show evidence suggesting constriction of deeper vessels and dilation of large SCP vessels during the transition from dark to light. This contrasts to redistribution of blood flow to deeper layers during dark adaptation and flicker stimulation.

Genetic analysis suggests extensive gene flow within and between catchments in a common and ecologically significant dryland river shrub species; Duma florulenta (Polygonaceae)

AIM

The conservation of plant species biodiversity has been identified as a crucial factor for the resilience of dryland ecosystems in the face of climate change and desertification. Duma florulenta (lignum) is a keystone species that facilitates biodiversity in the floodplains and wetlands of Australia's dryland river systems. This paper explores spatial genetic structure of lignum and investigates factors influencing dispersal and gene flow within and among river catchments of the northern Murray-Darling Basin.

LOCATION

Northern Murray-Darling Basin, eastern Australia.

METHODS

A total of 122 individual plants from subpopulations located on rivers in four adjacent catchments were genotyped using 10 microsatellite markers. Microsatellite data were then analyzed using population genetic techniques to evaluate levels of gene flow and genetic structure and identify factors influencing dispersal.

RESULTS

Results suggest high levels of gene flow between lignum subpopulations of the northern Murray-Darling Basin. AMOVA revealed small but significant differences between subpopulations, and STRUCTURE analysis did not detect meaningful structure when sampling information was not provided. However, when sampling information was supplied using the LOCPRIOR model, three genetic clusters were identified. All Lower Balonne subpopulations were assigned to cluster 1 while a number of the other subpopulations showed mixed ancestry. Weak relationships were identified between pairwise genetic distance and geographic as well as river distance, although the R 2 value of the former was only half that of the latter.

MAIN CONCLUSIONS

Patterns of genetic variation suggest frequent long-distance overland gene flow largely as a result of the movement of seeds via floodwater. Therefore, maintenance of natural variability in flow regime is key both to maintain conditions favorable to recruitment and to promote dispersal and gene flow across the landscape. However, given future climate change projections persistence may be more reliant on the species ability to endure long periods of drought between flood events.

Associations between changes in radial peripapillary capillaries and occurrence of disc hemorrhage in normal-tension glaucoma

PURPOSE

In order to clarify the association between peripapillary vascular changes and disc hemorrhage (DH) occurrences over time, we analyzed the density of radial peripapillary capillary (RPC) and clinical parameters during follow-up periods in patients with normal-tension glaucoma (NTG).

METHODS

Seventy-seven eyes of 77 NTG patients were subjected to analysis. We selected patients who had an initial optical coherence tomography angiography (OCTA) scan in 2015 and who had another OCTA scan in 2018 with both OCTA scans showing good-quality images. We investigated the relationships between DH occurrence and each of the following parameters: RPC density, circumpapillary retinal nerve fiber layer (cpRNFL) thickness slope and total deviation (TD) slope.

RESULTS

In the period between the initial and final OCTA, we categorized the patients into 53 sides with DH (DH group) and 101 sides without DH (non-DH group). The ΔRPC density of sides with DH was significantly greater than that of sides without DH (DH, - 4.42 ± 6.43%; without DH, - 2.48 ± 5.29%; p = 0.0469). The cpRNFL thickness slope of sides with DH was significantly faster than that of sides without DH (DH, - 2.85 ± 3.17; without DH, - 0.74 ± 2.46 μm/y; p < 0.0001). The TD slope of sides with DH was significantly faster than that of sides without DH (DH, - 0.50 ± 0.77; without DH, - 0.22 ± 0.53 dB/y; p = 0.0163). As DH occurrence increased, the RPC density significantly decreased (r = -0.255, p = 0.0014). Stepwise multiple regression analysis to identify factors influencing RPC changes showed that frequency of DH (β = - 0.224, p = 0.008) and central corneal thickness (β = - 0.220, p = 0.009) were significantly associated with RPC changes.

CONCLUSIONS

DH occurrence may prompt the structural and vascular deterioration of NTG.

Macular vascular circulation and retinal oxygen saturation changes for idiopathic macular epiretinal membrane after vitrectomy

PURPOSE

To investigate the postoperative changes in retinal-choroidal blood flow area and retinal vascular oxygen saturation among patients with idiopathic macular epiretinal membranes (iERMs).

METHODS

This study prospectively included 24 eyes of 24 consecutive patients who underwent vitrectomy for iERMs. The flow area of choriocapillary layer, retinal superficial capillary plexuses (SCPs) and retinal deep capillary plexuses (DCPs) were performed using optical coherence tomography angiography with angiovue prototype software, and retinal vascular oxygen saturation was measured using retinal oximeter with the built-in software. The flow area of choriocapillary layers and mean retinal vessel oxygen saturation before and after surgery were compared.

RESULTS

Three months after vitrectomy, the foveal flow area of choriocapillary layer increased clinically significantly from 1.5 ± 0.2 to 1.6 ± 0.2 mm² (p = 0.02). The retinal vascular changes of SCPs and DCPs were not statistically significant. The mean retinal arterial oxygen saturation was 89.9 ± 11.3% preoperatively and increased to 94.5 ± 9.7% postoperatively (p = 0.04). Foveal retinal thickness revealed a clinically significant decrease from 547.8 ± 88.2 μm to 403.0 ± 47.5 μm after surgery (p < 0.05). Postoperative best corrected visual acuity had no statistically significant correlation with foveal flow area of the choriocapillary layer and retinal vascular oxygen saturation.

