Quantitative optical coherence tomography angiography of vascular abnormalities in the living human eye

Abstract

Retinal vascular diseases are important causes of vision loss. A detailed evaluation of the vascular abnormalities facilitates diagnosis and treatment in these diseases. Optical coherence tomography (OCT) angiography using the highly efficient split-spectrum amplitude decorrelation angiography algorithm offers an alternative to conventional dye-based retinal angiography. OCT angiography has several advantages, including 3D visualization of retinal and choroidal circulations (including the choriocapillaris) and avoidance of dye injection-related complications. Results from six illustrative cases are reported. In diabetic retinopathy, OCT angiography can detect neovascularization and quantify ischemia. In age-related macular degeneration, choroidal neovascularization can be observed without the obscuration of details caused by dye leakage in conventional angiography. Choriocapillaris dysfunction can be detected in the nonneovascular form of the disease, furthering our understanding of pathogenesis. In choroideremia, OCT's ability to show choroidal and retinal vascular dysfunction separately may be valuable in predicting progression and assessing treatment response. OCT angiography shows promise as a noninvasive alternative to dye-based angiography for highly detailed, in vivo, 3D, quantitative evaluation of retinal vascular abnormalities.optical coherence tomography angiography | ophthalmic imaging | ocular circulation O ptical coherence tomography (OCT) has become the most commonly used imaging modality in ophthalmology. It provides cross-sectional and 3D imaging of the retina and optic nerve head with micrometer-scale depth resolution. Structural OCT enhances the clinician's ability to detect and monitor fluid exudation associated with retinal vascular diseases. Whereas anatomical alterations that impact vision are readily visible, structural OCT has a limited ability to image the retinal or choroidal vasculatures. Furthermore, it is unable to directly detect capillary dropout or pathologic new vessel growth (neovascularization) that are the major vascular changes associated with two of the leading causes of blindness, age-related macular degeneration (AMD) and diabetic retinopathy (1). To visualize these changes, traditional i.v. contrast dye-based angiography techniques are currently used.Fluorescein dye is primarily used to visualize the retinal vasculature. A separate dye, indocyanine green (ICG), is necessary to evaluate the choroidal vasculature. Both fluorescein angiography (FA) and ICG angiography require i.v. injection, which is time consuming, and which can cause nausea, vomiting, and, rarely, anaphylaxis (2). Dye leakage or staining provides information regarding vascular incompetence (e.g., from abnormal capillary growth), but it also obscures the image and blurs the boundaries of neovascularization. Additionally, conventional angiography is 2D, which makes it difficult to distinguish vascular abnormalities within different layers. Therefore, it is desirable to develop a no-injection, dye-free method...

The Importance of VRI and AOR Segmentations in Optical Coherence Tomography Angiography

“…Using by OCTA, the vasculature and blood flow of retina and choroid can be visualized in detail through detecting motion contrast of erythrocytes in the vessel, using serial optical coherence tomography B-scans. OCTA has an ability to perform the separate segmentations including the vitreoretinal interface (VRI), the superficial retinal layer, the deep retinal layer, avascular outer retina (AOR), the choriocapillaris and the choroid (Figure 1) [1][2][3][4][5][6][7][8].…”

“…In a healthy eye, the VRI has no vascular structure though the ganglion cell layer of the retina has the superficial retinal capillary plexus based on vitreo-retinal histology and VRI segmentation of OCTA ( Figure 1, VRI) [1][2][3][4][5][6][7][8]. Preretinal neovascularization (PNV) is characterized by networks of vessels lying on the surface of the retina and invading the cortical vitreous gel and extending into the vitreous cavity.…”

“…Using by OCTA, the vasculature and blood flow of retina and choroid can be visualized in detail through detecting motion contrast of erythrocytes in the vessel, using serial optical coherence tomography B-scans. OCTA has an ability to perform the separate segmentations including the vitreoretinal interface (VRI), the superficial retinal layer, the deep retinal layer, avascular outer retina (AOR), the choriocapillaris and the choroid (Figure 1) [1][2][3][4][5][6][7][8].In a healthy eye, the VRI has no vascular structure though the ganglion cell layer of the retina has the superficial retinal capillary plexus based on vitreo-retinal histology and VRI segmentation of OCTA (Figure 1, VRI) [1][2][3][4][5][6][7][8]. Preretinal neovascularization (PNV) is characterized by networks of vessels lying on the surface of the retina and invading the cortical vitreous gel and extending into the vitreous cavity.…”

“…AOR is the layer between the outer plexiform layer (OPL) in the inner border and ellipsoid zone in the outer border. The outer retina segmentation between the OPL and Bruch membrane by OCTA show no vascular blood flow in a normal eye (Figure 1, Avascular) [1][2][3][4][5][6][7][8]. Choroidal neovascularization (CNV) defines the development of the new blood vessels derived the choroid and the invasion into sub-retinal pigment epithelium (RPE) or subretinal space via a break in Bruch membrane.…”

Re: Spaide et al.: Volume-rendering optical coherence tomography angiography of macular telangiectasia type 2 (Ophthalmology 2015;122:2261-9)

“…Barton And pixel transparency of the retinal slab was adjusted to optimize the visualization of choroidal neovascularization. 5 We list these prior works here so the reader can appreciate the work of pioneers in this field. …”