Figure 10
Determination of Bruch’s membrane opening (BMO), anterior scleral opening (ASCO), and central retinal vascular trunk (CRVT) (left eye of 65-year-old man without glaucoma, axial length of 23.72 mm). (A) Disc photograph and OCT image. The white dotted line indicates the location of the OCT scan, as targeted to the CRVT (arrowheads). The B-scan OCT image clearly shows the emergence of the CRVT. The red dots indicate the BMO margin. The ASCO margin (blue dots) was determined as the termination of the anterior scleral surface (green lines) at the optic nerve head canal. (B) Infrared image obtained by OCT. The margins of the BMO (red dots) and ASCO (blue dots) are demarcated. The CRVT position (yellow dot) and the meridian of the longest externally oblique border (EOB, black dot) are marked on the same infrared image. (C) Optimal ellipse fitting to obtain BMO and ASCO centers. Recognition of every point by our software is expressed by an inner white dot. The best-fitted ellipse for the BMO (orange ellipse) and the ASCO (purple ellipse) are drawn in reference to their centers (orange dot for BMO center, purple dot for ASCO center). (D) Calculation of offsets from given set of dots. From the BMO center (orange dot), the angular deviation of CRVT (yellow arrow), and ASCO center (purple arrow) are measured clockwise, with the nasal horizontal midline as 0°. A positive value indicates the superior location and a negative value indicates the inferior location. Likewise, the meridian of the longest EOB (black arrow) is measured clockwise, with the temporal horizontal midline as 0°. A positive value indicates the superior location and a negative value indicates the inferior location. From the BMO center, the distances are measured to the CRVT (a) and to the BMO margin in the same direction (b). The ratio of these distances is defined as the “shift index” (a/b), which is used to measure the extent of shift. The extent of CRVT offset (yellow arrow) divided by that of ASCO offset (purple arrow) is defined as the “offset ratio”.