CONCLUSIONS

There was a decrease of retinal thickness, an improved flow area of choriocapillary layer in macular region, and an increase of retinal arterial vascular oxygen among iERMs patients after vitrectomy.

Association between retinal microvasculature and optic disc alterations in high myopia

Purpose

This study aimed to explore the characteristics of retinal perfusion and its associations with high myopia.

Methods

A total of 760 participants were included. Peripapillary radial peripapillary capillary perfusion, foveal avascular zone, and parafoveal perfusion were measured using optical coherence tomography angiography (OCTA). Tilted disc ratio and parapapillary atrophy were determined using swept-source optical coherence tomography.

Results

A total of 760 young healthy participants with myopic eyes were included in the analysis. The mean axial length and titled disc ratio were 26.43 ± 1.14 and 0.76 ± 0.08 mm in the high-myopia group and 24.79 ± 0.75 and 0.80 ± 0.09 mm in the control group, respectively. The high-myopia group exhibited significantly larger parapapillary atrophy, lower tilted disc ratio, lower radial peripapillary capillary vessel density, larger area of foveal avascular zone, and lower deep parafoveal vessel density. In the multivariate analysis, titled disc ratio significantly correlated with radial peripapillary capillary vessel density (P = 0.0134), larger foveal avascular zone (P = 0.0062), and lower deep parafoveal vessel density (P < 0.0001).

Conclusions

Reduced radial peripapillary capillary and deep parafoveal vessel density and enlarged area of foveal avascular zone were observed in high myopia. Tilted disc ratio correlated with retinal perfusion.

Variation in abundance of predicted resistance genes in the Brassica oleracea pangenome

Brassica oleracea is an important agricultural species encompassing many vegetable crops including cabbage, cauliflower, broccoli and kale; however, it can be susceptible to a variety of fungal diseases such as clubroot, blackleg, leaf spot and downy mildew. Resistance to these diseases is meditated by specific disease resistance genes analogs (RGAs) which are differently distributed across B. oleracea lines. The sequenced reference cultivar does not contain all B. oleracea genes due to gene presence/absence variation between individuals, which makes it necessary to search for RGA candidates in the B. oleracea pangenome. Here we present a comparative analysis of RGA candidates in the pangenome of B. oleracea. We show that the presence of RGA candidates differs between lines and suggests that in B. oleracea, SNPs and presence/absence variation drive RGA diversity using separate mechanisms. We identified 59 RGA candidates linked to Sclerotinia, clubroot, and Fusarium wilt resistance QTL, and these findings have implications for crop breeding in B. oleracea, which may also be applicable in other crops species.

Retinal structural-vascular-functional relationship using optical coherence tomography and optical coherence tomography - angiography in myopia

Background

To examine the retinal structure–vascular-function relationship using optical coherence tomography (OCT) and optical coherence tomography angiography (OCTA) in myopia.

Methods

This was a prospective cross-sectional study comprising 86 eyes of 45 individuals with varying axial lengths and spherical equivalents and no posterior segment abnormalities. All eyes underwent optical coherence tomography with the Spectralis SD-OCT and OCTA with RTVue-XR Avanti; Optovue. Individual macular retinal layer thicknesses and flow areas and vessel densities were measured on OCT and OCTA, respectively. Linear correlations were made between the macular layer thicknesses, flow areas and vessel densities with axial length, spherical equivalent and visual acuity.

Results

The participants’ mean ages were 33.34 ± 14.45 years, mean spherical equivalent refractions were − 7.17 ± 5.71 D and axial lengths were 25.95 ± 2.41 mm. There were significant positive correlations of foveal angle (r = 0.757, p = 0.001), inner retinal (r = 0.764, p = 0.001) and outer plexiform layer (r = 0.771, p = 0.001) thickness on OCT and vessel densities in deep capillary plexus (r = 0.313, p = 0.003) on OCTA with axial length and negative correlations with spherical equivalents and visual acuity. Significant negative correlations of outer nuclear layer (r = − 0.560, p = 0.03) and photoreceptor outer segment layer thickness (r = − 0.856, p < 0.001) were noted on OCT with axial length and positive correlations with spherical equivalents and visual acuity.

Conclusion

The lateral retinal stretching in myopia could possibly explain the correlation between retinal layer thickness, vascular density and visual acuity in these eyes. Further research is required to investigate this.

Macular perfusion changes assessed with optical coherence tomography angiography after vitrectomy for rhegmatogenous retinal detachment

PURPOSE

To explore macular perfusion changes in patients with rhegmatogenous retinal detachment (RRD) involved the macula following successful surgery and to evaluate the correlation between macular blood flow density and visual outcomes using optical coherence tomography angiography (OCTA).

METHODS

This retrospective study included 14 eyes (14 patients) with macular-off RRD that underwent a standard three-port 23-gauge pars plana vitrectomy (PPV) and intraocular gas tamponade combined with phacoemulsification, aspiration, and intraocular lens implantation. OCTA was used to evaluate the macular perfusion changes throughout postoperative 12 weeks in the superficial capillary plexus (SCP), deep capillary plexus (DCP), and choriocapillary plexus (CCP). The fellow unaffected eyes were used as controls for comparison.

