Figure 4

Measurement of disc parameters. The PPA and disc area (within the yellow dotted lines) were outlined manually, and the pixel area was calculated automatically using Image J software. Then the number of pixels in each area was calculated as a ratio to obtain the PPA-to-disc area ratio. The line connecting the fovea and the center of the optic disc, defined as the foveal-disc axis (red line), was used as the reference line. Disc tilt direction was defined as the deviation of the vertical axis of the disc’s longest diameter from the reference line (yellow arrow).