Optical coherence tomography angiography (OCTA) flow speed mapping technology for retinal diseases

Compartmental analysis of retinal vascular parameters and thickness in myopic eyes using SS-OCTA

Background

This study aimed to comprehensively explore the thickness and topographic distributions of retinal vessel alterations of different myopic eyes by using swept-source OCT angiography (SS-OCTA).

Methods

One hundred myopes were included in this observational cross-sectional study. All participants underwent a series of ocular examinations of biometrical parameters, including spherical equivalent refraction (SER), axial length (AL), intraocular pressure (IOP), curvature radius (CR), and others. Retinal parameters like vessel density (VD) of different compartments of papillary and peripapillary sectors were measured by SS-OCTA, respectively. Two sample-independent T-test was applied to identify intraocular differences in retinal biometrical indicators between groups, and correlation analysis was used to explore potential relationships between AL/CR ratio and some ocular variables.

Results

For high myopic participants, they exhibited a lower vessel density, a lower small vessel density, and a lower flow area, especially in the superficial layer and the nerve fiber layer (RNFL), along with a thinner superficial layer, RNFL and retina. More alterations were proved in nasal peripapillary sectors in high myopes. We also explored their hidden relationship with AL/CR ratio. We found that in non-high myopes, the thickness of the whole retina, RNFL and the superficial layer were all negatively correlated with AL/CR ratio in the papillary and peripapillary zone. In contrast, the vessel density and flow area of several vessel layers were positively correlated. However, there wasn't so much significance found in high myopic eyes.

Conclusion

Retinal vessel microstructure was more easily affected in highly myopic eyes, especially in superficial blood vessels, and compartmental analysis showed that alterations in nasal peripapillary sectors were more evident. Additionally, we highlighted hidden correlations between AL/CR ratio and blood flow characteristics of specific vascular layers, which could serve as sensitive biometrical indicators of early retinal damages.

Impact of preocular and ocular circulatory dynamics on the vascular density of retinal capillary plexuses and choriocapillaris

PURPOSE

To highlight the influence of preocular and ocular vascular circulatory dynamics on the vascular density (VD) of retinal capillary plexuses (RCPs) and choriocapillaris (CC) in patients with and without cardiovascular risk (CVR) factors.

METHODS

A retrospective observational study in patients with and without CVR factors (type 1 and 2 diabetes, arterial hypertension, and hypercholesterolemia). Fluorescein (FA) and indocyanine (ICGA) angiography circulatory times were arterial time (FAAT), start (FAstartLF) and end (FAendLF) of laminar flow, and arterial time (ICGAAT), respectively. OCT angiography VDs were superficial (VDSCP) and deep (VDDCP) RCPs and CC (VDCC) VDs. Correlation and regression analysis were performed after adjusting for confounding factors.

RESULTS

177 eyes of 177 patients (mean age: 65.2 ± 15.9 years, n = 92 with and 85 without CVR) were included. VDSCP and VDDCP were significantly inversely correlated with FAAT, FAstartLF and FAendLF likewise VDCC with ICGAAT. Correlations were stronger in patients without CVR than with CVR. CVR, FAAT, FAstartLF and FAendLF were more strongly correlated with VDDCP than VDSCP. FAAT, FAstartLF and FAendLF significantly impacted VDSCP and VDDCP, likewise ICGAAT impacted VDDCP. VDDCP was most strongly impacted by FAAT and FAstartLF.

CONCLUSION

Ocular and pre-ocular circulatory dynamics significantly impacted RCPs and CC VDs, especially deep RCP.

Optical coherence tomography angiography of the retina and choroid in systemic diseases

Optical coherence tomography angiography (OCTA) has transformed ocular vascular imaging, revealing microvascular changes linked to various systemic diseases. This review explores its applications in diabetes, hypertension, cardiovascular diseases, and neurodegenerative diseases. While OCTA provides a valuable window into the body's microvasculature, interpreting the findings can be complex. Additionally, challenges exist due to the relative non-specificity of its findings where changes observed in OCTA might not be unique to a specific disease, variations between OCTA machines, the lack of a standardized normative database for comparison, and potential image artifacts. Despite these limitations, OCTA holds immense potential for the future. The review highlights promising advancements like quantitative analysis of OCTA images, integration of artificial intelligence for faster and more accurate interpretation, and multi-modal imaging combining OCTA with other techniques for a more comprehensive characterization of the ocular vasculature. Furthermore, OCTA's potential future role in personalized medicine, enabling tailored treatment plans based on individual OCTA findings, community screening programs for early disease detection, and longitudinal studies tracking disease progression over time is also discussed. In conclusion, OCTA presents a significant opportunity to improve our understanding and management of systemic diseases. Addressing current limitations and pursuing these exciting future directions can solidify OCTA as an indispensable tool for diagnosis, monitoring disease progression, and potentially guiding treatment decisions across various systemic health conditions.

Time-Resolved Dynamic Optical Coherence Tomography for Retinal Blood Flow Analysis

Purpose

Optical coherence tomography (OCT) representations in clinical practice are static and do not allow for a dynamic visualization and quantification of blood flow. This study aims to present a method to analyze retinal blood flow dynamics using time-resolved structural OCT.

Methods

We developed novel imaging protocols to acquire video-rate time-resolved OCT B-scans (1024 × 496 pixels, 10 degrees field of view) at four different sensor integration times (integration time of 44.8 µs at a nominal A-scan rate of 20 kHz, 22.4 µs at 40 kHz, 11.2 µs at 85 kHz, and 7.24 µs at 125 kHz). The vessel centers were manually annotated for each B-scan and surrounding subvolumes were extracted. We used a velocity model based on signal-to-noise ratio (SNR) drops due to fringe washout to calculate blood flow velocity profiles in vessels within five optic disc diameters of the optic disc rim.

Results

Time-resolved dynamic structural OCT revealed pulsatile SNR changes in the analyzed vessels and allowed the calculation of potential blood flow velocities at all integration times. Fringe washout was stronger in acquisitions with longer integration times; however, the ratio of the average SNR to the peak SNR inside the vessel was similar across all integration times.

Conclusions

We demonstrated the feasibility of estimating blood flow profiles based on fringe washout analysis, showing pulsatile dynamics in vessels close to the optic nerve head using structural OCT. Time-resolved dynamic OCT has the potential to uncover valuable blood flow information in clinical settings.