RESULTS

A significant increase in the superficial capillary plexus flow density (SCPFD) (P = 0.000) was observed over time in RRD eyes with successful PPV, as well as the deep capillary plexus flow density (DCPFD) (P = 0.000) and the choriocapillary plexus flow density (CCPFD) (P = 0.000). Final best-corrected visual acuity (BCVA) was positively associated with CCPFD (r = - 0.577, P = 0.031) and non-correlated with SCPFD and DCPFD (P > 0.05).

CONCLUSIONS

Macular perfusion gradually recovered following successful RRD repair by PPV. OCTA provided a non-invasive method to explore the underlying reason for different postoperative visual outcomes in macular-off RRD patients.

ADULT-ONSET FOVEOMACULAR VITELLIFORM DYSTROPHY EVALUATED BY MEANS OF OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY: A Comparison With Dry Age-Related Macular Degeneration and Healthy Eyes

PURPOSE

To investigate alterations of superficial and deep retinal vascular densities, as well as of choroidal thickness, in patients affected by adult-onset foveomacular vitelliform dystrophy (AOFVD).

METHODS

A total of 22 eyes (15 patients) affected by AOFVD were recruited in the study. Furthermore, 20 eyes of 20 healthy subjects and 20 eyes of 18 patients affected by intermediate dry age-related macular degeneration (AMD) were enrolled. All patients underwent a complete ophthalmologic examination, including optical coherence tomography angiography. Outcome measures were superficial vessel density, deep vessel density, and choroidal thickness.

RESULTS

Parafoveal superficial vessel density was increased in patients with AOFVD compared with the AMD group (50.6 ± 4.3% and 46.3 ± 4.3%, respectively, P = 0.016). Parafoveal deep vessel density was 57.9 ± 6.4% in patients with AOFVD, 52.2 ± 3.8% in patients with AMD, and 52.7 ± 6.0% in healthy controls (P = 0.006 and P = 0.035, respectively, after comparison with the AOFVD group).

CONCLUSION

We demonstrated that both superficial and deep vessel densities were significantly increased in patients with AOFVD, after the comparison with intermediate patients with AMD. These findings suggest that the pathogenic mechanisms in AOFVD are different from those in AMD and that optical coherence tomography angiography could be useful in differentiate early stages of these two diseases.

Assessment of capillary dropout in the superficial retinal capillary plexus by optical coherence tomography angiography in the early stage of diabetic retinopathy

Background

To assess capillary dropout in the superficial retinal capillary plexus (SCP) by optical coherence tomography angiography (OCTA) in the early stage of diabetic retinopathy (DR).

Methods

This study was a cross-sectional observational study. Patients that underwent OCTA examinations in our hospital between November 2015 and May 2016 were included in the study. The subjects were divided into two groups: A) normal controls (41 eyes of 41 subjects) and B) the DR patients (49 eyes of 49 patients with mild non-proliferative DR (NPDR)). The retinal thickness and SCP vessel density were analyzed using built-in software in nine sections of the macular area; whole scan area; fovea; parafovea; and sub-sections of the parafovea, superior-hemi, inferior-hemi, temporal, superior, nasal, and inferior. The correlation between vessel density and retinal thickness was also analyzed.

Results

The SCP density was significantly lower (P < 0.05) in mild NPDR patients than in normal controls in all areas, with the exception of the fovea (P > 0.05). In the parafovea, superior-hemi, inferior-hemi, temporal, and nasal sectors of group B, the SCP density was negatively correlated with the corresponding retinal thickness (P < 0.05). Specifically, as the SCP density decreased, retinal thickness increased.

Conclusions

In the early stage of NPDR, retinal capillary dropout and retinal thickness changes can be clearly captured and analyzed by OCTA. The results confirm a negative correlation between vessel density and retinal thickness in diabetic patients. This noninvasive technique could be applied for DR detection and monitoring. Further study with a larger sample size is warranted.

OCTA vessel density changes in the macular zone in glaucomatous eyes

PURPOSE

To evaluate whether macular optical coherence tomography angiography (OCTA) can detect altered vessel density (VD) in the superficial and deep vascular plexus in glaucomatous eyes and to compare the diagnostic utility of the individual VD parameters.

METHODS

The macular VD of 135 eyes, comprising 85 eyes diagnosed with glaucoma and 50 healthy control eyes, was examined using two OCTA devices (AngioPlex-Zeiss Meditec, Inc., Dublin, CA, USA, and AngioVue-OptoVue, Inc., Fremont, CA, USA). All study participants had neither vascular pathology, diabetes, nor vasoactive medication. The macular VD was measured at two different levels of segmentation (superficial [SL] and deep [DL] retinal vascular plexus) with a 6 × 6-mm macula scan, and VD was correlated with various structural and functional measurements. In order to test the accuracy of differentiation between eyes with and without glaucoma, we calculated the receiver operating characteristic (ROC) curve and the area under the curve (AUC).

