Reliability of Optical Coherence Tomography Angiography Retinal Blood Flow Analyses.

Purpose: Investigate the association between the optical coherence tomography angiography (OCTA) metrics derived from different analysis programs to understand the comparability of studies using these different approaches. Methods: Secondary analysis of a prospective observational study (March 2018-September 2021). Forty-four right eyes and 42 left eyes from 44 patients were included. Patients were either undergoing upper gastrointestinal surgery with a critical care stay planned or were already in the critical care unit with sepsis. OCTA scans were obtained in an ophthalmology department or critical care setting. Fourteen OCTA metrics were compared within and between the programs, and agreement was measured by Pearson's R coefficient and intraclass correlation coefficient. Results: Correlation was highest between all Heidelberg metrics and Fractalyse (all >0.84), and lowest between Matlab skeletonized or foveal avascular zone metrics and all other measures (e.g., skeletal fractal dimension and vessel density at -0.02). Agreement between eyes was moderate to excellent in all metrics (0.60-0.90). Conclusions: The significant variability between metrics and programs used for OCTA analysis demonstrates that they are not interchangeable and supports a recommendation for perfusion density metrics to be reported as standard. Translational Relevance: Agreement between different OCTA analyses is variable and not interchangeable. The high agreement between non-skeletonized vessel density metrics suggests that these should be routinely reported.

High-resolution/High-Speed Gap Can Distinguish Different Intraretinal Perfusion Signals by Optical Coherence Tomography Angiography.

Purpose: The development of optical coherence tomography angiography (OCTA) has radically changed the diagnostic assessment of the intraretinal vascular network. Two different OCTA acquisition modalities have recently been introduced in clinical practice, namely high-resolution (HR) and high-speed (HS) scans. HR OCTA requires more acquisition time and provides higher quality data, whereas HS OCTA is faster but furnishes lower quality data. The main aim of the present study is to gauge how much extra blood flow perfusion information can be obtained through the combined use of HR and HS OCTA. Methods: We compared HR and HS OCTA acquisitions to assess the reliability of both techniques, also putting forward a new set of quantitative metrics to measure the HR/HS OCTA gap and to highlight different perfusion information. Results: In essence, both HR and HS OCTA acquisitions proved highly feasible in detecting the intraretinal vascular flow signal, as confirmed by the stability of quantitative OCTA metrics, thus displaying their suitability for use in clinical practice. We detected an HR/HS overlapping gap of 21.6 ± 6.5% for intraretinal capillaries, and 4.3 ± 1.2% for choriocapillaris, highlighting the greater information obtained by HR OCTA. Conclusions: This novel HR/HS OCTA gap assessment might pave the way for the development of new quantitative metrics for retinal diseases that would focus on the earlier detection of perfusion impairment and relate it to the stage of the disease and its progression. Translational Relevance: This study proposes a new quantitative way to detect different perfusion signals based on OCTA. The findings presented in this paper can lay the foundations for the development of new quantitative metrics focused on the separate analysis of high flow and low flow signals, enabling very early changes in intraretinal perfusion to be detected.

Confocal MultiColor Signal Depends on Perfusion Characteristics of Retinal Microaneurysms in Diabetic Retinopathy as Detected by OCTA.