Comparative quantitative analysis of optical coherence tomography angiography in varied morphologies of macular neovascularization following intravitreal conbercept and ranibizumab treatments for neovascular age‑related macular degeneration

The present study aimed to examine the optical coherence tomography angiography (OCTA) parameters associated with macular neovascularization (MNV) in patients diagnosed with neovascular age-related macular degeneration (nAMD) and treated with either intravitreal conbercept (IVC) or ranibizumab (IVR). It enrolled 39 nAMD patients presenting with MNV, including 23 in the IVC group and 16 in the IVR group. All participants were treatment-naïve with intravitreal therapy and they underwent treatment following a '3+PRN' regimen. The MNV patterns identified through OCTA were categorized as Medusa, tangled, seafan and other variations. Key outcome measures encompassed best-corrected visual acuity (BCVA), MNV vascular area (MNV-VA), MNV vascular density (MNV-VD) ratio and central macular thickness (CMT). In the present study, 44 eyes were included, with 28 eyes undergoing treatment with IVC and 18 eyes with IVR. On day 90, there was a statistically significant improvement in mean BCVA from baseline among all patients treated with IVC (P=0.002). Notably, improved outcomes were observed in those with the 'tangled' pattern compared with the other three patterns (P=0.007). CMT exhibited a significant decrease from baseline (P=0.007), with consistent improvement observed across all four patterns (P=0.052) on day 90. The mean MNV-VA decreased in all patients, reaching statistical significance for the Medusa pattern (P=0.008), although the improvement in visual acuity was deemed unsatisfactory. Patients with the seafan pattern treated with IVR improved significantly in BCVA (P=0.042). The mean CMT significantly improved from baseline (P=0.001), consistent across the four patterns (P=0.114). Significant improvements were noted in the mean MNV-VA for the seafan pattern and in the mean MNV-VD ratio for the other patterns. The two regimens had no significant differences regarding BCVA, CMT, and MNV parameters. Conbercept emerged as a viable treatment option for patients presenting with tangled MNV patterns. On the other hand, ranibizumab might be considered an effective intervention for individuals with seafan MNV patterns. Notably, the Medusa MNV pattern was associated with a morphologic configuration indicative of a poor prognosis.

Evaluation and comparison of optical coherence tomography angiography (OCTA) parameters in normal and moderate myopic individuals

OBJECTIVE

The objective of this study was to evaluate and compare Optical Coherence Tomography Angiography (OCTA) parameters in patients with moderate myopia and healthy individuals retrospectively.

METHODS

A total of 80 male individuals aged 18-20 years were included in the study with 40 moderate myopic and 40 healthy persons. All participants underwent detailed ocular examination including refraction, intraocular pressure (IOP), visual acuity, biomicroscopy, OCTA measurement and optic biometry measurement. Retinal, retinal nerve fiber layer and choroidal layer thicknesses were evaluated in µm with the help of the software available in the OCTA device.

RESULTS

The mean axial length (24.32 ± 0.53 mm) was statistically significantly higher in the moderate myopic group (24.32 mm) compared to the healthy group (23.33 ± 0.61 mm) (p < 0.001). Spherical equivalent (SE) was found as -3.79 ± 0.91 D in the moderate myopic group and -0.22 ± 0.32 D in the healthy group (p < 0.05). The mean superficial foveal mean density (FovSupMVD) and the mean deep foveal mean density (FovDepMVD) were statistically significantly lower in the moderate myopic group than in the healthy group (both, p < 0.001). The mean retinal temporal thickness (RTt) was statistically significantly lower in the moderate myopic group (p = 0.017). There was a mild negative correlation between axial length and FovSupMVD, FovDepMVD in myopes. In axial length ROC analysis, the cutoff value for moderate myopes was found to be 24.15 mm. Mean superficial foveal mean density (FovSupMVD) and mean deep foveal mean density (FovDepMVD), mean retinal temporal thickness (RTt) were significantly lower in the group above 24.15 mm axial length compared to the group below 24.15 mm axial length (all three, p < 0.001). Foveal avascular zone was significantly higher in the group above 24.15 mm axial length (p = 0.016) CONCLUSION: The results of our study indicate that the mean axial length and spherical equivalent were significantly higher, while retinal temporal thickness, the mean superficial foveal mean density and the mean deep foveal mean density were significantly lower in patients with myopia up to -6.0 D compared to the healthy individuals.

The Impact of Carotid Endarterectomy on Choriocapillaris Perfusion

Purpose

The impact of carotid endarterectomy (CEA) on choriocapillaris (CC) perfusion was investigated using swept-source optical coherence tomography angiography (SS-OCTA) imaging before and after surgery in patients with clinically significant carotid artery stenosis (CAS).

Methods

In this prospective observational study, patients with clinically significant CAS undergoing unilateral CEA had SS-OCTA imaging performed in both eyes before and within 1 week after surgery. The percent CC flow deficits (CC FD%) and CC thickness were assessed using previously validated algorithms. Multivariable regression analysis was conducted to evaluate the impact of variables on the change in CC measurements.

Results

A total of 112 eyes from 56 patients with an average age of 72.6 ± 6.9 years were enrolled. At baseline, significantly higher CC FD% and thinner CC thickness were observed on the surgical side (eyes ipsilateral to the side of CEA) versus the nonsurgical side (eyes contralateral to the side of CEA) (P = 0.001 and P = 0.03, respectively). Following CEA, a significant reduction in CC FD% and a significant increase in CC thickness were detected on the surgical as compared with the nonsurgical side (P = 0.008 and P = 0.01, respectively). Smoking status positively affected CC FD% change (coefficient of variation [CV] = 0.84, P = 0.01) on the surgical side and negatively affected CC thickness change on both the surgical side (CV = -0.382, P = 0.009) and the nonsurgical side (CV = -0.321, P = 0.04). The degree of stenosis demonstrated a positive influence on CC FD% change (CV = 0.040, P = 0.02) on the surgical side.

Conclusions

Unilateral CEA on the side of clinically significant CAS increases carotid blood flow, which further results in improved CC perfusion.

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.

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

Purpose

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

Methods

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

Results

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

Conclusions

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

THE EFFECT OF INCREASING ACQUISITION SPEED ON OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY IMAGES: A Qualitative and Quantitative Analysis

PURPOSE

To evaluate the effect of two different A-scan rates on qualitative and quantitative parameters on optical coherence tomography angiography images in a clinical setting.

