SWEPT SOURCE OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY OF NEOVASCULAR MACULAR TELANGIECTASIA TYPE 2

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.

Deep-learning visualization enhancement method for optical coherence tomography angiography in dermatology

Optical coherence tomography angiography (OCTA) in dermatology usually suffers from low image quality due to the highly scattering property of the skin, the complexity of cutaneous vasculature, and limited acquisition time. Deep-learning methods have achieved great success in many applications. However, the deep learning approach to improve dermatological OCTA images has not been investigated due to the requirement of high-performance OCTA systems and difficulty of obtaining high-quality images as ground truth. This study aims to generate proper datasets and develop a robust deep learning method to enhance the skin OCTA images. A swept-source skin OCTA system was employed to create low-quality and high-quality OCTA images with different scanning protocols. We propose a model named vascular visualization enhancement generative adversarial network and adopt an optimized data augmentation strategy and perceptual content loss function to achieve better image enhancement effect with small amount of training data. We demonstrate the superiority of the proposed method in skin OCTA image enhancement by quantitative and qualitative comparisons.

Rapid estimations of intensity standard deviations for optical coherence tomography angiography

Optical coherence tomography angiography (OCTA) can map microvascular networks and quantify blood flow velocities with high resolution by calculating intensity standard deviations of time-series signals. However, statistical calculations of the standard deviations need much processing time and reduce the analysis efficiency. In this study, we proposed three optimized OCTA algorithms incorporating rapid estimations of the intensity standard deviations, including the range algorithm, the mean absolute error algorithm and the maximum absolute error algorithm. The abilities of the optimized algorithms to quantify the flow velocities were validated by a flow phantom. After a rat cerebral cortex was imaged, the optimized OCTA algorithms were compared with the conventional relative standard deviation algorithm in the metrics of imaging quality and processing time. The results show that the optimized algorithms incorporating rapid estimations of the intensity standard deviations have faster processing speeds with equivalent image quality.

Imaging endpoints for clinical trials in MacTel type 2

INTRODUCTION

Macular Telangiectasia type 2 (MacTel) is a bilateral neurodegenerative disease associated with dysfunction in the serine and lipid metabolism resulting in loss of Muller cells and photoreceptors. Typical structural changes include vascular abnormalities, loss of retinal transparency, redistribution of macular pigment and thinning of the central retina with photoreceptor loss. The presence and extent of photoreceptor loss, as visible on Optical Coherence Tomography (OCT) ("disease severity scale"), correlate with functional loss and the limitation of photoreceptor loss appears to be the most promising therapeutic approach. Ongoing clinical trials of ciliary neurotrophic factor (CNTF) implants for the treatment of MacTel are using this outcome to evaluate efficacy. An ideal outcome measure provides the ability to quantify the extent of the disease progression with precision and reproducibility.

METHODS

This review describes the changes and findings on different imaging techniques including fluorescein- and OCT angiography, blue light reflectance, 1- and 2-wavelength autofluorescence and OCT.

RESULTS

The possibilities of objective quantification of the severity of MacTel and correlation with functional characteristics such as best-corrected visual acuity (BCVA) and microperimetry and their applications as quantitative imaging endpoints for clinical treatment trials are discussed. OCT and especially en face OCT could be demonstrated as precise and reproducible methods to quantify the area of photoreceptor loss, which correlated highly significantly with functional loss in microperimetry.

CONCLUSION

The analysis of the area of photoreceptor loss on en face OCT is the most reliable imaging endpoint for treatment trials in MacTel. This method is already being used in ongoing randomized trials.

Scalable mapping of myelin and neuron density in the human brain with micrometer resolution

Optical coherence tomography (OCT) is an emerging 3D imaging technique that allows quantification of intrinsic optical properties such as scattering coefficient and back-scattering coefficient, and has proved useful in distinguishing delicate microstructures in the human brain. The origins of scattering in brain tissues are contributed by the myelin content, neuron size and density primarily; however, no quantitative relationships between them have been reported, which hampers the use of OCT in fundamental studies of architectonic areas in the human brain and the pathological evaluations of diseases. Here, we built a generalized linear model based on Mie scattering theory that quantitatively links tissue scattering to myelin content and neuron density in the human brain. We report a strong linear relationship between scattering coefficient and the myelin content that is retained across different regions of the brain. Neuronal cell body turns out to be a secondary contribution to the overall scattering. The optical property of OCT provides a label-free solution for quantifying volumetric myelin content and neuron cells in the human brain.

MULTIMODAL EVIDENCE OF TYPE 3 NEOVASCULARIZATION IN ENHANCED S-CONE SYNDROME

PURPOSE

To investigate, using multimodal imaging, the anatomy of neovascularization in eyes with enhanced S-cone syndrome.

METHODS

Three eyes with neovascularization, from two patients with enhanced S-cone syndrome, were analyzed using fluorescein angiography, indocyanine-green and optical coherence tomography angiography imaging.

RESULTS

The eyes reported had a demonstrable Type 3 neovascularization with evidence of retinal-retinal anastomoses on fluorescein angiography, indocyanine-green and optical coherence tomography angiography imaging. One eye that was initially without neovascularization, but with chronic macular edema developed a macular hemorrhage. This eye was treated with 8 injections of intravitreal bevacizumab over 29-months resulting in a final fibrovascular lesion. The characteristics of this final lesion share similarities to the two other eyes described. In all eyes and all exams, retinal vessels are observed to communicate with the subretinal fibrovascular lesion.

CONCLUSION

We provide evidence of retinal arteriovenous anastomosis of the superficial retinal plexus to a subretinal neovascular complex in patients with enhanced S-cone syndrome and point to similarities with Type 3 neovascularization in macular telengiectasia Type 2 (MacTel2) and age-related macular degeneration. These findings provide insights into the anatomy of neovascularization in these pathologies and may lead to hypotheses of their etiologies.

Choroidal vascularity index: an enhanced depth optical coherence tomography-based parameter to determine vascular status in patients with proliferative and non-proliferative macular telangiectasia

KEY MESSAGES

The pathogenesis of subretinal neovascularization (SRNV) due to macular telengiectasia (MacTel 2) has not fully elucidated. This optical coherence tomography (OCT)-based method can provide better understanding of the pathogenesis of SRNV due to MacTel 2.

PURPOSE

To evaluate the choroidal vascular index (CVI) through optical coherence tomography (OCT) on eyes with proliferative macular telangiectasia type 2 (MacTel 2) or non-proliferative MacTel 2, and in healthy individuals.

METHODS

Macular enhanced depth imaging OCT scans on 42 eyes of 21 patients with non-proliferative MacTel 2, on 32 eyes of 20 patients with proliferative MacTel 2, and on 38 eyes of 32 control patients were analyzed by adjusting for age-gender-axial length. Proliferative MacTel 2 was diagnosed when subretinal neovascularization (SRNV) was simultaneously observed in the non-proliferative phase. Binarization methods of ImageJ software were used to analyze images, and total choroid area (TCA), luminal area (LA) and stromal area (SA) were obtained. CVI was characterized as the ratio of LA to TCA.

