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Imaging the Living Eye
Published in Margarida M. Barroso, Xavier Intes, In Vivo, 2020
Brian T. Soetikno, Lisa Beckmann, Hao F. Zhang
The retina possesses an intricate circulatory system that provides the nutrients necessary to meet the high metabolic demand of the tissue (Wangsa-Wirawan and Linsenmeier, 2003; Linsenmeier and Zhang, 2017). Unlike any other tissue in the body, retina has two independent circulations: the anterior, termed the retinal circulation, and the posterior, termed the choroidal circulation. Each is distinct by anatomy and by autoregulatory control. The retinal circulation is divided into a trilaminar network (Kornfield and Newman, 2014). Arterioles exit at the optic nerve head and spread outward at the level of the nerve–fiber layer and the ganglion-cell layer (Figure 14.1c). Branches dive deeper into the retina and form an intermediate capillary plexus at the boundary between the inner nuclear layer and the inner plexiform layer. A dense, deep capillary plexus is also formed at the boundary of the outer nuclear layer and the outer plexiform layer. The capillaries vertically ascend and drain to large veins that exit at the optic nerve head. The choroidal circulation consists of large vessels that ultimately branch to form the choriocapillaris, a dense mesh of capillaries beneath the RPE layer. The retinal circulation is autoregulated, while the choroidal circulation is not. Thus, the flow rate of the retinal circulation is controlled and varies depending on the metabolic demands of the eye. On the other hand, the flow rate of the choroidal circulation remains mostly constant with one of the highest flow rates in the body (Kur et al., 2012).
Retinal image enhancement and analysis for diabetic retinopathy assessment
Published in Ahmad Fadzil Mohamad Hani, Dileep Kumar, Optical Imaging for Biomedical and Clinical Applications, 2017
Ahmad Fadzil Mohamad Hani, Hanung Nugroho, Lila Iznita Izhar, Nor Fariza Ngah
The choroid is a layer of blood vessels that supplies oxygen and nutrients to the outer layers of the retina. The innermost choroid, called the choriocapillaris, is a dense net of flattened capillaries that forms a blood-filled shell lying parallel to the basal side of the RPE. Bruch's membrane separates the blood vessels of the choroid from the RPE layer. The rest of the choroid is filled with larger blood vessels and melanin-containing melanocytes. The melanin content of the RPE varies among individuals. However, only the melanin content of the choroid depends on skin pigmentation. The final layer of significance is the sclera, the fibrous, thick, white outer covering of the eye. Therefore, a reflectance of the fundus can be understood as a ratio of a total amount of reflected light to the total incident light propagating through several fundus layers. Figure 5.6 depicts a model of ocular fundus showing possible pathways of the remitted light.
Development of Ophthalmic Formulations
Published in Sandeep Nema, John D. Ludwig, Parenteral Medications, 2019
Paramita Sarkar, Martin Coffey, Mohannad Shawer
Two vascular beds supply the retina. Retinal vessels supply the inner two-thirds, while the outer retina is avascular and receives oxygen and nutrients from the choriocapillaris. The choriocapillaris is fenestrated to enhance transport of nutrients to the underlying retina. Plasma leaks from the choriocapillaris and diffuses through the Bruch’s membrane and through the RPE to the outer retina. RPE tight junctions constitute the outer blood–retina barrier.
Swept-source optical coherence tomography imaging of the retinochoroid and beyond
Published in Expert Review of Medical Devices, 2020
Jayesh Vira, Alessandro Marchese, Rohan Bir Singh, Aniruddha Agarwal
The fast-paced evolution of technology is resulting in rapid developments of tools useful to the clinicians in their practice and management of patients. SS-OCT imaging has significant advantages over the available SD technology and finds utility in various retinochoroidal conditions. SS-OCT and SS-OCTA are very useful in determining the anatomical location of the disease, and understanding the disease pathophysiology. This is exemplified by the SS-OCTA imaging in MEWDS, where this technology clearly shows a lack of choriocapillaris flow abnormality, which was otherwise thought to exist based on indocyanine green angiography. SS-OCT also aids in better imaging of patients with pachychoroid over conventional imaging, as this entity primarily involves the choroid. In our experience, SS-OCT imaging is desirable in most entities where imaging the deeper retinal layers and the choroid is essential, especially retinal vasculopathies including diabetic retinopathy, pachychoroid including polypoidal choroidal vasculopathy (and differentiating it from choroidal neovascularization due to age-related macular degeneration), inflammatory pathologies (including choriocapillaritis and stromal choroiditis), and neoplastic pathologies.
En face swept-source optical coherence tomography angiography choroidal vasculography (CVG) a tool to discriminate choroidal abnormalities in polypoidal choroidal vasculopathy
Published in Expert Review of Medical Devices, 2021
Juan D. Arias, M. Margarita Parra, Andrea T. Hoyos, Francisco Arango, Eduardo J. Viteri, J. Fernando Arevalo
Optical coherence tomography angiography (OCT-A) provides high-resolution images of retinal anatomy and microvasculature trough some modalities allowing signal penetration to the choroid. Nonetheless, the application of these features in PCV has produced divergent results [1–5]. Choroidal imaging using OCT-A has limitations owing to light scattering due to densely vascularized choriocapillaris and retinal pigment epithelium (RPE) [3,6].