RESULTS

Macular VD was significantly lower in both SL and DL in glaucomatous eyes than in healthy eyes (p = SL < 0.0001; DL = 0.009). There was no significant difference in VD between the SL and the DL (p = 6.60 · 10^-18). The greatest reduction of VD in glaucomatous eyes was found in the inferior macular sector. There was no correlation of VD with age or refractive error but moderate to high correlation with intraocular pressure, time of initial diagnosis, mean deviation, ganglion cell complex, peripapillary retinal nerve fiber layer thickness, cup to disc ratio, and rim area. Among the 14 individual features of macular VD, whole VD in the SL had the best diagnostic accuracy (77.6%) as measured by the area under the ROC.

CONCLUSION

OCTA detects glaucomatous damage by measuring the macular vessel density in the superficial and deep retinal vascular plexus. It can be an additional diagnostic tool to detect glaucoma independently of the optic nerve.

Determinants of Peripapillary and Macular Vessel Densities Measured by Optical Coherence Tomography Angiography in Normal Eyes

PURPOSE

The aim of this study was to evaluate the effect of subject-related (age, sex, and systemic hypertension and diabetes), eye-related (refractive error, optic disc size), and technology-related (signal strength index, SSI of the scans) determinants on the peripapillary and macular vessel densities measured with optical coherence tomography angiography (OCTA) in normal eyes.

METHODS

In a cross-sectional study, 181 normal eyes of 107 subjects (45 men, 62 women, median age: 50 y, range: 18 to 77 y) underwent OCTA imaging. Linear mixed models were used to analyze the effect of the determinants on the peripapillary and macular vessel densities measured with OCTA.

RESULTS

It was found that age and optic disc size did not affect the vessel densities of any of the regions (P>0.05 for all associations). En face optic disc (coefficient: 1.67, P<0.001) and most of the peripapillary vessel densities were higher in female individuals. En face disc (coefficient=-1.88, P=0.02) and most of the peripapillary vessel densities were lower, whereas the parafoveal vessel density was higher (coefficient=2.32, P=0.01), in subjects with hypertension. Most of the vessel densities were lower in subjects with diabetes. SSI showed a statistically significant association with the vessel densities of all regions (coefficients: 0.14 to 0.27 for peripapillary and 0.20 to 0.27 for macular sectors).

CONCLUSIONS

Most of the peripapillary vessel densities were higher in female subjects. Hypertension and diabetes also affected the vessel densities. Vessel densities in all the regions were significantly higher in scans with higher SSI. These results should be considered when interpreting the vessel densities in retinal diseases and glaucoma.

Optical coherence tomography angiography: Technical principles and clinical applications in ophthalmology

Optical coherence tomography angiography (OCTA) is a functional extension of OCT that provides information on retinal and choroidal circulations without the need for dye injections. With the recent development of high-speed OCT systems and efficient algorithms, OCTA has become clinically feasible. In this review article, we discuss the technical principles of OCTA, including image processing and artifacts, and its clinical applications in ophthalmology. We summarize recent studies which qualitatively or quantitatively assess disease presentation, progression, and/or response to treatment.

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.

Determination of Topographic Variations in Inner Retinal Blood Flow Areas in Young Chinese Subjects Using Optical Coherence Tomography Angiography

PURPOSE

To investigate (i) topographic variations in, and (ii) establish references for, inner retinal blood flow areas of the macular region of young Chinese subjects by means of optical coherence tomography (OCT) angiography.

METHODS

To measure inner retinal blood flow areas, we scanned an 8 × 8 mm² area and centered on the fovea of 336 eyes from 170 subjects using OCT angiography. Blood flow area measurements were made from a 1-mm radius circle, centered on the fovea, and 3 mm to the fovea superiorly, inferiorly, temporally, and nasally.

RESULTS

Mean inner retinal blood flow areas in the parafoveal, superior, inferior, nasal, and temporal macular regions were 1.78 ± 0.28, 1.76 ± 0.30, 1.69 ± 0.31, 1.91 ± 0.31, and 1.71 ± 0.28 mm,² respectively. Nasal inner retinal blood flow areas were significantly larger than other macular regions (p < 0.001). Gender was significantly associated with inner retinal blood flow areas of all macular regions studied. A gender-based subgroup analysis showed that inner retinal blood flow areas in superior, inferior, nasal, and temporal macular regions were significantly larger in women than men (all p < 0.05).

CONCLUSIONS

Nasal blood flow areas were larger than parafoveal blood flow areas, which were larger than superior blood flow areas, which were larger than temporal blood flow areas, which were larger than inferior blood flow areas in the macular regions studied. Gender was significantly associated with inner retinal blood flow areas in all macular regions studied.

OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY ASSESSMENT OF VASCULAR EFFECTS OCCURRING AFTER AFLIBERCEPT INTRAVITREAL INJECTIONS IN TREATMENT-NAIVE PATIENTS WITH WET AGE-RELATED MACULAR DEGENERATION

PURPOSE

To investigate vessel changes occurring after aflibercept injections in treatment-naive exudative age-related macular degeneration patients.

METHODS

Fifteen eyes of 15 patients affected by wet age-related macular degeneration were enrolled in the study. All the patients had a diagnosis of Type 1 choroidal neovascularization and were treated with 3 monthly aflibercept intravitreal injections (IVI). Subjects were evaluated by means of optical coherence tomography angiography at baseline, the day after the first injection and one month after both the first and the second IVI. At last, all the patients were followed up to 2 months after the third IVI.