RESULTS

The mean TCA and SA were significantly higher in group 1 and group 2 when compared with group 3 (3.36 ± 0.29 mm² vs. 3.27 ± 0.76 mm² vs. 2.49 ± 0.24 mm², p < 0.001; 1.15 ± 0.31 mm² vs. 1.10 ± 0.69 mm² vs. 0.35 ± 0.23 mm², respectively; p < 0.001). Although LA was relatively higher in group 1 and group 2 than group 3, no statistically significant difference was observed (2.22 ± 0.14 mm² vs. 2.17 ± 0.15 mm² vs. 2.13 ± 0.21 mm²) (p = 0.088). CVI was significantly lower in group 1 than other groups (0.65 ± 0.01 vs 0.67 ± 0.02 vs 0.68 ± 0.02) (p < 0.001).

CONCLUSION

As an OCT screening method, CVI may be used to assess the vascular status of the choroid on the eyes which are naive for or were exposed to SRNV secondary to MacTel 2, and to elucidate the pathogenesis of this disease.

Multimodal imaging of macular telangiectasia type 2 in a pediatric patient

Purpose

To describe findings of multimodal imaging in non-proliferative and proliferative stages of MacTel 2 in a pediatric patient, and results of aflibercept use for treating neovascularization secondary to MacTel 2.

Methods

Retrospective case report.

Results

An 11-year-old girl with no history of systemic disease. BCVA was 20/200 and 20/40 in the right and left eyes, respectively. FFA, SS-OCT and SS-OCTA revealed proliferative and non-proliferative stages of MacTel 2 in the right and left eyes, respectively. Intravitreal aflibercept (2mg/0.05mL) was started (PRN) in the right eye. The patient received 5 injections that led to involution of macular neovascularization and improvement of BCVA by 5 lines. BCVA in the left eye remained stable.

Conclusion

MacTel 2 can develop in an earlier age than previously reported. SS-OCTA is an effective alternative to conventional imaging in diagnosis and follow-up especially in pediatric patients. Intravitreal aflibercept is effective in treating proliferative MacTel 2.

COMPARISON BETWEEN SEVERAL OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY DEVICES AND INDOCYANINE GREEN ANGIOGRAPHY OF CHOROIDAL NEOVASCULARIZATION

PURPOSE

To compare indocyanine green angiography and four different optical coherence tomography angiography (OCTA) devices and to test their reproducibility in the evaluation of choroidal neovascularization (CNV).

METHODS

This study was an observational case series of Type 1 and Type 2 CNV presenting at the Eye Clinic, Department of Biomedical and Clinical Sciences, Luigi Sacco Hospital, University of Milan, imaged with indocyanine green angiography and four different OCTA devices: prototype PlexElite (Carl Zeiss Meditec), prototype Spectralis OCTA (Spectralis; Heidelberg Engineering, Heidelberg, Germany), Optovue RTVue XR Avanti (Optovue, Inc, Fremont, CA), and AngioPlex (Cirrus 5000 HD-OCT; Carl Zeiss Meditec, Inc, Dublin, CA). Optical coherence tomography angiography examinations were performed using a 3 × 3-mm or 6 × 6-mm volume scan pattern to capture the full lesion. The mean area of CNV, vessel density, and fractal dimension were compared between the devices.

RESULTS

Seventeen eyes of 17 patients with CNV were enrolled. The CNV area was significantly larger in indocyanine green angiography than in the OCTA devices. Moreover, the four different instruments produced measurements with different mean values of CNV area, vessel density, and fractal dimension. The Bland-Altman analysis revealed that the limits of agreement for the comparisons were not acceptable.

CONCLUSION

The choroidal neovascularization area is larger when imaged with standard indocyanine green angiography than with different OCTA devices with different algorithms, wavelengths, and scan patterns. The differences between several OCTA devices in the evaluation of quantitative parameters of CNV, such as CNV area, vessel density, and fractal dimension, suggest the necessity to standardize OCTA measurements for research and clinical practice.

CHARACTERIZING RETINAL-CHOROIDAL ANASTOMOSIS IN MACULAR TELANGIECTASIA TYPE 2 WITH OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY

PURPOSE

To characterize structural and angiographic findings in macular telangiectasia Type 2 (MacTel 2) and examine associations with visual acuity.

METHODS

MacTel 2 patients with complete ophthalmologic examination, including fundus photography, autofluorescence, spectral-domain optical coherence tomography, and projection-resolved optical coherence tomography angiography, were retrospectively evaluated.

RESULTS

There were 43 eyes of 22 patients with a mean age 63.9 (±10.3) years. Six patients had diabetes. Twenty-one eyes (48.8%) had retinal-choroidal anastomoses (RCAs) without any evidence of neovascularization extending laterally in a plane above or below the retinal pigment epithelium. None of the eyes had hemorrhage, lipid, or signs of subretinal exudation. When present, an average of 55 (±33.7) individual RCAs were clustered primarily in temporal juxtafoveal region of involved eyes. Right-angle veins were seen in all 21 eyes with RCAs, and hyperpigmentation was present in 18 (P < 0.001 for both). A conical collection of hyperreflective material spanning from Bruch membrane past external limiting membrane of ≥200-μm basal diameter was found in 21 eyes and labeled outer retinal hyperreflective lesion. Retinal-choroidal anastomoses occurred in clusters, often within the outer retinal hyperreflective lesion. This lesion colocalized with focal thinning of the outer nuclear layer and was surrounded by a larger defect in the ellipsoid zone. The presence of diabetes (P = 0.015), outer retinal hyperreflective lesion (P = 0.006), RCA (P = 0.005), and ellipsoid zone defect extent (P < 0.001) were associated with decreased visual acuity.

CONCLUSION

Retinal-choroidal anastomoses occur in eyes with MacTel 2 without signs of exudation. Retinal-choroidal anastomoses occur in numerous clusters particularly in the temporal juxtafoveal macula. Diabetes, ellipsoid zone defect extent, RCAs, and the outer retinal hyperreflective lesion predict poorer vision in MacTel 2.

Plexus-specific retinal vascular anatomy and pathologies as seen by projection-resolved optical coherence tomographic angiography

Optical coherence tomographic angiography (OCTA) is a novel technology capable of imaging retinal vasculature three-dimensionally at capillary scale without the need to inject any extrinsic dye contrast. However, projection artifacts cause superficial retinal vascular patterns to be duplicated in deeper layers, thus interfering with the clean visualization of some retinal plexuses and vascular pathologies. Projection-resolved OCTA (PR-OCTA) uses post-processing algorithms to reduce projection artifacts. With PR-OCTA, it is now possible to resolve up to 4 distinct retinal vascular plexuses in the living human eye. The technology also allows us to detect and distinguish between various retinal and optic nerve diseases. For example, optic nerve diseases such as glaucoma primarily reduces the capillary density in the superficial vascular complex, which comprises the nerve fiber layer plexus and the ganglion cell layer plexus. Outer retinal diseases such as retinitis pigmentosa primarily reduce the capillary density in the deep vascular complex, which comprises the intermediate capillary plexus and the deep capillary plexus. Retinal vascular diseases such as diabetic retinopathy and vein occlusion affect all plexuses, but with different patterns of capillary loss and vascular malformations. PR-OCTA is also useful in distinguishing various types of choroidal neovascularization and monitoring their response to anti-angiogenic medications. In retinal angiomatous proliferation and macular telangiectasia type 2, PR-OCTA can trace the pathologic vascular extension into deeper layers as the disease progress through stages. Plexus-specific visualization and measurement of retinal vascular changes are improving our ability to diagnose, stage, monitor, and assess treatment response in a wide variety of optic nerve and retinal diseases. These applications will be further enhanced with the continuing improvement of the speed and resolution of the OCT platforms, as well as the development of software algorithms to reduce artifacts, improve image quality, and make quantitative measurements.

