CVI and TCA were measured based on the 3.5-mm-sized ONH radial circle scan of the Spectralis OCT2 Glaucoma Module Premium Edition software. Details on the measurement of TCA and CVI are available elsewhere.
9,11,14 Briefly, the scanned image was segmented according to a modified version of the protocol described by Sonoda et al.
21,22 Image binarization was performed using public domain software, ImageJ (version 1.47; available in the public domain,
https://imagej.net/Citing), which can convert gray-scale images to binarized images. Niblack's
23 autolocal threshold techniques were used for image binarization.
9,11–14 The choroidal area was defined as the area between the upper border marked at the RPE and the lower border of light pixels at the choroid scleral junction (
Figs. 1A4, 1A5, 1B4, 1B5). Then, the image was converted to red, green, and blue color to allow the color threshold tool to select the dark pixels,
9 and the TCA was calculated as the area between the RPE and the choroid scleral junction (
Figs. 1A4, 1A5, 1B4, 1B5). The luminal area (LA) was defined as the vascular area of dark pixels within the choroid. To determine the choroidal vascularity, the CVI was computed by dividing the LA by the TCA (
Figs. 1A4, 1A5, 1B4, 1B5). The CVI and TCA were derived from the global area and the six sectors corresponding to those used to determine the location of MvD_P on OCT-A (
Figs. 1A3, 1A4, 1B3, 1B4).