Visualizing choriocapillaris using swept source optical coherence tomography angiography with various probe beam sizes

Imaging choriocapillaris (CC) is a long-term challenge for commercial OCT angiography (OCTA) systems due to limited transverse resolution. Effects of transverse resolution on the visualization of a CC microvascular network are explored and demonstrated in this paper. We use three probe beams with sizes of ~1.12 mm, ~2.51 mm and ~3.50 mm at the pupil plane, which deliver an estimated transverse resolution at the retina of 17.5 µm, 8.8 µm and 7.0 µm, respectively, to investigate the ability of OCTA to resolve the CC capillary vessels. The complex optical microangiography algorithm is applied to extract blood flow in the CC slab. Mean retinal pigment epithelium (RPE) to CC (RPE-CC) distance, mean CC inter-vascular spacing and the magnitude in the radially-averaged power spectrum are quantified. We demonstrate that a clearer CC lobular capillary network is resolved in the angiograms provided by a larger beam size. The image contrast of the CC angiogram with a large beam size of 3.50 mm is 114% higher than that with a small beam size of 1.12 mm. While the measurements of the mean RPE-CC distance and CC inter-vascular spacing are almost consistent regardless of the beam sizes, they are more reliable and stable with the larger beam size of 3.50 mm. We conclude that the beam size is a key parameter for CC angiography if the purpose of the investigation is to visualize the individual CC capillaries.</p

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

Automated Quantitation of Choroidal Neovascularization: A Comparison Study Between Spectral-Domain and Swept-Source OCT Angiograms

PURPOSE. To compare the lesion sizes of choroidal neovascularization (CNV) imaged with spectral-domain (SD) and swept-source (SS) optical coherence tomography angiography (OCTA) and measured using an automated detection algorithm. METHODS. Patients diagnosed with CNV were imaged by SD-OCTA and SS-OCTA systems using 3 x 3-mm and 6 x 6-mm scans. The complex optical microangiography (OMAG(C)) algorithm was used to generate the OCTA images. Optical coherence tomography A datasets for imaging CNV were derived by segmenting from the outer retina to 8 mu m below Bruch's membrane. An artifact removal algorithm was used to generate angiograms free of retinal vessel projection artifacts. An automated detection algorithm was developed to quantify the size of the CNV. Automated measurements were compared with manual measurements. Measurements from SD-OCTA and SS-OCTA instruments were compared as well. RESULTS. Twenty-seven eyes from 23 subjects diagnosed with CNV were analyzed. No significant differences were detected between manual and automatic measurements: SD-OCTA 3 x 3-mm (P = 0.61, paired t-test) and 6 x 6-mm (P = 0.09, paired t-test) scans and the SS-OCTA 3 x 3-mm (P = 0.41, paired t-test) and 6 x 6-mm (P = 0.16, paired t-test) scans. Bland-Altman analyses were performed to confirm the agreement between automatic and manual measurements. Mean lesion sizes were significantly larger for the SS-OCTA images compared with the SD-OCTA images: 3 3 3-mm scans (P = 0.011, paired sample t-test) and the 6 x 6-mm scans (P = 0.021, paired t-test). CONCLUSIONS. The automated algorithm measurements of CNV were in agreement with the hand-drawn measurements. On average, automated SS-OCTA measurements were larger than SD-OCTA measurements and consistent with the results from using hand-drawn measurements.Carl Zeiss Meditec, Inc. (Dublin, CA)National Eye InstituteResearch to Prevent Blindness, Inc., New York, New YorkNational Eye Institute Center Core GrantCAPES Foundation, Ministry of Education of Brazil, Brasilia-BrazilGerman Research Foundation (DFG)Research to Prevent BlindnessUniv Washington, Dept Bioengn, 3720 NE 15th Ave, Seattle, WA 98195 USAUniv Miami, Miller Sch Med, Bascom Palmer Eye Inst, Dept Ophthalmol, Miami, FL 33136 USAUniv Fed Sao Paulo, Dept Ophthalmol, Sao Paulo, BrazilCarl Zeiss Meditec Inc, Adv Dev, Dublin, CA USAUniv Washington, Dept Ophthalmol, 3720 NE 15th Ave, Seattle, WA 98195 USAUniv Fed Sao Paulo, Dept Ophthalmol, Sao Paulo, BrazilNational Eye Institute: R01EY024158National Eye Institute Center Core Grant: P30EY014801German Research Foundation (DFG): SCHA 1869/1-1Web of Scienc

Comparison Between Spectral-Domain and Swept-Source Optical Coherence Tomography Angiographic Imaging of Choroidal Neovascularization