Ocular microcirculation changes, measured with laser speckle flowgraphy and optical coherence tomography angiography, in branch retinal vein occlusion with macular edema treated by ranibizumab

PURPOSE

This study searched for early predictive vascular biomarkers for visual outcomes in eyes with macular edema caused by branch retinal vein occlusion (BRVOME).

METHODS

Twenty-four eyes of 24 subjects with BRVOME were treated with the intravitreal injection of ranibizumab (IVR) for at least 6 months. We measured mean blur rate (MBR) in the optic nerve head (ONH) and vessel density (VD) in the macula with laser speckle flowgraphy and optical coherence tomography angiography, respectively.

RESULTS

Six-month post-IVR best-corrected visual acuity (BCVA) was correlated positively with age, pre-IVR BCVA, 1-month post-IVR BCVA, 3-month post-IVR BCVA and pre-IVR systolic blood pressure (P < 0.001, P < 0.001, P < 0.001, P < 0.001 and P = 0.02, respectively) and negatively with pre-IVR overall MBR, 1-month post-IVR overall MBR, 6-month post-IVR overall MBR, 3-month post-IVR deep retinal capillary plexus (DCP) VD and 6-month post-IVR DCP VD (P = 0.03, P = 0.03, P = 0.02, P = 0.01 and P = 0.005, respectively). Furthermore, a multiple regression analysis showed that pre-IVR overall MBR (β =  - 0.67, P = 0.009) was among independent prognostic factors predicting 6-month post-IVR BCVA. Six-month post-IVR DCP VD was also correlated with overall MBR at all time points.

CONCLUSION

ONH blood flow may be a pre-IVR biomarker of both visual outcomes and post-IVR deep macular microcirculation in eyes with BRVOME.

Quantitative assessment of optical coherence tomography angiography algorithms for neuroimaging

Optical coherence tomography (OCT) angiography can noninvasively map microvascular networks and quantify blood flow in a cerebral cortex with a resolution of 1 to 10 μm and a penetration depth of 2 to 3 mm incorporating OCT signals and angiography algorithms. Different angiography algorithms have been developed in recent years; however, the performance of the algorithms has not been assessed quantitatively for neuroimaging applications. In this paper, we developed four metrics including vascular connectivity, contrast-to-noise ratio, signal-to-noise ratio and processing time to quantitatively assess the performance of OCT angiography algorithms in image quality and computation speed. After the imaging of a rat cortex using an OCT system, the cerebral microvascular networks were visualized by seven algorithms, and the performance of the algorithms was quantified and compared. Quantitative performance assessment of the algorithms can provide suggestions for the selection of appropriate OCT angiography algorithms in neuroimaging.

Optical Coherence Tomography Angiography in Neurodegenerative Diseases: A Review

Background

Optical coherence tomography angiography (OCT-A) has emerged as a novel, fast, safe and non-invasive imaging technique of analyzing the retinal and choroidal microvasculature in vivo. OCT-A captures multiple sequential B-scans performed repeatedly over a specific retinal area at high speed, thus enabling the composition of a vascular map with areas of contrast change (high flow zones) and areas of steady contrast (slow or no flow zones). It therefore provides unique insight into the exact retinal or choroidal layer and location at which abnormal blood flow develops. OCTA has evolved into a useful tool for understanding a number of retinal pathologies such as diabetic retinopathy, age-related macular degeneration, central serous chorioretinopathy, vascular occlusions, macular telangiectasia and choroidal neovascular membranes of other causes. OCT-A technology is also increasingly being used in the evaluation of optic disc perfusion and has been suggested as a valuable tool in the early detection of glaucomatous damage and monitoring progression.

Objective

To review the existing literature on the applications of optical coherence tomography angiography in neurodegenerative diseases.

Summary

A meticulous literature was performed until the present day. Google Scholar, PubMed, Mendeley search engines were used for this purpose. We used 123 published manuscripts as our references. OCT-A has been utilized so far to describe abnormalities in multiple sclerosis (MS), Alzheimer’s disease, arteritic and non-arteritic optic neuropathy (AION and NAION), Leber’s hereditary optic neuropathy (LHON) papilloedema, Parkinson’s disease, Huntington’s disease, amyotrophic lateral sclerosis (ALS), Wolfram syndrome, migraines, lesions of the visual pathway and cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). It appears that OCT-A findings correlate quite well with the severity of the aforementioned diseases. However, OCT-A has its own limitations, namely its lack of wide-field view of the peripheral retina and the inaccurate interpretation due to motion artifacts in uncooperative groups of patients (e.g. children). Larger prospective longitudinal studies will need to be conducted in order to eliminate the aforementioned limitations.

Optical coherence tomography angiography findings of fellow eye of proliferative macular telangiectasia type 2: Long term study

PURPOSE

To report the characteristics of non-proliferative fellow eyes in patients with unilateral proliferative macular telangiectasia type 2 (MacTel).

METHODS

This was a multicenter, retrospective study and included fellow eyes of eyes with subretinal neovascular membrane (SRNVM). Multimodal imaging including fundus photography, optical coherence tomography (OCT), and OCT angiography (OCTA) was performed. OCT and OCTA measurements included central macular thickness (CMT), subfoveal choroidal thickness (SFCT), foveal avascular zone (FAZ) area and qualitative parameters such as distortion or enlargement of FAZ, increased inter-vascular spacing, dilated, tortuous vessel at margin of FAZ, crowding of vessel, and loss of choriocapillaris (CC).

RESULTS

Thirteen fellow eyes of 13 patients with mean age of 63.6 ± 12.0 years were included. Fellow eyes had various stages of the diseases - stage 2 (four eyes), 3 (six eyes), and 4 (three eyes). OCTA showed increased intervascular spacing (8; 61.5%), dilated (11; 84.6%), and elongated vessels (8; 61.5%) at the margin of the FAZ, crowding of vessels (6; 46.2%), capillary non-perfusion areas outside the FAZ (4; 30.8%), and areas of CC loss (4; 30.8%). Mean follow-up was 9.1 ± 12.9 months. Out of six eyes with follow-up of ⩾12 months, two developed SRNVM at 18 and 33 months with OCTA showing crowding and entanglement of dilated retinal vessels in deep capillary plexus at baseline which corresponded to the area affected by SRNVM.

CONCLUSION

Fellow eyes of proliferative MacTel showed established disease stages on OCTA with progressive capillary crowding and entanglement of vessels likely corresponding to the future site of SRNVM.

Evaluation of choroidal thickness and retinal vessel density in patients with inactive Graves' orbitopathy

BACKGROUND

To investigate choroidal thickness using spectral domain-optical coherence tomography and retinal vessel density with optical coherence tomography angiography in patients with inactive Graves' orbitopathy.