METHODS

Subjects undergoing a comprehensive ophthalmic examination were scheduled for optical coherence tomography angiography imaging using a new SPECTRALIS device allowing for 85 and 125 kHz scan rate. Consecutive registered 20° × 20° optical coherence tomography angiography images using both speeds were acquired using the follow-up tool. The acquisition time and the quality values of each scan were extracted and analyzed. The image quality was also graded in pairs by two independent graders.

RESULTS

Two-hundred and one eyes of 128 consecutive patients (67 males, 52.3%) were included. Mean acquisition time significantly decreased from 56.92 ± 24.6 seconds on the 85 kHz images to 39.39 ± 15.5 seconds on the 125 kHz images (P < 0.001). The percentage change in acquisition time showed a mean decrease of 28.47%. Mean Q value significantly decreased from 32.97 ± 2.8 dB on the 85 kHz images to 31.43 ± 2.6 dB on the 125 kHz images (P < 0.001). Overall, 92.5% of images were graded as equal or better at 125 kHz A-scan rate.

CONCLUSION

The use of optical coherence tomography angiography in daily clinical practice may require higher A-scan rates for an optimal workflow. Increased speed may also reduce image sensitivity and thus image quality could be compromised. In this study, 125 kHz scan rate using SPECTRALIS showed significant benefit with reduction on the acquisition time and no clinically significant differences on image quality analysis. Further studies evaluating qualitative and quantitative data in specific retinal conditions and using other devices are required to confirm these results.

Macular retinal circulation in healthy eyes examined by optical coherence tomography angiography extended interscan time analysis

PURPOSE

To examine whether extended interscan time (IST) on optical coherence tomography angiography (OCTA) can detect slow retinal blood flow, which is undetectable on default IST, in the healthy macula.

METHODS

OCTA (OCT-A1, Canon Inc.) scanning of a macular area measuring 4 × 4 mm2 of 14 healthy eyes of 14 healthy volunteers with no history or evidence of systemic and macular diseases was performed. ISTs were set at 7.6 (IST7.6, default setting), 12.0 (IST12.0), and 20.6 msec (IST20.6). Ten OCTA images were acquired at each IST, and an averaged image was created. For each averaged OCTA image obtained at IST7.6, IST12.0, and IST20.6, we defined the area surrounded by the innermost capillary ring as the foveal avascular zone (FAZ). We qualitatively evaluated the delineation of the capillaries consisting of the FAZ and quantitatively measured the FAZ area at each IST.

RESULTS

Extensions from IST7.6 to IST12.0 and IST20.6 could newly delineated retinal capillaries that were undetectable at the default IST; new capillaries were detected in 10 (71%) eyes at IST12.0 and 11 (78%) eyes at IST20.0. The FAZ areas were 0.334 ± 0.137 mm2, 0.320 ± 0.132 mm2, and 0.319 ± 0.129 mm2 for IST7.6, IST12.0, and IST20.0, respectively; the FAZ areas at IST12.0 and IST20.0 were significantly decreased compared with that at IST7.6 (p = 0.004 and 0.002, respectively).

CONCLUSION

In OCTA for healthy participants, extensions of the ISTs newly detected retinal capillaries with slow blood flow around FAZ. The FAZ shapes varied with different ISTs. Thus, the blood flow dynamics are not physiologically uniform around FAZ. Compared with conventional OCTA, this protocol enables a more detailed evaluation of retinal circulation and provides a better understanding of the physiological circulatory status of the healthy retina, and may enable the assessment of circulation in the very early stages in diseased eyes.

Optical coherence tomography angiography aspects of the retinal and optic disc microvascular morphology in erythemato-telangectatic rosacea

BACKGROUND

To investigate retinal and optic disc (OD) microvascular morphological changes in erythemato-telangiectatic rosacea (ETR) patients using optical coherence tomography angiography (OCTA), and compare the findings to age- and gender-matched healthy individuals.

METHODS

This study included newly diagnosed 31 ETR patients (31 right eyes, group 1) who were clinically diagnosed by two experienced dermatologists. A control group had 32 healthy individuals (32 right eyes, group 2). Demographic data, including age and gender were collected, followed by a thorough ophthalmologic exam. A 6 × 6 mm macular OCTA analysis of superficial and deep capillary plexus (SCP and DCP) vessel densities (VDs), as well as foveal avascular zone (FAZ) area, FAZ perimeter (PERIM), foveal VDs 300 µm area around FAZ (FD-300), and flow areas in the outer retinal and choriocapillaris, was then performed.

RESULTS

Mean age in groups 1 and 2 was 43.70 ± 13.02 and 43.62 ± 12.30 years, respectively (p=0.979). Male-to-female ratio in group 1 was 4:27 and 4:28 in group 2. Capillary flow analysis revealed slightly higher values in group 1 than in group 2, with the former having a significantly higher select area in the outer retinal layer (p=0.001) and flow area in the choriocapillaris (p=0.002). Despite slightly higher values in group 1, there were no significant differences in SCP and DCP VDs (p > 0.05), FAZ area (p=0.471), PERIM (p=0.778), or FD-300 (p=0.527).

CONCLUSIONS

ETR appears to be associated with posterior segment changes, especially retinal microvascular morphology, even in asymptomatic ocular conditions. Given the disease's high rate of misdiagnosis, understanding rosacea-induced ocular manifestations is critical for ophthalmologists.

Recent Advances in Imaging Polypoidal Choroidal Vasculopathy with Swept-Source Optical Coherence Tomography Angiography

The gold standard for polypoidal choroidal vasculopathy (PCV) diagnosis is indocyanine green angiography (ICGA), but optical coherence tomography angiography (OCTA) has shown promise for PCV imaging in recent years. However, earlier generations of OCTA technology lacked the diagnostic efficacy to replace ICGA. Swept-source optical coherence tomography angiography (SS-OCTA), the latest generation of OCTA technology, has significantly improved penetrating ability, scanning speed, scanning range, and overall image quality compared with earlier generations of OCTA. SS-OCTA reveals a "tangled vasculature" pattern of polypoidal lesions (PLs), providing evidence that they are neovascular rather than aneurysmal structures. New choroidal biomarkers, such as the choriocapillaris flow void (FV), have been identified to explain the development of PCV lesions. Although no direct comparison between SS-OCTA and previous OCTA generations in terms of diagnostic capability has been performed, SS-OCTA has shown several advantages in differential diagnosis and monitoring early reactivation for PCV. These improvements make SS-OCTA a valuable tool for PCV diagnosis and follow-up, and it may become more important for this disease in the future. This review summarized recent advances in PCV morphology and structure, as well as the possible pathogenesis based on SS-OCTA findings. The value of SS-OCTA for PCV management is discussed, along with remaining issues, to provide an updated understanding of PCV and OCTA-guided management.