RESULTS

Foveal superficial vascular plexus flow density was 29.01% (21.13-37.32%) at baseline and was significantly reduced as soon as 1 month after the first IVI (median: 20.78%; interquartile range: 14.75-23.13%; P = 0.017). Parafoveal superficial vascular plexus flow density was 47.09% (44.91-51.72%) at baseline and significantly decreased as soon as 1 month after the second IVI (median: 44.40%; interquartile range: 41.59-49.29%; P = 0.034). Choroidal neovascularization lesion area remained stable throughout the follow-up. Nevertheless, interestingly, choroidal neovascularization flow area was significantly reduced as soon as the next day the first IVI (median: 0.37 mm and interquartile range: 0.27-0.72 mm at baseline; median: 0.30 mm and interquartile range: 0.24-0.64 mm at 1 day after the first IVI; P = 0.047).

CONCLUSION

Intravitreal aflibercept injections are associated with a significant change in native retinal and choroidal vasculature. Moreover, the treatment did not cause a reduction in lesion area, but rather reduced the flow in the choroidal neovascularization.

Retinal and choroidal vascular features in patients with retinitis pigmentosa imaged by OCT based microangiography

PURPOSE

To image vascular features of retinitis pigmentosa (RP) using optical coherence tomography angiography (OCTA).

METHODS

Patients with RP were imaged by spectral domain optical coherence tomography based angiography (OCTA). The optical microangiography (OMAG) algorithm was applied to scanned datasets to generate 3D OCTA retinal angiograms, i.e., OMAG angiograms. Motion tracking was used to minimize artifacts due to eye movement, and large field of view OMAG angiograms were achieved through a montage scanning protocol. For better visualization, depth volumes were segmented to separate the superficial retinal layers from deep outer retinal layers. The choriocapillaris and other choroidal layers were also segmented. To investigate the changes in retinal architecture, the inner segment/outer segment (IS/OS) junction to RPE layer was segmented to generate en face structural images through averaging intensity projection. Color fundus images and/or Goldmann visual fields were available for comparison of the findings to OMAG images.

RESULTS

A total of 25 eyes (13 patients, seven women and six men) diagnosed with RP at various stages were enrolled in this study from October 2014 to January 2016 and imaged by OCTA. The resulting OMAG angiograms provided detailed visualization of retinal and choroidal vascular networks presented within the retina and choroid in a large field of view (FOV) (∼6.7 mm × 6.7 mm). All patients with a severity score greater than 3 showed abnormal microvasculature in both deep retinal and choroidal layers on OMAG images. Images of patients with a score of 4 indicating only peripheral abnormalities demonstrated relatively normal vasculature networks. Microvascular changes in the retinal and choroidal vasculature correlate with structural changes in the slab from IS/OS junction to RPE layer.

CONCLUSIONS

OCTA is useful in evaluating the microvascular changes in a large FOV encompassing the maculae of patients with RP. The large FOV of OMAG angiograms, enabled by the motion tracking, provides visualization of high definition and high resolution microvascular networks at varying stages of RP. Microvascular imaging may have significant utility in the diagnosis and monitoring of disease progression in RP patients.

Spectral-Domain Optical Coherence Tomography Angiography of Central Retinal Artery Occlusion

The authors report the use of optical coherence tomography angiography (OCTA) to determine retinal blood flow in a patient with central retinal artery occlusion (CRAO). Spectral-domain OCTA (SD-OCTA) was performed on an eye with CRAO. En face vascular images were constructed using an optical microangiography algorithm. The retinal vasculature was clearly imaged with high fidelity; areas of perfused retina were identified with exquisite detail. This study supports use of OCTA in diagnosing and monitoring CRAOs. Future research is warranted to recognize full potential of this imaging modality. [Ophthalmic Surg Lasers Imaging Retina. 2016;47:467-470.].

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.

Interchangeability and reliability of macular perfusion parameter measurements using optical coherence tomography angiography

AIM

The aim of the study was to investigate the interchangeability and reliability of macular perfusion measurements using optical coherence tomography angiography.

METHODS

A prospective cross-sectional observational study. Healthy adult Chinese subjects were recruited. Macular perfusion parameters were automatically analysed by software included in a spectral-domain optical coherence tomography system. The vessel density (VD) of the whole, parafovea, superior-hemi, inferior-hemi, fovea, temporal, superior, nasal and inferior quadrants as well as the foveal avascular zone (FAZ) and choroidal capillary VD (CCVD) were quantified.

RESULTS

A total of 51 eyes in 27 subjects were included (8 men and 19 women, mean age 24±4 years). Significant differences in VD of all quadrants (all p<0.001) was detected between the 3×3 mm and 6×6 mm macular scan size. The biggest difference of VD between the two scan size was 5.14±4.03, which was not clinically meaningful. No statistically significant differences were found in FAZ or CCVD between the two different scan sizes. The mean intraclass correlation coefficient (ICC) between two measurements from the inter-rater of 20 eyes was from 0.560 to 0.893 for VD and 0.845 for FAZ. The mean ICC between two measurements from the intrarater of 20 eyes was from 0.497 to 0.870 for VD and 0.780 for FAZ.

CONCLUSIONS

FAZ and CCVD are interchangeable between the 3×3 mm and 6×6 mm macular scan sizes. The VD differences between the two different scan sizes are not clinically meaningful. The macular perfusion parameters presented good but not perfect reliability, which should be acknowledged in clinical practice.