METHODS

A total of 36 eyes of 36 patients with inactive Graves' orbitopathy (6 men and 30 women in Group 1) and 36 eyes from 36 controls (8 men and 28 women in Group 2) were recruited for this prospective case-control study. Choroidal thickness measurements were obtained using enhanced depth imaging with spectral domain-optical coherence tomography. Optical coherence tomography angiography images were generated with 6 × 6-mm angiographic optical coherence tomography scans. Retinal vessel densities of the superficial retinal layer and deep retinal layer of the macula and foveal avascular zone measurements were obtained for each eye.

RESULTS

The mean age was 42.5 ± 9.9 years in Group 1 and 42.8 ± 6.5 years in Group 2 (p = 0.76). The mean choroidal thickness was 370.7 ± 83.5 μm and 338.2 ± 72.4 μm in Group 1 and 2, respectively (p = 0.09). There was no significant difference between the groups in retinal vessel density either in superficial or deep retinal layers (p > 0.05 for all), and no difference was found between the groups in foveal avascular zone area and perimeter (p = 0.69, p = 0.73, respectively).

CONCLUSIONS

Similar retinal vessel density values were found in both superficial and deep retinal layers in Graves' orbitopathy compared with healthy subjects. Although statistically insignificant, choroidal thickness was slightly higher in patients with Graves' orbitopathy than in healthy subjects. Foveal avascular zone area and perimeter measurements were unaffected by the disease.

Optical coherence tomography-angiography for monitoring neovascularisations in macular telangiectasia type 2

PURPOSE

To evaluate the utility of optical coherence tomography-angiography (OCT-A) for monitoring activity, progression and response to therapy of neovascularisations (NVs) secondary to macular telangiectasia type 2 (MacTel).

METHODS

In a retrospective analysis, eyes with NVs secondary to MacTel were reviewed over a period of ≥8 months. Examinations at monthly intervals included visual acuity testing, dilated funduscopy, spectral domain-OCT and OCT-A. Eyes were treated with intravitreal VEGF (vascular endothelial growth factor)-inhibitors following a pro-re-nata (PRN) regime, and treatment decisions were based on morphological signs of activity as determined by B-scan OCT and funduscopy. Signs of neovascular activity were defined as an increase in retinal thickness, presence/increase of intraretinal/subretinal fluid and haemorrhages.

RESULTS

A total of 19 eyes from 17 patients were analysed. Patients were evaluated over a mean period of 13.4 months (range: 8.9 to 24.2). OCT-A permitted the monitoring of both treatment effects (regression) and progression (growth) of NVs, but not neovascular activity. The growth of neovascular vessels was detectable in OCT-A before signs of activity occurred on OCT. NVs showed a progressive growth over time despite PRN-treatment and preferentially grew and extended within areas characterised by a focal reduction of choriocapillaris perfusion.

CONCLUSIONS

The results indicate that OCT-A represents a useful imaging modality for monitoring NV-progression and treatment effects in MacTel. We demonstrate its advantages over conventional B-scan OCT imaging, including an earlier detection of NV-progression, and propose an adjustment of the current OCT-controlled PRN treatment regime in order to prevent NV-progression and subsequent functional loss in neovascular MacTel.

Association of retinal vessel density with retinal sensitivity in surgery for idiopathic epiretinal membrane

PURPOSE

The success of surgical treatment for idiopathic epiretinal membrane (ERM) is measured by postoperative best-corrected visual acuity (BCVA), metamorphopsia, and foveal retinal sensitivity (RS).This study searched for predictive biomarkers of surgical success by determining the association between foveal RS and various aspects of vessel density (VD) in the fovea of patients with ERM.

METHODS

The study examined 25 eyes of 25 patients with ERM who underwent 27-gauge microincision vitrectomy surgery (MIVS). RS was measured with microperimetry (MP-3; NIDEK) at four central points in the fovea with an interpoint distance of 2°. VD was measured with SD-OCT (RS 3000; NIDEK) within the 1-mm² square defined by the 4 RS points at various depths, including the superficial and deep retinal capillary plexus (SCP and DCP, respectively).

RESULTS

Though VD did not change throughout the follow-up period, BCVA and RS significantly improved 1 and 3 months after surgery, respectively (both P < 0.0017). Postoperative RS at 6 months was positively correlated with postoperative DCP VD at 1, 3, and 6 months (r = 0.62, P = 0.001; r = 0.40, P = 0.049; r = 0.53, P = 0.007, respectively), but not with SCP VD at any time point. Multiple regression analysis confirmed that postoperative RS at 6 months was associated with postoperative DCP VD at 1 month (P = 0.03).

CONCLUSION

Higher postoperative DCP VD at 1 month contributed to better postoperative foveal RS at 6 months. Early postoperative VD in the fovea might be a useful predictive biomarker of late postoperative RS in the fovea in ERM patients.

Artifacts and artifact removal in optical coherence tomographic angiography

Optical coherence tomographic angiography (OCTA) enables rapid imaging of retinal vasculature in three dimensions. While the technique has provided quantification of healthy vessels as well as pathology in several diseases, it is not unusual for OCTA data to contain artifacts that may influence measurement outcomes or defy image interpretation. In this review, we discuss the sources of several OCTA artifacts-including projection, motion, and signal reduction-as well as strategies for their removal. Artifact compensation can improve the accuracy of OCTA measurements, and the most effective use of the technology will incorporate hardware and software that can perform such correction.

Clinical Implications of Suspended Scattering Particles in Motion Observed by Optical Coherence Tomography Angiography

The objective of this study was to investigate the relationship between suspended scattering particles in motion (SSPiM) in optical coherence tomography angiography (OCTA) and treatment response in diabetic macular edema (DME). We retrospectively reviewed the medical records of patients diagnosed with DME who had undergone intravitreal injection. The optical density ratio (ODR) of the intraretinal cyst and the numbers of hyperreflective foci from OCT images and SSPiM from OCTA images were compared, and their association with treatment response was analyzed. Forty-five eyes from 45 patients were included in this study. Twenty-four patients were treated with anti-vascular endothelial growth factor, and 21 patients were treated with a steroid. Binary logistic regression model showed that SSPiM in OCTA images was associated with hyperreflective foci numbers (P = 0.038) and mean ODR of the intraretinal cyst (P = 0.006). Linear regression model showed that SSPiM in the inner nuclear layer was related to treatment response (P = 0.006). SSPiM on OCTA images is related to the poor structural response to treatment in DME.

Evaluation of Choroidal Thickness in Patients with Proliferative and Non-Proliferative Macular Telangiectasia Using Enhanced Depth Imaging Optical Coherence Tomography

Purpose: To compare subfoveal choroidal thickness (SFCT) in eyes with non-proliferative macular telangiectasia (MacTel) type 2 with or without subretinal neovascularization (SRNV) and healthy control eyes.Methods: Consecutive patients with non-proliferative and proliferative MacTel type 2 were included in the current study. For comparisons subjects with no ocular pathology were recruited and used as controls. Best corrected visual acuity (BCVA), central macular thickness (CMT), and subfoveal choroidal thickness (SFCT) were evaluated. Since axial length (AL) may affect choroidal thickness, AL measurements were performed to avoid confusion in SFCT between the groups.Results: Of the 63 eyes of 38 MacTel type 2 patients, 38 eyes had only MacTel type 2 (group 1) and 25 eyes had SRNV caused by MacTel type 2 (group 2). Fourty eyes of 20 subjects served as controls (group 3). BCVA was found to be significantly higher in control group compared with group 1 and group 2 (p < .005). Whereas, no difference was detected between group 1 and group 2 (p = .75). No difference was noted in CMT between the groups (p = .35). Axial length measurement was very similar among all three groups (p = .62). After adjusting for age and axial length SFCT was significantly thinner in group 3 than the other groups (p < .001), but no statistically significant difference was found between group 1 and group 2.Conclusions: Choroidal thickness did not vary between eyes with MacTel type 2 with SRNV and without SRNV. Choroid was significantly thicker in MacTel type 2 with SRNV and without SRNV than healthy eyes.

