Optical coherence tomography angiography (OCTA) flow speed mapping technology for retinal diseases

Abstract

Introduction: Optical coherence tomography angiography (OCTA) is a noninvasive imaging modality for depth-resolved visualization of retinal vasculature. Angiographic data couples with structural data to generate a cube scan, from which en-face images of vasculature can be obtained at various axial positions. OCTA has expanded understanding of retinal vascular disorders and has primarily been used for qualitative analysis. Areas Covered: Recent studies have explored the quantitative properties of OCTA, which would allow for objective assessment and follow-up of retinal pathologies. Various quantitative metrics have been developed, such as foveal avascular zone area and vessel density. However, quantitative assessment of the characteristics of retinal blood flow remains limited, as OCTA provides an image depicting either the presence or absence of flow at a particular region without information of relative velocities. The development of variable interscan time analysis (VISTA) overcomes this limitation. The VISTA algorithm generates a color-coded map of relative blood flow speeds. VISTA has already demonstrated utility in furthering our understanding of various retinal pathologies, such as geographic atrophy, choroidal neovascularization, aneurysmal type 1 neovascularization, and diabetic retinopathy. Expert Commentary: VISTA, an OCTA flow speed mapping technique, may have a role in developing the utility of OCTA as a screening tool.

Optical coherence tomography angiography findings of choroidal neovascularization secondary to decalcified choroidal osteoma treated with intravitreal aflibercept

“…[ 7 ] Secondly, OCTA is sensitive to observe the morphology and flow areas of CNV without obscured details due to dye leakage, which occurs on dye-based angiography. [ 4 ] The data of flow area values are measured according to the flow signals within the selected areas of CNV. [ 8 ] Thirdly, OCTA can compare the morphologic changes of CNV before and after the treatment, provide better assessment of the therapeutic effects.…”

“…[ 8 ] Thirdly, OCTA can compare the morphologic changes of CNV before and after the treatment, provide better assessment of the therapeutic effects. [ 4 ] These advantages of OCTA make it widely used in the diagnosis and assessment of CNV in clinical practice. In this present case, OCTA detected the CNV grew into the outer retina layer, 2 different morphologic changes of CNV were also detected during the follow-up period.…”

“…Besides, limitations of OCTA include higher requirement of flow velocity, limited field of view, and inability to identify afferent vessels. [ 4 ]…”

“…Optical coherence tomography angiography (OCTA) is a noninvasive imaging modality for depth-resolved visualization of retinal vasculature, which provides a high-resolution image of the microvasculature of the different layers in the retina. [ 3 ] It can detect the CNV and observe the morphology and flow areas of CNV without obscured details due to dye leakage in CO. [ 4 ]…”

Advances in Doppler optical coherence tomography and angiography

“…As such, OCTA is widely used in clinical research for characterizing various eye diseases, including: (a) dry age-related macular degeneration (AMD) where choriocapillaris flow and density are associated with the disease progression [69]; (b) wet AMD which is characterized by the presence of choroidal neovascularization [23]; (c) diabetic retinopathy which exhibits abnormalities in choriocapillaris and/or retinal microvascular network [24]; (d) retinal artery/vein occlusion in which non-perfusion in the capillary can be visualized; (e) glaucoma, which can be identified by an attenuated dense peripapillary microvascular network in both the superficial disc vasculature and the deeper lamina cribosa; (f) anterior segment ischemia (ASI) where iris vessel filling function and qualitative vessel density values can be evaluated to determine whether a patient is at risk to develop ASI during strabismus surgery [70,71]; and (g) ocular surface disorders where conjunctival and intrascleral vasculatures can be imaged for quantitative analysis of vessel density, vessel length density, vessel diameter index and fractal dimension of superficial-and deep-layer flows [72]. Currently, techniques, such as Hessian filtering, adaptive thresholding, variable interscan time analysis, machine learning and other numerical methods, have been utilized to quantify density, morphology, and flow velocity of the vasculature of the eye globe as well as suspicious lesion segmentation [73][74][75][76][77]. Figure 7 shows the representative OCTA images of the aforementioned diseases, where degradation of microvasculature can be clearly visualized.…”