Methods and algorithms for optical coherence tomography-based angiography: a review and comparison

MICROVASCULAR CHANGES IN TREATMENT-NAÏVE NONEXUDATIVE MACULAR NEOVASCULARIZATION COMPLICATED BY EXUDATION

PURPOSE

To assess differences in choriocapillaris (CC) and macular neovascularization (MNV) optical coherence tomography angiography quantitative parameters between long-term persistently nonexudative MNVs (NE-MNVs) and long-term activated NE-MNVs in age-related macular degeneration.

METHODS

Age-related macular degeneration patients with treatment-naïve NE-MNVs with >2 years of follow-up and no evidence of exudation within the first 6 months from diagnosis were retrospectively recruited. Two groups were considered according to the occurrence (EX group) or not (NE group) of exudation within the first 2 years of follow-up. Segmentation of the MNV and of the perilesional CC were obtained from enface optical coherence tomography angiography acquisitions at diagnosis and at 6-month follow-up. OCT B-scan images of the MNV were also collected. Fractal ratio was defined as the ratio between MNV fractal dimension (FrD) and CC FrD.

RESULTS

Fifty (50) eyes were included (20 EX group and 30 NE group). EX group showed higher flow deficit density and flow deficit number at the 6-month follow-up. It also showed higher MNV FrD, lower CC FrD, and higher fractal ratio at the 6-month follow-up. The fractal ratio significantly increased at 6-month acquisitions in the EX group, showing an area under the ROC curves of 0.887 (95% CI 0.869-0.922).

CONCLUSION

Fractal ratio at 6 months can predict exudation risk of MNV within 2 years from diagnosis. This suggests increased structural complexity of the NE-MNV accompanied by progressive capillary rarefaction of the perilesional CC as a key driving factor for the development of exudation in NE-MNV.

Rediscovering Age-Related Macular Degeneration with Swept-Source OCT Imaging: The 2022 Charles L. Schepens, MD, Lecture

PURPOSE

Swept-source OCT angiography (SS-OCTA) scans of eyes with age-related macular degeneration (AMD) were used to replace color, autofluorescence, infrared reflectance, and dye-based fundus angiographic imaging for the diagnosis and staging of AMD. Through the use of different algorithms with the SS-OCTA scans, both structural and angiographic information can be viewed and assessed using both cross sectional and en face imaging strategies.

DESIGN

Presented at the 2022 Charles L. Schepens, MD, Lecture at the American Academy of Ophthalmology Retina Subspecialty Day, Chicago, Illinois, on September 30, 2022.

PARTICIPANTS

Patients with AMD.

METHODS

Review of published literature and ongoing clinical research using SS-OCTA imaging in AMD.

MAIN OUTCOME MEASURES

Swept-source OCT angiography imaging of AMD at different stages of disease progression.

RESULTS

Volumetric SS-OCTA dense raster scans were used to diagnose and stage both exudative and nonexudative AMD. In eyes with nonexudative AMD, a single SS-OCTA scan was used to detect and measure structural features in the macula such as the area and volume of both typical soft drusen and calcified drusen, the presence and location of hyperreflective foci, the presence of reticular pseudodrusen, also known as subretinal drusenoid deposits, the thickness of the outer retinal layer, the presence and thickness of basal laminar deposits, the presence and area of persistent choroidal hypertransmission defects, and the presence of treatment-naïve nonexudative macular neovascularization. In eyes with exudative AMD, the same SS-OCTA scan pattern was used to detect and measure the presence of macular fluid, the presence and type of macular neovascularization, and the response of exudation to treatment with vascular endothelial growth factor inhibitors. In addition, the same scan pattern was used to quantitate choriocapillaris (CC) perfusion, CC thickness, choroidal thickness, and the vascularity of the choroid.

CONCLUSIONS

Compared with using several different instruments to perform multimodal imaging, a single SS-OCTA scan provides a convenient, comfortable, and comprehensive approach for obtaining qualitative and quantitative anatomic and angiographic information to monitor the onset, progression, and response to therapies in both nonexudative and exudative AMD.

FINANCIAL DISCLOSURE(S)

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

Probe fusion all-optic OCT-PAM dual-mode imaging system for biomedical imaging

We proposed a non-contact photoacoustic (PA) detection method using spectral domain optical coherence tomography (SDOCT). Two interference spectrums (A-lines) were acquired before and after the PA excitation with SDOCT. PA signal propagated within the sample causing the vibration. The vibration inner the sample introduced phase change between the acquired two A-lines. Thus, the PA signal can be detected by evaluating the difference in phase between the two A-lines. Based on the method, an OCT-PAM dual-mode imaging system was constructed. In the system, SDOCT served as the detection unit for PAM. Thus, the combination of the two imaging modalities was simplified. Another advantage of the system is that it realizes non-contact all-optic detection, which is attractive for biomedical imaging. Using the system, we imaged phantoms of carbon fibers, asparagus leaves and human hairs. Furthermore, the cortical vasculature of rat was imaged in vivo and the flow status was evaluated quantitatively.

Robust Ultrafast Projection Pipeline for Structural and Angiography Imaging of Fourier-Domain Optical Coherence Tomography

The current methods to generate projections for structural and angiography imaging of Fourier-Domain optical coherence tomography (FD-OCT) are significantly slow for prediagnosis improvement, prognosis, real-time surgery guidance, treatments, and lesion boundary definition. This study introduced a robust ultrafast projection pipeline (RUPP) and aimed to develop and evaluate the efficacy of RUPP. RUPP processes raw interference signals to generate structural projections without the need for Fourier Transform. Various angiography reconstruction algorithms were utilized for efficient projections. Traditional methods were compared to RUPP using PSNR, SSIM, and processing time as evaluation metrics. The study used 22 datasets (hand skin: 9; labial mucosa: 13) from 8 volunteers, acquired with a swept-source optical coherence tomography system. RUPP significantly outperformed traditional methods in processing time, requiring only 0.040 s for structural projections, which is 27 times faster than traditional summation projections. For angiography projections, the best RUPP variation took 0.15 s, making it 7518 times faster than the windowed eigen decomposition method. However, PSNR decreased by 41-45% and SSIM saw reductions of 25-74%. RUPP demonstrated remarkable speed improvements over traditional methods, indicating its potential for real-time structural and angiography projections in FD-OCT, thereby enhancing clinical prediagnosis, prognosis, surgery guidance, and treatment efficacy.

OCT Angiography of the Retina and the Choroid in the Macula in Patients with Normal Tension Glaucoma and Primary Open Angle Glaucoma

The aim of this study was to compare vessel density (VD) in the retina and choroid in eyes with primary open angle glaucoma (POAG), normal tension glaucoma (NTG) and controls. Patients with POAG, NTG and controls underwent OCT scanning of the macula and the disc followed by 6 × 6 mm macula OCT angiography (OCTA) imaging. Global and hemifield VD were recorded for the superficial (SVP) and deep (DVP) vascular plexus and the choriocapillaris (CC). The OCT thickness of the nerve fiber layer (NFL) and ganglion cell layer (GCC) was also measured. Data from 65 POAG, 33 NTG and 40 control eyes matched for age were analyzed. Mean SVP VD was lower in NTG and POAG eyes compared to controls (38.8 ± 5.3, 40.7 ± 6.8 and 48.5 ± 4.0%, p < 0.001). Mean DVP VD was lower in NTG and POAG eyes compared to controls (43.1 ± 6.1, 44.5 ± 7.6 and 48.6 ± 5.8%, p = 0.002). There was no difference in SVP VD or DVP VD between the glaucoma groups (p > 0.050). No difference was noted in CC VD between the groups (68.3 ± 2.3, 67.6 ± 3.7 and 68.5 ± 2.6%, p = 0.287). Lower SVP and DVP VD was seen in eyes with glaucoma compared to normal eyes. NTG and POAG eyes had similar VD loss. Eyes with glaucoma manifested similar CC VD compared to controls.