Clinical application of optical coherence tomography angiography in diabetic macular edema

Diabetic macular edema (DME) is characterized by a retinal thickening or hard exudation deposition in the fundus microvasculature, capillary leakage, increased vascular permeability, extracellular fluid accumulation in the fovea of a foveal disc. Optical coherence tomography angiography (OCTA) is a new item of fundus structure examination. OCTA is to reconstruct the retinal choroidal vascular structure from the continuous same cross-sectional views and blood flow signals obtained by optical scanning, thereby obtaining an image. It is very significant to evaluate, diagnose, treat and manage the disease.

Review article: Non-penetrating neck artery dissection in young adults: Not to be missed!

Young adults who present to the ED with neck pain following non-penetrating, seemingly trivial trauma to the neck, are at risk of neck artery dissection and subsequent stroke. Sport-related neck injury is the chief cause. Physical examination may often be unremarkable, and although there may be reluctance to expose young patients to radiation, radiological imaging is central to making a diagnosis of arterial wall disruption. A comprehensive literature search was performed in relation to neck artery dissection, and the evidence was scrutinised. We discuss the typical mechanism of injury, symptoms, anatomical considerations and clinical aids in diagnosis of neck artery dissection. Although the incidence is low, neck artery dissection has a mortality of 7%. As such, it is important for front-line physicians to have a high suspicion of the diagnosis and a low threshold to organise radiological examinations, specifically computerised tomography. Early detection of neck artery dissection will trigger clinical protocols that call for multi-disciplinary team management of this condition. In general, guideline-based recommendation for the management of neck artery dissection involving an intimal flap is by anti-platelet therapy while treatment of neck artery dissection that results in a pseudo-aneurysm or thrombosis is managed by surgical intervention or endovascular techniques. Close follow up combined with antithrombotic treatment is recommended in these individuals, the goal being prevention of stroke.

Evaluation of Retinal Microvascular Features in Patients with Amblyopia Based on Optical Coherence Tomography Angiography: A Systematic Review and Meta-Analysis

BACKGROUND

The performance of optical coherence tomography angiography (OCTA) in macular microvasculature of patients with amblyopia has been widely studied, but these studies have yielded different and controversial results.

OBJECTIVES

The aim of this study is to investigate retinal microvascular features in patients with amblyopia undergoing OCTA.

METHODS

PubMed, Embase, and Web of Science were searched for published articles comparing the retinal microvascular features between individuals with amblyopia and controls until April 2022. The mean difference with a 95% confidence interval was used to assess continuous variables.

RESULTS

The analysis included 17 studies. The whole vessel density of the superficial capillary plexus (SCPVD) was lower in amblyopic eyes (AE) than in normal eyes (NE) in 3 × 3 mm2 scans, while the perifoveal vessel density of superficial and deep capillary plexus was lower in 6 × 6 mm2 scans. The whole, parafoveal vessel density of deep capillary plexus (DCPVD) and parafoveal SCPVD were lower in both scans. The comparison between AE and fellow eyes (FE) revealed no statistical difference in all quadrants except the parafoveal and perifoveal SCPVD and the foveal DCPVD. Additionally, SCPVD in all quadrants except the fovea and DCPVD in all quadrants except the parafoveal were higher in FE compared to NE. No significant difference was found in the foveal avascular area between AE and NE, AE and FE, or NE and FE.

CONCLUSIONS

The retinal vessel density of superficial and deep capillary plexus in AE and FE was lower than in NE, and differences were more likely discovered using 6 × 6 mm2 scans. Consequently, OCTA might be explored as a diagnostic tool to identify and monitor patients with amblyopia.

Associations between Body Mass Index and Choroidal Thickness, Superficial and Deep Retinal Vascular Indices, and Foveal Avascular Zone measured by OCTA

AIM

The present study explores the effects of Body Mass Index (BMI) on choroidal thickness, the deep and superficial retinal capillary plexuses, and the foveal avascular zone (FAZ).

METHODS

The subjects in this prospective study were divided into five groups based on their calculated BMI. Choroidal thickness, superficial and deep retinal capillary plexuses, and FAZ were measured using enhance depth imaging (EDI) and optical coherence tomography angiography (OCTA). The groups were then compared and correlations with BMI were evaluated.

RESULTS

The study included 210 eyes of 105 subjects. The comparison of the BMI groups revealed a significant decrease in the mean choroidal thicknesses in the obese groups (p = 0.001), and a significant negative correlation between BMI and mean choroidal thickness (p = 0.02). The results of the analysis of the mean superficial and deep retinal capillary plexuses did not differ between the groups (p = 0.089, p = 0.808 respectively), while the deep FAZ measurements revealed a significant decrease in the obese groups (p = 0.003).

CONCLUSION

Choroidal thickness and deep FAZ are significantly negatively correlated with BMI, suggesting potential choroidal and retinal microvascular effects of obesity.

Persistent diabetic macular edema: Definition, incidence, biomarkers, and treatment methods

Intravitreal antivascular endothelial growth factor (anti-VEGF) treatment has drastically improved the visual and anatomical outcomes in patients with diabetic macular edema (DME); however, success is not always guaranteed, and a proportion of these eyes demonstrate persistent DME (pDME) despite intensive treatment. While standardized criteria to define these treatment-resistant eyes have not yet been established, many studies refer to eyes with no clinical response or an unsatisfactory partial response as having pDME. A patient is considered to have pDME if the retinal thickness improves less than 10-25% after 6 months of treatment. A range of treatment options have been recommended for eyes with pDME, including switching anti-VEGF agents, using corticosteroids and/or antioxidant drugs in adjunct with anti-VEGF therapy, and vitrectomy. In addition, multimodal imaging of DME eyes may be advantageous in predicting the responsiveness to treatment; this is beneficial when initiating alternative therapies. We explore the literature on persistent DME regarding its defining criteria, incidence, the baseline biological markers that may be useful in anticipating the response to treatment, and the available treatment options.