PURPOSE. The purpose of this study was to compare imaging of choroidal neovascularization (CNV) using swept-source (SS) and spectral-domain (SD) optical coherence tomography angiography (OCTA). METHODS. Optical coherence tomography angiography was performed using a 100-kHz SS-OCT instrument and a 68-kHz SD-OCTA instrument (Carl Zeiss Meditec, Inc.). Both 3 x 3-and 6 x 6-mm(2) scans were obtained on both instruments. The 3 x 3-mm(2) SS-OCTA scans consisted of 300 A-scans per B-scan at 300 B-scan positions, and the SD-OCTA scans consisted of 245 A-scans at 245 B-scan positions. The 6 x 6-mm(2) SS-OCTA scans consisted of 420 A-scans per B-scan at 420 B-scan positions, and the SD-OCTA scans consisted of 350 A-scans and 350 B-scan positions. B-scans were repeated four times at each position in the 3 x 3-mm(2) scans and twice in the 6 x 6-mm(2) scans. Choroidal neovascularization was excluded if not fully contained within the 3 x 3-mm(2) scans. The same algorithm was used to detect CNV on both instruments. Two graders outlined the CNV, and the lesion areas were compared between instruments. RESULTS. Twenty-seven consecutive eyes from 23 patients were analyzed. For the 3 x 3-mm(2) scans, the mean lesion areas for the SS-OCTA and SD-OCTA instruments were 1.17 and 1.01 mm(2), respectively (P = 0.047). For the 6 x 6-mm(2) scans, the mean lesion areas for the SS-OCTA and SD-OCTA instruments were 1.24 and 0.74 mm(2) (P = 0.003). CONCLUSIONS. The areas of CNV tended to be larger when imaged with SS-OCTA than with SD-OCTA, and this difference was greater for the 6 x 6-mm(2) scans.Carl Zeiss Meditec, Inc.National Eye InstituteResearch to Prevent Blindness, Inc. (New York, NY)National Eye Institute Center Core GrantCAPES Foundation, Ministry of Education of Brazil (Brasilia, Brazil)German Research FoundationUniv Miami, Miller Sch Med, Bascom Palmer Eye Inst, Dept Ophthalmol, Miami, FL 33136 USAUniv Fed Sao Paulo, Dept Ophthalmol, Sao Paulo, BrazilUniv Washington, Dept Bioengn, Seattle, WA 98195 USACarl Zeiss Meditec Inc, Adv Dev, Dublin, CA USAUniv Fed Sao Paulo, Dept Ophthalmol, Sao Paulo, BrazilNational Eye Institute: R01EY024158National Eye Institute Center Core Grant: P30EY014801German Research Foundation: SCHA 1869/1-1Web of Scienc

Quantitative Applications of Optical Coherence Tomography Angiography in Ophthalmology

Thesis (Ph.D.)--University of Washington, 2019Optical coherence tomography (OCT) angiography (OCTA) is a recently developed non-invasive functional imaging technique that have been widely utilized in ophthalmology. OCTA is capable of providing three dimensional detailed information of ocular vasculature and has great potentials for vascular quantification. In this thesis, OCTA’s capacity in imaging microvasculature in great detail was demonstrated in human eyes, techniques to improve image quality and contrast were proposed and validated. With clinically available OCTA systems’ data, quantitative analysis tools for both retinal choroidal microvasculature were developed and tested on diseased subjects. The reliability of proposed quantitative algorithms was tested with intra-visit scans and the robustness was tested with data from a wide range of disease diagnoses. Overall, this dissertation presents a set of tools that can describe the integrity of human ocular microvasculature reliably and objectively

Ophthalmic Application of Optical Coherence Tomography Based Angiography for Choroidal Imaging

Thesis (Master's)--University of Washington, 2015We demonstrated in vivo choriocapillaris imaging in normal human subjects with a Cirrus HD 5000 spectral domain OCT prototype. With the tracking system installed in the prototype and the montage scanning protocol, wide field OCT angiograms of 9 mm * 11 mm were created. OCT angiography utilizes the intrinsic motion of red blood cells as contrast mechanism therefore requires no exogenous contrast agents as fluorescein angiography and indocyanine green angiography do. Four consecutive OCT scans were acquired at the same location for angiography generating, intensity based, phase based and complex signal based OCTA were all computed and compared. With the ability to resolve fine and detailed vascular lobules, complex signal based OMAG were selected for en face visualization. In consistency with histological studies, lobular vascular networks were observed and corresponding feeding arterioles were identified in OMAG images. Structural OCT en face image was also generated and at periphery regions, lobular structures can also be recognized with distinct brightness patterns. This study showcased the feasibility of using commercialized SD-OCT for in vivo choriocapillaris visualization and essentially opens the possibility for clinical imaging studies on choriocapillaris’ role in pathogenesis and early diagnosis of ocular disease

