Kasra Rezaei

Wide-field optical coherence tomography based microangiography for retinal imaging

Optical coherence tomography angiography (OCTA) allows for the evaluation of functional retinal vascular networks without a need for contrast dyes. For sophisticated monitoring and diagnosis of retinal diseases, OCTA capable of providing wide-field and high definition images of retinal vasculature in a single image is desirable. We report OCTA with motion tracking through an auxiliary real-time line scan ophthalmoscope that is clinically feasible to image functional retinal vasculature in patients, with a coverage of more than 60 degrees of retina while still maintaining high definition and resolution. We demonstrate six illustrative cases with unprecedented details of vascular involvement in retinal diseases. In each case, OCTA yields images of the normal and diseased microvasculature at all levels of the retina, with higher resolution than observed with fluorescein angiography. Wide-field OCTA technology will be an important next step in augmenting the utility of OCT technology in clinical practice.

Projection Artifact Removal Improves Visualization and Quantitation of Macular Neovascularization Imaged by Optical Coherence Tomography Angiography

PURPOSE To visualize and quantify the size and vessel density of macular neovascularization (MNV) using optical coherence tomography angiography (OCTA) with a projection artifact removal algorithm. DESIGN Multicenter, observational study. PARTICIPANTS Subjects with MNV in at least one eye. METHODS Patients were imaged using either a swept-source OCT angiography (SS-OCTA) prototype system or a spectral-domain OCT angiography (SD-OCTA) prototype system. The optical microangiography (OMAG) algorithm was used to generate the OCTA images. Projection artifacts from the overlying retinal circulation were removed from the OMAG OCTA images using a novel algorithm. Following removal of the projection artifacts from the OCTA images, we assessed the size and vascularity of the MNV. Concurrent fluorescein angiography (FA) and indocyanine green angiography (ICGA) images were used to validate the artifact-free OMAG images whenever available. MAIN OUTCOME MEASURES Size and vascularity of MNV imaged with OCTA before and after the use of a projection-artifact removal algorithm. RESULTS A total of 30 subjects (40 eyes) diagnosed with MNV were imaged. Five patients were imaged before and after intravitreal injections of vascular endothelial growth factor (VEGF) inhibitors. Following the use of the projection artifact removal algorithm, we found improved visualization of the MNV. Lesion sizes and vascular densities were more easily measured on all the artifact-free OMAG images. In eyes treated with vascular endothelial growth factor inhibitors, vascular density was reduced in all five eyes after treatment, and in four eyes, the size of the MNV decreased. One of five patients showed a slight increase in lesion size, but a decrease in vascular density. CONCLUSIONS OCTA imaging of MNV using the OMAG algorithm combined with removal of projection artifacts resulted in improved visualization and measurements of the neovascular lesions. OMAG with projection artifact removal should be useful for assessing the response of MNV to treatment using OCTA imaging.

Association between OCT-based microangiography perfusion indices and diabetic retinopathy severity

Aim To evaluate the association between retinal capillary non-perfusion and diabetic retinopathy (DR) severity using optical coherence tomography-based microangiography (OMAG). Methods 33 patients (51 eyes) with a history of diabetes underwent imaging with a 68 kHz Cirrus-5000 spectral domain OMAG prototype. Demographic and clinical characteristics were collected. The perfusion index (PI) was defined as per cent coverage of area by retinal vessels with flow, measured within a minimum of 6.8×6.8 mm2 OMAG scan. The PI in each ETDRS zone was analysed using an automated algorithm. Univariate and multivariate analyses were used to determine the degree of association between PI and DR severity. Results 51 eyes with different DR severities were imaged. More severe DR was significantly associated with lower PI after adjusting for logarithm of the minimum angle of resolution best-corrected visual acuity, hyperlipidaemia, diabetes type and ETDRS ring in a multivariate mixed linear model. Compared with the none–mild non-proliferative diabetic retinopathy (NPDR) group, the moderate–severe NPDR group had 2.7 lower PI (p=0.03) and proliferative DR group had 4.3 lower PI (p=0.003). All ETDRS zones except for the foveal centre showed inverse associations between PI and DR severity (p values<0.001 to 0.862). Conclusions A statistically significant inverse association exists between PI and DR severity. Our study suggests that PI may become a useful biomarker in evaluating and following the progression of DR.

Comparison of retina specialist preferences regarding spectral-domain and swept-source optical coherence tomography angiography

Purpose The aim of this study was to compare physician preferences regarding the commercially available spectral-domain (SD) optical coherence tomography angiography (OCTA) and swept-source (SS) OCTA prototype device. Design Comparative analysis of diagnostic instruments was performed. Patients and methods Subjects at the University of Washington Eye Institute and Harborview Medical Center were prospectively recruited and imaged with the Zeiss SD OCTA (HD-5000, Angioplex) and Zeiss SS OCTA (Plex Elite, Everest) devices on the same day. The study included 10 eyes from 10 subjects diagnosed with a retinal/choroidal disease. Deidentified images were compiled into a survey and sent to retina specialists in various countries. The survey presented masked SD and SS images of each eye for each retinal sublayer side by side. Respondents were asked about their image preference and impact on clinical management. A priori and post hoc preferences for SD vs SS were collected. Results Fifty-four retina specialists responded to the survey. Median years in practice was 3.00 (interquartile range [IQR] 1.50–17.00). At baseline, 23 (48%) physicians owned an OCTA machine. The majority of physician responses showed a preference for the SS over SD OCTA, independent of the retinal pathology shown (n=454 overall responses, 74%). Nevertheless, the majority indicated that both SD and SS would be equally valuable in informing clinical decisions (n=374 overall responses, 61%). Conclusion These findings indicate that the majority of retina specialists surveyed prefer SS over SD OCTA based on image quality, regardless of the retinal pathology shown. Regarding the clinical utility of each modality, the majority of physicians perceive SD and SS as equally effective.

