The retinal map allows quantification of the decreased retinal thickness. In a case of retinal atrophy, the OCT shows a highly reflective choroidal signal due to retinal thinning and RPE hypopigmentation, which allows greater beam penetration into the choroid and greater reflectivity. Geographic atrophy (GA) represents the final stage of dry AMD. The reduced retinal thickness and volume can be determined by the retinal maps that display the areas of greatest atrophy, identify the extent of the atrophy, and monitor progression. OCT can detect decreases in retinal thickness and increases in the reflectivity of the RPE detachment, which results from the decreased ability of the atrophic retinal tissue to attenuate light and allows greater penetration of the laser beam to deeper structures as the choroid (Figure 3). In the macular region, progressive atrophy of the RPE, the outer retinal layers, the choriocapillaris, and dense clusters of In the macular region, progressive atrophy of the RPE, the outer retinal layers, the choriocapillaris, and dense clusters of drusen can be seen. Drusen are seen as undulations and elevations in the hyperreflective band of the RPE with less reflective material beneath them, while the inner retinal layers remain generally intact. The risk is based on the lesion number, size and confluence of drusen. Drusen can progress to an atrophic form (dry) or exudative form (wet) of AMD. On OCT, drusen appear as RPE deformation or thickening that may form irregularities and undulations (Figure 2).ĭrusen are classified histologically as hard formations, defined as small hyaline deposits with delimited margins that are considered age-related low-risk changes, and soft drusen, which are deposits of granular or amorphous material considered to be precursors of AMD. Drusen is the earliest AMD sign that is detected clinically in fundus examinations. Neurosensory Retinal Detachmenttive nodular formations located mainly in Bruch’s membrane, are accumulations of proteins, lipids, mucopolysaccharides and other components that appear in adulthood and tend to increase in size and number over time. When soft drusen in the macular region are associated with focal areas of pigmentary changes (hypopigmentation and hyperpigmentation), there is an increased risk of progression to AMD. Blood vessels are identified by their high reflectivity and the masking effect generated on adjacent tissues (Table 1) ( 7,8,11)Īge-related maculopathy, which is currently considered a previous stage of age-related macular degeneration (AMD), is defined as the presence of areas of hyperpigmentation or hypopigmentation of the RPE and/or confluent or soft drusen. The choriocapillaris and choroid are highly reflective layers, because they are vascular and limit light penetration into the deeper layers. The posterior hyaloid usually is indistinguishable from the retinal surface except when the posterior vitreous is detached and appears as a weakly reflective band. The vitreous transmits light without reflecting it and is depicted in black in OCT images (Figure 1). Therefore, the image is not real but represents the true dimensions of the measured structures ( 1-10) It should be noted that the color shown in the images represents the optical properties of the tissues and not the tissues themselves. Tissues that moderately reflect light are shown as green or yellow. More concisely, tissues that reflect more light or disperse more light are shown in red and white, respectively, while the ones that reflect or disperse less light are shown in blue and black. The images are presented in a color (or gray) scale based on the different reflectivity of the tissue structures. These capabilities facilitate an understanding of the differences between the classic membranes, occult membranes, retinal angiomatous proliferation (RAP) and disciform scars in the natural course of the disease and assess the response to anti-vascular endothelial growth factor (VEGF) drugs. OCT provides important information on serous retinal detachments, hemorrhages and subretinal neovascular membranes that are components of exudative macular degeneration and allows a more precise and detailed analysis of anatomic structures and neovascular membrane lesions subtypes. These capabilities allow detection of newly emerging fluid and/or intraretinal or subretinal tissue and tissue below the retinal pigment epitheliumĬ. It permits to define the location and nature of the changes in the retina and adjacent structures and objectively evaluates the thickness of the retina and surrounding structures. Optical coherence tomography (OCT) technology allows the acquisition of cross-sectional images of the retina with semihistologic resolution.
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