Optical Coherence Tomography Angiography in Monitoring Proliferative Macular Telangiectasia Type 2 Treatment Response

BACKGROUND AND OBJECTIVE

Difficulty exists in the follow-up of proliferative macular telangiectasia type 2 (MacTel 2) cases after anti-vascular endothelial growth factor (VEGF) treatment due to staining in fluorescein angiography (FA) and alteration in retinal layers by optical coherence tomography (OCT). Herein, the authors report three cases in which OCT angiography (OCTA) could resolve this issue.

PATIENTS AND METHODS

In this retrospective, observational case series, diagnosis of MacTel 2 was made based on clinical examination, FA, OCT, and OCTA at presentation. Regression of neovessels was monitored by OCT and OCTA.

RESULTS

OCTA could delineate neovessels before treatment in all cases and facilitate differentiation between active and regressed lesions after treatment. Simultaneous OCT images were less easily appreciated due to altered retinal structure secondary to degenerative nature of the disease.

CONCLUSION

OCTA could be the tool of choice to monitor neovascular response to anti-VEGF treatment in proliferative MacTel 2. [Ophthalmic Surg Lasers Imaging Retina. 2019;50:485-491.].

Two-Year Risk of Exudation in Eyes with Nonexudative Age-Related Macular Degeneration and Subclinical Neovascularization Detected with Swept Source Optical Coherence Tomography Angiography

PURPOSE

Swept source optical coherence tomography angiography (SS-OCTA) was used to study the prevalence, incidence, and natural history of subclinical macular neovascularization (MNV) in eyes with unilateral nonexudative age-related macular degeneration.

DESIGN

Prospective cohort study.

METHODS

Patients were imaged using 3- × 3-mm and 6- × 6-mm SS-OCTA scan patterns. MNV was detected using the outer retina to choriocapillaris en face slab. Prevalence and incidence of subclinical MNV, Kaplan-Meier cumulative estimates for the overall risk of exudation, and the association between neovascular lesion size and the risk of exudation were assessed through 2 years.

RESULTS

From August 2014 through March 2018, 227 patients (154 intermediate and 73 late age-related macular degeneration eyes) underwent SS-OCTA imaging. Thirty eyes (13.2%) had subclinical MNV at first imaging and 12 eyes (8.9%) developed subclinical MNV during follow-up. Of the 191 eyes with >1 visit, 19 developed exudation. Fourteen of these eyes had pre-existing subclinical MNV. The incidence of exudation from the time of first detection of any subclinical MNV was 34.5%. The relative risk of exudation after detection of subclinical MNV was 13.6 times greater (95% confidence interval 4.9-37.7) than in the absence of subclinical MNV (P < .001). There was no significant risk of exudation based on lesion size alone (P = .91).

CONCLUSIONS

By 24 months, the risk of exudation was 13.6 times greater for eyes with subclinical MNV detected by SS-OCTA compared with eyes without subclinical MNV. For eyes with subclinical MNV in the absence of symptomatic exudation, we recommend close follow-up without treatment.

Optical Coherence Tomography Angiography Imaging in Inherited Retinal Diseases

Optical coherence tomography angiography (OCTA) is a novel, noninvasive imaging modality that allows depth-resolved imaging of the microvasculature in the retina and the choroid. It is a powerful research tool to study the pathobiology of retinal diseases, including inherited retinal dystrophies. In this review, we provide an overview of the evolution of OCTA technology, compare the specifications of various OCTA devices, and summarize key findings from published OCTA studies in inherited retinal dystrophies including retinitis pigmentosa, Stargardt disease, Best vitelliform macular dystrophy, and choroideremia. OCTA imaging has provided new data on characteristics of these conditions and has contributed to a deeper understanding of inherited retinal disease.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Comparison of Retinal Layer Thickness and Vascular Density between Acute and Chronic Branch Retinal Vein Occlusion

Purpose

To compare retinal layer thickness and chorioretinal vascular density (VD) between acute and chronic branch retinal vein occlusion (BRVO).

Methods

This study included patients with BRVO. The VD of the superficial capillary plexus (VDs), the VD of the deep capillary plexus (VDd), and VD of the choriocapillaris were obtained using optical coherence tomography angiography. Acute and chronic BRVO data were compared to assess differences between the involved and uninvolved areas.

Results

We included 17 eyes with acute BRVO and 23 eyes with chronic BRVO. The VDs in the involved area were not significantly different between the involved area and in the uninvolved area in acute BRVO (p = 0.551). However, the difference was significant in chronic BRVO (p = 0.013). The VDd in the involved area was lower than in the uninvolved area in both acute and chronic BRVO (p = 0.020, p = 0.003, respectively). In addition, the VD of the choriocapillaris values did not differ significantly between acute and chronic BRVO, or between involved and uninvolved areas. The VDs in the involved area in chronic BRVO were lower than in acute BRVO (p = 0.047), and the VDd did not differ between acute and chronic BRVO in all areas.

Conclusions

Vascular impaired patterns in the retinal layer differed between acute and chronic BRVO. These results may suggest that vascular change and remodeling develops differently in acute and chronic phases in BRVO.

Quantitative analysis of the macula with optical coherence tomography angiography in normal Japanese subjects: The Taiwa Study

This study evaluated age-related changes in the superficial and deep retinal capillary plexus (SCP and DCP, respectively) and in the foveal avascular zone (FAZ). SCP and DCP perfusion density (PD) were measured in optical coherence tomography angiography (OCTA) macular scans of 145 eyes of 145 healthy Japanese subjects, and findings were compared with SCP FAZ and clinical data. We found that age was negatively correlated with SCP and DCP PD (r = -0.17, P = 0.04 and r = -0.20, P = 0.02, respectively) and positively correlated with FAZ area (r = 0.18, P = 0.03). SCP and DCP PD were correlated with each other (r = 0.67, P < 0.001). FAZ area was negatively correlated with SCP PD, DCP PD and central macular thickness (CMT) (r = -0.18, P = 0.03; r = -0.25, P < 0.01; and r = -0.39, P < 0.001, respectively). FAZ was larger and CMT was lower (P = 0.01 and P < 0.001, respectively) in women than men. SCP and DCP PD were positively correlated with estimated glomerular filtration rate (r = 0.17, P = 0.03 and r = 0.24, P < 0.01, respectively). Multiple regression analysis confirmed that age independently affected DCP PD and FAZ (P = 0.02 and P < 0.01, respectively) and that CMT independently affected FAZ area (P < 0.001). Thus, normal subjects showed age-related decreases in macular PD and renal function. FAZ and CMT were related, suggesting that age-related changes in macular thickness also affect capillary vasculature.