Optical coherence tomography based microangiography findings in hydroxychloroquine toxicity

Optical coherence tomography based microangiography (OMAG) is a new, non-invasive imaging modality capable of providing three dimentional (3D) retinal and choroidal microvascular maps without a need for exogenous dye. In this study, we evaluated the retinal and choroidal microvascular architecture of the macula in a patient with hydroxychloroquine (HCQ) toxicity using OMAG. Detailed microvascular information of the retina and the underlying choroid showed loss of parafoveal outer retinal vasculature with sparing of the central fovea vasculature.

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 clinicians 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.

Optical Coherence Tomography Microangiography Imaging of Circumscribed Choroidal Hemangioma

Optical coherence tomography angiography (OCTA) is a new imaging technology capable of providing three-dimensional (3-D) retinal and choroidal microvascular maps without a need for exogenous dye. In this study, the authors evaluate the retinal and choroidal microvascular architecture of the macula in a patient with choroidal hemangioma using OCTA. Widefield OCTA with tracking capability and segmentation was performed to provide images with a field of view at 9 × 9 mm2. The en face maximum projection was used to generate 2-D angiograms of different layers with color-coded images. Variable levels of perfusion within the lesion were identified, which correlate well with the known vascular abnormalities of choroidal hemangiomas. OCTA demonstrated an accurate modality to measure the 3-D borders of this lesion. This is the novel utilization of OCTA imaging on choroidal hemangioma. OCTA may provide detailed vascular findings in circumscribed choroidal hemangiomas, which may aid in the diagnosis and evaluation of the treatment response. [Ophthalmic Surg Lasers Imaging Retina. 2018;49:134-137.].

Letter to the Editor: Optical Coherence Tomography Angiography of Choroidal Hemangioma

Dear Editor, We read with interest the article on optical coherence tomography angiography (OCTA) of a suspected case of choroidal hemangioma.1 We want to humbly discuss a few facts. The authors mention that “To date, findings from optical coherence tomography angiography (OCTA) have yet to be reported for a choroidal hemangioma.” However, in 2017 we had published our findings in cases of choroidal hemangioma before and after treatment with laser.2 In an asymptomatic patient with an incidentally detected choroidal mass multiple differential diagnoses are possible, including metastasis. It would be interesting to know how the authors excluded other potential mimickers. In our paper, we noted that the choriocapillaris layer had multiple, well-defined hypoflow areas.2 We hypothesize that the changes seen in choriocapillaris layer may not be due to involvement by the hemangioma itself. Vascular alterations in the choriocapillaris layer could just be due to an underlying mass effect of the hemangioma. Also, laser leads to a loss of the choriocapillaris layer. Following this, the visibility of deeper vessels improved, and we could show the vessels within and around the hemangioma by sweptsource OCTA.2 Koushik Tripathy, MD Rohan Chawla, MD ICARE Eye Hospital & Postgraduate Institute Uttar Pradesh, India All India Institute of Medical Sciences New Delhi, India

Optical coherence tomography angiography as an imaging modality for evaluation of diabetic macular edema

359 Diabetic retinopathy remains a leading cause of blindness worldwide in patients aged 20–64 years.[1] Diabetic macular edema (DME) threating or involving the fovea is a common etiology for vision loss. Traditionally, treatment methods have been guided by contact and non‐contact slit lamp biomicroscopy, fluorescein angiography and fundus stereo photography. [1] Fluorescein angiography (FA) is a dynamic, invasive imaging technique first described in 1961 and more thoroughly invested and popularized by Gass in 1967.[2] In principle, this technique uses a series of exciting and barrier filters to visualize fluorescein dye excursion through retinal arterial, capillary, and venous structures as well as the underlying choroid. It remains the gold standard in evaluation of macular perfusion and localizes the area of leakage in non‐proliferative diabetic retinopathy, neovascularization in proliferative diabetic disease and detecting choroidal neovascular membrane (CNVM) and other retinal vascular diseases. Though FA provides detailed anatomy of retinal vascular structure and dynamic circulation parameters, it has several limitations: it requires intravenous administration of fluorescein dye, which infrequently results in nausea, gastrointestinal upset, very rarely serious allergic reaction and anaphylaxis. In addition, its time‐consuming nature hinders its use in busy clinical settings.[3] Furthermore, interpretation of images is subjective and user dependent. Finally, its use in patients with small pupils or media clarity issues such as vitreous hemorrhage is limited. In 1991, the advent of a new non‐invasive imaging technique known as optical coherence tomography (OCT) revolutionized the management of a variety of retinal diseases including macular edema.[4] The principle behind OCT involves directing a beam of infra‐red light (830 nm) orthogonal to the surface of the retina while a recorder captures and analyzes the signal reflection.[5] The result is a 3‐D reflectance image that provides detailed anatomy of the intra‐retinal structures, posterior hyaloid and macular Optical Coherence Tomography Angiography as an Imaging Modality for Evaluation of Diabetic Macular Edema