Optical Coherence Tomography Angiography (OCTA) of the eye: A review on basic principles, advantages, disadvantages and device specifications

Optical Coherence Tomography Angiography (OCTA) is a relatively new imaging technique in ophthalmology for the visualization of the retinal microcirculation and other tissues of the human eye. This review paper aims to describe the basic definitions and principles of OCT and OCTA in the most straightforward possible language without complex mathematical and engineering analysis. This is done to help health professionals of various disciplines improve their understanding of OCTA and design further clinical research more efficiently. First, the basic technical principles of OCT and OCTA and related terminology are described. Then, a list of OCTA advantages and disadvantages, with a special reference to blood flow quantification limitations. Finally, an updated list of the basic hardware and software specifications of some of the commercially available OCTA devices is presented.

Mingmu Xiaoyao granules regulate the PI3K/Akt/mTOR signaling pathway to reduce anxiety and depression and reverse retinal abnormalities in rats

Objective: To investigate the effects of Mingmu Xiaoyao granules (MMXY) on the morphology and function of the retina and the mechanism of PI3K/Akt/mTOR pathway-related proteins in rats with anxiety and depression induced by chronic unpredictable mild stress (CUMS).

Methods: Fifty-two male Sprague Dawley rats were randomly allocated to either a control (n = 14) or a simulated CUMS group (n = 38). The CUMS model was established successfully at 4 weeks. Six rats in each group were randomly selected to be sacrificed and their retinas isolated for histological examination. At 5 weeks, rats in the CUMS group were randomly allocated to the following groups: Model (CUMS + pure water), MMXY-H (CUMS + MMXY 7.2 g/kg/d), MMXY-L (CUMS + MMXY 3.6 g/kg/d), and CBZ (CUMS + Carbamazepine 20 mg/kg/d), with eight rats in each group. All rats were given the relevant intervention once a day. At 12 weeks, sucrose preference and open field tests were performed to evaluate the anxiety and depression status of rats. In live rats, optical coherence tomography angiography was used to measure retinal thickness and blood flow, while electroretinograms (ERGs) and visual evoked potentials (VEPs) were used to evaluate retinal function. The next day, the specimens were sacrificed for serological, histological, immunofluorescence, Western blot and transmission electron microscopy examinations to explore the mechanism of MMXY in CUMS rats.

Results: MMXY improved the anxiety and depression-like behavior of rats. Results of optical coherence tomography angiography showed that MMXY improved retinal inner thickness and blood flow in CUMS rats. MMXY improved the amplitude of a- and b-waves in the scotopic and photopic ERG, as well as N2 and P2 peak time and amplitude in the flash-VEP in CUMS rats. Retinal histological staining and transmission electron microscopy showed that MMXY reversed retinal morphology and ultrastructure in CUMS rats. MMXY reduced the expression of Beclin1 and LC3I/II proteins, regulated the PI3K/Akt/mTOR pathway, inhibited autophagy, and had a protective effect on the retina in CUMS rats.

Conclusion: MMXY may effectively improve retinal morphology and function as well as anxiety and depression-like behaviors in CUMS rats by regulating the PI3K/Akt/mTOR signaling pathway.

Imaging-based Assessment of Choriocapillaris: A Comprehensive Review

PURPOSE

Over the past two decades, advancements in imaging modalities have significantly evolved the diagnosis and management of retinal diseases. Through these novel platforms, we have developed a deeper understanding of the anatomy of the choroidal vasculature and the choriocapillaris. The recently developed tools such as optical coherence tomography (OCT) and OCT angiography (OCTA) have helped elucidate the pathological mechanisms of several posterior segment diseases. In this review, we have explained the anatomy of the choriocapillaris and its close relationship to the outer retina and retinal pigment epithelium.

METHODS

A comprehensive search of medical literature was performed through the Medline/PubMed database using search terms: choriocapillaris, choroid, quantification, biomarkers, diabetic retinopathy, age-related macular degeneration, choroidal blood flow, mean blur rate, flow deficit, optical coherence tomography, optical coherence tomography angiography, fluorescein angiography, indocyanine green angiography, OCTA, Doppler imaging, uveitis, choroiditis, white dot syndrome, tubercular serpiginous-like choroiditis, choroidal granuloma, pachychoroid, toxoplasmosis, central serous chorioretinopathy, multifocal choroiditis, choroidal neovascularization, choroidal thickness, choroidal vascularity index, choroidal vascular density, and choroidal blood supply. The search terms were used either independently or combined with choriocapillaris/choroid.

RESULTS

The imaging techniques which are used to qualitatively and quantitatively analyze choriocapillaris are described. The pathological alterations in the choriocapillaris in an array of conditions such as diabetes mellitus, age-related macular degeneration, pachychoroid spectrum of diseases, and inflammatory disorders have been comprehensively reviewed. The future directions in the study of choriocapillaris have also been discussed.

CONCLUSION

The development of imaging tools such as OCT and OCTA has dramatically improved the assessment of choriocapillaris in health and disease. The choriocapillaris can be delineated from the stromal choroid using the OCT and quantified by manual or automated methods. However, these techniques have inherent limitations due to the lack of an anatomical distinction between the choriocapillaris and the stromal choroid, which can be overcome with the use of predefined segmentation slabs on OCT and OCTA. These segmentation slabs help in standardizing the choriocapillaris imaging and obtain repeatable measurements in various conditions such as diabetic retinopathy, age-related macular degeneration, pachychoroid spectrum, and ocular inflammations. Additionally, Doppler imaging has also been effectively used to evaluate the choroidal blood flow and quantifying the choriocapillaris and establishing its role in the pathogenesis of various retinochoroidal diseases. As tremendous technological advancements such as wide-field and ultra-wide field imaging take place, there will be a significant improvement in the ease and accuracy of quantifying the choriocapillaris.