RETINAL-CHOROIDAL ANASTOMOSIS IN MACULAR TELANGIECTASIA TYPE 2

PURPOSE

To investigate the deep retinal vascular changes potentially present in macular telangiectasis Type 2 (MacTel 2) with projection resolved optical coherence tomography angiography including volume rendering.

METHODS

Retrospective consecutive evaluation of patients with MacTel 2 in a community-based retinal referral practice with a comprehensive ophthalmologic examination to include optical coherence tomography and projection-resolved optical coherence tomography angiography with volume rendering. Main outcome measures were the characterization of vessel presence and anatomical arrangement in the outer retina.

RESULTS

There were 26 eyes of 13 patients with a mean age of 64.9 (±11.3) years, and 6 were men. The mean visual acuity was logMAR 0.4 (Snellen equivalent 20/50). No eye had signs of choroidal neovascularization or exudation. Focal hyperpigmentation was seen in 13 (50%) and right-angle veins in 17 (65%) eyes. Retinal-choroidal anastomoses were seen in 17 (65%) eyes. These anastomoses typically occurred in multiple clusters of small vessels. The presence of anastomoses was associated with pigment (P < 0.001), although the anastomoses did not necessarily colocalize with the pigment, and right-angle veins (P < 0.001), which were found in every eye with a retinal-choroidal anastomosis.

CONCLUSION

Retinal-choroidal anastomoses were commonly observed in eyes with MacTel 2 using projection-resolved optical coherence tomography angiography. One animal model for MacTel 2 uses very low-density lipoprotein receptor mutant mice and shows multiple retinal-choroidal anastomoses in the disease pathogenesis as well. These findings suggest MacTel 2 is more than just a neurodegenerative disease with secondary vascular abnormalities, as the choroid may be involved in the disease process.

Optical Coherence Tomography Angiography: Review of Current Technical Aspects and Applications in Chorioretinal Disease

Optical coherence tomography angiography (OCT-A) has enabled fast, non-invasive, high-resolution visualization of vasculature within the eye. In the past few years, it has become increasingly utilized for a range of disorders including age-related macular degeneration, diabetic retinopathy, retinal vein occlusions, and uveitis among others. This article reviews technical aspects of OCT-A, its applications in chorioretinal disease, and known limitations of the technology.

Right-angled vessels in macular telangiectasia type 2

PURPOSE

To evaluate the role of right-angled vessels (RAVs) during disease progression in macular telangiectasia type 2 (MacTel).

METHODS

In this study, 100 eyes of 52 patients and 52 eyes of 26 age-related controls were examined using fundus photography, spectral-domain optical coherence tomography (SD-OCT), OCT angiography (OCT-A) and fundus fluorescein angiography (FFA). Two masked readers graded fundus photographs of patients' eyes into five disease stages according to Gass and Blodi, and evaluated all eyes for the presence of RAVs. If RAVs were present, their course and origin (arterial vs venous) was evaluated with OCT-A and FFA, respectively. Additionally, we looked for morphological correlates of these vessels on SD-OCT scans. Neovascular eyes were analysed for the presence of RAVs and for morphological changes on formation of neovascularisations (NVs).

RESULTS

In OCT-A, RAVs were already detectable in eyes with early stages (1 to 2), could be tracked from superficial to outer retinal layers and were shown to form anastomoses in the outer retina with disease progression. These vessels were of both arterial and venous origin as shown by early phase FFA. Dilated capillaries and RAVs in OCT-A corresponded to hyper-reflective alterations of the outer retina on SD-OCT scans. In 19/19 eyes, NVs were associated with the presence of RAVs, and RAVs were shown to directly connect to neovascular complexes and to undergo morphological changes upon NV formation.

CONCLUSIONS

The results emphasise the role of RAVs during disease progression from an early stage on and demonstrate their involvement in the development of secondary NVs in MacTel.

Retinal vascular density evaluated by optical coherence tomography angiography in macular telangiectasia type 2

PURPOSE

To evaluate the retinal and choroidal vascular changes through optical coherence tomography angiography (OCTA) in patients with macular telangiectasia type 2 (MacTel 2).

METHODS

Our study included 20 patients (40 eyes) with MacTel 2, and age-matched and sex-matched 18 subjects (36 eyes) in the control group. Fundus color photographs, fundus autofluorescence, fundus fluorescein angiography, spectral-domain optical coherence tomography and OCTA were performed. Foveal vascular density and parafoveal vascular density (PFVD), and foveal retinal thickness and parafoveal retinal thickness, choroidal thickness (CT) and retinal ganglion cell-inner plexiform layer (GCIPL) were compared between MacTel 2 patients and normal age-matched controls.

RESULTS

The retinal whole vascular density and PFVD of the deep plexus were significantly lower in patients with MacTel 2 than that of the control group (56.93% vs. 58.54%, p = 0.003; and 60.38% vs. 61.66%, p = 0.045). The foveal avascular zone (FAZ) of the deep plexus was significantly enlarged in patients with MacTel 2 than that of the control group (0.44 vs. 0.36, p = 0.009). There was a positive and statistically significant correlation between the FAZ of the superficial and deep plexus and CT in patients with MacTel 2. There was a positive and statistically significant correlation between retinal whole, parafoveal temporal quadrant vascular density of the superficial and deep plexus and GCIPL thickness in patients with MacTel 2.

CONCLUSIONS

Our study demonstrated that important retinal vascular density and FAZ changes in MacTel 2 occur in the deep capillary plexus of the retina.

Choroidal thickness and vascular density in macular telangiectasia type 2 using enface swept-source optical coherence tomography

Purpose

To investigate the choroidal thickness (CT) and choroidal vascular densities (CVD) of patients with macular telangiectasia type 2 (MacTel2) and their association with other multimodal imaging features, using swept-source optical coherence tomography (SS-OCT).

Methods

Prospective, cross-sectional study. Consecutive patients with MacTel2 along with controls without any macular disease were included. Fundus photography, confocal blue reflectance, near-infrared reflectance, autofluorescence, fluorescein angiography, spectral domain OCT and SS-OCT were performed. Images were independently analysed by two graders, and CVD was calculated from binarised en face SS-OCT images. CT was obtained from the SS-OCT platform via built-in automated segmentation. Multilevel mixed-effects models were used for statistical analysis.

Results

Thirty-nine eyes of 20 patients with MacTel2 and 29 eyes of 15 control patients were included. Average CT and perifoveal temporal CT did not differ significantly between eyes with MacTel2 and control eyes (p≥0.350), when accounting for confounding factors. Overall and temporal CVD also did not significantly differ between the two groups (p≥0.490).

Conclusion

CT and CVD did not significantly differ between MacTel2 and control eyes in this study using SS-OCT. Even though MacTel2 may include abnormalities involving the choroid, these are likely minor in comparison to the predominant retinal changes.

