Abstract
.Age-related macular degeneration (AMD) is a vision-threatening disease that affects the outer retina and choroid of elderly adults. Because photoreceptors are found in the outer retina and rely primarily on the trophic support of the underlying choriocapillaris, imaging of flow or lack thereof in choriocapillaris by optical coherence tomography angiography (OCTA) has great clinical potential in AMD assessment. We introduce a metric using OCTA, named “focal perfusion loss” (FPL) to describe the effects of age and non-neovascular AMD on choriocapillaris flow. Because OCTA imaging of choriocapillaris is vulnerable to artifacts—namely motion, projections, segmentation errors, and shadows—they are removed by postprocessing software. The shadow detection software is a machine learning algorithm recently developed for the evaluation of the retinal circulation and here adapted for choriocapillaris analysis. It aims to exclude areas with unreliable flow signal due to blocking of the OCT beam by objects anterior to the choriocapillaris (e.g., drusen, retinal vessels, vitreous floaters, and iris). We found that both the FPL and the capillary density were able to detect changes in the choriocapillaris of AMD and healthy age-matched subjects with respect to young controls. The dominant cause of shadowing in AMD is drusen, and the shadow exclusion algorithm helps determine which areas under drusen retain sufficient signal for perfusion evaluation and which areas must be excluded. Such analysis allowed us to determine unambiguously that choriocapillaris density under drusen is indeed reduced.
Highlights
Optical coherence tomography angiography (OCTA)[1,2] is an imaging modality that allows depth-resolved and noninvasive imaging of the retinal and choroidal flow.[3,4,5,6,7] OCTA algorithms use the variation of optical coherence tomography (OCT) signal over time to detect blood flow against avascular tissue
We introduced a parameter to evaluate the choriocapillaris in low-perfusion areas (LPA), named focal perfusion loss (FPL)
Choriocapillaris focal perfusion loss” (FPL) and capillary density were calculated for forty young healthy eyes, 26 eyes with intermediate Age-related macular degeneration (AMD), and 18 age-matched controls
Summary
Optical coherence tomography angiography (OCTA)[1,2] is an imaging modality that allows depth-resolved and noninvasive imaging of the retinal and choroidal flow.[3,4,5,6,7] OCTA algorithms use the variation of optical coherence tomography (OCT) signal over time to detect blood flow against avascular tissue. The resolution of current OCTA devices is not sufficient to resolve either the true caliber of choroidal capillaries or the minuscule intravascular spaces,[8] signal defects such as flow voids are large enough to be detected and measured.[5,7]. Numerous studies have been dedicated to quantifying reduced choriocapillaris flow automatically.[3,7,9,10] Despite the potential clinical applications, quantification of flow impairments is challenged by the prevalence of different types of artifacts: projections, segmentation errors, motion, and shadows. Erroneous segmentation of the very thin choriocapillaris layer can produce incorrect visualization, the reason for which some previous studies have preferred to project a slab that is anatomically inaccurate but robust to segmentation errors.[11,12] Motion artifacts due to
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