Abstract
The advent of optical coherence tomography angiography (OCTA) has allowed for remarkable advancements in our understanding of the role of the choriocapillaris in age-related macular degeneration (AMD). As a relatively new imaging modality, techniques to analyze and quantify choriocapillaris images are still evolving. Quantification of the choriocapillaris requires careful consideration of many factors, including the type of OCTA device, segmentation of the choriocapillaris slab, image processing techniques, and thresholding method. OCTA imaging shows that the choriocapillaris is impaired in intermediate non-neovascular AMD, and the severity of impairment may predict the advancement of disease. In advanced atrophic AMD, the choriocapillaris is severely impaired underneath the area of geographic atrophy, and the level of impairment surrounding the lesion predicts the rate of atrophy enlargement. Macular neovascularization can be readily identified and classified using OCTA, but it is still unclear if neovascularization features with OCTA can predict the lesion’s level of activity. The choriocapillaris surrounding macular neovascularization is impaired while the more peripheral choriocapillaris is spared, implying that choriocapillaris disruption may drive neovascularization growth. With continued innovation in OCTA image acquisition and analysis methods, advancement in clinical applications and pathophysiologic discoveries in AMD are set to follow.
Highlights
Introduction published maps and institutional affilInnovation in ophthalmic imaging has led to remarkable advancements in our understanding of age-related macular degeneration (AMD)
With the advent of optical coherence tomography angiography (OCTA), blood flow in the choriocapillaris can be identified with far greater detail than ever before
In order to compensate for projection artifacts, OCTA devices are equipped with projection artifact removal software
Summary
OCTA is a noninvasive tool that creates a reconstruction of the retinal capillary and inner choroidal vasculature [2,3], by recognizing the intrinsic movement of particles in these tissues. The device captures a dense volume of OCT scans at the same location and detects differences between the scans over a short, designated time interval. A calculation is performed for each pixel in every frame to identify which pixels are changing (in phase and/or amplitude) over time, thereby isolating or contrasting moving structures. OCTA images combine the structural information of a standard OCT scan with blood flow visualization. The moving elements are commonly coded as bright/white pixels on the OCTA scans to represent blood flow, while the dark areas represent areas with blood flow below the decorrelation threshold referred to as “flow deficits” [4,5,6]. Different devices employ unique calculation methods to analyze OCT intensity information. Angiography based on only the phase of the OCT signal (Doppler OCT) [7]
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