OCT Angiography: A Technique for the Assessment of Retinal and Optic Nerve Diseases in the Pediatric Population

Optical coherence tomography angiography (OCT-A) is a novel, rapidly evolving, non-invasive imaging technique that allows images of the retinal vasculature to be obtained in a few seconds. Blood vessels of different retinal vascular plexuses and the foveal avascular zone (FAZ) can be examined without the administration of any contrast or dye. Due to these characteristics, OCT-A could be an excellent complementary test to study retinal vascularization in children. Until now, most of the studies with OCT-A have been conducted in adults and only a few have been carried out in children. In this review, we describe the principles and advantages of OCT-A over traditional imaging methods and provide a summary of the OCT-A findings in retinopathy of prematurity and other retinal and optic disc pathologies in children. In view of the promising results from studies, the advantages of a relatively rapid and non-invasive method to assess the retinal vasculature makes OCT-A a tool of which applications in the field of pediatric ophthalmology will be expanded in the near future for patient diagnosis and follow-up in every day clinical practice.

A quantitative comparison of five optical coherence tomography angiography systems in clinical performance

AIM

To compare the clinical performance of 4 spectral-domain (SD) optical coherence tomography angiography (OCTA) systems: AngioVue™, AngioPlex™, Spectralis^® OCTA, AngioScan, and 1 swept-source (SS) OCTA SS OCT Angio™.

METHODS

Twenty-seven undilated right eyes of 27 participants underwent OCTA examination using five different systems respectively for both 3×3 and 6×6 mm² scan pattern (Spectralis OCTA for 3×3 mm² scan only). Image quality, including vessel valid visibility and the number of motion artifacts, and acquisition time were evaluated. Repeated measures analysis of variance (ANOVA) with Bonferroni's post-test and Friedman test with Dunn's post-test were used to compare measurements.

RESULTS

The age of the subjects was 28.19±5.55y (range, 23-49y). The spherical equivalent refraction was -2.55±1.84 D (range, 0.00 to -5.25 D). Significant difference was observed in the evaluation of vessel valid visibility (AngioVue the highest: 0.111±0.031 for 3×3 mm² scan and 0.128±0.020 for 6×6 mm² scan), number of motion artifacts (AngioVue the fewest: 0.778±1.086 for 3×3 mm² scan and 0.333±0.620 for 6×6 mm² scan) and acquisition time (AngioPlex the shortest: 8.537±1.921s for 3×3 mm² scan and 8.298±1.741s for 6×6 mm² scan; all P<0.001).

CONCLUSION

There is poor agreement of measurements among systems. AngioVue provides images with the highest vessel valid visibility and the fewest motion artifacts. AngioPlex achieves the shortest acquisition.

Principles of OCTA and Applications in Clinical Neurology

PURPOSE OF REVIEW

The article reviews the recent findings on the use of optical coherence tomography angiography (OCTA) in neurology.

RECENT FINDINGS

OCTA is a new addition to the powerful and complementary technology of the OCT. Due to its noninvasiveness, and reproducibility, it is possible to obtain high-resolution 3D images of the vessels of the human eye. As the vessels of the retina with the presence of endothelial cell's tight junctions resemble the brain vessels, it was hypothesized that the imaging of the retinal vessels might bring insight into brain vessels. OCTA has been effectively used to predict retinal vessel abnormalities in dementia, demyelization, optic disc neuropathies, and inherited degenerative diseases. Most common findings were decrease of vascular density and flow and an increase of avascular zones. Although OCTA is a relative new technology, recent studies show that it can be successfully applied in neurology.

Ultra-wide optical coherence tomography angiography in diabetic retinopathy

Background

To implement an ultra-wide optical coherence tomography angiography imaging (UW-OCTA) modality in eyes with diabetic retinopathy (DR) with the aim of quantifying the burden of microvascular disease at baseline and subsequent clinic visits.

Methods

UW-OCTA was implemented on a 1,060 nm swept source (SS) OCTA engine running at 100 kHz A-line rate with a motion tracking mechanism. A montage scanning protocol was used to capture a 100-degree field of view (FOV) using a 4×4 grid of sixteen total individual 6×6 mm² scans. Typical OCTA images with a FOV of 3×3, 6×6 and 12×12 mm² were obtained for comparison. DR patients were scanned at baseline and follow-up. They were treated at the clinician's discretion. Vessel density and non-perfusion area maps were calculated based on the UW-OCTA images.

Results

Three proliferative DR patients were included in the study. UW-OCTA images provided more detailed visualization of vascular networks compared to 50-degree fluorescein angiography (FA) and showed higher burden of pathology in the retinal periphery that was not captured by typical OCTA. Neovascularization complexes were clearly detected in the two patients with active PDR. Vessel density and non-perfusion maps were used to measure progressive capillary non-perfusion and regression of neovascularization between visits.

Conclusions

UW-OCTA provides approximately 100-degree OCTA images of the fundus comparable to that of wide-angle fundus photography, and may be more applicable in conditions such as DR which affect the peripheral retina in contrast to standard OCTA.

Accurate estimation of choriocapillaris flow deficits beyond normal intercapillary spacing with swept source OCT angiography

Background

To estimate choriocapillaris flow deficits beyond normal intercapillary distance with swept source optical coherence tomography angiography (SS-OCTA).

Methods

Subjects were enrolled and repeated SS-OCTA scans were performed using the 3 mm × 3 mm scan pattern. Blood flow was identified using the complex optical microangiography (OMAG^c) algorithm. The choriocapillaris (CC) was defined as a 20 µm slab of the flow volume beneath the outer boundary of Bruch's membrane (BM) and was compensated with the corresponding structural image for flow deficits measurement. Flow deficits were segmented based on one mean standard deviation from a normal database. A histogram based thresholding method was developed to remove small flow deficits that were determined by examining intercapillary spacing within normal CC networks. A registration method based on affine and B-spline transformation was utilized for the CC angiogram averaging. Four repeated scans were averaged, and results were compared with and without removal of small flow deficits after averaging a different number of scans (N=1, group 1; N=2, group 2; N=3, group 3 and N=4, group 4).

Results

Seven normal subjects were enrolled. Intercapillary distance was found to be 24 µm for the CC networks under OCTA, which was used as the threshold to exclude small flow deficits for CC quantification. After averaging, significant reduction in background noise and improvement in continuity of blood vessel networks were observed both on retinal and choriocapillaris angiograms. Flow deficit percentages of the choriocapillaris were significantly reduced with averaging (group 1 vs. group 2: P<0.0001; group 2 vs. group 3: P<0.001; group 3 vs. group 4: P<0.001). The flow deficit percentages were also significantly reduced after removing the small flow deficits (≤24 µm in diameter) in all groups (P<0.01). A statistically significant difference was found after removing small flow deficits (≤24 µm in diameter) between group 1 and group 2 (P<0.001), between group 2 and group 3 (P<0.05), and between group 3 and group 4 (P<0.05). However, the significance was decreased compared to that without small flow deficits removal.

Conclusions

A method was developed to improve the robust estimation of choriocapillaris flow deficits by removing the small flow deficits corresponding to normal intercapillary spacing. After the removal of small flow deficits, fewer repeats were required for image averaging to achieve comparable accuracy of flow deficit measurements with SS-OCTA.

SPECTRAL DOMAIN VERSUS SWEPT SOURCE OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY OF THE RETINAL CAPILLARY PLEXUSES IN SICKLE CELL MACULOPATHY

PURPOSE

To compare the spectral domain and swept source optical coherence tomography angiography findings in two cases of sickle cell maculopathy.