Optical coherence tomography angiography in primary eye care

Optical coherence tomography angiography (OCT-A) is a non-invasive imaging modality for assessing the vasculature within ocular structures including the retina, macula, choroid and optic nerve. OCT-A has a wide range of clinical applications in various optometric conditions which have been independently reported in the literature. This paper aims to present a review of the current literature on the clinical application of OCT-A in optometric practice as well as to analyse and evaluate the quality of the available evidence. This review included 78 articles from a literature search conducted on 26 May 2019 across the following databases: Cochrane Library of Systematic Reviews, Medline, Scopus and Web of Science. Primary ocular pathologies discussed in this review include glaucoma, diabetic retinopathy, age-related macular degeneration, myopia, acquired and congenital macular dystrophies, epiretinal membrane, retinal vein occlusion, retinitis pigmentosa, choroidal melanoma, uveitis, central serous chorioretinopathy, amblyopia and optic neuropathies. Primary outcome variables included vessel density, foveal avascular zone area and diameter, flow velocity and flow index. This review aims to evaluate the evidence available for OCT-A applications in diagnosis and prognosis of ocular conditions in an optometric setting.

Development of a Preclinical Laser Speckle Contrast Imaging Instrument for Assessing Systemic and Retinal Vascular Function in Small Rodents

Purpose

To develop and test a non-contact, contrast-free, retinal laser speckle contrast imaging (LSCI) instrument for use in small rodents to assess vascular anatomy, quantify hemodynamics, and measure physiological changes in response to retinal vascular dysfunction over a wide field of view (FOV).

Methods

A custom LSCI instrument capable of wide-field and non-contact imaging in small rodents was constructed. The effect of camera gain, laser power, and exposure duration on speckle contrast variance was standardized before the repeatability of LSCI measurements was determined in vivo. Finally, the ability of LSCI to detect alterations in local and systemic vascular function was evaluated using a laser-induced branch retinal vein occlusion and isoflurane anesthesia model, respectively.

Results

The LSCI system generates contrast-free maps of retinal blood flow with a 50° FOV at >376 frames per second (fps) and under a short exposure duration (>50 µs) with high reliability (intraclass correlation R = 0.946). LSCI was utilized to characterize retinal vascular anatomy affected by laser injury and longitudinally measure alterations in perfusion and blood flow profile. Under varied doses of isoflurane, LSCI could assess cardiac and systemic vascular function, including heart rate, peripheral resistance, contractility, and pulse propagation.

Conclusions

We present a LSCI system for detecting anatomical and physiological changes in retinal and systemic vascular health and function in small rodents.

Translational Relevance

Detecting and quantifying early anatomical and physiological changes in vascular function in animal models of retinal, systemic, and neurodegenerative diseases could strengthen our understanding of disease progression and enable the identification of new prognostic and diagnostic biomarkers for disease management and for assessing treatment efficacies.

Characterizing Flow and Structure of Diabetic Retinal Neovascularization after Intravitreal Anti-VEGF Using Optical Coherence Tomography Angiography: A Pilot Study

Background/Aims. This study evaluates changes of flow and structure of diabetic retinal neovascularization (NV) treated with intravitreal antivascular endothelial growth factor (VEGF) agents using optical coherence tomography angiography (OCTA). With OCTA, retinal blood vessels are visualized at high resolution to separately look at flow and structure information without the need for dye injection. We introduce a new measurement method including and combining information of flow and structure. Methods. Retrospective observational case series. Patients with proliferative diabetic retinopathy (PDR) were treated with intravitreal antiVEGF injections. Retinal NV were repeatedly imaged using swept-source OCTA (Zeiss PlexElite 9000) at baseline, after initial treatment block with 3-4 monthly injections, and during a follow-up period of up to 51 weeks. Change of size and flow density of the structural and angio area of NV was assessed. Results. Nine NV in eight eyes of five patients were analyzed with a median follow-up time of 45 weeks. After the initial treatment block, en face structural area regressed, 18.7% ± 39.0% (95% CI 44.2–6.8%, p=0.26), and en face angio area regressed, 51.9% ± 29.5% (95% CI 32.6 to 71.2%, p=0.007). Flow density within the en face structural area decreased by 33% ± 19.2% (95% CI 20.5–45.5%, p=0.0077). Flow density within the en face angio area decreased by mean 17.9% ± 25.2% (95% CI 1.4–34.4%, p=0.066). In two fellow eyes, NV recurrence could be observed before the onset of vitreous bleeding in one. Conclusion. Our study introduces a new quantitative measurement for NV in PDR, combining structure and flow measurement. The structure area remained after treatment, while its flow density and angio area regressed. We propose this measurement method as a more physiological and possibly more comparable metrics.

Mean macular intercapillary area in eyes with diabetic macular oedema after anti-vascular endothelial growth factor therapy and its association with treatment response

BACKGROUND

To evaluate the changes in the mean macular intercapillary area (ICA) from sequential enface optical coherence tomography angiography (OCTA) images following intravitreal anti-vascular endothelial growth factor (VEGF) therapy in initially treatment-naïve eyes with diabetic macular oedema (DME).

METHODS

In this multicentre retrospective study, 6 × 6 and 3 × 3 mm customised, total retinal projection enface OCTA images were collected and processed for quantitative assessment of ICA by a customised MATLAB software. Measurements were done in concentric regions centred on the fovea-with the exclusion of foveal avascular zone (FAZ)-in 0.5 mm diameter increments as well as within the intervening rings.

RESULTS

In this study, 6 × 6 mm OCTA images from 46 eyes of 29 patients, and 3 × 3 mm OCTA images from 23 eyes of 15 patients were included. There was no significant change in mean ICA after treatment in either scan size or in any measurement regions (all p > 0.05). Multivariate analysis revealed that baseline BCVA was significantly correlated with the visual outcome (p = 0.039). Additionally, after correction for age, baseline central retinal thickness (CRT), baseline BCVA, and retinopathy severity, mean ICA in the 1.5 mm circle was found to be a significant predictor of post treatment CRT, (p = 0.006).

CONCLUSIONS

Absence of significant change in mean ICA after a minimum of three intravitreal anti-VEGF injections, may indicate that, in the short term, anti-VEGF injections neither impair nor improve macular perfusion in DME. Baseline BCVA was found to be a robust predictor of functional outcome, while inner mean ICA was a significant predictor for macular thickness outcomes.

The role of magnification correction in macular vessel density assessment: a contralateral eye study in anisometropia patients

Background

Investigating the impact of magnification correction in macular vessel density using optical coherence tomography angiography (OCTA) in patients with anisometropia.