Reproducibility of Perfusion Parameters of Optic Disc and Macula in Rhesus Monkeys by Optical Coherence Tomography Angiography

BACKGROUND

Optical coherence tomography (OCT) angiography is a novel technique by which we can detect the local perfusion of fundus directly. The aim of this study was to evaluate the reproducibility of optic disc and macular flow perfusion parameters in rhesus monkeys using OCT angiography.

METHODS

Eighteen healthy monkeys (18 eyes) were subjected to optic disc and macula flow index measurements via a high-speed and high-resolution spectral-domain OCT XR Avanti with a split-spectrum amplitude de-correlation angiography algorithm. Right eye was imaged 3 times during the first examination and once during each of the two following examinations. The intra-visit and inter-visit intraclass correlation coefficients (ICCs) were both determined.

RESULTS

The average flow indices of the four optic disc area layers were 0.171 ± 0.009 (optic nerve head), 0.015 ± 0.004 (vitreous), 0.052 ± 0.009 (radial peripapillary capillary), and 0.167 ± 0.011 (choroid). Average flow indices of the four macula area layers were 0.044 ± 0.011 (superficial retina), 0.036 ± 0.011 (deep retina), 0.016 ± 0.009 (outer retina), and 0.155 ± 0.013 (choroid). Intra-visit (ICC value: 0.821-0.954) and inter-visit (ICC value: 0.844-0.899) repeatability were both high.

CONCLUSIONS

The study is about the reproducibility of optic disc and macular perfusion parameters as measured by OCT angiography in healthy rhesus monkeys. Flow index measurement reproducibility is high for both the optic disc and macula of normal monkey eyes. OCT angiography might be a useful technique to assess changes when examining monkeys with experimental ocular diseases.

OCT angiography quantifying choriocapillary circulation in idiopathic macular hole before and after surgery

PURPOSE

To investigate the choriocapillary circulation in the macular area for eyes with unilateral idiopathic macular hole (IMH) before and after vitrectomy using optical coherence tomography angiography (OCTA).

METHODS

A prospective study of 25 patients with unilateral IMH who underwent vitrectomy and 30 age- and sex-matched healthy controls were recruited. Choriocapillary circulation was measured by OCTA to obtain two measurements: flow area and parafovea vessel density.

RESULTS

Flow area and parafovea vessel density of choriocapillaris in the macular area were significantly smaller and lower in IMH eyes than unaffected fellow eyes and healthy control eyes (p < 0.001), while no difference was found between unaffected fellow eyes and the healthy control eyes. One month after vitrectomy, the choriocapillary flow area and parafovea vessel density of IMH eyes significantly increased compared to the peroperative measurements (p < 0.001). Association analysis found that choriocapillary circulation measurements were negatively correlated with macular hole diameters in IMH eyes (p < 0.001), but was independent with best-corrected visual acuity (BCVA).

CONCLUSIONS

The macular choriocapillary flow area and parafovea vessel density in IMH eyes were lower than those of normal controls. In addition, the choriocapillary circulation was negatively correlated with macular hole diameter. Our findings suggested that choroidal circulation in the macular area might be affected by the intact structure of the fovea.

Concurrent OCT imaging of stimulus evoked retinal neural activation and hemodynamic responses

It is well established that major retinal diseases involve distortions of the retinal neural physiology and blood vascular structures. However, the details of distortions in retinal neurovascular coupling associated with major eye diseases are not well understood. In this study, a multi-modal optical coherence tomography (OCT) imaging system was developed to enable concurrent imaging of retinal neural activity and vascular hemodynamics. Flicker light stimulation was applied to mouse retinas to evoke retinal neural responses and hemodynamic changes. The OCT images were acquired continuously during the pre-stimulation, light-stimulation, and post-stimulation phases. Stimulus-evoked intrinsic optical signals (IOSs) and hemodynamic changes were observed over time in blood-free and blood regions, respectively. Rapid IOSs change occurred almost immediately after stimulation. Both positive and negative signals were observed in adjacent retinal areas. The hemodynamic changes showed time delays after stimulation. The signal magnitudes induced by light stimulation were observed in blood regions and did not show significant changes in blood-free regions. These differences may arise from different mechanisms in blood vessels and neural tissues in response to light stimulation. These characteristics agreed well with our previous observations in mouse retinas. Further development of the multi-modal OCT may provide a new imaging method for studying how retinal structures and metabolic and neural functions are affected by age-related macular degeneration (AMD), glaucoma, diabetic retinopathy (DR), and other diseases, which promises novel noninvasive biomarkers for early disease detection and reliable treatment evaluations of eye diseases.

Optical coherence tomography angiography of macular telangiectasia type 1: Comparison with mild diabetic macular edema

OBJECTIVE

The present study aimed to investigate the characteristics of macular telangiectasia type 1 (Mac tel type 1) using spectral-domain optical coherence tomography angiography (OCTA) and compare them with the characteristics of mild diabetic macular edema (DME), to provide a new objective method for quick clinical diagnosis and treatment.

METHODS

A retrospective comparative analysis of 9 Mac tel type 1, 15 DME, and 15 normal eyes was performed using fluorescein angiography, spectral-domain optical coherence tomography, and OCTA. The morphological changes, retinal vessel density, and nonperfused areas were evaluated using split-spectrum amplitude-decorrelation angiography algorithm.

