Using the Pathophysiology of Dry AMD to Guide Binarization of the Choriocapillaris on OCTA: A Model

Abstract

Especially since the incorporation of swept laser sources, optical coherence tomography angiography (OCTA) has enabled quantification of choriocapillaris perfusion. A critical step in this process is binarization, which makes angiographic images quantifiable in terms of perfusion metrics. It remains challenging to have confidence that choriocapillaris perfusion metrics reflect the reality of pathophysiologic flow, largely because choice of binarization method can result in significantly different perfusion metric outcomes. This commentary discusses a proof-of-concept case involving comparative assessment of binarization methods for a set of dry age-related macular degeneration OCTA data. One of these methods was deemed preferable based on superior agreement with suspected physiologic and pathophysiologic characteristics, thus demonstrating the principle that, in the absence of gold standards for measurement of choriocapillaris perfusion, the best available approximations of pathophysiology may be used to guide choice of binarization method.

Keywords: AMD; OCTA; binarization; choriocapillaris; quantification.

Figure.

Example of 6 × 6-mm, macula-centered choriocapillaris angiogram from eye with intermediate AMD (original, left) after binarization with the Phansalkar local method, radius 15 pixels (center), versus the Otsu global method (right). Per the analysis in our study investigating the relationship between dry AMD stage and CC flow deficit metrics, each image previously underwent compensation for signal attenuation beneath drusen. Flow is shown in white, and regions of analysis corresponding to those in Tables 2 and 3 are shown by the blue overlay.