Quantification of Choriocapillaris with Optical Coherence Tomography Angiography: A Comparison Study

To demonstrate the variation in quantitative choriocapillaris (CC) metrics with various binarization approaches using optical coherence tomography angiography (OCTA). Retrospective, observational, cross-sectional case series. Macular OCTA scans, 3- × 3-mm and 6- × 6-mm, were obtained from normal eyes and from eyes with drusen secondary to age-related macular degeneration (AMD). The CC slab was extracted, and the CC flow deficits (FDs) were segmented with 2 previously published algorithms: the fuzzy C-means approach (FCM method) and Phansalkar's local thresholding (Phansalkar method). Four different values for the radius were used in order to investigate the effect on the FD segmentation when using the Phansalkar method. FD density (FDD), mean FD size (MFDS), FD number (FDN), FD area (FDA) and intercapillary distance (ICD) were calculated for comparison. Repeatability was assessed as coefficient of variation (CV), and Pearson's correlation analysis was conducted. Six eyes from 6 subjects with normal eyes and 6 eyes from 6 subjects with drusen secondary to AMD were scanned. The 3- × 3-mm scans resulted in higher repeatability than the 6- × 6-mm scans. For the Phansalkar method, larger values of the radius resulted in higher repeatability. ANOVA tests resulted in significant differences (P < 0.001) among the FCM method and the Phansalkar method with different radius options for all CC metrics and scan sizes investigated. In 3- × 3-mm scans, significant correlation was found between the FCM method and the Phansalkar method for all quantitative CC metrics other than FDN (all P < 0.001; 0.90 < r <0.99). Quantitative CC analysis with commercially available OCTA is complicated and researchers need to pay close attention to how they conduct such analyses

Guidelines for Imaging the Choriocapillaris Using OCT Angiography

To provide guidance on how to appropriately quantitate various choriocapillaris (CC) parameters with optical coherence tomography angiography (OCTA). Evidence-based perspective. Review of literature and experience of authors. Accurate and reliable quantification of CC using OCTA requires that CC can be visualized and that the measurements of various CC parameters are validated. For accurate visualization, the selected CC slab must be physiologically sound, must produce images consistent with histology, and must yield qualitatively similar images when viewing repeats of the same scan or scans of different sizes. For accurate quantification, the measured intercapillary distances (ICDs) should be consistent with known measurements using histology and adaptive optics and/or OCTA, the selected CC parameters must be physiologically and physically meaningful based on the resolution of the instrument and the density of the scans, the selected algorithm for CC binarization must be appropriate and generate meaningful results, and the CC measurements calculated from multiple scans of the same and different sizes should be quantitatively similar. If the Phansalkar local thresholding method is used, then its parameters must be optimized for CC based on the OCTA instrument and scan patterns used. It is recommended that the window radius used in the Phansalkar method should be related to the expected average ICD in normal eyes. Quantitative analysis of CC using commercially available OCTA instruments is complicated, and researchers need to tailor their strategies based on the instrument, scan patterns, anatomy, and thresholding strategies to achieve accurate and reliable measurements

Impaired layer specific retinal vascular reactivity among diabetic subjects.

PurposeTo investigate layer specific retinal vascular reactivity (RVR) in capillaries of diabetic subjects without DR or with only mild non-proliferative diabetic retinopathy (NPDR).MethodsA previously described nonrebreathing apparatus was used to deliver room air, 5% CO2, or 100% O2 to 41 controls and 22 diabetic subjects (with mild or no NPDR) while simultaneously acquiring fovea-centered 3x3mm2 Swept-Source Optical Coherence Tomography Angiography (SS-OCTA) images. Vessel skeleton density (VSD) and vessel diameter index (VDI) were calculated for each gas condition for the superficial retinal layer (SRL) and deep retinal layer (DRL). The superficial layer analysis excluded arterioles and venules. Data analysis was performed using mixed factorial analysis of covariance stratified by diabetic status. All models were adjusted for age, gender, and hypertension, and statistical significance for multiple comparisons from posthoc comparisons were defined at pResultsAmong controls, there was a significant difference in capillary VSD between all gas conditions (pConclusionsImpairment in RVR in diabetic subjects is characterized by a paradoxical response to CO2 in both the SRL and DRL as well as an attenuated response to O2 in the DRL. These layer and gas specific impairments in diabetics seem to occur early in the disease and to be driven primarily at the capillary level