RESULTS

OCTA revealed obvious saccular capillary telangiectasia and loss of parafoveal vascular density of Mac tel type 1. However, a number of line segment hyperreflective signals around the macula and more distinct nonperfusion in DME were observed. The quantitative foveal avascular zone mean area in Mac tel type 1 was larger than that in the normal eyes (0.40 ± 0.06 mm² vs. 0.88 ± 0.19 mm² , P < 0.001). However, the area in DME (1.52 ± 0.38 mm² ) was larger than that in Mac tel type 1 (P < 0.001), and the foveal zone area in DME (1.127 ± 0.05 mm² ) was also lager than it in Mac tel (P < 0.05). The vascular density of the superficial layer reduced in both Mac tel type 1 and DME (compared with normal eyes). The difference between Mac tel type 1 (49.56 ± 5.23)% and DME(44.58 ± 3.82)% was significant in the superficial capillary layer (P < 0.01). The vascular density of the retinal deep layer also reduced in both Mac tel type 1 and DME (compared with normal eyes). The difference between Mac tel type 1 (53.78 ± 7.36)% and DME (53.64 ± 4.96)% was no significant in this layer (P > 0.05).

CONCLUSION

Morphological differences between Mac tel 1 and DME can be observed on OCTA. Superficial vascular density and non-perfusion area may serve as a quantitative method to identify them. Lasers Surg. Med. 49:225-232, 2017. © 2017 Wiley Periodicals, Inc.

Peripapillary retinal vessel density in eyes with acute primary angle closure: an optical coherence tomography angiography study

PURPOSE

The purpose was to investigate peripapillary retinal vessel density in resolved acute primary angle closure (APAC) eyes.

METHODS

This was a prospective, cross-sectional observational study. Thirty-four eyes of 34 patients with unilateral APAC were included, together with the fellow eyes with primary angle closure suspect (PACS) as controls. Peripapillary retinal vessel density was measured using optical coherence tomography (OCT) angiography. Peripapillary retinal vessel density was compared in both eyes and the potential relationship with visual field (VF) test results was evaluated.

RESULTS

After an acute attack, the peripapillary retinal vessel density was lower in the APAC than in the PACS eyes (79.3 ± 8.2 versus 85.6 ± 4.9, respectively; P = 0.001). The VF mean deviation (MD) (-7.7 ± 6.7 versus -3.3 ± 1.8 dB, P = 0.002), and the pattern standard deviation (PSD) (4.6 ± 3.3 versus 2.4 ± 0.9 dB, P = 0.001) were worse for the APAC than the PACS eyes, but both had similar thicknesses of the retinal nerve fiber layer (RNFL) (111.8 ± 9.6 versus 114.1 ± 29.1 μm, P = 0.880) and ganglion cell complex (GCC) (94.7 ± 7.5 versus 91.8 ± 9.3 μm, P = 0.328). The peripapillary retinal vessel density was significantly correlated with the VF MD (vessel density: r = 0.455, P = 0.008) and PSD (vessel density: r = -0.592, P < 0.001) in the APAC eyes.

CONCLUSIONS

Even when IOP was normalized after the acute attack, the APAC eyes had a lower peripapillary retinal vessel density, which was correlated with the VF values. OCT angiography is a reliable method for detecting vascular changes in glaucomatous eyes that show no thinning of the RNFL and GCC.

Vascular flow density in pathological myopia: an optical coherence tomography angiography study

OBJECTIVES

To investigate vascular flow density in pathological myopia with optical coherence tomography (OCT) angiography.

DESIGN

A prospective comparative study was conducted from December 2015 to March 2016.

SETTING

Participants were recruited in Beijing Tongren Hospital.

PARTICIPANTS

A total of 131 eyes were enrolled, which were divided into three groups: 45 eyes with emmetropia (EM; mean spherical equivalent (MSE) 0.50D to -0.50D), 41 eyes with high myopia (HM; MSE ≤-6.00D, without pathological changes), and 45 eyes with pathological myopia (PM; MSE ≤-6.00D and axial length (AL) ≥26.5 mm, and with pathological changes).

MAIN OUTCOME MEASURES

Macular, choriocapillaris and radial peripapillary capillary (RPC) flow densities were measured and compared between groups, and their relationships with AL and best corrected visual acuity (BCVA) were analysed.

RESULTS

Significant differences were found in macular, choriocapillaris and RPC flow densities among the three groups (p<0.05). Multiple comparisons revealed that, compared with the EM and HM groups, macular and RPC flow densities of the PM group were significantly decreased (p<0.05), but no significant difference in choriocapillaris flow density was found between the PM and HM groups (p=0.731). Compared with the EM group, retinal flow density in the macular and arcuate fibre region was not decreased in the HM group. In addition, there was a negative correlation between AL and superficial macular flow density (β=-0.542, p<0.001), deep macular flow density (β=-0.282, p=0.002) and RPC flow density (β=-0.522, p<0.001); and a positive correlation between BCVA and superficial macular flow density (β=0.194, p=0.021), deep macular flow density (β=0.373, p<0.001), and choriocapillaris flow density (β=0.291, p=0.001).