Purpose: To propose a noninvasive way of classifying multimodal imaging of retinal microaneurysms (MA) secondary to diabetic retinopathy (DR). Methods: The research was designed as a cross-sectional, observational study of patients affected by DR. Multimodal imaging included confocal MultiColor imaging, optical coherence tomography (OCT) and OCT angiography (OCTA). MA green- and infrared-reflectance components were assessed by confocal MultiColor imaging, reflectivity properties by OCT, and MA perfusion features by OCTA. In addition, we included high-resolution (HR) and high-speed (HS) OCTA scans to assess HR-HS agreement in detecting retinal MA and to highlight different perfusion features detected by both OCTA acquisitions. Results: We analyzed 216 retinal MAs, divided into green (46; 21%), red (58; 27%) and mixed types (112; 52%). Green MAs were mainly hyper-reflective on OCT, with no or poor filling on OCTA. Red MAs were characterized by an isoreflective signal on OCT and full filling on OCTA. Mixed MAs showed a hyper-reflective border and a hyporeflective core on OCT and partial filling on OCTA. No differences in red MA HR/HS size discrepancy and reflectivity were found, whereas these progressively increased as the MA MultiColor signal changed from infrared to green. MA types significantly correlated with visual acuity, DR duration, and DR severity. Conclusions: Retinal MA can be classified reliably by means of a fully noninvasive multimodal imaging-based assessment. MA types are matched with visual acuity, DR duration and DR severity. Both HR and HS OCTA are highly effective in detecting MA, although HR OCTA is to be preferred in the presence of fibrotic evolution. Translational Relevance: This study outlines a proposed novel MA classification based on noninvasive multimodal imaging. The findings presented in this paper endorse the clinical relevance of this approach, highlighting how this classification is associated with both DR duration and severity.

Distribution of macular pigments in macular telangiectasia type 2 and correlation with optical coherence tomography characteristics and visual acuity.

BACKGROUND: To estimate macular pigment values in macular telangiectasia (MacTel) Type 2 in comparison with healthy subjects in the South Indian population across different spatial profiles and to quantify the regional differences of macular pigment optical density (MPOD) in MacTel Type 2. METHODS: In this prospective cross-sectional study, healthy controls and patients diagnosed with various stages of MacTel Type 2 underwent MPOD measurement using dual-wavelength autofluorescence technique with Spectralis HRA + OCT. RESULTS: Sixty eyes of 31 healthy subjects and 41 eyes of 22 MacTel type 2 patients were included. We found an overall decrease in MPOD values in MacTel type 2 patients (-0.109, -0.11, -0.001) in comparison with healthy subjects (0.38, 0.23, 0.06) at 1°, 2° & 6° foveal eccentricities (P < 0.001). In various stages of MacTel type 2, the mean MPOD was found to be higher in the peripheral region compared to the central region. We found a significantly lower mean MPOD in the central region in association with specific optical coherence tomography (OCT) parameters like inner retinal cavities (P = 0.035) and ellipsoid zone disruption (P = 0.034). CONCLUSIONS: In MacTel type 2, MPOD distribution varies in different spatial profiles with higher MPOD levels in the peripheral region compared to the central region. The macular pigment levels are associated with inner retinal cavities and ellipsoid zone disruption seen on OCT.

Quantitative Parameters from OCT Angiography in Patients with Diabetic Retinopathy and in Those with Only Peripheral Retinopathy Compared with Control Participants.

Purpose: To describe the differences in a range of quantitative OCT angiography (OCTA) metrics across early stages of diabetic retinopathy (DR), providing robust effect estimates as well as sensitivity and specificity. Design: Cross-sectional study with population-based sampling. Participants: Four hundred forty-one eyes from 296 individuals: 328 control eyes (no diabetes mellitus [DM] and no DR), 55 eyes with DM and no DR, and 58 eyes with early nonproliferative DR. Methods: Multimodal retinal imaging included color fundus photography, color Optomap ultra-widefield imaging, and spectral-domain OCT (Spectralis OCT2; Heidelberg Engineering GmbH) with the OCTA module. All images were graded for the presence and severity of DR features. OCTA images were assessed manually for inclusion based on quality. Binary OCTA metrics were assessed after 3-dimensional projection artifact removal including from the nerve fiber layer vascular plexus, superficial vascular plexus (SVC), and deep vascular plexus (DVC) by Early Treatment Diabetic Retinopathy Study (ETDRS) grid, foveal avascular zone (FAZ) area, FAZ minimum and maximum diameter, perimeter length, and circularity. Main Outcome Measures: Diabetes mellitus and DR status and presence or absence of DR in the retinal periphery. Results: The reduction in vessel densities in participants with DM and manifest DR compared with control participants tended to be twice that of those with DM, but no DR, compared with control participants. Some evidence of spatial heterogeneity in vessel reductions was found in those yet to develop DR, whereas those with manifest DR had significant reductions across the ETDRS grid. The FAZ perimeter and circularity were impacted most significantly by DM, and those with DR showed decreased multispectral fractal dimensions compared with control participants. Eyes with peripheral DR had reduced vessel density compared with those with DM and no DR only in the superior outer, temporal inner, and temporal outer regions in the DVC and SVC. The area under the receiver operating characteristic curve ranged between 0.48 and 0.73. Conclusions: Significant differences in OCTA metrics can be found in those with DM before manifest DR using commercially available equipment with minimal image postprocessing. Although diagnostic performance was poor, these metrics may be useful for measuring change over time in clinical trials.