Optimization of handheld spectrally encoded coherence tomography and reflectometry for point-of-care ophthalmic diagnostic imaging

Significance

Handheld optical coherence tomography (HH-OCT) systems enable point-of-care ophthalmic imaging in bedridden, uncooperative, and pediatric patients. Handheld spectrally encoded coherence tomography and reflectometry (HH-SECTR) combines OCT and spectrally encoded reflectometry (SER) to address critical clinical challenges in HH-OCT imaging with real-time en face retinal aiming for OCT volume alignment and volumetric correction of motion artifacts that occur during HH-OCT imaging.

Aim

We aim to enable robust clinical translation of HH-SECTR and improve clinical ergonomics during point-of-care OCT imaging for ophthalmic diagnostics.

Approach

HH-SECTR is redesigned with (1) optimized SER optical imaging for en face retinal aiming and retinal tracking for motion correction, (2) a modular aluminum form factor for sustained alignment and probe stability for longitudinal clinical studies, and (3) one-handed photographer-ergonomic motorized focus adjustment.

Results

We demonstrate an HH-SECTR imaging probe with micron-scale optical-optomechanical stability and use it for in vivo human retinal imaging and volumetric motion correction.

Conclusions

This research will benefit the clinical translation of HH-SECTR for point-of-care ophthalmic diagnostics.

Edible oil based optical clearing for optical coherence tomography angiography imaging

In optical imaging, optical clearing agents are commonly used to enhance the structural details of a sample. The current study investigates how to use it to improve the data obtained by an optical coherence tomography angiography system. A natural edible oil with no chemical base has been used for optical clearing. In-vivo testing on mice and humans yielded excellent optical clearing. Using computational techniques, the improvement in angiography signal caused by the optical clearing agent is investigated qualitatively and quantitatively. Compared to the control group, applying the edible oil-based optical clearing agent demonstrated improved vessel percentage and refined vascular signal intensity along depth.

Decreased Macular Choriocapillaris Perfusion Correlates with Contrast Sensitivity Function in Dry Age-Related Macular Degeneration

PURPOSE

To investigate the relationships between contrast sensitivity (CS), choriocapillaris perfusion, and other structural OCT biomarkers in dry age-related macular degeneration (AMD).

DESIGN

Cross-sectional, observational study.

PARTICIPANTS

One hundred AMD eyes (22 early, 52 intermediate, and 26 late) from 74 patients and 45 control eyes from 37 age-similar subjects.

METHODS

All participants had visual acuity (VA) assessment, quantitative CS function (qCSF) testing, macular OCT, and 6 × 6-mm swept-source OCT angiography scans on the same day. OCT volumes were analyzed for subretinal drusenoid deposits and hyporeflective drusen cores, and to measure thickness of the outer nuclear layer. OCT angiography scans were utilized to calculate drusen volume and inner choroid flow deficit percentage (IC-FD%), and to measure the area of choroidal hypertransmission defects (HTDs). Inner choroid flow deficit percentage was measured from a 16-μm thick choriocapillaris slab after compensation and binarization with Phansalkar's method. Generalized linear mixed-effects models were used to evaluate the associations between functional and structural variables.

MAIN OUTCOME MEASURES

To explore the associations between qCSF-measured CS, IC-FD%, and various AMD imaging biomarkers.

RESULTS

Age-related macular degeneration exhibited significantly reduced qCSF metrics eyes across all stages compared with controls. Univariate analysis revealed significant associations between various imaging biomarkers, reduced qCSF metrics, and VA in both groups. Multivariate analysis confirmed that higher IC-FD% in the central 5 mm was significantly associated with decreases in all qCSF metrics in AMD eyes (β = -0.74 to -0.25, all P < 0.05), but not with VA (P > 0.05). Outer nuclear layer thickness in the central 3 mm correlated with both VA (β = 2.85, P < 0.001) and several qCSF metrics (β = 0.01-0.90, all P < 0.05), especially in AMD eyes. Further, larger HTD areas were associated with decreased VA (β = -0.89, P < 0.001) and reduced CS at low-intermediate frequencies across AMD stages (β = -0.30 to -0.29, P < 0.001).

CONCLUSIONS

The significant association between IC-FD% in the central 5 mm and qCSF-measured CS reinforces the hypothesis that decreased macular choriocapillaris perfusion contributes to visual function changes in AMD, which are more pronounced in CS than in VA.

FINANCIAL DISCLOSURE(S)

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

Calcified Drusen Prevent the Detection of Underlying Choriocapillaris Using Swept-Source Optical Coherence Tomography Angiography

Purpose

In age-related macular degeneration (AMD), choriocapillaris flow deficits (CCFDs) under soft drusen can be measured using established compensation strategies. This study investigated whether CCFDs can be quantified under calcified drusen (CaD).

Methods

CCFDs were measured in normal eyes (n = 30) and AMD eyes with soft drusen (n = 30) or CaD (n = 30). CCFD density masks were generated to highlight regions with higher CCFDs. Masks were also generated for soft drusen and CaD based on both structural en face OCT images and corresponding B-scans. Dice similarity coefficients were calculated between the CCFD density masks and both the soft drusen and CaD masks. A phantom experiment was conducted to simulate the impact of light scattering that arises from CaD.

Results

Area measurements of CCFDs were highly correlated with those of CaD but not soft drusen, suggesting an association between CaD and underlying CCFDs. However, unlike soft drusen, the detected optical coherence tomography (OCT) signals underlying CaD did not arise from the defined CC layer but were artifacts caused by the multiple scattering property of CaD. Phantom experiments showed that the presence of highly scattering material similar to the contents of CaD caused an artifactual scattering tail that falsely generated a signal in the CC structural layer but the underlying flow could not be detected. Similarly, CaD also caused an artifactual scattering tail and prevented the penetration of light into the choroid, resulting in en face hypotransmission defects and an inability to detect blood flow within the choriocapillaris. Upon resolution of the CaD, the CC perfusion became detectable.

Conclusions

The high scattering property of CaD leads to a scattering tail under these drusen that gives the illusion of a quantifiable optical coherence tomography angiography signal, but this signal does not contain the angiographic information required to assess CCFDs. For this reason, CCFDs cannot be reliably measured under CaD, and CaD must be identified and excluded from macular CCFD measurements.

Quantitative Microvascular Change Analysis Using a Semi-Automated Software in Macula-off Rhegmatogenous Retinal Detachment Assessed by Swept-Source Optical Coherence Tomography Angiography

Objective: To analyze the performance of custom semi-automated software for quantitative analysis of retinal capillaries in eyes with macula-off rhegmatogenous retinal detachment (RRD) and the role of these microvascular measures as potential biomarkers of postoperative visual outcomes. Methods: A prospective, observational, and single-center study was conducted on consecutive patients who underwent 25G pars-plana vitrectomy for primary uncomplicated macula-off RRD. Optical coherence tomography angiography (OCTA) was performed in the fellow and RRD eyes before surgery and in months 1, 3, and 6 after surgery. The preoperative values of the fellow eyes were used as surrogates of macula-off ones. The primary endpoints were the mean vessel diameter index (VDI); vessel area density (VAD); and vessel skeleton density (VSD) at month 6. Results: Forty-four eyes (44 patients) were included in the study. Considering the fellow eyes as a surrogate of preoperative values of macula-off eyes, VDI in superficial (SCP) and deep (DCP) capillary plexuses was significantly reduced at month 6 (p = 0.0087 and p = 0.0402, respectively); whereas VSD in SCP increased significantly from preoperative values (p = 0.0278). OCTA built-in software parameters were significantly reduced from month 1 to month 6 in both SCP and DCP (p values ranged between 0.0235 and <0.0001). At month 6, 25 (56.8%) eyes achieved a best-corrected visual acuity BCVA ≥ 0.3 (LogMAR). The greater the preoperative BCVA, the greater the probability of achieving good visual outcomes (Odds ratio: 11.06; p = 0.0037). However, none of the OCTA parameters were associated with the probability of achieving a BCVA improvement ≥ 0.3. Conclusions: Quantitative evaluation of capillary density and morphology through OCTA and semi-automated software represents a valuable tool for clinical assessment and managing the disease comprehensively.