Methods

Cross-sectional study. Totally 47 patients (11 male, 36 female) aged >18 years with high myopia were analyzed. All patients underwent evaluation of visual acuity, subjective refraction, and axial length. Anisometropia (n=37) was defined as a refraction difference between paired eyes ≥0.75 D. The control group (n=10) consisted patients with a refraction difference ≤0.5 D. Superficial vessel density was performed using 3 mm × 3 mm Cirrus-HD OCTA protocol. The vessel length density (VLD) and foveal avascular zone area (FAZA) were analyzed before and after magnification correction using Bennett’s formula.

Results

The mean spherical equivalent (SE) was −10.54±3.47 D in the more myopic eye and −8.05±3.47 D in the contralateral eye (P<0.001). Before magnification correction, the mean perfusion density (PD) and VLD were both significantly lower in the more myopic eyes. After magnification correction, the VLD and PD did not differ between paired eyes. No statistical difference was found in terms of the FAZA between paired eyes regardless of magnification correction. The magnification-induced differences in both VLD and PD were positively correlated with the difference in SE (both r=0.86, P<0.001).

Conclusions

In OCTA analysis, magnification correction should be performed to reduce refraction error-induced image error, which deserves attention in the clinical application.

Looking Ahead: Visual and Anatomical Endpoints in Future Trials of Diabetic Macular Ischemia

Diabetic macular ischemia (DMI) is a common complication of diabetic retinopathy that can lead to progressive and irreversible visual loss. Despite substantial clinical burden, there are no treatments for DMI, no validated clinical trial endpoints, and few clinical trials focusing on DMI. Therefore, generating consensus on validated endpoints that can be used in DMI for the development of effective interventions is vital. In this review, we discuss potential endpoints appropriate for use in clinical trials of DMI, and consider the data required to establish acceptable and meaningful endpoints. A combination of anatomical, functional, and patient-reported outcome measures will provide the most complete picture of changes that occur during the progression of DMI. Potential endpoint measures include change in size of the foveal avascular zone measured by optical coherence tomography angiography and change over time in best-corrected visual acuity. However, these endpoints must be supported by further research. We also recommend studies to investigate the natural history and progression of DMI. In addition to improving understanding of how patient demographics and comorbidities such as diabetic macular edema affect clinical trial endpoints, these studies would help to build the consensus definition of DMI that is currently missing from clinical practice and research.

Effect of A-scan rate and interscan interval on optical coherence angiography

Optical coherence tomography angiography (OCTA) can provide rapid, volumetric, and noninvasive imaging of tissue microvasculature without the requirement of exogenous contrast agents. To investigate how A-scan rate and interscan time affected the contrast and dynamic range of OCTA, we developed a 1.06-µm swept-source OCT system enabling 100-kHz or 200-kHz OCT using two light sources. After system settings were carefully adjusted, almost the same detection sensitivity was achieved between the 100-kHz and 200-kHz modalities. OCTA of ear skin was performed on five mice. We used the variable interscan time analysis algorithm (VISTA) and the designated scanning protocol with OCTA images reconstructed through the correlation mapping method. With a relatively long interscan time (e.g., 12.5 ms vs. 6.25 ms for 200-kHz OCT), OCTA can identify more intricate microvascular networks. OCTA image sets with the same interscan time (e.g., 12.5 ms) were compared. OCTA images acquired with a 100-kHz A-scan rate showed finer microvasculature than did other imaging modalities. We performed quantitative analysis on the contrast from OCTA images reconstructed with different A-scan rates and interscan time intervals in terms of vessel area, total vessel length, and junction density.

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.

Optical flow optical coherence tomography for determining accurate velocity fields

Determining micron-scale fluid flow velocities using optical coherence tomography (OCT) is important in both biomedical research and clinical diagnosis. Numerous methods have been explored to quantify the flow information, which can be divided into either phase-based or amplitude-based methods. However, phase-based methods, such as Doppler methods, are less sensitive to transverse velocity components and suffer from wrapped phase and phase instability problems for axial velocity components. On the other hand, amplitude-based methods, such as speckle variance OCT, correlation mapping OCT and split-spectrum amplitude-decorrelation angiography, focus more on segmenting flow areas than quantifying flow velocities. In this paper, we propose optical flow OCT (OFOCT) to quantify accurate velocity fields. The equivalence between optical flow and real velocity fields is validated in OCT imaging. The sensitivity fall-off of a Fourier-domain OCT (FDOCT) system is considered in the modified optical flow continuity constraint. Spatial-temporal smoothness constraints are used to make the optical flow problem well-posed and reduce noises in the velocity fields. An iteration solution to the optical flow problem is implemented in a graphics processing unit (GPU) for real-time processing. The accuracy of the velocity fields is verified through phantom flow experiments by using a diluted milk powder solution as a scattering medium. Velocity fields are then used to detect flow turbulence and reconstruct flow trajectory. The results show that OFOCT is accurate in determining velocity fields and applicable to research concerning fluid dynamics.

Optical Coherence Tomography-Angiography in Geographic Atrophy

Geographic atrophy (GA) represents the non-exudative late stage of age-related macular degeneration and constitutes a leading cause of legal blindness in the developed world. It is characterized by areas of loss of outer retinal layers including photoreceptors, degeneration of the retinal pigment epithelium, and rarefication of the choriocapillaris. As all three layers are functionally connected, the precise temporal sequence and relative contribution of these layers towards the development and progression of GA is unclear. The advent of optical coherence tomography angiography (OCT-A) has allowed for three-dimensional visualization of retinal blood flow. Using OCT-A, recent studies have demonstrated that choriocapillaris flow alterations are particularly associated with the development of GA, exceed atrophy boundaries spatially, and are a prognostic factor for future GA progression. Furthermore, OCT-A may be helpful to differentiate GA from mimicking diseases. Evidence for a potential protective effect of specific forms of choroidal neovascularization in the context of GA has been reported. This article aims to give a comprehensive review of the current literature concerning the application of OCT-A in GA, and summarizes the opportunities and limitations with regard to pathophysiologic considerations, differential diagnosis, study design, and patient assessment.