MultiColor imaging to detect different subtypes of retinal microaneurysms in diabetic retinopathy.

BACKGROUND: Retinal microaneurysms (MAs) are among the earliest signs of diabetic retinopathy (DR) and are typically detected by fluorescein angiography (FA). Confocal MultiColor is a noninvasive-imaging technique able to analyze different retinal features by capturing three simultaneous reflectance images. The main aim of the present study was to characterize morphological features of MAs by means of MultiColor images and to compare these with spectral domain optical coherence tomography (SD-OCT) and FA findings. METHODS: A cross-sectional, observational study setting was chosen. Multimodal imaging included MultiColor, SD-OCT and FA images. We performed a qualitative analysis in order to assess the relationship between MultiColor and its green- and red-reflectance components, SD-OCT (hyperreflective, hyporeflective and mixed reflectivity) and FA findings. MAs detected on our MultiColor images were then categorized in accordance with a previously published histological classification. RESULTS: In our study FA images were used to detect 153 MAs in 30 eyes displaying DR. MultiColor was able to distinguish 122 MAs (80%). We identified green (16%), red (19%), and mixed (65%) MAs, corresponding to different reflectivity features detected by SD-OCT. MAs not visualized on MultiColor images corresponded to tiny hyperreflective lesions on SD-OCT. We compared our imaging findings with a histological MA classification reported in the literature. Our findings showed a strict relationship between MA subtypes and SD-OCT, suggesting that the composition of MAs (cells + endothelium + fibrosis) may influence the signal detected in MultiColor images. CONCLUSIONS: MultiColor appears to be a useful technique for investigating MA features in patients with DR.

Evaluation of Macular Pigment Optical Density in Healthy Eyes Based on Dual-Wavelength Autofluorescence Imaging in South Indian Population.

Purpose: To estimate macular pigment optical density (MPOD) values across different age groups in the South Indian population across various spatial profiles using dual-wavelength autofluorescence. Methods: Sixty eyes of 31 healthy subjects underwent MPOD measurement with Spectralis HRA+OCT. The average MPOD and macular pigment optical volume (MPOV) at 1°, 2°, and 6° radii, the mean MPOD in the classical Early Treatment Diabetic Retinopathy Study (ETDRS) grid, and the spatial profiles of two different age groups across 12 plots covering the radial sectors were recorded. Results: The mean age was 39.1 ± 12.7 years. The mean MPOD and MPOV values were 0.38 ± 0.11 and 787.95 ± 225.13 at 1° eccentricity, 0.23 ± 0.08 and 2000 ± 708.24 at 2° eccentricity, and 0.05 ± 0.02 and 4335 ± 2007.71 at 6° eccentricity, respectively. In the ETDRS grid, the mean MPOD was found to be highest in the central sector and lowest in the inferior peripheral ring. We also found that along the radial sectors the lower quadrants tended to have low MPOD as compared to the upper quadrants. Subjects 40 years of age or older had significantly higher averaged MPOD in certain areas (-15° to 15° and 75° to 105°) along the radial sectors than subjects less than 40 years of age. Conclusions: This study establishes a reference value for future studies of diseased eyes in the South Indian population. Translational Relevance: Our study is unique in that it reports MPOD among the South Indian population across different age groups, as well as the distribution of MPOD in all nine zones of the classical ETDRS grid and various spatial profiles covering the 30° radial sectors centered on the fovea.

Inspection of the Human Retina by Optical Coherence Tomography.