METHODS

A 53-year-old man and a 24-year-old man both with sickle cell disease (hemoglobin SS) presented with no visual complaints; Humphrey visual field testing demonstrated asymptomatic paracentral scotomas that extended nasally in the involved eyes. Clinical examination and multimodal imaging including spectral domain and swept source optical coherence tomography, and spectral domain optical coherence tomography angiography and swept source optical coherence tomography angiography (Carl Zeiss Meditec Inc, Dublin, CA) were performed.

RESULTS

Fundus examination of both patients revealed subtle thinning of the macula. En-face swept source optical coherence tomography confirmed the extent of the thinning correlating with the functional paracentral scotomas on Humphrey visual field. Swept source optical coherence tomography B-scan revealed multiple confluent areas of inner nuclear thinning and significant temporal retinal atrophy. En-face 6 × 6-mm spectral domain optical coherence tomography angiography of the macula demonstrated greater loss of the deep capillary plexus compared with the superficial capillary plexus. Swept source optical coherence tomography angiography 12 × 12-mm imaging captured the same macular findings and loss of both plexuses temporally outside the macula.

CONCLUSION

In these two cases of sickle cell maculopathy, deep capillary plexus ischemia is more extensive within the macula, whereas both the superficial capillary plexus and deep capillary plexus are involved outside the macula likely due to the greater oxygen demands and watershed nature of these areas. Swept source optical coherence tomography angiography clearly demonstrates the angiographic extent of the disease correlating with the Humphrey visual field scotomas and confluent areas of inner nuclear atrophy.

Emerging Applications of Optical Coherence Tomography Angiography (OCTA) in neurological research

Purpose

To review the clinical and research value of optical coherence tomography angiography (OCTA) in the field of neurology.

Methods

Current literature involving OCTA were reviewed through PubMed using the search terms “optical coherence tomography angiography”, with “multiple sclerosis”, “Alzheimer’s disease”, “optic neuropathy”, or other closely-related terms.

Results

OCTA has been applied in research to advance our understanding of the pathobiology of neurological disorders. OCTA-derived blood flow and vessel density measures are altered in multiple sclerosis (MS), Alzheimer’s disease (AD), and various optic neuropathies (ON) in varying regions of the posterior segment vasculature of the eye. These emerging research findings support the occurrence of retinal vascular alterations across a host of neurological disorders and raise the possibility that vasculopathy can be clinically relevant since it contributes to the pathobiology of several neurological disorders.

Conclusion

OCTA may be beneficial for neurological research. Additional investigations using OCTA in neurological disorders will help to further validate its clinical and research utilities in terms of characterizing the role of vasculopathy in neurological disorders.

OCT Angiography Helps Distinguish Between Proliferative Macular Telangiectasia Type 2 and Neovascular Age-Related Macular Degeneration

BACKGROUND AND OBJECTIVE

To demonstrate the advantage of optical coherence tomography angiography (OCTA) for the diagnosis and management of proliferative macular telangiectasia type 2 (MacTel2) masquerading as neovascular age-related macular degeneration (AMD).

PATIENTS AND METHODS

This is an observational cases series. Three patients referred with the diagnosis of neovascular AMD were identified in this retrospective study. In addition to color fundus, fluorescein angiography, and spectral-domain OCT (SD-OCT) imaging, SD-OCTA (AngioPlex; Carl Zeiss Meditec, Dublin, CA) was performed.

RESULTS

SD-OCTA revealed bilateral parafoveal retinal microvascular changes in three patients and unambiguously confirmed the diagnosis of MacTel2.

CONCLUSION

OCTA is an important tool for the correct diagnosis of MacTel2 in older patients with the concomitant or masquerading diagnosis of AMD. [Ophthalmic Surg Lasers Imaging Retina. 2018;49:303-312.].

Factors associated with deep circulation in the peripapillary chorioretinal atrophy zone in normal-tension glaucoma with myopic disc

PURPOSE

To investigate factors associated with choroidal microcirculation in the peripapillary chorioretinal atrophy (PPA) zone in eyes with normal-tension glaucoma (NTG) and myopic disc.

METHODS

In 100 eyes of 100 NTG patients with myopic disc and 20 eyes of 20 age-matched myopic controls, 4.5 × 4.5 mm scans were made of the optic nerve head with optical coherence tomography angiography (OCTA). Peripapillary chorioretinal atrophy (PPA) area and PPA superficial choroidal image intensity (PPA-CI) were calculated with image j software. Clinical characteristics, laser speckle flowgraphy-measured mean blur rate in the temporal tissue area (temporal MT), the central thresholds (the averaged standard automated perimetry-measured visual field thresholds in the four paracentral points) and 3D-OCT-measured ganglion cell complex thickness in the papillomacular bundle (PMB-GCCT) were recorded.

RESULTS

The NTG patients had significantly lower intraocular pressure, PMB-GCCT and central threshold values, and a larger PPA area, than the controls. The area under the receiver operating characteristics curve to differentiate NTG with parafoveal scotoma (PFS) from controls was 0.76 for temporal MT, 0.85 for PPA-CI and 0.87 for PMB-GCCT. Univariate and multivariate analyses revealed that PPA-CI was negatively correlated with age, pulse rate, best-corrected visual acuity, axial length and PPA area, and positively correlated with temporal MT, PMB-GCCT and the central thresholds.

CONCLUSION

Peripapillary chorioretinal atrophy (PPA)-CI was associated with temporal MT, ageing, bradycardia, axial length elongation and changes in central retinal structure and visual function in patients with NTG and myopic disc. Thus, microcirculation deep within the PPA zone might be a clinically useful biomarker of PFS in NTG.

Effective bidirectional scanning pattern for optical coherence tomography angiography

We demonstrate the utility of a novel scanning method for optical coherence tomography angiography (OCTA). Although raster scanning is commonly used for OCTA imaging, a bidirectional approach would lessen the distortion caused by galvanometer-based scanners as sources continue to increase sweep rates. As shown, a unidirectional raster scan approach has a lower effective scanning time than bidirectional approaches; however, a strictly bidirectional approach causes contrast variation along the B-scan direction due to the non-uniform time interval between B-scans. Therefore, a stepped bidirectional approach is introduced and successfully applied to retinal imaging in normal controls and in a pathological subject with diabetic retinopathy.

Advances in Retinal Optical Imaging

Retinal imaging has undergone a revolution in the past 50 years to allow for better understanding of the eye in health and disease. Significant improvements have occurred both in hardware such as lasers and optics in addition to software image analysis. Optical imaging modalities include optical coherence tomography (OCT), OCT angiography (OCTA), photoacoustic microscopy (PAM), scanning laser ophthalmoscopy (SLO), adaptive optics (AO), fundus autofluorescence (FAF), and molecular imaging (MI). These imaging modalities have enabled improved visualization of retinal pathophysiology and have had a substantial impact on basic and translational medical research. These improvements in technology have translated into early disease detection, more accurate diagnosis, and improved management of numerous chorioretinal diseases. This article summarizes recent advances and applications of retinal optical imaging techniques, discusses current clinical challenges, and predicts future directions in retinal optical imaging.