CONCLUSIONS

Macular and RPC flow densities decreased in pathological myopia compared with high myopia and emmetropia. No significant decrease of retinal flow density in the macular and arcuate fibre region was found in high myopic eyes compared with emmetropic eyes. Moreover, macular and RPC flow densities were negatively related to AL, and macular flow density was positively related to BCVA.

Visualization of micro-capillaries using optical coherence tomography angiography with and without adaptive optics

The purpose of this work is to investigate the benefits of adaptive optics (AO) technology for optical coherence tomography angiography (OCTA). OCTA has shown great potential in non-invasively enhancing the contrast of vessels and small capillaries. Especially the capability of the technique to visualize capillaries with a lateral extension that is below the transverse resolution of the system opens unique opportunities in diagnosing retinal vascular diseases. However, there are some limitations of this technology such as shadowing and projection artifacts caused by overlying vasculature or the inability to determine the true extension of a vessel. Thus, the evaluation of the vascular structure and density based on OCTA alone can be misleading. In this paper we compare the performance of AO-OCT, AO-OCTA and OCTA for imaging retinal vasculature. The improved transverse resolution and the reduced depth of focus of AO-OCT and AO-OCTA greatly reduce shadowing artifacts allowing for a better differentiation and segmentation of different vasculature layers of the inner retina. The comparison is done on images recorded in healthy volunteers and in diabetic patients with distinct pathologies of the retinal microvasculature.

Application of optical coherence tomography angiography in assessment of posterior scleral reinforcement for pathologic myopia

AIM

To investigate the effect of posterior scleral reinforcement (PSR) on circulation of pathologic myopia eyes with posterior staphyloma by optical coherence tomography angiography (OCTA).

METHODS

The study included 30 pathologic myopia eyes with posterior staphyloma which underwent PSR (PSR group) for 6 to 18mo ago, and 30 age and myopia matched eyes without PSR surgery as control group. Macular, choriocapillaris and radial peripapillary capillary (RPC) flow density were measured by OCTA, and the measurements were compared between groups.

RESULTS

OCTA found no significant differences in macular flow density between PSR and control groups. For the superficial flow, whole enface flow density (WED), fovea density (FD), and parafoveal density (PD) were 46.55%±5.19% vs 47.29%±4.12% (P=0.542), 31.45%±6.35% vs 31.17%±4.48% (P=0.841), and 48.82%±5.66% vs 49.21%±4.15% (P=0.756) in PSR and control groups, respectively. For the deep flow, WED, FD, and PD were 52.07%±5.78% vs 53.95%±4.62% (P=0.168), 29.62%±6.55% vs 29.50%±6.38% (P=0.940), and 56.93%±6.17% vs 58.15%±5.13% (P=0.407) in PSR and control groups, respectively. The choriocapillary flow density was 61.18±3.25% in PSR group vs 60.88%±2.56% in control group (P=0.692). Also, OCTA found no significant differences in RPCs flow density between PSR and control groups. The optic disc WED, inside disc flow density and peripapillary flow density were 48.47%±4.77% vs 48.11%±4.57% (P=0.813), 45.47%±11.44% vs 46.68%±9.02% (P=0.709), 54.32%±5.29% vs 52.47%±6.62% (P=0.349) in PSR and control groups, respectively.

CONCLUSION

OCTA provides a non-invasive and quantitative approach for monitoring macular and papillary blood flow in pathologic myopia. PSR can not improve but may maintain the circulation of pathologic myopia eyes with posterior staphyloma.

Regional Comparisons of Optical Coherence Tomography Angiography Vessel Density in Primary Open-Angle Glaucoma

PURPOSE

To compare the diagnostic abilities of the vessel densities in optic nerve head (ONH), peripapillary, and macular regions measured using optical coherence tomography angiography (OCTA) in eyes with primary open-angle glaucoma (POAG), and to evaluate the effect of glaucoma severity (based on the mean deviation, MD), optic disc size, and pretreatment intraocular pressure (IOP).

DESIGN

Cross-sectional study.

METHODS

Seventy-eight eyes of 53 control subjects and 64 eyes of 39 POAG patients underwent OCTA imaging. Area under receiver operating characteristic (ROC) curves (AUC) and sensitivities at fixed specificities of vessel densities in ONH, peripapillary, and macular regions were analyzed. ROC regression was used to evaluate the effect of covariates on the diagnostic abilities.

RESULTS

The AUCs of ONH vessel densities ranged between 0.59 (superonasal sector) and 0.73 (average inside disc), peripapillary between 0.70 (nasal, superonasal and temporal) and 0.89 (inferotemporal), and macular between 0.56 (nasal) and 0.64 (temporal). AUC of the average peripapillary vessel density was significantly better than the average inside disc (P = .05) and macular (P = .005) measurement. MD showed a negative association with the AUCs of the vessel densities of all regions. Pretreatment IOP (coefficient: 0.09) showed a significant (P < .05) effect on the AUC of ONH vessel density.

CONCLUSIONS

Diagnostic ability of the vessel density parameters of OCTA was only moderate. Macular and inside disc densities had significantly lower diagnostic abilities in POAG than the peripapillary density. Diagnostic abilities of vessel densities increased with increasing severity of glaucoma and that of ONH vessel density with higher pretreatment IOPs.