Optical coherence tomography (OCT) is a high-resolution, three-dimensional, noninvasive imaging modality to examine the human retina. Since the introduction of spectral domain (SD-) OCT-the currently most used variant of OCT-previously unknown details of in vivo retinal morphology of a broad variety of pathologies have become visible. This chapter explains the basic principles of the OCT technology, deals with possible pitfalls in OCT examination or analysis, and hints at the use of OCT technology in functional imaging.

Lipofuscin-associated photo-oxidative stress during fundus autofluorescence imaging.

PURPOSE: Current standards and guidelines aimed at preventing retinal phototoxicity during intentional exposures do not specifically evaluate the contribution of endogenous photosensitizers. However, certain retinal diseases are characterized by abnormal accumulations of potential photosensitizers such as lipofuscin bisretinoids in the retinal pigment epithelium (RPE). We sought to determine these contributions by a numerical assessment of in-vivo photo-oxidative stress during irradiation of RPE lipofuscin. METHODS: Based on the literature, we calculated the retinal exposure levels, optical filtering of incident radiation by the ocular lens, media, photoreceptors, and RPE melanin, light absorption by lipofuscin, and photochemical effects in the RPE in two situations: exposure to short-wavelength (λ = 488 nm) fundus autofluorescence (SW-AF) excitation light and exposure to indirect (diffuse) sunlight. RESULTS: In healthy persons at age 20, 40, and 60, respectively, the rate of oxygen photoconsumption by lipofuscin increases by 1.3, 1.7, and 2.4 fold during SW-AF-imaging as compared to diffuse sunlight. In patients with STGD1 below the age of 30, this rate was 3.3-fold higher compared to age-matched controls during either sunlight or SW-AF imaging. CONCLUSIONS: Our results suggest that the RPE of patients with STGD1 is generally at increased risk of photo-oxidative stress, while exposure during SW-AF-imaging amplifies this risk. These theoretical results have not yet been verified with in-vivo data due to a lack of sufficiently sensitive in-vivo measurement techniques.

Multimodal imaging of the disease progression of birdshot chorioretinopathy.

PURPOSE: To study outer retinal deterioration in relation to clinical disease activity in patients with birdshot chorioretinopathy using fundus autofluorescence and spectral-domain optical coherence tomography (OCT). METHODS: A single-centre retrospective cohort study was carried out on 42 eyes of 21 patients with birdshot disease, using a multimodal imaging approach including fundus autofluorescence, OCT, fluorescein angiography and indocyanine green angiography in combination with a patient chart review. The patients' overall clinical activity of retinal vasculitis during the follow-up period was determined by periods of clinical activity as indicated by fluorescein angiography and associated treatment decisions. Image analysis was performed to examine the spatial correspondence between autofluorescence changes and disruption of the photoreceptor inner segment ellipsoid zone on OCT. RESULTS: Three common types of outer retinal lesions were observed in fovea-centred images of 43% of patients: circular patches of chorioretinal atrophy, ellipsoid zone disruption on OCT, and outer retinal atrophy on autofluorescence and OCT. There was good spatial correspondence between ellipsoid zone disruption and areas of diffuse hyper-autofluorescence outside the fovea. Interestingly, the ellipsoid zone disruption recovered in four out of seven patients upon intensified therapeutic immunosuppression. CONCLUSION: Most patients only developed peripapillary atrophy and occasional perivascular hypo-autofluorescence. A multimodal imaging approach with autofluorescence imaging and OCT may help to detect ellipsoid zone disruption in the central retina of patients with birdshot disease. Our results suggest that ellipsoid zone disruption may be related to both the activity and duration of retinal vasculitis, and could help to determine therapeutic success in birdshot disease.

OCT Angiography Compared to Fluorescein and Indocyanine Green Angiography in Chronic Central Serous Chorioretinopathy.