Reducing noise in polarization-sensitive optical coherence tomography for high-quality local phase retardation imaging

Local phase retardation (LPR) is increasingly recognized as a crucial biomarker for assessing disease progression. However, the presence of speckle noise significantly challenges its accuracy and polarization contrast. To address this challenge, we propose a signal-processing strategy aimed at reducing the impact of noise on LPR measurements. In this approach, the LPR is reconstructed by polar decomposition after averaging multiple Mueller matrices from different overlapping sub-spectra. To optimize measurement accuracy, we systematically combined and traversed different sub-spectral numbers and bandwidths. By examining the quarter-wave plate and glass slide, high-accuracy phase retardation measurements were successfully verified, and the maximum polarization contrast was improved by 23%. Moreover, experimental results from multi-tissue imaging vividly illustrate that the equivalent number of looks (ENL) and polarization contrast were improved by 18% and 19%, respectively. This outcome indicates that our proposed strategy can effectively reduce the noise spikes, enhancing tissue discrimination capabilities.

Quantitative Microvascular Change Analysis Using a Semi-Automated Algorithm in Macula-on Rhegmatogenous Retinal Detachment Assessed by Swept-Source Optical Coherence Tomography Angiography

PURPOSE

The purpose of this study was to objectively evaluate the longitudinal changes observed in the retinal capillaries in eyes with macula-on rhegmatogenous retinal detachment (RRD), assessed with optical coherence tomography angiography (OCTA), and to assess the role of these microvascular measures as potential biomarkers of postoperative visual outcomes.

METHODS

This was a prospective, longitudinal study conducted on consecutive patients who underwent 25 G pars plana vitrectomy for primary RRD. The vessel area density (VAD), vessel skeleton density (VSD), and vessel diameter index (VDI) were assessed in the superficial (SCP) and deep (DCP) capillary plexuses.

RESULTS

Twenty-three eyes with macula-on RRD were included in the study. The mean preoperative VDI, VAD, and VSD of the RRD eye were 18.6 ± 1.1, 0.43 ± 0.02, and 0.17 ± 0.01 in the SCP; and 18.6 ± 0.6, 0.38 ± 0.03, and 0.15 ± 0.01 in the DCP, respectively. At month 6, eight (34.8%) eyes achieved a best-corrected visual acuity (BCVA) gain ≥ 0.1 LogMAR. A preoperative VDI > 17.80, VSD > 0.170, and VDI-change > -0.395 in the SCP; and VDI > 18.11 and VDI change > -0.039 in the DCP were predictors of achieving a BCVA-gain ≥ 0.1 LogMAR.

CONCLUSIONS

The preoperative VDI in SCP and DCP, the preoperative VSD in SCP, and their changes from preoperative values were predictors of visual outcomes. A quantitative OCTA analysis of capillary density and morphology may represent a potential predictive tool for surgical outcomes in RRD. The results reported in this study suggest that OCTA is a useful ancillary test for clinical disease management.

Multi-window approach enables two-fold improvement in OCT axial resolution with strong side-lobe suppression and improved phase sensitivity

A common processing approach for optical coherence tomography (OCT) uses a window function (e.g., Hann or rectangular window) for spectral shaping prior to calculating the Fourier transform. Here we build on a multi-window approach [Opt. Express8, 5267 (2017)10.1364/BOE.8.005267] that enables improved resolution while still suppressing side-lobe intensity. The shape of the window function defines the trade-off between main-lobe width (resolution) and side-lobe intensity. We have extended the approach to include the interferometric phase for phase-sensitive applications like vibrometry and Doppler OCT. Using the Hann window as a reference, we show that 11 Taylor windows are sufficient to achieve 50% improvement in axial resolution, -31 dB side-lobe intensity, and 20% improvement in phase sensitivity with low computational cost.

Electronic frequency shifting enables long, variable working distance optical coherence tomography

Increased imaging range is of growing interest in many applications of optical coherence tomography to reduce constraints on sample location, size, and topography. The design of optical coherence tomography systems with sufficient imaging range (e.g., 10s of centimeters) is a significant challenge due to the direct link between imaging range and acquisition bandwidth. We have developed a novel and flexible method to extend the imaging range in optical coherence tomography using electronic frequency shifting, enabling imaging in dynamic environments. In our approach, a laser with a quasi-linear sweep is used to limit the interferometric bandwidth, enabling decoupling of imaging range and acquisition bandwidth, while a tunable lens allows dynamic refocusing in the sample arm. Electronic frequency shifting then removes the need for high frequency digitization. This strategy is demonstrated to achieve high contrast morphological imaging over a > 21 cm working distance range, while maintaining high resolution and phase sensitivity. The system design is flexible to the application while requiring only a simple phase correction in post-processing. By implementing this approach in an auto-focusing paradigm, the proposed method demonstrates strong potential for the translation of optical coherence tomography into emerging applications requiring variable and centimeter-scale imaging ranges.

3D imaging of aqueous veins and surrounding sclera using a dual-wavelength photoacoustic microscopy

Understanding aqueous outflow resistance at the level of aqueous veins has been a challenge to the management of glaucoma. This study investigated resolving the anatomies of aqueous veins and the textures of surrounding sclera using photoacoustic microscopy (PAM). A dual wavelength PAM system was established and validated using imaging phantoms, porcine and human globes perfused with an optical contrast agent ex vivo. The system shows lateral resolution of 8.23 µm and 4.70 µm at 1200 nm and 532 nm, respectively, and an axial resolution of 27.6 µm. The system is able to separately distinguish the aqueous veins and the sclera with high contrast in full circumference of the porcine and human globes.

Tracking the dynamics of thrombus formation in a blood vessel-on-chip with visible-light optical coherence tomography

Thrombus formation is a physiological response to damage in a blood vessel that relies on a complex interplay of platelets, coagulation factors, immune cells, and the vessel wall. The dynamics of thrombus formation are essential for a deeper understanding of many disease processes, like bleeding, wound healing, and thrombosis. However, monitoring thrombus formation is challenging due to the limited imaging options available to analyze flowing blood. In this work, we use a visible-light optical coherence tomography (vis-OCT) system to monitor the dynamic process of the formation of thrombi in a microfluidic blood vessel-on-chip (VoC) device. Inside the VoC, thrombi form in a channel lined with a monolayer of endothelial cells and perfused by human whole blood. We show that the correlation of the vis-OCT signal can be utilized as a marker for thrombus formation. By thresholding the correlation during thrombus formation, we track and quantify the growth of the thrombi over time. We validate our results with fluorescence microscopic imaging of fibrin and platelet markers at the end of the blood perfusion assay. In conclusion, we demonstrate that the correlation of the vis-OCT signal can be used to visualize both the spatial and temporal behavior of the thrombus formation in flowing human whole blood.

Onset and Progression of Persistent Choroidal Hypertransmission Defects in Intermediate Age-Related Macular Degeneration: A Novel Clinical Trial Endpoint

PURPOSE

The appearance and growth of persistent choroidal hypertransmission defects (hyperTDs) detected on en face swept-source optical coherence tomography (SS-OCT) images from eyes with intermediate age-related macular degeneration (iAMD) were studied to determine if they could serve as novel clinical trial endpoints.

DESIGN

Post hoc subgroup analysis of a prospective study.

METHODS

Subjects with iAMD underwent 6 × 6 mm SS-OCT angiography imaging at their baseline and follow-up visits. The drusen volumes were obtained using a validated SS-OCT algorithm. Two graders independently evaluated all en face structural images for the presence of persistent hyperTDs. The number and area of all hyperTDs along with drusen volume were obtained from all SS-OCT angiography scans. Eyes were censored from further follow-up once exudative AMD developed.

RESULTS

A total of 171 eyes from 121 patients with iAMD were included. Sixty-eight eyes developed at least 1 hyperTD. Within 1 year after developing a hyperTD, 25% of eyes developed new hyperTDs for an average of 0.44 additional hyperTDs. Over 2 years, as hyperTDs appeared, enlarged, and merged, the average area growth rate was 0.220 mm/yr using the square-root transformation strategy. A clinical trial design using the onset and enlargement of these hyperTDs for the study of disease progression in eyes with iAMD is proposed.

CONCLUSIONS

The appearance and growth of persistent choroidal hyperTDs in eyes with iAMD can be easily detected and measured using en face OCT imaging and can serve as novel clinical trial endpoints for the study of therapies that may slow disease progression from iAMD to late AMD.