Optical coherence tomography angiography findings of choroidal neovascularization secondary to decalcified choroidal osteoma treated with intravitreal aflibercept: A case report

INTRODUCTION

Choroidal osteoma (CO) is a rare benign ocular tumor characterized by ossifying choroid lesions. To the best of our knowledge, this is the first detailed report to describe the optical coherence tomography angiography (OCTA) findings of choroidal neovascularization (CNV) complicated by a rare decalcified CO following intravitreal aflibercept injection.

PATIENT CONCERNS

A 26-year-old woman presented with a spontaneous but painless reduction in visual acuity in her left eye that had commenced 5 days prior.

DIAGNOSIS

Clinical manifestations and multimodal imaging, including OCTA, spectral-domain optical coherence tomography, fundus fluorescein angiography and indocyanine green angiography, indicated decalcified CO with CNV.

INTERVENTIONS

After receiving an appropriately detailed explanation of the procedure, the patient was treated via intravitreal aflibercept(2.0 mg) injection once.

OUTCOMES

One month after the therapy, OCTA revealed that the flow areas of CNV were narrowed, the best-corrected visual acuity was improved to 20/30, however, 2 months follow-up OCTA revealed that the CNV reoccurred, the best-corrected visual acuity was dropped to 20/50.

CONCLUSION

Intravitreal aflibercept injection was an effective treatment for CO with CNV, but the effects may not last long. The OCTA findings provide a better appreciation of evaluating the effects of intravitreal aflibercept injection for CO complicating CNV.

Morphological changes in intraretinal microvascular abnormalities after anti-VEGF therapy visualized on optical coherence tomography angiography

Background

To examine the baseline morphological characteristics and alterations in intraretinal microvascular abnormalities (IRMAs) in response to anti-vascular endothelial growth factor (anti-VEGF) treatment, documented by optical coherence tomography angiography (OCTA) in diabetic eyes.

Methods

In this retrospective study, IRMAs were evaluated with multimodal imaging (fundus photography, fluorescein angiography, OCTA) in treatment-naïve diabetic eyes before and after anti-VEGF treatment for diabetic macular edema (DME) and/or proliferative diabetic retinopathy (PDR) and compared to diabetic control eyes with similar diabetic retinopathy (DR) severity that did not receive anti-VEGF therapy. The morphological characteristics of IRMAs on enface OCTA imaging were graded by masked readers at baseline, then after anti-VEGF therapy in treated eyes or after observation in control eyes. Characterization of interval changes in an IRMA were based on the following parameters: branching, vessel caliber and area of adjacent capillary non-perfusion.

Results

The treated group included 45 IRMA foci from 15 eyes of 11 patients, while the control group included 27 IRMA foci from 15 eyes of 14 patients. Following anti-VEGF treatment, enface OCTA demonstrated that 14 foci of IRMA (31%) demonstrated regression with normalization of appearance of the capillary bed, 20 IRMAs (44%) remained unchanged, six IRMAs (13%) progressed with enlargement or development of new IRMAs and five IRMAs (11%) demonstrated complete obliteration defined as IRMA disappearance with advancing capillary drop-out. In the control group, 17 IRMA (63%) remained stable, 8 IRMAs (29.6%) progressed and 2 experienced total obliteration (7.4%). The difference in rank order between the two groups was statistically significant (p = 0.022).

Conclusions

In eyes with DR status post anti-VEGF therapy, foci of IRMAs have a variable course demonstrating one of four possible outcomes: regression, stability, progression or complete obliteration. In contrast, none of the untreated control diabetic eyes demonstrated regression of IRMAs, consistent with known progression of DR severity in high risk eyes. Morphologic evaluation of IRMAs with OCTA may help to monitor changes in retinal blood flow as well as the response to anti-VEGF treatment.

Feasibility and Safety of a Coaxial Dual-Wavelength Optical Coherence Tomography Apparatus

PURPOSE

To evaluate the feasibility and safety of a coaxial dual-wavelength optical coherence tomography (OCT) device (marked as Hydra-OCT).

METHODS

Healthy participants without ocular pathology underwent retinal imaging using the Hydra-OCT allowing for simultaneous measurement of retinal scanning of 840 and 1,072 nm wavelength. Before and after measurement, best-corrected visual acuity and patients' comfort were assessed. Representative OCT images from both wavelengths were compared by 5 independent graders using a subjective grading scheme.

RESULTS

A total of 30 eyes of 30 participants (8 females and 22 males) with a mean age of 26.5 years (range from 19 to 55 years) were included. Dual-wavelength image acquisition was made possible in each subject. The participant's effort and comfort assessment using the Hydra-OCT imaging revealed an equivalent value as compared to the commercially available OCT machine. No adverse events were reported, and visual acuity was not altered by the Hydra-OCT. Imaging between the systems was comparable.

CONCLUSIONS

This study provides evidence for the feasibility and safety of a coaxial dual-wavelength OCT imaging method under real-life conditions. The novel Hydra-OCT imaging device may offer additional insights into the pathology of retinal and choroidal diseases.

Advances in Doppler optical coherence tomography and angiography

Since the first demonstration of Doppler optical coherence tomography (OCT) in 1997, several functional extensions of Doppler OCT have been developed, including velocimetry, angiogram, and optical coherence elastography. These functional techniques have been widely used in research and clinical applications, particularly in ophthalmology. Here, we review the principles, representative methods, and applications of different Doppler OCT techniques, followed by discussion on the innovations, limitations, and future directions of each of these techniques.

Automated retinal microvascular velocimetry based on erythrocyte mediated angiography

Retinal blood flow is an emerging biomarker in ocular and systemic disease. Erythrocyte mediated angiography (EMA) is a novel technique that provides an easily interpretable blood flow velocity quantification by directly tracing individual moving erythrocyte ghosts over time in vivo, imaged using a scanning laser ophthalmoscope (Heidelberg Retina Angiograph platform). This tracking procedure, however, requires time-consuming manual analysis to determine blood flow. To overcome this current bottleneck, we developed an objective and automated velocimetry approach, EMA - Automated Velocimetry (EMA-AV), which is based on a modified sequential Monte Carlo method. The intra-class correlation coefficient (ICC) between trained human graders and EMA-AV is 0.98 for mean vessel velocity estimation and 0.92 for frame by frame erythrocyte velocity estimation. This study proves EMA-AV is a reliable tool for quantification of retinal microvascular velocity and flow and establishes EMA-AV as a reliable and interpretable tool for quantifying retinal microvascular velocity.