PURPOSE: Abnormal choroidal blood flow is considered important in the pathogenesis of chronic central serous chorioretinopathy (CSC). Optical coherence tomography (OCT) angiography can image ocular blood cell flow and could thus provide novel insights in disease mechanisms of CSC. We evaluated depth-resolved flow in chronic CSC by OCT angiography compared to fluorescein angiography (FA) and indocyanine green angiography (ICGA). METHODS: Eighteen eyes with chronic CSC, and six healthy controls, were included. Two human observers annotated areas of staining, hypofluorescence, and hotspots on FA and ICGA, and areas of abnormal flow on OCT angiography. Interobserver agreement in annotating OCT angiography and FA/ICGA was measured by Jaccard indices (JIs). We assessed colocation of flow abnormalities and subretinal fluid visible on OCT, and the distance between hotspots on ICGA from flow abnormalities. RESULTS: Abnormal areas were most frequently annotated in late-phase ICGA and choriocapillary OCT angiography, with moderately high (median JI, 0.74) and moderate (median JI, 0.52) interobserver agreement, respectively. Abnormalities on late-phase ICGA and FA colocated with those on OCT angiography. Aberrant choriocapillary OCT angiography presented as foci of reduced flow surrounded by hyperperfused areas. Hotspots on ICGA were located near hypoperfused spots on OCT angiography (mean distance, 168 µm). Areas with current or former subretinal fluid were colocated with flow abnormalities. CONCLUSIONS: On OCT angiography, chronic CSC showed irregular choriocapillary flow patterns, corresponding to ICGA abnormalities. These results suggest focal choriocapillary ischemia with surrounding hyperperfusion that may lead to subretinal fluid leakage.

Impact of motion-associated noise on intrinsic optical signal imaging in humans with optical coherence tomography.

A growing body of evidence suggests that phototransduction can be studied in the human eye in vivo by imaging of fast intrinsic optical signals (IOS). There is consensus concerning the limiting influence of motion-associated imaging noise on the reproducibility of IOS-measurements, especially in those employing spectral-domain optical coherence tomography (SD-OCT). However, no study to date has conducted a comprehensive analysis of this noise in the context of IOS-imaging. In this study, we discuss biophysical correlates of IOS, and we address motion-associated imaging noise by providing correctional post-processing methods. In order to avoid cross-talk of adjacent IOS of opposite signal polarity, cellular resolution and stability of imaging to the level of individual cones is likely needed. The optical Stiles-Crawford effect can be a source of significant IOS-imaging noise if alignment with the peak of the Stiles-Crawford function cannot be maintained. Therefore, complete head stabilization by implementation of a bite-bar may be critical to maintain a constant pupil entry position of the OCT beam. Due to depth-dependent sensitivity fall-off, heartbeat and breathing associated axial movements can cause tissue reflectivity to vary by 29% over time, although known methods can be implemented to null these effects. Substantial variations in reflectivity can be caused by variable illumination due to changes in the beam pupil entry position and angle, which can be reduced by an adaptive algorithm based on slope-fitting of optical attenuation in the choriocapillary lamina.

The effect of light deprivation in patients with Stargardt disease.

PURPOSE: To investigate whether long-term protection from light exposure affects the rate of disease progression in patients with autosomal recessive Stargardt disease (STGD1), measured using fundus autofluorescence imaging. DESIGN: Longitudinal, retrospective, interventional case series. METHODS: Five patients with Stargardt disease protected 1 eye from light exposure by applying a black contact lens during waking hours for ≥12 months. Disease progression was followed by performing autofluorescence imaging at semi-regular intervals. Longitudinal changes in autofluorescence were studied by evaluating areas of decreased autofluorescence and areas of increased autofluorescence as a measure of retinal pigment epithelium damage and lipofuscin accumulation, respectively. RESULTS: We observed less progression of decreased autofluorescence in 4 out of 5 light-protected eyes relative to their respective nonprotected eyes. The progression of increased autofluorescence, on the other hand, was highly variable and did not respond consistently to treatment. CONCLUSIONS: Areas of decreased autofluorescence may serve as a useful biomarker for measuring the progression of Stargardt disease. The reduced progression of decreased autofluorescence in the light-protected eyes suggests that light deprivation might be beneficial in patients with Stargardt disease.