OCTA changes following loading phase with intravitreal aflibercept for DME

OBJECTIVE

To quantify changes in optical coherence tomography angiography (OCTA) parameters following intravitreal anti-vascular endothelial growth factor treatment for diabetic macular edema (DME), and to assess associations between pretreatment OCTA parameters and visual outcomes.

DESIGN

Prospective cohort study.

METHODS

Twenty-nine patients with DME received 5 monthly intravitreal injections of aflibercept. OCTA data obtained at baseline and at 6 months were compared using the Wilcoxon signed-rank test. OCTA parameters were foveal avascular zone (FAZ) area, FAZ perimeter, FAZ circularity, vessel density in the superficial vascular plexus (segmented into central, inner, outer, and full Early Treatment of Diabetic Retinopathy Study [ETDRS] map regions. Subanalysis divided patients into treatment responders (reduction of central subfield thickness >50 µm over treatment) and nonresponders. Associations between pretreatment OCTA parameters and visual acuity outcomes were analyzed using multivariable linear and logistic regression.

RESULTS

A total of 29 patients were included: 25 patients (86.2%) had nonproliferative diabetic retinopathy, and 4 patients (13.8%) had proliferative diabetic retinopathy. Vessel density was reduced in the central (p = 0.004) and inner (p = 0.013) ETDRS map regions. This effect was significant only among treatment responders (central p = 0.002; inner p = 0.017). Pretreatment OCT and OCTA parameters were not associated with final visual acuity outcomes.

CONCLUSION

Following intravitreal aflibercept treatment for DME, there was a significant decrease in vessel density of the superficial vascular plexus at the central and inner ETDRS map regions. This was seen only among treatment responders. Observations here are likely to represent the limits of OCTA technology itself, where pretreatment vessel density may have been artifactually overestimated by suspended scattering particles in motion. Pretreatment OCTA parameters did not serve as biomarkers for visual outcome following anti-vascular endothelial growth factor therapy.

Decreased Central Macular Choriocapillaris Perfusion Correlates With Increased Low Luminance Visual Acuity Deficits

PURPOSE

Correlations between low luminance visual acuity deficits (LLVADs) and central choriocapillaris perfusion deficits were investigated to help explain how increases in LLVAD scores at baseline predict annual growth rates of geographic atrophy (GA).

DESIGN

Prospective cross-sectional study.

METHODS

Photopic luminance best-corrected visual acuity (PL-BCVA) and low luminance BCVA (LL-BCVA) were measured using the Early Treatment Diabetic Retinopathy Study chart. LL-BCVA was measured using a 2.0-log unit neutral density filter. LLVADs were calculated as the difference between PL-BCVA and LL-BCVA. Within a fovea-centered 1-mm circle, the percentage of choriocapillaris flow deficits (CC FD%), drusen volume, optical attenuation coefficient (OAC) elevation volume, and outer retinal layer (ORL) thickness were assessed.

RESULTS

In all 90 eyes (30 normal eyes; 31 drusen-only eyes; 29 non-foveal GA eyes), significant correlations were found between the central CC FD% and PL-BCVA (r = -0.393, P < .001), LL-BCVA (r = -0.534, P < .001), and the LLVAD (r = 0.439, P < .001). Central cube root (cubrt) drusen volume, cubrt OAC elevation volume, and ORL thickness were correlated with PL-BCVA, LL-BCVA, and LLVADs (all P < .05). Stepwise regression models showed that central cubrt OAC elevation volume and ORL thickness were associated with PL-BCVA (R2 = 0.24, P < .05); central CC FD%, cubrt OAC elevation volume, and ORL thickness were associated with LL-BCVA (R2 = 0.44, P < .01); and central CC FD% and ORL thickness were associated with LLVAD (R2 = 0.24, P < .01).

CONCLUSIONS

The significant correlations between central CC FD% and LLVAD support the hypothesis that the ability of LLVAD to predict the growth of GA is mediated through a decrease in macular choriocapillaris perfusion.

Evaluation of Automated Measurement of Macular Ischemic Changes in Retinal Vein Occlusion With Optical Coherence Tomography Angiography

OBJECTIVE

The foveal avascular zone (FAZ) is altered in patients with retinal vein occlusion (RVO) and correlates inversely with visual acuity. Optical coherence tomography angiography (OCTA) is an imaging tool to visualize FAZ safely and easily. Automated measurements can facilitate interpretation of OCTA images. In this comparative cross-sectional study, we compare the results of manual measurement of the FAZ with automated measurement by built-in application (Metrix).

METHODS

The study included patients with RVO who underwent OCTA. Manual measurement was compared with automated evaluation by Metrix in 3 mm x 3 mm and 6 mm x 6 mm scan sizes and correlations of the circularity, circumference, and size of the FAZ were calculated.

RESULTS

Forty-seven eyes were included in the study. A reliable measurement result in both Metrix 3 mm x 3 mm and 6 mm x 6 mm was found in only 25 of 47 eyes. The mean FAZ in these eyes by manual measurement was 0.50 mm2 compared with 0.20 mm2 and 0.24 mm2, respectively, by automated measurement. A statistically significant inverse correlation was found in both the automated 3 mm x 3 mm and 6 mm x 6 mm measurements for FAZ circumference with FAZ circularity but not FAZ area.

CONCLUSION

The two automated measurements showed no significant bias regarding the size of the FAZ, but the plausibility of the data should be checked on a case-by-case basis. The manual measurements were higher, indicating limited agreement of manual and automated measurements. The information on circularity can point to ischemic maculopathy early in the course of the disease. [Ophthalmic Surg Lasers Imaging Retina 2023;54:462-469.].

Longitudinal Changes in Peripapillary and Macular Vessel Densities in Glaucomatous Eyes With a Single-Hemifield Retinal Nerve Fiber Layer Defect

PRCIS

The peripapillary vessel density decreased significantly in the affected hemiretina compared with that in the intact hemiretina in glaucomatous eyes with a single-hemifield retinal nerve fiber layer defect.

PURPOSE

To evaluate the difference in the change rates of peripapillary vessel density (pVD) and macular vessel density (mVD) measured using optical coherence tomography angiography (OCTA) in glaucomatous eyes with a single-hemifield retinal nerve fiber layer (RNFL) defect.

MATERIALS AND METHODS

We performed a retrospective, longitudinal study of 25 patients with glaucoma who were followed up for at least 3 years, with a minimum of 4 visits after baseline OCTA. At each visit, all participants underwent OCTA examination, and the pVD, mVD were measured by removing the large vessels. Changes in the pVD, mVD, peripapillary RNFL thickness (pRNFLT), and macular ganglion cell inner plexiform layer thickness were investigated in the affected and intact hemispheres, and the differences between the 2 hemispheres were compared.

RESULTS

In the affected hemiretina, the pVD, mVD, pRNFLT, and mCGIPLT were reduced than that in the intact hemiretina (all, P < 0.001). The changes in pVD and mVD were statistically significant at the 2-year and 3-year follow-ups in the affected hemifield (all, P <0.05). However, pVD and mVD did not show statistically significant changes in the intact hemiretina throughout the follow-up visits. Although the pRNFLT decreased significantly at the 3-year follow-up, the macular ganglion cell inner plexiform layer thickness showed no statistical change at any follow-up visit. Compared with the intact hemisphere, pVD was the only parameter that showed significant changes throughout the follow-up period.

CONCLUSION

Although pVD and mVD decreased in the affected hemiretina, the reduction in pVD was significant compared with that in the intact hemiretina.

Optical Coherence Tomography Angiography in Retinal Vascular Disorders

Traditionally, abnormalities of the retinal vasculature and perfusion in retinal vascular disorders, such as diabetic retinopathy and retinal vascular occlusions, have been visualized with dye-based fluorescein angiography (FA). Optical coherence tomography angiography (OCTA) is a newer, alternative modality for imaging the retinal vasculature, which has some advantages over FA, such as its dye-free, non-invasive nature, and depth resolution. The depth resolution of OCTA allows for characterization of the retinal microvasculature in distinct anatomic layers, and commercial OCTA platforms also provide automated quantitative vascular and perfusion metrics. Quantitative and qualitative OCTA analysis in various retinal vascular disorders has facilitated the detection of pre-clinical vascular changes, greater understanding of known clinical signs, and the development of imaging biomarkers to prognosticate and guide treatment. With further technological improvements, such as a greater field of view and better image quality processing algorithms, it is likely that OCTA will play an integral role in the study and management of retinal vascular disorders. Artificial intelligence methods-in particular, deep learning-show promise in refining the insights to be gained from the use of OCTA in retinal vascular disorders. This review aims to summarize the current literature on this imaging modality in relation to common retinal vascular disorders.

