Figure 8

Critical disadvantage of determining anterior scleral opening (ASCO) based on radial scans centered on Bruch’s membrane opening (BMO) (right eye of 55 year-old-man without glaucoma, axial length of 25.50 mm). (A) Disc photograph. The dotted lines indicate the location of the OCT scan. (B) Infrared images. (B₁) Bruch’s membrane opening (BMO, red dots), anterior scleral opening (ASCO, blue dots), and meridian of longest externally oblique border (EOB, black dot) are marked. (B₂) Best-fitted ellipses for BMO (orange ellipse) and ASCO (purple ellipse) are drawn with their centers (orange dot for BMO center, purple dot for ASCO center). (C) B-scan OCT images. (top row: original images, bottom row: images with labels). The red dots indicate the BMO margin; the blue dots indicate the ASCO margin; the green lines indicate the anterior scleral surface. Please note that the B-scans between the red-dotted lines (B₂) cannot yield any information about the ASCO, because they simply cannot capture the optic nerve canal at all (C₂). Also, the B-scans between the blue-dotted lines (B₂) produce uneven sampling for the ASCO: the ASCO margin closer to the BMO center (orange dot) is clustered within a very limited range (B₂). Therefore, the ASCO itself is largely influenced by the ASCO/BMO offset, because no radial scans can focus on two different centers simultaneously. In this context, the ASCO/BMO offset as defined by BMO-oriented radial scans has irreparable disadvantage.