Clinical Applications of Optical Coherence Tomography Angiography in Inherited Retinal Diseases: An Up-to-Date Review of the Literature

Optical coherence tomography angiography (OCT-A) is a valuable imaging technique, allowing non-invasive, depth-resolved, motion-contrast, high-resolution images of both retinal and choroidal vascular networks. The imaging capabilities of OCT-A have enhanced our understanding of the retinal and choroidal alterations that occur in inherited retinal diseases (IRDs), a group of clinically and genetically heterogeneous disorders that may be complicated by several vascular conditions requiring a prompt diagnosis. In this review, we aimed to comprehensively summarize all clinical applications of OCT-A in the diagnosis and management of IRDs, highlighting significant vascular findings on retinitis pigmentosa, Stargardt disease, choroideremia, Best disease and other less common forms of retinal dystrophies. All advantages and limitations of this novel imaging modality will be also discussed.

Decreased Macular Choriocapillaris Perfusion in Eyes With Macular Reticular Pseudodrusen Imaged With Swept-Source OCT Angiography

Purpose

To determine if macular reticular pseudodrusen (RPD) were associated with markers of impaired macular choroidal perfusion, we investigated measurements of macular choriocapillaris (CC) flow deficits (FDs), CC thickness, and mean choroidal thickness (MCT) in eyes with macular RPD compared with normal eyes and eyes with soft drusen.

Methods

Eyes with intermediate age-related macular degeneration (iAMD) and normal eyes underwent 6 × 6 mm swept-source optical coherence tomography angiography (SS-OCTA) imaging to diagnose macular RPD, occupying over 25% of the fovea-centered 5 mm diameter circle, and measure outer retinal layer (ORL) thickness, CC FDs, CC thickness, MCT, and choroidal vascularity index (CVI) using previously published strategies within the same fovea-centered 5 mm circle.

Results

Ninety eyes were included; 30 normal eyes, 30 eyes with soft drusen, and 30 eyes with macular RPD. The RPD eyes showed higher macular CC FDs than normal eyes (P < 0.001) and soft drusen eyes (P = 0.019). Macular CC thickness was decreased in RPD eyes compared with normal eyes (P < 0.001) and soft drusen eyes (P = 0.016). Macular MCT in RPD eyes was thinner than normal eyes (P = 0.005) and soft drusen eyes (P < 0.001). No statistically and clinically significant differences were found in the ORL thickness and CVI measurements between RPD eyes and the other two groups (all P > 0.05).

Conclusions

Eyes with macular RPD had decreased macular CC perfusion, decreased CC thickness, and decreased MCT measurements compared with normal and soft drusen eyes, suggesting that RPD may result from impaired choroidal perfusion.

Age-related macular degeneration

Age-related macular degeneration is an increasingly important public health issue due to ageing populations and increased longevity. Age-related macular degeneration affects individuals older than 55 years and threatens high-acuity central vision required for important tasks such as reading, driving, and recognising faces. Advances in retinal imaging have identified biomarkers of progression to late age-related macular degeneration. New treatments for neovascular age-related macular degeneration offer potentially longer-lasting effects, and progress is being made towards a treatment for atrophic late age-related macular degeneration. An effective intervention to slow progression in the earlier stages of disease, or to prevent late age-related macular degeneration development remains elusive, and our understanding of underlying mechanistic pathways continues to evolve.

Dynamic 3D imaging of cerebral blood flow in awake mice using self-supervised-learning-enhanced optical coherence Doppler tomography

Cerebral blood flow (CBF) is widely used to assess brain function. However, most preclinical CBF studies have been performed under anesthesia, which confounds findings. High spatiotemporal-resolution CBF imaging of awake animals is challenging due to motion artifacts and background noise, particularly for Doppler-based flow imaging. Here, we report ultrahigh-resolution optical coherence Doppler tomography (µODT) for 3D imaging of CBF velocity (CBFv) dynamics in awake mice by developing self-supervised deep-learning for effective image denoising and motion-artifact removal. We compare cortical CBFv in awake vs. anesthetized mice and their dynamic responses in arteriolar, venular and capillary networks to acute cocaine (1 mg/kg, i.v.), a highly addictive drug associated with neurovascular toxicity. Compared with awake, isoflurane (2-2.5%) induces vasodilation and increases CBFv within 2-4 min, whereas dexmedetomidine (0.025 mg/kg, i.p.) does not change vessel diameters nor flow. Acute cocaine decreases CBFv to the same extent in dexmedetomidine and awake states, whereas decreases are larger under isoflurane, suggesting that isoflurane-induced vasodilation might have facilitated detection of cocaine-induced vasoconstriction. Awake mice after chronic cocaine show severe vasoconstriction, CBFv decreases and vascular adaptations with extended diving arteriolar/venular vessels that prioritize blood supply to deeper cortical capillaries. The 3D imaging platform we present provides a powerful tool to study dynamic changes in vessel diameters and morphology alongside CBFv networks in the brain of awake animals that can advance our understanding of the effects of drugs and disease conditions (ischemia, tumors, wound healing).

Retinal vascular density in CADASIL (Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy)

Background and objective

Retinal vascular density (VD) measured using optical coherence tomography with angiography (OCTA) has been suggested as a potential marker of intracerebral vascular changes in Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL). We aimed to determine whether VD is related to the clinical and imaging manifestations of the disease.

Methods

OCTA was performed in 104 CADASIL patients (parallel to their clinical and imaging assessment) and in 83 healthy individuals.

Results

A significant reduction of VD related to age was detected in patients and controls in the superficial and deep vascular plexus of the whole foveal or parafoveal retinal area (p<0.0001). After adjustment for age, these parameters were found significantly lower in patients than in controls (p<0.03). Multivariable analysis did not show any association between retinal VD and history of stroke, modified Rankin Scale or Mini-Mental Status Examination scores. No significant association was found with MRI lesions either.

Conclusion

In CADASIL, retinal VD is decreased early and progresses with ageing but does not appear related to the severity of clinical or imaging manifestations.

Use of optical coherence tomography angiography in the uveitis clinic

As optical coherence tomography angiography is revolutionizing the ophthalmology world, the uveitis community is learning to understand where and how this new powerful imaging tool fits into the management of the panorama of ocular inflammations and infections. A non-invasive method of studying the retinal and choroidal vasculature, OCTA allows for the assessment of vessel density changes during active and inactive uveitis making it the natural imaging application of choice in uveitis clinical trials. However, these data and results are of limited utility to the ophthalmologists who are looking to apply OCTA in their everyday uveitis clinic. If employed strategically, OCTA can be a powerful tool for the uveitis specialist to evaluate iris involvement in viral uveitis; to assess the integrity of the vascular layers in the settings of white dot syndromes; to distinguish inflammatory choroidal neovascularization from outer retinal avascular inflammatory material; and to diagnose and follow infectious choroidal granulomas and satellite foci of chorioretinal inflammation without the need to administer dyes. The present review will analyze all the recent publications that apply OCTA in uveitis to offer the reader a guide on how to maximize the utility of this imaging modality in a clinical practice.

FBG array based wavelength calibration scheme for Fourier domain mode-locked laser with pm resolution and hourly stability

We demonstrate a fiber Bragg grating (FBG) array based wavelength calibration scheme for Fourier domain mode-locked (FDML) laser. The wavelength interval and the temperature feedback module of the FBG array are designed to ensure the reference stability of the wavelength calibration scheme. Combined with the calibration scheme, the FDML laser with a tunable wavelength range of ∼60 nm, a center wavelength of 1300 nm and a sweep frequency of 39.63 kHz is built up to demonstrate its feasibility. The FBG wavelength demodulation based on the calibrated FDML laser system shows a wavelength resolution of 2.76 pm and hourly stability of 10.22 pm.

The Role of Optical Coherence Tomography Angiography in Optic Nerve Head Edema: A Narrative Review

Optic nerve head (ONH) edema is a clinical manifestation of many ocular and systemic disorders. Ocular and central nervous system imaging has been used to differentiate the underlying cause of ONH edema and monitor the disease course. ONH vessel abnormalities are among the earliest signs of impaired axonal transportation. Optical coherence tomography angiography (OCTA) is a noninvasive method for imaging ONH and peripapillary vessels and has been used extensively for studying vascular changes in ONH disorders, including ONH edema. In this narrative review, we describe OCTA findings of the most common causes of ONH edema and its differential diagnoses including ONH drusen.

Comparative study of OCTA algorithms with a high-sensitivity multi-contrast Jones matrix OCT system for human skin imaging

The multi-contrast Jones matrix OCT (JMT) system can not only improve the tissue-specific contrast but also enhance the sensitivity of detecting flow, which is gaining increasing attention. However, for the JMT system, there is currently a lack of studies evaluating and guiding the selection of suitable angiography algorithms to map the most appealing quality of angiograms for clinical use. In this paper, by a homemade high-sensitivity multi-contrast JMT system based 200 kHz swept source, the performance of two complex-signal-based OCTA methods that are insensitive to phase instability and one amplitude-signal-based OCTA method are compared for in-vivo imaging of human skin qualitatively and quantitatively. Six metrics, including vascular connectivity, image contrast-to-noise ratio, image signal-to-noise ratio, vessel diameter index, blood vessel density, and processing time, are assessed. The results show that the vascular networks processed by all OCTA methods and the texture of skin could be visualized simultaneously and markedly. Additionally, the complex-signal-based OCTA methods successfully suppress phase instabilities and even outperform the amplitude-signal-based OCTA algorithm in some indicators. This paper has a certain guiding significance for selecting an appropriate angiography algorithm and expanding the application field with this system.

Quantitative assessment of retinal vessel density and thickness changes in internal carotid artery stenosis patients using optical coherence tomography angiography

OBJECTIVE

To quantitatively assess the retinal features of patients with different degrees of internal carotid artery stenosis (ICAS), particularly mild ICAS patients, utilizing optical coherence tomography angiography (OCTA).

METHODS

Thirty-two mild ICAS patients (mild ICAS group), 34 moderate to severe ICAS patients (nonmild ICAS group), and 40 controls were enrolled in this study. Retinal vessel density was quantitatively measured by OCTA, including radial peripapillary capillary vessel density (RPC-VD), superficial and deep capillary plexus vessel density (SCP/DCP-VD). Structural parameters were collected from optical coherence tomography (OCT), including retinal thickness and subfoveal choroidal thickness (SFCT). Furthermore, LASSO-penalized logistic regression was used to construct the diagnostic model based on retinal parameters. ROC curves and nomogram plots were used to assess the diagnostic ability of this model for ICAS.

RESULTS

The macular SCP-VD of mild ICAS patients was significantly lower than that of controls and lower than that of nonmild ICAS patients (all p < 0.05). However, there was no difference among the three groups in terms of DCP-VD (p > 0.05). RPC-VD could effectively discriminate between the mild ICAS group and the nonmild ICAS group (p = 0.005). For structural OCT, only the SFCT decreased as the ICAS degree increased (p < 0.05). Diagnostic scores based on retinal parameters showed a strong diagnostic capability for mild ICAS (AUC = 0.8656).

CONCLUSION

Mild ICAS patients exhibited distinct retinal features compared to nonmild ICAS patients and control subjects. OCTA potentially represents a promising method for the early detection of ICAS patients and the noninvasive surveillance of haemodynamic changes in those patients.

Normative Data and Determinants of Macular, Disc, and Peripapillary Vascular Density in Healthy Myopic Children Using Optical Coherence Tomography Angiography

Objective

To establish a normative database for the vascular density (VD) in macular, disc, and peripapillary regions in healthy myopic children and to evaluate associated ocular features with optical coherence tomography angiography (OCTA).

Methods

This was an observational, prospective and cross-sectional study. 776 Chinese healthy myopic children (375 boys and 401 girls) were enrolled, mean (±SD) age 9.84 ± 1.98 (range 6–16) years. En-face angiogram OCTA was performed on 6 mm × 6 mm retinal and 4.5 mm × 4.5 mm disc regions. VD measurements in the macular retina were segmented into the four regions: superficial capillary plexus (SCP), intermediate capillary plexus (ICP), deep capillary plexus (DCP), and choriocapillaris (CC). Correlations between macular, disc, and peripapillary VD and possible influencing factors [age, gender, axial length (AL), spherical equivalent refraction (SER), right/left eye, and signal strength index (SSI)] were assessed by Pearson’s correlation and multivariate regression analysis.

Results

For macular scans, the corrected VD in the ICP region was (48.25 ± 4.24)% for the whole macular retina. The macular ICP VD in most sections was lower than the SCP, DCP, and CC (all P < 0.001). The corrected VD in CC was (72.96 ± 4.42)% for the whole macular retina. The macular CC VD in every section was all higher than the SCP, ICP, and DCP (all P < 0.001). The size of foveal avascular zone (FAZ) and foveal VD 300 (FD-300) was 0.28 mm²± 0.10 mm² and (58.43 ± 4.17)% respectively. For disc scans, the corrected VD was (58.04 ± 2.73)% for the whole disc area. Both AL and SER were strongly correlated with ICP, DCP, and CC VD in all regions (all P < 0.01). Larger SSI was correlated with a lower VD in the SCP and ICP, and a higher VD in DCP and CC (all P < 0.01).

Conclusion

Vascular density values provide large scale normative data on macular, disc, and peripapillary vascular parameters in a large sample of healthy myopic children with OCTA measured in the four different retinal plexuses and regions. The VD in different regions had various influencing factors; mainly a close correlation with AL and SSI.

Dynamic inverse SNR-decorrelation OCT angiography with GPU acceleration

Dynamic OCT angiography (OCTA) is an attractive approach for monitoring stimulus-evoked hemodynamics; however, a 4D (3D space and time) dataset requires a long acquisition time and has a large data size, thereby posing a great challenge to data processing. This study proposed a GPU-based real-time data processing pipeline for dynamic inverse SNR-decorrelation OCTA (ID-OCTA), offering a measured line-process rate of 133 kHz for displaying OCT and OCTA cross-sections in real time. Real-time processing enabled automatic optimization of angiogram quality, which improved the vessel SNR, contrast-to-noise ratio, and connectivity by 14.37, 14.08, and 9.76%, respectively. Furthermore, motion-contrast 4D angiographic imaging of stimulus-evoked hemodynamics was achieved within a single trail in the mouse retina. Consequently, a flicker light stimulus evoked an apparent dilation of the retinal arterioles and venules and an elevation of the decorrelation value in the retinal plexuses. Therefore, GPU ID-OCTA enables real-time and high-quality angiographic imaging and is particularly suitable for hemodynamic studies.

Optical Coherence Tomography Angiography: Clinical Utility and Future Directions

Purpose

This work aims to review the principles of optical coherence tomography angiography (OCTA), to survey its clinical utility, and to highlight the strengths of this technology as well as barriers to adoption.

Methods

A literature review with editorial discussion of the current applications for OCTA is presented.

Results

There have been recent advances in multiple domains in OCTA imaging, including devices, algorithms, and new observations pertaining to a range of pathologies. New devices have improved the scanning speed, signal-to-noise ratio, and spatial resolution and offer an increased field of view. New algorithms have been proposed to optimize image processing and reduce artifacts. Numerous studies employing OCTA have been published describing changes to the microvasculature in diabetic retinopathy, age-related macular degeneration, central serous chorioretinopathy, retinal vein occlusion, and uveitis.

Conclusions

OCTA provides noninvasive, high-resolution volumetric scans of the retinal and choroidal vasculature. OCTA can provide valuable data to augment traditional dye-based angiography in a range of chorioretinal diseases.

Persistent Hypertransmission Defects Detected on En Face Swept Source Optical Computed Tomography Images Predict the Formation of Geographic Atrophy in Age-Related Macular Degeneration

PURPOSE

To determine whether persistent hypertransmission defects (hyperTDs), previously shown to have a greatest linear dimension (GLD) ≥250 µm on en face swept source OCT (SS-OCT) images, serve as a stand-alone early biomarker for the future formation geographic atrophy (GA).

DESIGN

Post hoc cohort study using a subgroup of a prospective study.

METHODS

Patients with intermediate age-related macular degeneration (iAMD) underwent 6- × 6-mm SS-OCT raster scans at baseline and during their follow-up period. En face images were generated using a slab with segmentation boundaries positioned 64 µm to 400 µm beneath the Bruch's membrane. Two graders independently evaluated all en face structural images for the presence of hyperTDs with a GLD ≥250 µm and GA.

RESULTS

A total of 190 eyes were included with a mean ± SD follow-up of 31 ± 13.2 months. At baseline, 31 eyes (16%) had at least 1 hyperTD ≥250 µm, and 13 eyes (42%) progressed to GA. In those eyes without a hyperTD ≥250 µm at baseline, 42 (26%) developed hyperTDs ≥250 µm during their follow-up, and 11 eyes (7%) progressed to GA. At the last available follow-up visit, 25 eyes (13%) progressed to GA and of these 25 eyes, a prior hyperTD ≥250 µm was detected in 24 eyes before GA formed. A time-dependent Cox-survival regression analysis estimated an 80-fold (95% CI, 10.7-614, P < .001) increased risk of developing GA once a hyperTD ≥250 µm appeared.

CONCLUSIONS

Persistent hyperTDs detected on en face OCT images were shown to serve as an early stand-alone OCT biomarker for the future formation of GA.

Spatial-Temporal Speckle Variance in the En-Face View as a Contrast for Optical Coherence Tomography Angiography (OCTA)

Optical Coherence Tomography (OCT) is an adaptable depth-resolved imaging modality capable of creating a non-invasive 'digital biopsy' of the eye. One of the latest advances in OCT is optical coherence tomography angiography (OCTA), which uses the speckle variance or phase change in the signal to differentiate static tissue from blood flow. Unlike fluorescein angiography (FA), OCTA is contrast free and depth resolved. By combining high-density scan patterns and image processing algorithms, both morphometric and functional data can be extracted into a depth-resolved vascular map of the retina. The algorithm that we explored takes advantage of the temporal-spatial relationship of the speckle variance to improve the contrast of the vessels in the en-face OCT with a single frame. It also does not require the computationally inefficient decorrelation of multiple A-scans to detect vasculature, as used in conventional OCTA analysis. Furthermore, the spatial temporal OCTA (ST-OCTA) methodology tested offers the potential for post hoc analysis to improve the depth-resolved contrast of specific ocular structures, such as blood vessels, with the capability of using only a single frame for efficient screening of large sample volumes, and additional enhancement by processing with choice of frame averaging methods. Applications of this method in pre-clinical studies suggest that the OCTA algorithm and spatial temporal methodology reported here can be employed to investigate microvascularization and blood flow in the retina, and possibly other compartments of the eye.

Optical Coherence Tomography Angiography in Healthy Adult Subjects: Normative Values, Frequency, and Impact of Artifacts

Aim

This cross-sectional study is aimed at identifying normative ocular coherence tomography angiography (OCTA) values in a cohort of healthy adult Jordanian individuals and assessing the prevalence of different image artifacts and their impact on quantitative OCTA measurements.

Materials and Methods

One hundred and eighty-one eyes from 100 healthy participants were included in this study. All participants underwent a comprehensive ophthalmological examination including best corrected visual acuity, slit lamp examination, and dilated fundoscopy. Swept-source OCTA images were obtained and analyzed for all 181 eyes. We recorded vascularity measurements and analyzed the prevalence and effect of ten different artifacts on superficial and deep retinal and choriocapillaris layer images.

Results

Sixty-two percent of the participants were men (n = 62), and 38% (n = 38) were women. The age of participants ranged between 24 and 75 years (mean 50.5 ± 10.92). The mean central macular thickness was 237.71 (±22.905) μm, and the mean choroidal thickness was 257.73 (±77.027) μm. Artifacts were present in 46.4% of the acquired scans. Images with artifacts had higher mean age (p = 0.03), lower image quality (p < 0.001), higher central vascular density (p < 0.001), and lower inferior vascular density (p < 0.001) compared to artifact-free tomographs. Motion artifact was the most common type, which was present in 29 (16%) of images, followed by blink artifact 18 (9.9%), and Z offset 8 (4.4%).

Conclusion

OCTA artifact detection and correction remains a challenging aspect of the diagnostic and follow-up process of patients with retinal pathologies. To our knowledge, this is the first study to examine the association between OCTA outputs and artifacts in healthy eyes. We report that in this cohort of normal individuals, images with artifacts had a significantly higher central vascular density (22.62 vs. 16.60) and a lower inferior vascular density (46.09 vs. 48.81). We also found that a significant increase in central vascular density is only present in images with Z offset artifact type (49.03). Motion artifact was the most common artifact seen in our series. However, we observed no alteration in quantitative parameters in images with motion artifacts.

The three-dimensional structural configuration of the central retinal vessel trunk and branches as a glaucoma biomarker

PURPOSE

To assess whether the 3-dimensional (3D) structural configuration of the central retinal vessel trunk and its branches (CRVT&B) could be used as a diagnostic marker for glaucoma.

DESIGN

Retrospective, deep-learning approach diagnosis study.

METHODS

We trained a deep learning network to automatically segment the CRVT&B from the B-scans of the optical coherence tomography (OCT) volume of the optic nerve head. Subsequently, 2 different approaches were used for glaucoma diagnosis using the structural configuration of the CRVT&B as extracted from the OCT volumes. In the first approach, we aimed to provide a diagnosis using only 3D convolutional neural networks and the 3D structure of the CRVT&B. For the second approach, we projected the 3D structure of the CRVT&B orthographically onto sagittal, frontal, and transverse planes to obtain 3 two-dimensional (2D) images, and then a 2D convolutional neural network was used for diagnosis. The segmentation accuracy was evaluated using the Dice coefficient, whereas the diagnostic accuracy was assessed using the area under the receiver operating characteristic curves (AUCs). The diagnostic performance of the CRVT&B was also compared with that of retinal nerve fiber layer (RNFL) thickness (calculated in the same cohorts).

RESULTS

Our segmentation network was able to efficiently segment retinal blood vessels from OCT scans. On a test set, we achieved a Dice coefficient of 0.81 ± 0.07. The 3D and 2D diagnostic networks were able to differentiate glaucoma from nonglaucoma subjects with accuracies of 82.7% and 83.3%, respectively. The corresponding AUCs for the CRVT&B were 0.89 and 0.90, higher than those obtained with RNFL thickness alone (AUCs ranging from 0.74 to 0.80).

CONCLUSIONS

Our work demonstrated that the diagnostic power of the CRVT&B is superior to that of a gold-standard glaucoma parameter, that is, RNFL thickness. Our work also suggested that the major retinal blood vessels form a "skeleton"-the configuration of which may be representative of major optic nerve head structural changes as typically observed with the development and progression of glaucoma.

Optical Coherence Tomography Angiography in Diabetic Patients: A Systematic Review

Background: Diabetic retinopathy (DR) is the leading cause of legal blindness in the working population in developed countries. Optical coherence tomography (OCT) angiography (OCTA) has risen as an essential tool in the diagnosis and control of diabetic patients, with and without DR, allowing visualisation of the retinal and choroidal microvasculature, their qualitative and quantitative changes, the progression of vascular disease, quantification of ischaemic areas, and the detection of preclinical changes. The aim of this article is to analyse the current applications of OCTA and provide an updated overview of them in the evaluation of DR. Methods: A systematic literature search was performed in PubMed and Embase, including the keywords “OCTA” OR “OCT angiography” OR “optical coherence tomography angiography” AND “diabetes” OR “diabetes mellitus” OR “diabetic retinopathy” OR “diabetic maculopathy” OR “diabetic macular oedema” OR “diabetic macular ischaemia”. Of the 1456 studies initially identified, 107 studies were screened after duplication, and those articles that did not meet the selection criteria were removed. Finally, after looking for missing data, we included 135 studies in this review. Results: We present the common and distinctive findings in the analysed papers after the literature search including the diagnostic use of OCTA in diabetes mellitus (DM) patients. We describe previous findings in retinal vascularization, including microaneurysms, foveal avascular zone (FAZ) changes in both size and morphology, changes in vascular perfusion, the appearance of retinal microvascular abnormalities or new vessels, and diabetic macular oedema (DME) and the use of deep learning technology applied to this disease. Conclusion: OCTA findings enable the diagnosis and follow-up of DM patients, including those with no detectable lesions with other devices. The evaluation of retinal and choroidal plexuses using OCTA is a fundamental tool for the diagnosis and prognosis of DR.

Assessment of Retinal Capillary Dropout after Transcatheter Aortic Valve Implantation by Optical Coherence Tomography Angiography

Transcatheter aortic valve implantation (TAVI) is an alternative to open heart surgery in the treatment of symptomatic aortic valve stenosis, which is often the treatment of choice in elderly and frail patients. It carries a risk of embolic complications in the whole cerebral vascular bed, which includes the retinal vasculature. The main objective was the evaluation of retinal emboli visible on optical coherence tomography angiography (OCTA) following TAVI. This is a prospective, single center, observational study enrolling consecutive patients over two years. Patients were assessed pre- and post-TAVI. Twenty-eight patients were included in the final analysis, 82.1% were male, median age was 79.5 (range 52–88), median BCVA was 82.5 letters (range 75–93). Eight patients (28.6%) presented new capillary dropout lesions in their post-TAVI OCTA scans. There was no statistically significant change in BCVA. Quantitative analysis of macular or peripapillary OCTA parameters did not show any statistically significant difference in pre- and post-intervention. In conclusion, capillary dropout lesions could frequently be found in patients after TAVI. Quantitative measurements of macular and peripapillary flow remained stable, possibly indicating effective ocular blood flow regulation within the range of left ventricular ejection fraction in our cohort.

Optical coherence tomography-angiography in diabetic retinopathy diagnosis and monitoring

Optical coherence tomography-angiography is a modern noninvasive method of 3D imaging and quantitative analysis of the retinal and choroidal microvasculature. It allows detecting manifestation and progression of diabetic retinopathy, planning treatment and evaluating its results.Optical coherence tomography angiography expands our understanding of microvascular changes in retinal vascular plexuses at different disease stages and deepens the understanding of its pathogenesis.

Method for the biomechanical analysis of aqueous veins and perilimbal sclera by three-dimensional photoacoustic imaging and strain field calculation

A method motivated by the eye's aqueous veins is described for the imaging and strain calculation within soft biological tissues. A challenge to the investigation of the biomechanics of the aqueous vein-perilimbal sclera tissue complex is resolution of tissue deformations as a function of intraocular pressure and the subsequent calculation of strain (a normalized measure of deformation). The method involves perfusion of the eye with a contrast agent during conduction of non-invasive, optical resolution photoacoustic microscopy. This imaging technique permits three-dimensional displacement measurements of tracked points on the inner walls of the veins which are used in a finite element model to determine the corresponding strains. The methods are validated against two standard strain measurement methods. Representative porcine globe perfusion experiments are presented that demonstrate the power of the method to determine complex strain fields in the veins dependent on intraocular pressure as well as vein anatomy. In these cases, veins are observed to move radially outward during increases in intraocular pressure and to possess significant spatial strain variation, possibly influenced by their branching patterns. To the authors' knowledge, these are the only such quantitative, data driven, calculations of the aqueous vein strains available in the open literature.

Evaluation of flow of chorioretinal capillaries in healthy black and white subjects using optical coherence tomography angiography

This study compared macular capillary parameters between healthy black and white subjects using optical coherence tomography angiography (OCTA). We measured vessel density (VD) of superficial (SCP), intermediate (ICP), and deep (DCP) capillary plexuses and choriocapillaris blood flow area (BFA) of the fovea, parafovea and total 3 mm-diameter circular area centered on the fovea, as well as the foveal avascular zone (FAZ) parameters, controlling for axial length. Black subjects had lower foveal and parafoveal VD in the SCP (p = 0.043 and p = 0.014) and the ICP (p = 0.014 and p = 0.002). In the DCP, black subjects had a trend toward lower foveal and parafoveal VD. Black subjects had decreased choriocapillaris BFA in the total 3 mm area (p = 0.011) and the parafovea (p = 0.033), larger FAZ area (p = 0.006) and perimeter (p = 0.014), and a higher capillary density in a 300 μm wide region around the FAZ (FD-300) (p = 0.001). There was no significant difference in FAZ acircularity index. To our knowledge, this is the first report analyzing the three distinct retinal capillary plexuses and identifying differing baseline VD, choriocapillaris and FAZ parameters in healthy young black compared to white subjects. Larger studies are needed to validate these findings and better understand racial differences in vulnerability to ocular diseases.

Steps to Measurement Floor of an Optical Microangiography Device in Glaucoma

PURPOSE

To compare dynamic ranges and steps to measurement floors of peripapillary and macular metrics from a complex signal-based optical microangiography (OMAG^C) optical coherence tomography angiography (OCTA) device for glaucoma with those of OCT measurements.

DESIGN

Cross-sectional study.

METHODS

Imaging of 252 eyes from 173 patients with glaucoma and 123 eyes from 92 subjects without glaucoma from a glaucoma clinic was quantified using custom and commercial software. Metrics from OCT (retinal nerve fiber layer [RNFL], ganglion cell/inner plexiform layer [GCIPL]) and OCTA (custom: peripapillary vessel area density [pVAD], macular vessel area density [mVAD], and macular vessel skeleton density [mVSD]; commercial: peripapillary perfusion density [pPD^Z], macular perfusion density [mPD^Z], and macular vessel density [mVD^Z]) were plotted against visual field mean deviation (MD) with linear change-point analyses, measurement floors, and steps to floors.

RESULTS

Mean MD (dB) for glaucomatous eyes was -5.77 (-6.45 to -5.10). The number of eyes with mild glaucoma (MD >-6), moderate glaucoma (MD -6 to -12), and severe glaucoma (MD <-12) were 164, 50, and 38, respectively. pPD^Z yielded the lowest estimated floor at -26.6 dB (standard error [SE] 1.53), followed by OCTA macular metrics (-25 to -21 dB; SE 1.03) and pVAD (-17.6 dB, SE 1.06). RNFL and GCIPL produced floors at -17.8 (SE 0.927) and -23.6 dB (SE 1.14). The highest number of steps to measurement floor belonged to RNFL (7.20) and GCIPL (7.33), followed by pPD^Z (4.25), mVAD (3.87), and mVSD (3.81), with 2.5 or fewer steps for pVAD, mPD^Z, and mVD^Z.

CONCLUSIONS

pPD^Z, mVAD, and mVSD had approximately 4 steps within their dynamic ranges, without true measurement floors, and thus may be useful in evaluating advanced glaucomatous progression. Improving OCTA test-retest repeatability could augment number of steps for OCTA metrics, increasing their clinical utility.

Optical Coherence Tomography and Glaucoma

Early detection and monitoring are critical to the diagnosis and management of glaucoma, a progressive optic neuropathy that causes irreversible blindness. Optical coherence tomography (OCT) has become a commonly utilized imaging modality that aids in the detection and monitoring of structural glaucomatous damage. Since its inception in 1991, OCT has progressed through multiple iterations, from time-domain OCT, to spectral-domain OCT, to swept-source OCT, all of which have progressively improved the resolution and speed of scans. Even newer technological advancements and OCT applications, such as adaptive optics, visible-light OCT, and OCT-angiography, have enriched the use of OCT in the evaluation of glaucoma. This article reviews current commercial and state-of-the-art OCT technologies and analytic techniques in the context of their utility for glaucoma diagnosis and management, as well as promising future directions.

Predictors of Peripapillary and Macular Optical Microangiography Measurements in Healthy Eyes

PRECIS

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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